A layered antenna

Abstract: The present invention provides a layered antenna (otherwise known as a flat-plate antenna) having a number of radiating elements (201), each radiating element comprising a first substantially rectilinear aperture (210), having a first pair of oppositely directed probes (220,222) extending into an area defined by the aperture with secondary apertures (212,214) arranged coextensive with and on opposite sides of the primary aperture, adjacent said first pair of probes, said secondary apertures operable to modify the beamwidth in a plane coextensive with said first pair of probes. There is also provided a method of receiving and transmitting signals by means of a layered antenna of this conctruction.

Description: This invention relates to layered antennas and in particular relates to beamwidth control means for such. Layered antennas, also known as flat plate antennas comprise a ground plane having an aperture or an array of apertures, a dielectric spacer, a feed probe network (typically copper tracks printed on a thin dielectric such as polyester) a second dielectric spacer and a second apertured ground plane. Such an antenna is known from GB 2261554 (Northern Telecom). The ground planes may be shaped about an axis of the apertures to improve azimuth beamwidth GB 95 02528.4 (GB 2 286 926) (Northern Telecom). The array may be dual polarised, with e.g. a first set of feed probes in a vertical direction and with a second set of feed probes perpendicular to the first set of feed probes. Advantageously the dual polarised arrangement is defined by two layered antennas separated by a common ground plane, to reduce coupling between the polarisations. A particular problem encountered with dual-polarised linear array antennas is that the azimuthal beamwidth of the two polarisations is dissimilar. Typically the axis of the array is arranged in a vertical orientation and the height and power of the array determine the size of each aperture. Such an optimum will have an azimuthal beamwidth of e.g. 75°-90°. Ideally the beamwidth of the two polarisation overlap. Under such circumstances, however, the edge portions of the ground plane - which cover the feed network for the probes - modify the beamwidth to e.g. 60° resulting in a requirement for either a) more vertical arrays or b) a modification of the width of each aperture so that it is unacceptably wide. The present invention seeks to provide an antenna which overcomes or reduces the aforementioned problems. In accordance with the present invention there is provided a layered antenna comprising a first aperture having a first pair of oppositely directed probes extending into an area defined by the aperture, characterised in that secondary apertures are arranged coextensive with and on opposite sides of the aperture adjacent said first pair of probes, said secondary apertures operable to modify the beamwidth in a plane perpendicular to the first and secondary apertures coextensive with said first pair of probes. Preferred aspects of the invention are set out in the appendant claims. In order that the invention may be understood, reference shall now be made to the Figures wherein: Figure 1 shows a typical beam pattern in horizontal section of a prior art dual polarised antenna; Figure 2 shows a plan view of a first embodiment of the invention; Figure 3 shows a section through the dual polarised layered antenna shown in Fig. 2; Figure 4 shows a second embodiment of the invention; Figure 5 shows a third embodiment of the invention; Figure 6 shows a typical beam pattern in horizontal section as produced by a dual polarised antenna made in accordance with the present invention, and; Figure 7 shows a further embodiment of the invention. Figure 1 shows a typical azimuthal beam pattern as provided by a known dual polarised antenna 10. The azimuthal beam pattern determined by the vertically oriented probes provides a narrower angular beam coverage 110 than the angular beam coverage 120 determined by the horizontally oriented probes. Figure 2 shows a four element vertically oriented layered antenna array 200 wherein each element 201 comprises a central rectangular aperture 210 having both horizontally and vertically arranged probes. Either side of the central aperture 210 there are further apertures 212, 214. Vertical probes 216, 218 determine the vertical polarisation beam shape and horizontal probes 220, 222 in conjunction with aperture 212, 214 determine the horizontal polarisation beam shape. Figure 3 shows a cross-section through the dual polarised array; the apertures 212, 214 extend through all ground planes 224, 226, 228. Between ground planes 224 and 226 and ground planes 226 and 228 are positioned first dielectric spacers 232, 240, dielectric films 234, 242 and second dielectric spacers 238, 246. Dielectric films 234, 242 have feed circuits 236, 244 printed thereon. In the case of a single polarisation antenna being employed, then ground plane 228, dielectric spacers 240, 246 and dielectric film 242 are not required. It is believed that surface currents acting in the ground plane about the horizontal probes 220, 222 are directed by the side aperture 212, 214 and this has the effect of modifying the horizontal beamwidth. The side apertures may extend an equal distance in the vertical direction as the central aperture but this is not mandatory. Figure 4 shows a variant of the invention wherein additional horizontal probes 412, 414 are provided in the side apertures 212, 214. These additional feed probes can conveniently be arranged on a dielectric film with the feed circuit being shielded by the ground plane between the two apertures. Figure 5 shows a further variant of the invention wherein the antenna 500 is formed about a vertical axis 510. Such a feature or bend in the plane can broaden the vertical beamwidth pattern of the antenna. Figure 6 shows an azimuthal cross section of a beam formed by an antenna made in accordance with the present invention wherein the antenna provides a dual polarised beam shape having the vertical beam shape 610 correspond with the horizontal beam shape 620 in the same plane. Figure 7 shows a two element layered array antenna 700 wherein only horizontal polarisation feed probes 720, 722 are provided: the beam shape has a greater angular coverage than an equivalent array having only a single aperture provided with feed elements.

Claims: A layered antenna 201 comprising a first aperture 210 having a first pair of oppositely directed probes 220, 222 extending into an area defined by the aperture, characterised in that secondary apertures 212, 214 are arranged coextensive with and on opposite sides of the aperture adjacent said first pair of probes, said secondary apertures operable to modify the beamwidth in a plane perpendicular to the first and secondary apertures coextensive with said first pair of probes. A layered antenna having a linear array of radiating elements, each radiating element comprising an antenna according to claim 1 wherein the first apertures of each element define an array axis and wherein the secondary apertures are operable to modify the beamwidth in a direction perpendicular to said axis. A layered antenna according to claim 1 or 2 wherein a reflecting backplane is situated behind the probes. A layered antenna according to any one of claims 1 to 3, wherein a second set of probes extend into the first aperture in a direction perpendicular to the first set of probes operable in a second mode of polarisation. A layered antenna according to any one of claims 1 to 4 wherein further probes extend into the secondary apertures. A layered antenna according to any one of claims 1 to 3 wherein the antenna comprises a first apertured groundplane, a first dielectric spacer, a dielectric film having a feed circuit printed thereon, a second dielectric spacer and a second groundplane. A layered antenna according to claim 4 wherein the antenna comprises a first apertured groundplane, a first dielectric spacer, a dielectric film having a feed circuit for a first polarisation printed thereon, a second dielectric spacer, a second apertured groundplane, a third dielectric spacer, a dielectric film having a feed circuit for a second polarisation printed thereon, a fourth dielectric spacer and a third ground plane. A layered antenna according to any one of claims 1 to 7 wherein said secondary apertures extend the beamwidth in the plane perpendicular to the first and secondary apertures coextensive with said first pair of probes.

Inventors: WEBB ROGER CHARLES, WEBB, ROGER CHARLES
Applicants: NORTEL NETWORKS LTD, NORTEL NETWORKS LIMITED
Application year: 1995
Main classification: H01Q21
IPC codes: H01Q21