Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/0428—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave
  • H01Q9/0435—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave using two feed points
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/0428—Substantially flat resonant element parallel to ground plane, e.g. patch antenna radiating a circular polarised wave
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/04—Resonant antennas
  • H01Q9/0407—Substantially flat resonant element parallel to ground plane, e.g. patch antenna
  • H01Q9/045—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means
  • H01Q9/0457—Substantially flat resonant element parallel to ground plane, e.g. patch antenna with particular feeding means electromagnetically coupled to the feed line

Definitions

• the present invention relates to a patch antenna element, and specifically to a dual polarised aperture coupled patch antenna element for the microwave range.
• Dual polarised or X-polarised antennas are commonly used today in base stations for mobile communication systems. With such antennas polarisation diversity techniques to combat signal fading in a radio transmission channel is made possible. Compared to systems employing vertical polarised antennas combined with space diversity techniques the number of antennas needed is reduced to half which saves cost and reduces the visual appearance of the antenna installation.
• One important performance measure for dual polarised antennas is the isolation between the two antenna ports which feed the two polarisations. Typically, more than 30 dB isolation between the ports is specified which corresponds to a power coupling of less than 1/1000 between said antenna ports.
• An aperture coupled patch antenna is a commonly employed antenna type for dual polarised systems.
• One or more metallic patches are fed by a micro strip feeding arrangement through a cross shaped aperture in a ground plane. Because of the symmetrical shape of the feeding arrangement the feed lines need to cross each other in at least one point. This crossing is typically achieved by using a so called air-bridge on one of the polarisations e.g. as shown in document US 4,903,033 (Tsao et al).
• a problem with the above prior art solution is the fact that a design with an air-bridge destroys the feeding symmetry and imposes an unwanted coupling between the two antenna ports which reduces the performance of the antenna.
• the object of the present invention is to solve the aforementioned prior art problem of unwanted coupling between the antenna ports due to one or more crossings of the feed lines.
• An advantage with the present invention is that the coupling between the antenna ports imposed by one or more crossings is reduced while the radiation pattern remains symmetric. Another advantage with the present invention is that a high degree of freedom is possible when designing antennas of the present type.
• FIG. 2 shows a first embodiment of the present invention where at least one feeding junctions is displaced;
• FIG. 3 shows a second embodiment of the present invention where at least one pair of feed lines is displaced;
• FIG. 4 shows a third embodiment of the present invention where at least one aperture slot is displaced
• FIG. 5 A shows a diagram of measured S-parameters for a feeding arrangement according to prior art
• FIG. 5B shows a diagram of measured S-parameters for a feeding arrangement according to one of the embodiments of the present invention where an irregular configuration is employed;
• FIG. 6 shows the radiation pattern of an antenna with a feeding arrangement according to one of the embodiments of the present invention.
• Figure IA shows a feeding arrangement according to prior art with a regular configuration.
• One or more metallic patches C are fed by a cross shaped aperture in the ground plane.
• a feeding arrangement D shown in figure IA comprises a ground plane with a first aperture slot Ia and a second aperture slot Ib where the slots cross each other perpendicularly to form a cross shaped aperture in the ground plane. Furthermore, the aperture slots in figure IA cross each other perpendicularly and centrally so as to form a symmetric configuration.
• the feeding arrangement further comprises a feeding plane with a first antenna port Pa for feeding microwave energy via a first feeding junction 3a into a first pair of feed lines Ya which extend in parallel along the first aperture slot Ia on each side of thereof, and a second antenna port Pb for feeding microwave energy via a second feeding junction 3b into a second pair of feed lines Yb which extend in parallel along the second aperture slot Ib on each side thereof.
• the feeding junctions 3a and 3b are arranged on a centre line, A and B, of their associated pair of feed lines, and hence are symmetrically arranged in respect to said associated pair of feed lines.
• each pair of feed lines Ya and Yb extend in parallel and equidistant (with a distance d ) along their respective aperture slots Ia and Ib, and on each side thereof, respectively.
• each pair of feed lines, Ya and Yb incorporates two stubs, 4a-4b and 4c-4d, of equal length.
• the feed lines cross each other in one point 5 at a mutual distance from each other to avoid direct conductive connection between the feed lines.
• a common solution is to use air as a dielectric between the feed lines and therefore an air-bridge is often employed, but a person skilled in the art realises that the present invention is also applicable to solutions with other dielectric material in the crossing.
• figure IB an alternative regular configured feeding arrangement according to prior art is shown.
• the main difference between the feeding arrangements in figure IA and IB is the number of crossings, there being four crossings 5a-5d in figure IB.
• PCB Printed Circuit Boards
• Another difference between the arrangements in figure IA and IB is that no stubs are present in the arrangement in figure IB. Obviously, stubs may be added to the feed lines in the arrangement in figure IB.
• the present invention solves the aforementioned problem with a novel design of the feeding arrangement in which the regular configuration of the feeding arrangement according to prior art is replaced by an irregular configuration of the feeding arrangement, and thereby compensating for the imbalance caused by one or more crossings.
• the isolation between the antenna ports is improved if the feeding arrangement is irregularly configured compared to the prior art solutions.
• the irregular configuration will result in an additional asymmetrical feeding which will compensate for the feeding asymmetry imposed by the one or more crossings, and hence reduced coupling is achieved while the radiating pattern of the antenna remains symmetric.
• Figure 2 shows a first embodiment of the present invention.
• two feeding junctions 3a and 3b are shown.
• the irregular configuration of the feeding arrangement involves the displacement of a first feeding junction 3 a in relation to a symmetrical centre line A which passes centrally through a first pair of feed lines Ya.
• the purpose of the displacement is to compensate for the coupling introduced by the crossing 5.
• the feeding junction is displaced a distance e along one of the feed lines.
• the displacement of a distance e from the symmetrical line A will depend upon the degree of coupling introduced by the crossing.
• a second feeding junction 3b could be displaced relative to a centre line B instead of the feeding junction 3a relative to the line A 5 or both feeding junctions 3a and 3b could be displaced in relation to their respective centre lines A and B.
• a second embodiment is shown in figure 3.
• the feeding arrangement is irregularly configured in that a first pair of feed lines Ya is displaced in relation to an associated aperture slot Ia which extends parallel thereto.
• the distance from the two feed lines to the centre of the aperture slot Ia is d x andc? 2 , respectively, where d ⁇ ⁇ d 2 .
• the pair of feed lines Ya are displaced sideways in respect of the centre line of the aperture slot with an amount which compensates for the coupling imposed by the crossing 5.
• the pair of feed lines Ya could also be displaced sideways in the other direction in relation to the slot Ia.
• a second pair of feed lines Yb could be displaced sideways in relation to an associated aperture slot Ib instead of the pair of feed lines Ya relative to the slot Ia, or both pair of feed lines Ya and Yb could be displaced in any direction in parallel to their associated slots Ia and Ib, respectively.
• FIG 4 a third embodiment of the present invention is shown.
• the feeding arrangement in figure 4 is irregularly configured where a first aperture slot Ia is displaced sideways in relation to a second aperture slot Ib with a distance/ from a symmetrical centre line A, but still remains perpendicular with the aperture slot Ib, while the pair of feed lines Ya and Yb are placed on their respective centre line A and B.
• the aperture slot Ib could be displaced sideways in relation to the aperture slot Ia 5 or both aperture slots Ia and Ib could be displaced sideways in relation to each other while still remaining perpendicular to each other.
• FIG. 5 A shows a diagram of measured S-parameters for a feeding arrangement according to prior art
• Figure 5B shows a diagram of measured S-parameters for a feeding arrangement according to the first embodiment of the present invention where feeding junctions are displaced.
• the feeding junctions 3 a and 3b were each displaced by approximately 14 mm from the symmetrical lines A and B, respectively, i.e. e « 14 mm. From figures 5A and 5B it can be concluded that the isolation with a feeding arrangement according to the present invention (figure 5B) is substantially improved over the relevant microwave range compared to the prior art solution (figure 5A).
• Figure 6 shows simulation results of the radiation pattern of a patch antenna with a feeding arrangement according to one of the embodiments of the present invention. It can be seen from the diagram that the radiation pattern shows excellent radiation characteristics with minimum coupling in the desired main beam direction. Hence, figure 6 shows that the present invention has a good radiation directivity which is another important performance measure when designing dual polarised patch antennas of the present type.
• a feeding arrangement according to the present invention may incorporate one, two, three or all four of the characteristics of the above embodiments. Therefore, the present invention offers the skilled person a high degree of freedom, in respect to design parameters, when designing a feeding arrangement which requires high isolation between the antenna ports in the presence of one or more crossings.
• the present invention may be combined with other well known antenna isolation techniques in the art, e.g. the use of parasitic elements on the radiating side of the antenna and/or shield wall and/or non-quadratic patches etc. Hence, even more combinations are available to the skilled person in the design process.
• the present invention is not limited by the described embodiments.
• the disclosed embodiments should merely be seen as possible alternatives of the inventive concept of the present invention which is only limited by the scope of the appended claims.
• the shape of the aperture slots may have other geometrical shapes than those shown in the figures, but remain substantially rectangular; and the length of the different stubs may differ, and further the stubs may extend in both orthogonal directions from the top of the feed lines with different amounts.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Waveguide Aerials (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

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ID=41016328

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (5)

• 2008
  • 2008-02-25 SE SE0800435A patent/SE532035C2/sv not_active IP Right Cessation
• 2009
  • 2009-01-14 EP EP09715016.3A patent/EP2248223A4/en not_active Withdrawn
  • 2009-01-14 WO PCT/SE2009/000009 patent/WO2009108097A1/en not_active Ceased

Patent Citations (5)

Non-Patent Citations (1)

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