HK1074534B - Antenna system - Google Patents

Description

Antenna system

The present invention relates to antenna systems and in particular, but not exclusively, to phased array antenna systems having a plurality of antenna elements arranged in at least two sub-arrays. The antenna system is suitable for many telecommunication systems but finds particular application in cellular mobile radio networks, commonly referred to as mobile telephone networks. More particularly, the antenna system of the present invention may be used in the context of third generation (3G) mobile phone networks and Universal Mobile Telephone Systems (UMTS).

Operators of cellular mobile radio networks typically utilize their own base stations, each of which includes one or more antennas. In a cellular mobile radio network, the antennas are a factor in defining the required coverage, which is typically divided into several overlapping cells, each cell being associated with a respective antenna and base station. Each cell contains a fixed location base station that communicates with mobile radios in that cell. The base stations themselves are interconnected by other means of communication, either radio links or fixed land lines, and are arranged in a network or mesh structure that allows mobile radios throughout the cell coverage area to communicate with each other and with the public telephone network outside the cellular mobile radio network.

The antennas used in such networks are often composite devices known as phased array antennas, which comprise a plurality (typically 8 or more) or array of individual antenna elements or dipoles. The direction of maximum sensitivity of the antenna, i.e. the vertical or horizontal direction of the main radiation beam or "aim" of the antenna pattern, can be changed by adjusting the phase relationship between these elements. This has the effect of allowing the radiation beam to be controlled to vary the coverage of the antenna.

In particular, operators of phased array antennas in cellular mobile radio networks have a requirement to adjust the Vertical Radiation Pattern (VRP) (also known as "tilt") of the antenna, as this has a significant effect on the coverage area of the antenna. For example, due to changes in network structure or the addition or removal of other base stations or antennas in a cell, an adjustment of the coverage may be required.

It is known that adjustment of the tilt angle of an antenna is conventionally achieved by mechanical means, electrical means or both within the antenna itself. When the tilt is mechanically adjusted, for example by mechanically moving the antenna elements themselves or by mechanically moving the antenna support, such adjustment is often referred to as "mechanical tilt angle adjustment". The effect of adjusting the mechanical tilt angle is to change the pointing position to point either above or below the horizon. When the tilt is adjusted electrically by adjusting the phase of the signal supplied to the antenna element, rather than physically moving the element's mount, the antenna elements themselves, or any other component of the radome, such adjustment is commonly referred to as "electrical tilt angle adjustment". Adjusting the electrical tilt angle also serves to change the position of aim to point either above or below the horizon, in which case this is achieved by changing the time delay of the signal fed to each element (or group of elements) in the array.

A disadvantage of the mechanical adjustment of the electrical tilt angle is that it has to be performed in situ by manual adjustment of the antenna.

It is an object of the present invention to provide an improved antenna which overcomes the above problems.

In the following description, the term "antenna system" used in place of the previous term "antenna" describes a system having an "antenna assembly" which is an array of antenna elements and control means for controlling the signals supplied to the antenna elements in the antenna assembly.

There is thus provided, in accordance with an aspect of the present invention, an antenna system. Such an antenna system comprises: an antenna assembly having an electrical tilt angle and a plurality of antenna elements mounted on an antenna carrier and arranged in at least two sub-arrays, each sub-array comprising one or more of said elements; control means for electrically controlling the phase of signals supplied to at least one of said sub-arrays from a location remote from said antenna assembly, wherein said control means includes phase adjustment means for connecting to a respective one of said sub-arrays via first and second input feeds, thereby to adjust the phase of signals supplied thereto; and additional mechanical phase adjustment means for additionally adjusting the phase of the signal supplied to each element of the antenna assembly.

Conveniently, the antenna assembly may include first and second phase adjustment means, each of said first and second phase adjustment means being connected to a respective one of said sub-arrays via a respective first or second input feed, thereby to adjust the phase of the signal supplied to said respective one of said sub-arrays.

Typically the antenna carrier may be an antenna mast.

In a first embodiment, the control device may be placed at the base of the antenna carrier, remote from the antenna assembly. In an alternative embodiment the control device is arranged at a location remote from the antenna carrier or mast base, for example a few metres away.

The control means may comprise a separate port for receiving a separate input signal and means for splitting said input signal into first and second split signals to be supplied to respective ones of said first and second phase adjusting means.

Conveniently, the system further comprises means for automatically controlling the phase of the signal supplied to a first of said arrays in relation to the phase of the signal supplied to a second of said arrays.

In a preferred embodiment, said elements of said antenna assembly are arranged in first, second and third sub-arrays, and said antenna system comprises:

first control means for controlling the phase of the signals supplied to said first sub-array, and

third control means for controlling the phase of the signals supplied to said third sub-array, an

Second control means for automatically controlling the phase of signals supplied to said second sub-array in relation to a predetermined function of the phase of signals supplied to said first and third sub-arrays.

Conveniently, said predetermined function is the vector sum of the phases of the signals supplied to said first and third sub-arrays.

Preferably said second control means may comprise a combiner unit for receiving a first input signal having the phase of the signals supplied to said first sub-array and a second input signal having the phase of the signals supplied to said third sub-array and for providing an output signal to the second sub-array in dependence on a predetermined function of the phase of the signals supplied to said first and third sub-arrays.

In one embodiment, the predetermined function is the vector sum of the phases of the signals supplied to said first and third sub-arrays.

In another preferred embodiment the second control means comprises at least one quadrature combiner unit for receiving a first input signal having the phase of the signals supplied to said first sub-array and a second input signal having the phase of the signals supplied to said third sub-array, and for providing a first output signal to one element of the second sub-array and a second output signal to a different element of the second sub-array, wherein said first and second output signals are related to a predetermined function of the phase of the first and second input signals.

The quadrature combiner unit may be arranged such that the phase of said output signal provided by the quadrature combiner unit is an average of the phases of the first and second input signals.

The first control means may be arranged to control and/or adjust the phase of said signals supplied to said first sub-array by a first predetermined amount and the second control means may be arranged to control and/or adjust the phase of said signals supplied to said second sub-array by a second predetermined amount, different in magnitude and/or polarity to said first predetermined amount.

The antenna assembly is conventionally supplied with the largest of the two signal feeds from said first and second phase adjustment means.

The antenna assembly conventionally includes respective signal distribution means associated with each sub-array for separating and distributing signals across the elements of the associated sub-array. Preferably, each of said signal distribution means comprises splitter means for distributing signals to one or more of said sub-arrays. Conventionally, splitter means are provided to distribute the signal strength of said signals substantially uniformly to said sub-arrays, thereby increasing the aiming gain.

In one embodiment at least one output signal from said distribution means associated with the first sub-array is spatially combined or superimposed with at least one output signal from said distribution means associated with the third sub-array, thereby providing first and second combined output signals to the first and second elements of the second sub-array. The combination of signals can be achieved only in the air and provides the further advantage that higher aiming gain and lower side lobe levels can be achieved, especially when electrically ramping the system up.

The additional mechanical phase adjustment means may comprise an array of movable dielectric elements. The signal path to each array element may be provided with the associated dielectric element, unique to that element, or the dielectric element may be shared with the signal path to another of the array elements.

Each element has an associated input transmission line and, in one embodiment, each of the dielectric elements is arranged for linear movement relative to the associated transmission line so as to vary the further phase shift of the signal supplied to the element via the transmission line.

Alternatively, each of the dielectric elements is arranged for rotational movement relative to the associated transmission line so as to vary a further phase shift of the signal supplied to said element via said transmission line.

Thus, the additional mechanical phase adjustment means may comprise either rotary or linear motion means for moving the dielectric element. Each additional mechanical phase adjustment means may be so identical as to provide a substantially equal amount of further phase adjustment to the signal supplied to each array element on linear or rotational movement of the dielectric element. Alternatively, each additional mechanical phase adjustment means may be so different that linear or rotational movement produces a different number of further phase adjustments to the signal to each element.

According to another aspect of the present invention, there is provided an antenna system. Such an antenna system comprises:

an antenna assembly having a plurality of elements arranged in at least two sub-arrays, each sub-array comprising one or more of said elements;

first control means for controlling the phase of the signal supplied to a first one of said sub-arrays, and

second control means for automatically controlling the phase of signals supplied to another of said sub-arrays in relation to the phase of signals supplied to said first of said sub-arrays.

Preferably, said elements of said antenna assembly are arranged in first, second and third sub-arrays, and said assembly comprises:

first control means for controlling the phase of signals supplied to said first sub-array; and

third control means for controlling the phase of signals supplied to said third sub-array;

wherein said second control means is arranged to automatically control the phase of signals supplied to said second sub-array in relation to a predetermined function of the phase of said signals supplied to said first and third sub-arrays.

Conveniently, the predetermined function is the vector sum of the phases of the signals supplied to said first and third sub-arrays.

It will be appreciated that features as described optionally and/or alternatively to the first aspect of the invention may also be applicable to further aspects of the invention.

According to yet another aspect of the present invention, there is provided an antenna system. Such an antenna system comprises:

an antenna assembly having a plurality of elements arranged in at least first, second and third sub-arrays, each sub-array comprising one or more of said elements; and

control means for controlling the phase of the signals supplied to each of said sub-arrays. Wherein the antenna assembly is fed to the largest of the two signal feeds.

The system of the present invention as described in the preceding sections provides several advantages over existing systems. In particular, control and/or adjustment of the phase of the signals supplied to each sub-array in the antenna assembly can be achieved simply and quickly from a location remote from the antenna assembly. It is known to adjust the tilt angle of an antenna by means of manual mechanical adjustment of the antenna elements and/or the antenna supports mounted on the antenna carrier or mast itself. Such an adjustment process is inconvenient and labor intensive. The invention provides the advantage that the tilt angle can be adjusted electrically from a location remote from the mast, for example from a base station or control centre at the base of the mast or a base station located several kilometres from the mast. Furthermore, the system is suitable for multi-user (i.e. multi-operator) applications by providing each user with independently operable control means and by combining the user signals in a frequency selective combiner device.

The invention also provides the advantage of controlling the phase and amplitude distribution of the signals fed to each antenna element in such a way as to provide improved control of the antenna gain and side lobe levels, particularly when electrically ramping the system. The provision of mechanical phase adjustment means, for example for further adjusting the phase of the signal supplied to each element of the array, provides the user with means to tune the vertical radiation pattern, allowing further optimisation of the aiming gain and side lobe levels.

This aspect of the invention also provides an advantage over other known techniques in that a reduction in the number of components required to adjust the electrical tilt of the antenna assembly can be achieved with a reduction in system complexity and cost.

For the purposes of this specification it will be appreciated that the intended term "user" means the user of the system of the present invention (i.e. the system operator) and not the user of the telephone handset used for the reception/transmission of signals to/from the system.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which,

fig. 1 illustrates the Vertical Radiation Pattern (VRP) of a known phased array antenna assembly;

FIG. 2 is a schematic block diagram of a known antenna assembly equipped with a mechanism for adjusting the electrical tilt angle;

fig. 3 is a schematic block diagram of a first embodiment of a dual sub-array antenna system in accordance with the present invention;

FIG. 4 is a schematic block diagram of a practical implementation of the antenna system of FIG. 3;

FIG. 5 is a schematic block diagram of a three sub-array antenna system utilizing an alternate embodiment of the spatial overlap of the sub-arrays;

fig. 6 shows a schematic block diagram of an alternative three sub-array antenna system to that shown in fig. 5;

fig. 7 shows a schematic block diagram of a practical implementation of the antenna system of fig. 6;

fig. 8 shows a schematic block diagram of a further alternative embodiment of a five-subarray antenna system;

FIG. 9 shows one embodiment of a mechanical phase adjustment apparatus forming part of the system of FIGS. 3 to 8;

FIG. 10 illustrates an alternative to the mechanical phase adjustment arrangement shown in FIG. 9;

fig. 11 is a further alternative embodiment of a three sub-array antenna system showing details of the mechanical phase adjustment arrangement of fig. 10;

fig. 12 is a further alternative embodiment of a three sub-array antenna system showing details of the mechanical phase adjustment arrangement of fig. 9; and

fig. 13 is a schematic block diagram of an alternative form of system in accordance with the present invention incorporating a dual polarity antenna assembly.

In the figures, like reference numerals are used to indicate similar parts. In the following description, the invention is described in the context of an antenna system suitable for use in a cellular mobile radio network, in particular for use in a universal mobile telephone system (UTMS). It will be appreciated, however, that the invention is not limited to such use and would be equally applicable to other communication systems.

Fig. 1 shows the Vertical Radiation Pattern (VRP) of a conventional phased array antenna assembly. The figure is a side view representation with the antenna assembly represented by point 1.

The VRP of the antenna assembly consists of a main lobe or "aim" 2. The main lobe diverges in the vertical plane as it extends from the antenna assembly and represents the region of maximum radiation intensity of the beam radiated by the antenna assembly. The VRP of the antenna assembly also includes several side lobes 4 representing much lower radiation intensity regions. The side lobes extend in vertical planes in directions approximately equiangularly spaced around the antenna assembly. The side lobes 3 immediately adjacent to the collimation 2 are referred to as first upper and lower side lobes, respectively.

In mechanically adjusting the tilt angle of an antenna assembly by physically moving the antenna elements and/or their supports or housings, the tilt angle of the antenna assembly is referred to as the "mechanical tilt" angle, which is conventionally accomplished by changing the point of aim to point either above or below the horizon. When electrically adjusted, the tilt angle of the antenna assembly is referred to as "electrical tilt" and it moves the line of sight up or down by changing the time delay or phase of the signals supplied to groups of elements in the antenna, rather than by mechanical movement of the elements themselves. The time delay may be achieved by changing the phase of the radio frequency carrier. The phase delay creates a time delay if it is proportional to the frequency on the band of interest and has zero intercept. Therefore, phase shift and time delay are synonymous.

It is noted that this will be helpful to the reader in understanding the following description. That is, both "electrical tilt" and "mechanical tilt" may be controlled and/or adjusted by either electrical means or mechanical means or both such that, for example, electrical phase adjustment may be accomplished using mechanical movement of components, wherein the antenna elements themselves are not physically moved to adjust the home position.

In fig. 2, an antenna assembly of a known antenna system equipped with a mechanism for adjusting the electrical tilt angle is indicated generally in principle block form at 10. The antenna assembly is a phased array antenna consisting of an array of twelve elements or dipoles E1-E12. The twelve elements are arranged in three sub-arrays labeled A, B and C.

Each sub-array A, B, C includes four elements connected in parallel with each other and coupled to respective first, second and third delay devices 12, 14, 16. The delay devices 12, 14, 16 include conventional mechanical phase adjustment mechanisms as shown in fig. 9 and 10 and described in further detail below. A Radio Frequency (RF) signal to be transmitted by the antenna is supplied to each of the delay devices 12, 14, 16 from a common RF port or feed line 18.

The function of the delay devices 12, 14, 16 is to adjust the phase of the RF signals supplied to the respective sub-arrays A, B, C by a predetermined amount. The second delay device 14 connected to the central sub-array B is a fixed delay device arranged to shift the phase of the signal supplied to the sub-array B by a fixed amount. In another aspect, the first and third delay devices 12, 16 connected to the sub-arrays a and C, respectively, are variable delay devices, each of which is operable to shift the phase of the RF signals supplied to the sub-arrays a and C, respectively, by a variable amount.

The first and third delay devices 12, 16 may apply a phase shift of typically between 0 and ± 45 ° to the RF signals supplied to the sub-arrays a and C and are adjustable by means of a mechanical arrangement 20 as shown in fig. 6 and 7. The mechanical means 20 comprise means, represented representatively at 22, for reversing the direction of the phase shift applied to the signal by the third delay device 16 as compared to that applied by the first delay device 12. Thus, the phase shifts applied to the RF signal by the first and third delay devices 12, 16 are equal in magnitude but opposite in polarity. In other words, if the first delay device 12 shifts the phase of the signal supplied to sub-array A by +45 °, the third delay device 16 shifts the phase of the signal supplied to sub-array C by-45 °. Although the second delay device 14 is a fixed delay device, in practice a phase shift is applied to the signal supplied to the sub-array B which is the median of the phase shifts applied by the first and third delay devices 12, 16.

The electrical tilt angle of such antenna assemblies typically varies by ± 5 ° for a ± 45 ° phase shift per sub-array. This gives a tilt sensitivity of about 18 ° phase shift per electrical tilt. Thus, in this example, the electrical tilt of the antenna assembly is about 5 ° since the RF signals supplied to sub-arrays a and C are 90 ° apart. The direction of electrical tilt of the antenna assembly depends on the polarity of the phase shift applied to the signals supplied to the sub-array. In the case where the signal to the upper sub-array (in this case sub-array a) has a positive phase and the lower sub-array (in this case sub-array C) has a negative phase shift, the electrical tilt angle will be positive, i.e. above the normal line of sight. For a phase shift of opposite polarity, the electrical tilt angle will be negative.

The antenna assembly of fig. 2 has several disadvantages. In particular, manual adjustment of the mechanism 20 is required to adjust the phase shift applied by the first and third delay devices 12, 16 in order to change the electrical tilt angle of the antenna assembly. Furthermore, due to the common mechanical adjustment means 20, the magnitudes of the phase shifts applied by the first and third delay devices 12, 16 are always equal in magnitude and opposite in direction (polarity), thereby limiting the tilt of the antenna elements. In addition, the sidelobe levels increase relative to the aiming level. Therefore, the gain of the antenna assembly is disadvantageously reduced.

In fig. 3, a preferred form of the antenna system according to the invention is shown in block form generally at 100. In this embodiment, the antenna system 100 includes an antenna assembly, indicated at 102, and a control unit 104. The antenna assembly 102 comprises a phased array antenna having an array of eight elements E1 to E8 mounted on an antenna carrier or mast (not shown). The elements E1 to E8 are arranged in two sub-arrays: an upper subarray 100A comprising E1 through E4 and a lower subarray 100B comprising E5 through E8. The elements in each of the sub-arrays 100A, 100B are connected in parallel to signal distribution means in the form of respective distribution networks 151N1, 151N 2. Distribution networks 151N1, 151N2 are fed via carrier lines 120, 122, respectively, and will be described in further detail below.

Antenna assembly 102 includes two input ports, represented by squares 112, 114, each of which is connected to a respective distribution network 151N1, 151N2 via a respective input carrier line 120, 122. The control unit also includes an input splitter/combiner unit 125 to which the common port is connected to the output of the individual RF ports 126. The input splitter/combiner unit 125 has two ports which are connected to first and second phase adjusters 132, 134 via first and second splitter lines 128, 130 respectively. The first phase adjuster 132 is connected at its output to the input port 112 via a first input feed 136, whilst the second phase adjuster 134 is connected to the input port 114 via a second input feed 138. Thus, the component 102 is provided with a signal from the control unit 104 via the dual feed antenna.

In addition to the phase adjustment performed by the first and second phase adjusters 132, 134, additional phase adjustment means 150E1-150E8 are also provided in the signal path to each element of the antenna feed assembly. Each additional phase adjustment device 150E1-150E8 takes the form of a mechanical phase adjustment device, a version of which is described in further detail below with reference to either fig. 9 or fig. 10. Each mechanical phase adjustment device 150E1-150E8 is used to further adjust the phase of the signals supplied to the individual elements in each subarray 100A, 100B when controlled by a servo motor 101 under the control of a servo controller 103. The servo controller 103 controls the servo motor 101 through a control cable 206. The control cable 206 may be long enough so that the servo controller 103 may form part of the control unit 104 that is located remotely from the antenna assembly 102.

The distribution networks 151N1, 151N2 are shown in further detail in fig. 4. The distribution network 151N1 associated with the upper subarray 100A includes first, second and third splitter/combiner units 116A, 116B, 116C, respectively. The input carrier line 120 supplies the second splitter/combiner unit 116B with a signal and the second splitter/combiner unit 116B supplies the first and second output signals of substantially equal strength to a respective one of the first and third splitter/combiner units 116A, 116C. The first and third splitter units 116A, 116C subdivide the signals so that each provides first and second output signals of substantially equal strength to a respective one of the phase adjusting devices 150E1-150E 4. The second distribution network 151N2 of the lower sub-array 100B comprises the same arrangement of splitter units 118A, 118B, 118C. The arrangement of the splitter/combiner units 116A-116C, 118A-118C ensures equal power distribution to each element E1 to E8 of the array and thus maximum aiming gain and the same beam pattern in both transmit and receive modes.

Referring to fig. 3 and 4, in operation, a signal to be transmitted by the antenna system is fed from the RF port 126 to the input of the input splitter 125 the input splitter unit 125 splits the signal into two output signals of equal strength and supplies one split signal to the first and second phase adjusters 132, 134 respectively. The first and second phase adjusters 132, 134 are operable to adjust the phase of the signal supplied thereto within a range of ± 60 °. Each phase adjuster 132, 134 is controlled such that if the first phase adjuster 132 is arranged to apply a positive phase shift to an RF signal, the second phase adjuster 134 is arranged to apply a negative phase shift to that signal; the reverse is also true. However, each phase adjuster is arranged to adjust the phase of the signal supplied thereto independently such that the magnitude of the phase shift applied by each phase adjuster may be different.

The phase shifted signal from the first phase adjuster 132 is fed to the input port 112 on the antenna assembly 102 via a first feed line 136. Similarly, the phase shifted signal from the second phase adjuster 134 is supplied to the input port 114 via a second feed line 138. In practice, the first and second feed lines 136 and 138 may be made as long as desired so that the control device 104 for adjusting the electrical tilt angle of the antenna assembly 102 may be located at a location remote from the antenna assembly itself.

The phase shifted signals supplied to the input ports 112, 114 are supplied as signals Sa and Sb on input carrier lines 120, 122 to first and second main splitter units 116B, 118B, respectively. The first main splitter unit 116B serves to split the signal Sa and supply the component split signals in the sub-array 100A from its two outputs via the upper sub-array splitters 116A, 116C and the associated phase adjusting means 150E1 to 150E 4.

Likewise, the second main splitter unit 118B serves to split the signal Sb and supply the component split signals in the sub-array 100C from its two outputs through the lower sub-array splitter units 118A, 118C and associated phase adjusting means 150E5 to 150E 8.

The skilled person will immediately appreciate from the way in which the splitter units are interconnected according to him the way in which the signals Sa, Sb are split and distributed into the elements of the antenna assembly. That is, the signal strength of each of the two outputs of the splitter unit will be substantially half the input signal strength. Therefore, the signal strength of the signal supplied to each of the elements E1 to E8 is substantially the same.

Fig. 5 is an alternative to the embodiment shown in fig. 3 and 4, in which the antenna assembly 102 comprises 8 antenna elements E1 to E8 arranged on 3 sub-arrays; the upper sub-array 100A includes antenna elements E1 through E3, the central sub-array 100B includes E4 and E5 and the lower sub-array 100C includes antenna elements E6 through E8. Each of the elements E1 to E4 (i.e. 3 elements of the upper sub-array 100A and 1 element of the central sub-array 100B) is fed by a distribution network 151N1 and is equipped with additional phase adjusting means 150E1-150E4, respectively. Each of the elements E5 to E8 (i.e. 3 elements of the lower sub-array 100A and 1 element of the central sub-array 100B) is fed by a distribution network 151N2 and is equipped with additional phase adjusting means 150E5-150E8, respectively. The phase adjusted signals to the central subarray elements, 150E4 and 150E5, are driven by spatial combinations in air at 160, one of these output signals from the first distribution network 151N1 and one of these output signals from the second distribution network 151N 2. The driving of the aerial combination of the two signals to the input of the central sub-array 100B takes place after the signals output from the distribution networks 151N1, 151N2 have been phase adjusted by the relevant phase adjustment means 150E4, 150E 5.

The distribution networks 151N1, 151N2 on fig. 5 may comprise substantially the same splitter devices as shown in fig. 4. Thus, the elements E1 and E2 are fed from the output of the first splitter unit 116A of the first distribution network 151N1, one of the elements E3 being fed from the output of the third splitter unit 116C. The element E5 is fed from the second output of the third splitter unit 116C of the first distribution network 151N1, as is the reciprocal feeding of elements E4 and E5 in the fig. 5 embodiment. Likewise, the two output feed elements E7 and E8 of the third splitter unit 118C of the second distribution network 151N2 are fed from one of the outputs of the first splitter unit 118C, E6. The element E4 is fed from one of the outputs of the first splitter unit 118A of the second distribution network 151N2, as is the case when the feeds to elements E4 and E5 are interchanged.

The advantage gained by spatially overlapping the inputs driven to the central sub-array 100B from the two elements of the upper and lower sub-arrays 100A, 100C is that the phase distribution over the array elements is a closer near linear distribution. Higher aiming gain and lower side lobe levels can thus be achieved, especially when electrically tilting the antenna.

Figure 6 shows another alternative embodiment of an antenna assembly, in the form of three subgroups, a variable electrical tilt assembly. The antenna assembly 102 comprises twelve elements, E1 to E12, divided into three sub-arrays 100A, 100B, 100C, such that each sub-array comprises four elements, E1 to E4, E5 to E8, and E9 to E12, respectively. The same components as represented in the embodiment of fig. 3 to 5 are indicated with the same reference numerals and will not be described in further detail. The input carrier lines 120, 122 feed respective signals Sa and Sb to main splitter units 140A, 140B, respectively, each providing two outputs of equal strength. A first output of the first main splitter unit 140A is connected to the first output carrier line 106 and a second output of the first main splitter unit 140A is connected to a first input of the combiner unit 124. A first output of the second main splitter unit 140B is connected to the second output carrier line 110 and a second output of the second main splitter unit 140B is connected to a second input of the combiner unit 124.

The combiner unit 124 is operable to output a vector sum of the two signals on the output carrier line 108. In the case of combining the signals output from the first and second main splitter units 140, 140B, the signal output by the combiner unit 124 has the same signal strength as any one of the signals Sa, Sb if the signal strength of each of the input signals input to the combiner unit 124 is half the signal strength of the signals Sa, Sb that have been halved by the first and second main splitter units 140, 140B, respectively. In addition, since the combiner unit 124 produces a vector sum of the two signals Sa, Sb and since the phases of the signals Sa, Sb have been adjusted differently (i.e., in opposite polarities), the phase of the signal output by the combiner unit 124 along the carrier line 108 is the median of the phases of Sa and Sb. Furthermore, the combiner unit 124 provides the median value of the phases of the signals Sa and Sb without any loss of signal power to the subgroup 100B.

The combiner unit 124 provides the vector sum signal on the carrier line 108 to the second distribution network 151N2, which second distribution network 151N2 in turn provides the signal to each of the elements E5 to E8 via the associated phase adjusting means 150E5 to 150E 8. This configuration provides a further improvement in phase linearity when the output from the combiner unit 124 is the average phase of the signals on the input carrier lines 120, 122. Therefore, the total power fed to the elements of the central sub-matrix 100B (elements E5 to E8) remains substantially constant, while there is a phase difference between the carrier lines 120, 122.

Fig. 7 shows a practical embodiment of the three sub-groups of antennas of fig. 6, in order to show the distribution networks 151N1, 151N2, 151N3 in more detail. The first and second splitter units 140A, 140B are fed by respective ones of the input carrier lines 120, 122, with each of the splitter units 140A, 140B producing two output signals. The first output signal from the first splitter unit 140A is supplied to the phase shift unit 170A of the first distribution network 151N1 to impart an additional phase shift, typically between-45 degrees and-60 degrees, to the signal from the main splitter unit 140A. The phase shifted output signals are provided to a splitter unit 116B forming part of a splitter arrangement 116A, 116B, 116C of the kind shown in fig. 4. The splitter devices 116A, 116B, 116C provide output signals to the phase adjustment devices 150E1-150E4, respectively, so that each element receives a signal of substantially equal strength.

The second output from the splitter unit 140A is supplied to a further splitter unit 172A forming part of the second distribution network 151N2, the splitter unit 172A splitting the input it receives into a first output signal supplied to one input (a) of the first quadrature hybrid combiner unit 174A and a second output signal supplied to one input (a) of the second quadrature hybrid combiner unit 174B.

The second splitter unit 140B provides the first output signal to a further splitter unit 172B forming part of the second distribution network 151N 2. The further splitter unit 172B provides an output signal to a second input (B) of the first quadrature hybrid combiner unit 174A and an output signal to a second input (B) of the second quadrature combiner unit 174B.

Each of the first and second quadrature hybrid combiner units 174A, 174B provides first and second output signals to two elements of the central sub-array 100B: the first quadrature hybrid combiner unit 174A provides signals to elements E5 and E6, while the second quadrature hybrid combiner unit 174B provides signals to elements E7 and E8. The first and second quadrature hybrid combiner units 174A, 174B ensure that the phase of the signal provided to elements E5 through E8 is the average of the phases of the signals on the input carrier lines 120, 122. For example, the power fed to element E5 is reduced and the power fed to element E6 is increased so that the power fed to elements E5, E6 remains substantially unchanged.

The second output signal from the second splitter unit 140B is transmitted through a second phase shifting unit 170B forming part of the third distribution network 151N 3. The second phase shifting unit 170B applies a phase shift of +45 degrees (i.e., opposite polarity to the phase shifting unit 170A) to the splitter unit 118B. The splitter unit 118B forms part of a splitter arrangement 118A, 118B, 118C of the kind shown in fig. 4, which provides output signals to respective phase adjusting arrangements 150E9-150E122 of elements E9 through E12 of the lower sub-array 100C.

Fig. 8 is an alternative embodiment of the present invention in which the antenna assembly includes 5 sub-arrays 100A-100E (i.e., five sub-arrays). Here, the third and fourth sub-arrays 100B, 100D are obtained by spatially overlapping elements of 3 sub-array components as shown in fig. 6, and the same components as those shown in fig. 6 are denoted by the same reference numerals. The input carrier lines 120, 122 supply signals Sa, Sb to the first and second main splitter units 140A, 140B, respectively. First splitter unit 140A provides a first output signal to first distribution network 151N1 and a second output signal to combiner unit 124 along output carrier line 106. Second splitter unit 140B provides a first output signal to third distribution network 151N3 and a second output signal to combiner unit 124 along output carrier line 110. The output signal of combiner unit 124 along output carrier line 108 to second distribution network 151N2,

each distribution network 151N1, 151N2, 151N3 provides four output signals, each of which is provided to an element of the array via an associated phase adjustment arrangement 150E1-150E 12. One 180A of the output signals from the first distribution network 151N1 spatially overlaps with one 180B of the output signals from the second distribution network 151N2 by combining the signals over the air, providing signals to elements E4 and E5 of the sub-array 100B. Likewise, one 180C of the output signals from the second distribution network 151N2 spatially overlaps with one 180D of the output signals from the third distribution network 151N3 by combining the signals over the air, providing signals to elements E8 and E9 of the sub-array 100D. The configuration in fig. 8 provides further improvement in phase linearity over elements E1-E12, and further improves on-target gain and sidelobe suppression when electrically ramping components.

Indeed, the distribution network 151N1 on fig. 8 may include the splitter devices 116A, 116B, 116C and phase shift units 170A of the fig. 7 embodiment, while the third distribution network 151N3 may include the splitter devices 118A, 118B, 118C and phase shift units 170B of the fig. 7 embodiment. The combiner unit 24 and the second distribution network 151N2 may comprise first and second splitter units 172A, 172B and first and second quadrature combiner units 174A, 174 as previously described with reference to fig. 7.

Fig. 9 and 10 illustrate known methods for mechanically adjusting the phase of the signal fed to each element in an antenna assembly. Either or both of these methods may be used in the antenna assemblies of fig. 3-8 as phase adjustment devices 150E1-150En (where n is the number of elements in the antenna assembly).

In fig. 9, the mechanical adjustment of the phase of the signal on the transmission line is achieved by a linear movement of the dielectric material element below the transmission line. The mechanical adjustment means 601 comprises a base plate 602 and a generally planar sheet 604 of dielectric material. Transmission lines T to the antenna elements run opposite the substrate 602. A plate of dielectric material 604 is placed between the bottom plate 602 and the transmission line T. The dielectric material plate 604 (commonly referred to as a "wedge") is generally rectangular with a triangular or V-shaped portion 606 cut from one longitudinal edge thereof. The wedge 604 is movable relative to the base 602 and the transmission line T in the direction indicated by arrow a, generally transverse to the transmission line T. Due to its shape, the linear movement of the wedge 604 causes a larger or smaller amount of dielectric material to be inserted between the transmission line and the bottom plate 602, thereby causing the propagation speed of any signal on the transmission line T and, thus, the phase to be moved depending on the amount of linear position of the wedge. Such linear movement is typically achieved with a linear actuator in the form of a servo or other moving transducer. The amount of phase shift applied to the signal on the transmission line T is set by the position of the wedge 604 below the transmission line T and the "wedge angle" that is cut into the interior angle of the wedge's V-shape.

Fig. 10 shows a mechanical phase adjustment device, generally designated 701. The mechanical phase adjustment device is operable to change the phase by changing the transmission line delay of a signal on the transmission line by rotational movement of a movable length of the transmission line capacitively coupled to a fixed line length. The device 701 comprises a base plate 702 on which is a layer 704 of dielectric material. The fixed length of the transmission line T together with the bottom plate 702 and the dielectric layer 704 constitute a transmission line. The transmission line is discontinuous, forming two transmission line segments T1, T2, a first segment T1 extending over the dielectric layer 704, forming a quadrant having a radius R; a second segment T2 extends over dielectric layer 704 forming a quadrant with radius r.

A planar disc 706 of dielectric material is disposed on transmission line T and is rotatable relative thereto about an axis coaxial with the center of the circle defined by first and second transmission line segments T1, T2. The dielectric disc 706 carries a U-shaped length of transmission line U having a first arm U1 defining a quadrant having a radius R and a second arm U2 defining a surrounding quadrant having a radius R.

The transmission lines T, U are coupled together by the dielectric disc 706 and phase adjustment of the signal on the transmission line T can be achieved by rotating the dielectric disc 706 to adjust the position of the transmission line U relative to the transmission line T. When the disc is rotated through 90 deg., the coupling between the two transmission lines and thus the effective length of the transmission lines to the antenna elements changes, thereby shifting the phase of the signal carried by the transmission lines.

Although not shown in fig. 10, it is possible to control the phase of more than one antenna element using the instrument of fig. 10. For example, for such a device that controls the phase of signals on two separate transmission lines, the second configuration of transmission line T, U may be arranged on opposite quarter circles of dielectric disc 706. The phase shift applied to each antenna element or each subset of elements may be set by the radius of transmission line T, U on each disk, the coupling between transmission lines, or both.

Fig. 11 illustrates an alternative embodiment of the present invention. Wherein the arrangement of splitter units is a so-called "family tree" configuration, which allows signals of equal strength to be supplied to each element in the assembly. Such a configuration is suitable where phase adjustment of the individual antenna elements occurs, since a voltage division to maximize the aiming gain cosine squared is not necessary.

In this particular embodiment, the antenna assembly consists of eight elements E1 to E8; the upper subarray 100A includes elements E1-E3, the central subarray 100B includes elements E4 and E5, and the lower subarray includes elements E6 through E8 (i.e., a three subarray system). Remote adjustment of the electrical tilt angle of the antenna assembly is achieved by servo control of the mechanical phase adjustment instrument in conjunction with differential phase shifts applied by the electrical device to the signals supplied to the antenna elements.

The base station control unit 104 comprises an input splitter/combiner unit 125, an RF port 126 and first and second phase adjusters 132, 234 (neither of which is shown) to which first and second phase shifted signals Sa, Sb are supplied to input ports 112, 114 via first and second feeders 136, 138, respectively. Input ports 112, 114 apply the signal to input carrier lines 120, 122, respectively. The phase shifted signals Sa, Sb on the input carrier line are supplied to the first and second main splitter units 116, 118, respectively. The splitter units are arranged such that each output of the first and second main splitter units 116, 118 is connected to an input of a respective splitter unit in the second row of splitter units 116A, 116B, 118A, 118B.

The two outputs of the splitter unit 116A are connected to the elements E1 and E2, respectively, via the same first phase adjustment device D1 as shown in fig. 10. A first output of the splitter unit 116B is connected to the element E3 via second phase adjustment means D2. A second output of splitter unit 116B is connected to a first input of combiner unit 124 as is a first output of splitter unit 118A. The combiner unit 124 has two outputs, each of which is connected to the elements E4 and E5 via second and third phase adjusting means D2, D3, respectively. The second output of splitter unit 118A is connected to element E6 via a third phase adjusting device D3, while the two outputs of splitter unit 118B are connected to elements E7, E8 via a fourth phase adjusting device D4, respectively.

In fig. 11, rotation of the discs in the phase adjusters D1 to D4 is achieved by linear movement of the drive rod 200 pivotally and eccentrically mounted to each of the rotary discs 706 of the mechanical phase adjuster 701. For example, the linear motion of the driving rod 200 may be achieved by a servo motor 101 controlled by a servo controller 103. The control cable 206 may be any desired length that enables the servo motor 103 to be controlled from a location remote from the antenna assembly 100. The phase adjusting devices D1 through D4 may be configured such that movement of the respective discs past the individual control points results in substantially equal degrees of rotation for each disc. However, depending on the coupling between the transmission line T, U in each phase adjustment mechanism, a different amount of phase shift may be applied to the signal to each antenna element.

Fig. 12 illustrates a three subarray embodiment of an antenna system. Wherein the mechanical phase adjusting means 601 connected to each of the antenna elements E1 to E8 is the same mechanism as shown in fig. 9, and wherein an increased number of mechanical adjusting means is required for performing individual mechanical tilting of each of the elements E1 to E8. In other words, the embodiment of FIG. 12 differs from the embodiment of FIG. 11 in that there is a separate and distinct movable dielectric element associated with each element E1 through E8. The servo motor 101 and the servo controller 103 are provided, and as explained again before, remote adjustment of the electrical tilt angle of the antenna assembly 100 is achieved by means of servo control of the mechanical phase adjustment device 601 via the cable 206 in combination with differential phase shifts applied to the signals Sa, Sb feeding the antenna elements E1 to E8.

The phase of the signal supplied to each element E1 to E8 is controlled by the linear motion of the dielectric wedges in each mechanism, each dielectric wedge being connected to the drive rod 200. It will be noted that the phase adjustment devices connected to the lower four elements E5-E8 are inverted compared to the phase adjustment devices connected to the upper four elements E1-E4. Therefore, an increase in the delay (negative phase shift) applied to the signals supplied to the elements E1 through E4 will cause a decrease in the delay (positive phase shift) applied to the signals supplied to the elements E5 through E8.

To maintain control of the maximum aiming gain and side lobe levels when changing the electrical tilt angle of the antenna assembly, each antenna element may require a different amount of delay for a given movement of the drive rod 200. In a linear mechanical phase adjustment device, this can be achieved by changing the angle of the V-shaped portion 606 (as shown in fig. 9) of the wedge 604.

It will be appreciated that the rotary mechanical phase adjustment arrangement of fig. 10 may be used in place of the linear mechanical phase adjustment arrangement 600 of fig. 12. With the rotary mechanical phase adjustment arrangement of fig. 10, different amounts of delay for a given drive rod 200 movement can be achieved by using different radii for the transmission lines mounted on each rotatable disk.

Although the arrangement of splitter units 116A-116C, 118A-118C and combiner unit 124 in fig. 12 is different from that previously described, it will be apparent from the previous description how this configuration distributes signal strength across elements E1 through E8.

Fig. 13 shows yet another embodiment and illustrates how the system of the present invention may be used with a bipolar antenna assembly. The use of bipolar antenna assemblies is well known and common in telecommunication systems. In this embodiment, the antenna assembly includes a set of four crossed dipole elements C1 through C4 arranged in a first column of four elements at an angle of +45 ° to the vertical and a second column of four elements at an angle of-45 ° to the vertical. The first and second columns are effectively electrically separate from the respective RF feed lines 1110, 1112 feeding each column. The first and second columns share common characteristics: the mechanical phase adjustment/shunt arrangement (generally 114 and 116) to each individual component (where present) is adjusted by means of a common servomechanism so that both the first and second columns have the same electrical tilt angle. Further, the servo motor 101 is controlled by a servo controller 103, and the servo controller 103 communicates with the servo motor 101 through a control cable.

It will be appreciated that the means by which the drive rod 200 of the mechanical phase adjustment means 601, 701, 1114, 1116 is moved need not take the form of the servo control means 101, 103 but may be in the form of alternative means operable from a location remote from the drive rod 200.

It will also be appreciated that the present invention provides an efficient way of remotely adjusting the electrical tilt angle of a phased array antenna. For example, it is possible to control and/or adjust the electrical tilt from a base station provided at the base of the mast on which the antenna elements are mounted, or from a location several miles from the mast, however without any manual adjustment of the antenna elements themselves. Furthermore, the present invention allows independent phase shifting of the signals to the individual sub-arrays within the antenna assembly and automatic differential phase adjustment of the signals to the central sub-array to allow the use of only two RF inputs. In addition, the signals to the upper and lower subarrays may be phase shifted by varying the degree to which they are not necessarily equal in magnitude. The vector summation of the signals supplied by the combiner 124 to the outer sub-arrays allows the signals supplied to the central sub-array to always be shifted to their median value, if required.

The combined mechanical and electrical control of the antenna system electrical tilt allows the optimal beam pattern of the antenna system to be produced with maximum aiming gain and low side lobe levels. Furthermore, such control may be achieved from a location remote from the antenna assembly, for example, several kilometers from the mast base. The performance of such an antenna system is significantly improved compared to existing systems.

It will be appreciated that while various embodiments of the present invention are shown and described as having different numbers of antenna elements (e.g., 1 through E5 on FIG. 5, E1 through E12 on FIG. 6), any of these embodiments may be adapted to include more or less antenna elements. These elements are subdivided into suitable arrangements of more or less sub-arrays than shown in a manner apparent to the skilled person from the above description, while still retaining the advantages described above.

Although the servo control mechanism 103 of the additional mechanical phase adjusting devices 150E1-150En is shown as forming part of the control unit 104, this need not be the case. The servo controller 103 may also be located remotely from the antenna assembly 100, as may the control unit 104, but need not be located at the same location.

Throughout the specification, reference to "electrical tilt" is intended to mean adjustment of the radiation pattern transmitted and/or received from an antenna assembly, which is not physically moving the radome or antenna elements, but is done by adjusting the phase of the signal supplied to one or more antenna elements. It will be appreciated, however, that the electrical tilt may be adjusted by a device having both mechanical and electrical adjustment elements, as shown, for example, in fig. 11.

Claims (19)

1. An antenna system (100) comprising:

an antenna assembly (102) having an electrical tilt angle, a plurality of elements (E1-En) mounted on an antenna carrier and arranged in at least two sub-arrays (100A, 100B), each sub-array comprising one or more of said elements;

a control device (104) configured to electrically control the phase of signals supplied to at least one of the sub-arrays (100A, 100B) from a location remote from the antenna assembly (102), wherein the control device comprises phase adjustment means (132, 134) for connection to the respective sub-array (100A, 100B) via first and second input feed lines (136, 138), respectively, to adjust the phase of signals supplied to the sub-array, and

additional mechanical phase adjustment devices (150E1-150En) for further adjusting the phase of the signals supplied to each element (E1-En) of the antenna assembly (102).

2. The antenna system of claim 1, wherein the control device (104) is placed at a base of the antenna carrier.

3. An antenna system as claimed in claim 1, comprising first and second phase adjustment means (132, 134) for connection to respective sub-arrays (100A, 100B) via said first and second input feeds (136, 138) respectively, for adjusting the phase of signals supplied to said sub-arrays.

4. An antenna system as claimed in claim 3, wherein said control means (104) comprises a separate port (126) for receiving a separate input signal to the system and means for dividing said input signal into first and second signals to be supplied to said first and second phase adjustment means (132, 134), respectively.

5. The antenna system of claim 1, further comprising:

means (124) for automatically controlling the phase of signals supplied to a first one (100A) of said sub-arrays in dependence on the phase of signals supplied to a second one (100B) of said sub-arrays.

6. The antenna system of claim 1, wherein said elements of said antenna assembly (102) are arranged in first, second and third sub-arrays (100A, 100B, 100C), and said antenna system comprises:

first control means (132) for controlling the phase of signals supplied to said first sub-array (100A);

third control means (134) for controlling the phase of the signal supplied to said third sub-array (100C); and

second control means (124) for automatically controlling the phase of signals supplied to said second sub-array (100B) in dependence on a predetermined function of the phase of signals supplied to said first and third sub-arrays (100A, 100C).

7. An antenna system as claimed in claim 6, wherein said second control means comprises a combiner unit (124) for receiving a first input signal having the phase of the signals supplied to said first sub-array (100A) and a second input signal having the phase of the signals supplied to said third sub-array (100C) and for providing an output signal to the second sub-array (100B) in dependence on a predetermined function of the phases of the signals supplied to said first and third sub-arrays (100A, 100C).

8. The antenna system of claim 6, wherein said predetermined function is the vector sum of the phases of the signals supplied to said first and third sub-arrays (100A, 100C).

9. An antenna system as claimed in claim 6, wherein the second control means comprises at least one quadrature combiner unit (174A, 174B) for receiving a first input signal having the phase of the signals supplied to the first sub-array (100A) and a second input signal having the phase of the signals supplied to the third sub-array (100C) and for providing a first output signal to one element of the second sub-array (100B) and a second output signal to a different element of the second sub-array (100B), wherein said first and second output signals are predetermined functions dependent on the phase of the first and second input signals.

10. The antenna system of claim 9, wherein the quadrature combiner unit (174A, 174B) combines to said first and second input signals such that the phase of said first and second output signals provided by the quadrature combiner unit (174A, 174B) is an average of the phase of said first and second input signals.

11. The antenna system of claim 1, comprising:

first control means (132) for controlling and/or adjusting the phase of signals supplied to a first one (100A) of said sub-arrays by a first amount; and

second control means (134) for controlling and/or adjusting the phase of signals supplied to a second one (100B) of said sub-arrays by a second number, wherein the magnitude and/or polarity of said second number is different from said first number.

12. The antenna system of claim 1, wherein said antenna assembly (102) is free of input feeds different from said first and second input feeds (136, 138).

13. An antenna system as claimed in claim 1, comprising respective signal distribution means (151N1-151N2) associated with each sub-array (100A, 100B) for separating and distributing signals to the respective sub-array elements (E1-E4, E5-E8).

14. The antenna system of claim 13, wherein each of said signal distribution means (151N1-151N2) includes splitter means (116A, 116B, 116C, 118A, 118B, 118C) for distributing the signal strength of said signal to said sub-arrays (100A, 100B) with a substantially uniform distribution.

15. The antenna system of claim 13, wherein the sub-arrays are first and second sub-arrays (100A, 100B), the distributing means are first and second distributing means (151N1, 151N2) associated with the first and second sub-arrays (100A, 100B), respectively, the antenna system is configured to divide the signals before input to the first and second distributing means (151N1, 151N2), and to combine the divided signals associated with different ones of the first and second distributing means (151N1, 151N2) to provide signals for input to first and second elements of a third sub-array (100C).

16. The antenna system of claim 1, wherein the additional mechanical phase adjustment means comprises an array of movable dielectric elements (606, 706).

17. The antenna system of claim 16, wherein each dielectric element is associated with a respective one of said elements (E1, En) of said sub-array (100A, 100B).

18. The antenna system of claim 17, wherein the elements (E1, En) of the sub-array (100A, 100B) and their associated dielectric elements have respective associated input transmission lines (T), and each of the dielectric elements (606) is configured for linear movement relative to the associated transmission line (T) to further adjust the phase of signals supplied to the elements (E1, En) of the sub-array (100A, 100B) via the associated transmission line (T).

19. The antenna system of claim 17, wherein the elements (E1, En) of the sub-array (100A, 100B) and their associated dielectric elements have respective associated input transmission lines (T), and each of the dielectric elements (706) is configured for rotational movement relative to the associated transmission line (T) to further adjust the phase of signals supplied to the elements (E1, En) of the sub-array (100A, 100B) via the associated transmission line (T).