WO2006018567A1

WO2006018567A1 - Integrated frequency filtering radiating device and appropriate filtering method

Info

Publication number: WO2006018567A1
Application number: PCT/FR2005/050590
Authority: WO
Inventors: Philippe Minard; Ali Louzir; Christophe Goujon
Original assignee: Thomson Licensing
Priority date: 2004-07-28
Filing date: 2005-07-18
Publication date: 2006-02-23
Also published as: FR2873857A1; WO2006018567A9

Abstract

The invention relates to an electromagnetically coupling radiating device which is embodied such that coupling conditions are selected in such a way that at least one undesirable frequency is rejected. In particular, the electromagnetic coupling is carried out with the aid of an (M)/slot (S) transition line, the coupling conditions are selectable by adjusting the length(L1 and/or L2) of the line (M) and/or slot (S).

Description

RADIANT DEVICE WITH INTEGRATED FREQUENCY FILTERING AND CORRESPONDING FILTERING METHOD

The present invention relates to a radiating device operating by electromagnetic coupling in which a signal is filtered in order to reject at least one undesirable frequency. The invention also relates to a method for filtering a signal in order to reject at least one undesirable frequency in a radiating device operating by electromagnetic coupling. Wireless telecommunications have undergone a strong development since the advent of consumer mobile telephony. These communications systems have considerably diversified and no longer affect not only telephone networks but also wireless LAN systems, for example WLAN networks at 2.4GHz and 5GHz. Radiant devices using electromagnetic coupling to effect power transfer are commonly used in such systems. We note that these systems require spectral resources increasingly important to meet the demand for new expensive services in terms of throughput. Thus it becomes necessary to manage the spectral resources at best. The exploitation of resources allocated for each of the communication systems must therefore be optimized and the possible interactions between wireless systems must be reduced.

In addition, bidirectional communication systems, such as satellite systems or wireless home multimedia applications, incorporate transmit / receive functions that require significant isolation between these two channels, given the significant relationship between signal levels. transmission and reception channels.

Thus, the invention is part of a process of reducing interactions and consists in rejecting unwanted frequencies such as lines interference from other systems, noise from the transmit / receive system, harmonic, subband of a broadband antenna ...

The elimination of unwanted frequencies in communication systems is generally achieved using one or more conventional filters known to those skilled in the art and placed in the system transmission chain. However, it is known that the filters add losses in the useful band of the communication system.

The present invention provides a radiating device having means for filtering a signal so as to reject at least one undesirable frequency that does not have the drawbacks of the filtering means of the prior art and a corresponding filtering method.

The present invention relates to a radiating device such that the coupling conditions are chosen so as to allow rejection of at least one undesirable frequency.

Thus, the radiating device has an integrated filtering function. Indeed, the use of the electromagnetic coupling itself to filter unwanted frequencies allows according to the invention to integrate this function in the radiating device itself. This makes it possible to relax the filtering constraints in the transmission chain and / or to improve the filtering without increasing the number of poles of an already existing filter. It also observes a minimization of filtering losses since filtering is allowed by non-coupling conditions at the transition.

Thus, the invention makes it possible, for example, to eliminate parasitic lines coming from other systems (for example: dual mode antenna), to eliminate the parasites coming from the transmission / reception chain, to eliminate the noise. harmonic of an antenna, to eliminate a sub-band of a broadband antenna (example: to eliminate the 5GHz of an antenna Ultra Large Band e 3-10GHz), to improve the isolation of the accesses of a bi-antenna bandaged.

In one embodiment, the electromagnetic coupling being done using a line / slot transition, the coupling conditions are selected by adjusting the length of the line.

In another embodiment, the electromagnetic coupling being done using a line / slot transition, the coupling conditions are selected by adjusting the length of the slot. Thus, according to these last two modes of realization, the unwanted frequency (s) are eliminated at the level of the radiating device itself and thanks to the line / slot transition.

In one embodiment, the adjustment of the length is a function of the ratio of two frequencies: one desired, the other undesirable. The invention also relates to a method for filtering a signal to reject at least one undesired frequency, said method of selecting electromagnetic coupling conditions for rejecting the undesired frequency.

Other features and advantages of the present invention will appear on reading the description of various embodiments, the description being made with reference to the attached drawings in which:

Fig. 1 is a diagram of a radiating device according to the prior art.

Fig. 2 is a diagram of a radiating device according to the invention. Fig. 3a to Fig. 3e show several examples of radiant devices in which the invention can be implemented.

Fig. 4a represents a radiopaque positive according to the prior art and FIG. 4b represents a radiating device similar to that of FIG. 4a in which the invention has been implemented. Fig. Figure 5 shows the spectrum of the radiating devices shown in Figures 4a and 4b as a function of frequency.

Fig. 6a represents a radiating device according to the prior art, FIG. 6b and FIG. 6c represent two radiating devices similar to those of Figure 6a in which the invention has been implemented.

Fig. 7a to 7c show the results obtained with the radiating devices shown in FIGS. 6a to 6c.

In Figure 1 is shown a radiating device operating by electromagnetic coupling according to the prior art. According to this representative figure of an example of electromagnetic coupling, the coupling is done in a transition zone 1 between a line M and a slot S. The line M is for example a microstrip line and its role is to convey the signals to the radiating device, from a power port 2. In order to achieve optimum electromagnetic coupling, the slot S and the line M are arranged in a precise geometric structure.

The optimal coupling condition within a Knorr line / slot transition is defined by the following equation:

where H _M is the field H of the microstrip line and £ _M is the E field of the slit

This results in the following way: for the coupling to be maximal, the field H of the microstrip line must be maximum in the plane of the transition and the field E must be maximum in the plane of the transition. This implies that we bring back in the plane of the transition a short-circuit (CC) on the microstrip line and an open circuit (CO) in the slot.

FIG. 1 is thus presented by way of example a known method for reducing the optimal coupling conditions in the plane of the transition, namely a guided quarter-wave λ _û s / 4 in the slot S terminated by a CC and a guided quarter-wave X _GM M under the line M terminated by a CO. X _GM and _û s λ are respectively the guided wavelength in the line and M in the slot S.

According to the invention the coupling conditions are such that they allow the filtering of one or more unwanted frequencies. Thus, according to the invention, the optimum coupling conditions are degraded by going into planes, where either the field E _s or the field H _M is not maximum. Thus a degree of freedom is available to filter the unwanted frequencies.

The invention starts from the observation that the coupling takes place since one of the two fields E _s and H _M is not zero. Indeed, according to the formula of the coupling in the transition line / slot (C =

AH _M ), the coupling still takes place as long as one of the two fields E _s or H _M is different from zero.

Thus, according to the invention, filtering a frequency amounts to adjusting the length, either of the microstrip line or of the slot, so as to reject the unwanted frequency of the line / slot transitions.

Depending on whether the microstrip line or the slot ends with an open circuit or a short-circuit, eight configurations are then possible and shown in the table below.

FIG. 2 shows an exemplary embodiment according to configuration No. 7. The lengths of the slot L _s and the line L _M are determined so that the coupling itself allows the filtering of an undesirable frequency F2, while allowing correct operation at the frequency F1.

In order to allow correct operation at the frequency F1, the length of the slot L _s between the line / slot transition is of the order of α λ _GS1 / 4 where λ _GS1 is the guided wavelength in the slot at the frequency F1 and α an odd integer.

The length L _s is for example λ _GS1 / 4.

The length L _M of the microstrip line is determined as follows: to reject the frequency F2, the length of the line L _M must be of the order of k - λ _GM2 / 2 where λ _GM2 is the length of d guided wave of the micro - ribbon line at the frequency F2 and k an integer. To ensure the coupling at the frequency F1, the length of the line L _M must also be of the order of λ _GM i / 4 + k '- λ _GM1 / 2 where λ _GM1 is the guided wavelength of the line microstrip at frequency F1 and k 'an integer.

Hence the length L _M must satisfy the following equation:

Let A = ^ ₁ = ^{1 + 2} - * ^' λ', GMl 2 - k

Thus, for any ratio of two frequencies (F1, F2), there exists a pair (k, k ') close to this ratio. For example a table as proposed below and taking the possible values for a certain number of couples (k, k '), lets you choose the most important pair (k, k') of the frequency ratio (F1.F2).

The length L _M is then chosen equal to k • λ _GM2 / 2.

Calculations similar to those made above for configuration No. 7 can be easily performed for the other configurations. For generalization, we call in the following L _ND , the length which corresponds to non-degraded conditions, that this length corresponds to a length of line or slot, and L _D to degraded conditions, that this length corresponds to a length of lign e or cleft.

To determine the length L _ND , four cases are distinguished according to whether the micro-ribbon line or the slot ends with a CC or a CO. These four cases are summarized in the following table where λ _GMl is the guided wavelength of the microstrip line for frequency F1 and λ _GS1 denotes the guided wavelength of the slot for frequency F1, this table gives lengths L _ND for which the coupling conditions are undegraded:

For example, in case No. 1, the coupling condition is not degraded for the microstrip line which is terminated by a CO, when the length L _ND is of the order of α •

To determine the length L ₀ which generates degraded coupling conditions, four cases are distinguished again according to whether the slot or the line ends with a DC or a CO. These four cases are summarized in the table below which gives the lengths L ₀ for each degradation configuration of the coupling conditions. In this table, λ _GMι is the guided wavelength of the microstrip line at the frequency Fi and λ _GSι denotes the guided wavelength of the slot line at the frequency Fi.

Type of

Type Filter Condition Coupling Condition Conditions on

Termination case F1 / F2 to F2 on L _D to F1 on L _D k and k ¹ line of the line k integer no

Micro¬ F, 1 + 2 k

N ° 1 CO k KMI / ² K _M J ^{4 +} ^ KMJ ² null ribbon F ₂ 2 kk 'integer k integer

Micro-F, 2 k '

No. 2 CC ^λ GM1 / ⁴ + k KMI / ² k 'whole non-ribbon k' KMI / ² F ₂ 1 + 2 k no k integer F, 2 k '

N ° 3 Slot CO Ks _I i ^{4 +} k λ _GS2 / 2 k 'λ _GSl / 2 k' integer no F ₂ 1 + 2 k none k integer no F, 1 + 2 k

N ° 4 Slot CC KsJ ⁴ + k ^' KsJ ² null F ₂ 2 kk' whole

In the case No. 1, where the coupling conditions are degraded on a microstrip line terminated by a CO, the length L _{D must} be of the order of k - λ _GM2 / 2 where k is an integer not zero to reject the frequency F2. To ensure the coupling at the frequency F1, the line L _D must also be of the order ^of K _M J ^{4 + k} 'K _M J ^{2 OR k} ' ^an integer.

Hence the length L _D must satisfy the following equation:

_* 1 + 2 - fr '

Let ^ * L-Λ = GM 2 _ λ, GMl 2 - k Thus, for any ratio of two frequencies (F1, F2), there exists a pair (k, k ') close to this ratio. The table of the function F ₁ 1 + 2 k 'set above Y ^~ 2 k above allows to select the pair (k, k') closest to the ratio of the frequencies (F1, F2).

The length L ₀ is then chosen equal to k • λ _GM2 / 2.

The table below shows the value of the function ¹ 1 _ 2 k 'in

K 1 + 2 k function of k and k 'for k integer and for k' nonzero integer. It makes it possible to choose the pair (k, k ') when the function ^F i ₌ ^{2 k} is considered.

1 + 2 - Â:

For lengths of L _D important, it is possible to reduce this length by taking a value k lower (k integer). Changing this value k slightly modifies the coupling of the line / slot transition. It also acts on the periodicity P of filter harmonics where P = F ₂ Jk.

Note that to move from a LD line terminated by a CO to a LD line terminated by a DC, it is simply necessary to subtract a quarter of guided wavelength to the initial value.

The invention can be applied to all radiating devices including a line / slot transition, in particular a slot antenna, an annular slot antenna, a longitudinal radiation antenna (LTSA, Vivaldi, etc.), a printed dipole. There are line / slot transitions, in particular in the half-wave slot antennas, as shown in FIG. 3b, antennae with longitudinal radiation as shown in FIG. 3c, the dipole antennas as shown in FIG. 3d, or in the line / slot-to-slot transitions as shown in FIG. 3rd. Two examples of embodiments of structures designed on a Rogers RO4003 type substrate with the following characteristics are given below: Er = 3.38, TanD = 0.0027, h = 0.81 mm.

^1st example: Filtering the harmonic 3 in an annular slot antenna. FIG. 4 shows on the one hand, FIG. 4a, an annular slot antenna sized at a frequency F1 = 5.5 GHz according to the conventional methods, and on the other hand, FIG. 4b, an annular slot antenna sized according to the design rules of FIG. invention for rejecting the harmonic 3, the frequency F2 = 16.5 GHz. This antenna was designed according to configuration No. 8 presented in the table above, ie with a DC at the end of the micro-ribbon line to minimize the length of the line inside the annular slot. The length of the line between the transition and the DC is λ _GM2 / 4.

Figure 5 shows the gain of the radiators shown in Figure 4a (solid line) and Figure 4b (dotted line) as a function of frequency. This figure shows that the harmonic 3 of the annular slot antenna has been removed for the radiating device of FIG. 4b.

^2nd example: filtering of a line in a line / slot transition. In Figures 6 are shown different structures for filtering such a line. In Figures 7, are shown the results obtained with the various structures shown in Figure 6 in the form of two curves. The first curve in solid line represents the reflection coefficient denoted dB (S11) or dB (S22). Reading this curve makes it possible to see how the device is adapted in the frequency band. This device is therefore adapted to operate at the frequency 5.5GHz. The second curve in dashed line represents insertion losses and is referred to as dB (S21) or dB (S12). Reading this curve makes it possible to see how the device attenuates the signal between the two ports 1 and 2 of the structures of FIG. 6.

Figure 6a shows a conventional structure with a line-to-slot transition from head to tail at F1 = 5.5 GHz. It is desired to filter the frequency F2 = 3 GHz according to the configuration No. 7. As shown in Figure 7a, the frequency F2 is attenuated by 2.5 dB on the dB curve (S21). The F1 / F2 ratio is 1.83. From the table presented before, we deduce k and k 'is k = 3, k' = 5. Thus L _D becomes 3 λ _GM2 / 2. This new structure is proposed in Figure 6b on a different scale. With this new structure, it is noted that the frequency F2 is attenuated by 20 dB on the curve dB (S21), as represented in FIG. 7b.

We also note that we can reduce the length of the line on which the coupling conditions are degraded by choosing a value of k lower, for example k = 1. Thus L ₀ becomes λ _GM2 / 2. The structure is then actually shorter as shown in FIG. 6c and it is however observed that the frequency F2 = 3GHz is always attenuated by at least 20 dB as represented on the curve dB (S21) of FIG. 7c. is not limited to the embodiments described and those skilled in the art will recognize the existence of various embodiments such as the possibility of bending the lines and / or slots in the event that they are too long, or modify the length of the line and that of the slot simultaneously with respect to the optimal conditions of coupling. The open circuits may also in particular be radial stubs or any other structure fulfilling this function.

Claims

1 - radiating device operating by electromagnetic coupling, the electromagnetic coupling being done by means of a line transition (M) / slot (S), characterized in that the coupling conditions are chosen by adjusting a length chosen from the length (L1) of the line (M) or the length (L2) of the slot (S).

2 - radiating device according to claim 1, characterized in that the adjustment of the length is fo nction of the ratio of two frequencies: one desired, the other undesirable.

3 - Process for filtering a signal in order to reject at least one undesirable frequency in a radiating device operating by electromagnetic coupling, the electromagnetic coupling being done using a line (M) / slot (S) transition, characterized in that the coupling conditions are selected by adjusting a length selected from the length (L ₁ ) of the line (M) or the length (L ₂ ) of the slot (S).

4 - Process according to claim 3, characterized in that the adjustment of the length is a function of the ratio of two frequencies: one desired, the other undesirable.