Patent GB-1470884-A (GB)
Title: Microstrip antenna structures and arrays
IPC: H01Q9/04
Filed: 1974-03-27
Abstract: 1470884 Aerials BALL BROS RESEARCH CORP 27 March 1974 [17 April 1973] 13512/74 Heading H4A An antenna or antenna array comprises an electrically conducting ground surface, a single layer electrically conducting surface including both an R.F. radiator conducting area and an R.F. feedline conducting area, and a dielectric sheet between the ground surface and the single layer conducting surface. As described, a square microstrip radiator 22, Fig. 1, having alternative feed lines 20, 21 extending respectively from the centre of one of its sides, and from one of its corners, is formed upon a substrate 26 of dielectric material by a conventional printed circuit process. The underside of the substrate 26 is positioned over a ground plane 28, which may be a conductive cladding on said underside. The length of each side of the radiator 22 is approximately half the wavelength in the dielectric material at the anticipated operating frequency. It is made slightly less in order to ensure that the input impedance of the radiator is substantially wholly real. The feed lines 20, 21 may be tapered for matching purposes. When the feed line 20 is used, linearly polarized waves are radiated, and when the feed line 21 is used, circularly polarized waves are radiated. In a second embodiment, a rectangular radiator has alternative feed lines connected respectively to the centre of a long side, and to the centre of a short side (Fig. 2, not shown). This enables operation at either of two frequencies. In a third embodiment, a square shaped radiator 40, Fig. 3, is fed simultaneously at the centres of two adjacent sides 42, 44 by feed lines 46, 48 from a printed circuit 90 degree phase shifter 50. When R.F. input is applied to the corner 52 of the phase shifter the radiator 40 emits L.H. circularly polarized waves, and when the input is applied to the corner 54 it emits R.H. circularly polarized waves. In a fourth embodiment, a circular radiator is used instead of the square radiator of the Fig. 3 embodiment (Fig. 4, not shown). A number of the radiators may be assembled to form an aerial array. Thus, four square radiators 80, 82, 84, 86, Fig. 5, in linear formation are fed at the centres of corresponding sides by a corporate R.F. feed line through respective microstrip phase shifters, 100, 102, 104, 106 which are variable to provide beam steering. The phase shifters may be of the kind in which stepwise variations are obtained by open- or short-circuiting lengths of microstrip transmission line by means of switching diode  (Fig. 9, not shown). Tapering of the amplitude across the aperture of an array, for side lobe reduction, may be obtained by inserting wholewavelength sections of lossy microstrip transmission line in the feeds to radiators which are away from the centre of the array (Fig. 10, not shown). In another array, each radiator element is rectangular, with a width that is approximately half the wavelength in the dielectric material at the anticipated operating frequency and a length that is more than that wavelength. The radiators are spaced apart by half-wavelengths, and each is fed on one long side at at least two points which are spaced apart by not less than a wavelength (Fig. 8, not shown).