Patent GB-812027-A (GB)
Title: Waveguide
Inventor: BARLOW EDWARD JOSEPH
IPC: H01Q15/06
Filed: 1956-08-17
Abstract: 812,027. Aerials; radar. SPERRY RAND CORPORATION. Aug. 17,1956, No. 25289/56. Class 40 (7). The invention relates to a wave transmission arrangement for the production of a directive radiation pattern the direction of whose maxima is dependent on the frequency of the wave energy. As described, it is applied to radar systems for the purpose of obtaining an elevational sweep. Fig. 1 shows such a system in which energy is fed from a number of radar sets 19, 21, 23, 25, 27 and 29, operating in sequence and at slightly increasing frequencies to a dipole radiating system 13 mounted at the focus of a vertically directed paraboloidal reflector 11. Above the reflector is situated a stacked plurality of the wave transmission arrangements 40. These are each waveguides, with side walls parallel to the plane of the paper as shown, the side walls being stepped inwards along the lines 41, 43, 45, 47, 49 and 51. The guides are finally closed by a rear wall 77 which is extended downwards at 79. The bottom and front faces of the guides are open except that they may possibly be protected by a layer of dielectric. The steps 41 and the like are oblique and make increasing angles with the horizontal. If energy of the lowest frequency f 1, from radar 19 is fed to the system it will propagate in the guides only as far as the steps 41, being lower in frequency than the cut-off frequency of the next narrower section of the guides, and will be reflected there to be radiated with a directive pattern 119. The next lowest frequency f2, from radar 21 will in the same way reach, and be reflected at, the steps 43 to be radiated with the pattern 121. Radars 23, 25, 27 and 29 with successively increasing frequencies will in like manner operate with the patterns indicated at 123, 125, 127 and 129 respectively. The assembly 40 may be supported by flanged wheels on a circular track for rotation about a vertical axis by azimuth drive motor 61. The dipole system 13 must be attached to the system for rotation therewith and a suitable joint provided in the feed. Instead of the waveguide walls being stepped as described above, they may be smoothly tapered to produce the same result. The front elevation of such an arrangement is shown in Fig. 3. In this embodiment the dipole system is connected through rotating joint 16 with a single radar. The tuning of both the transmitter and receiver of this radar are synchronously varied to effect a smooth vertical scan and the information obtained may be shown on a slant range/angle of elevation display. Instead of the steps in the guide walls being straight they may be curved in the plane of the walls and are preferably made parabolic so as to collimate energy in one plane. If this is done the dipole system may be directed to a simple cylindrical parabolic reflector instead of a paraboloidal one (Fig. 4, not shown). This parabolic reflector may, in turn, be eliminated if the dipole system is directed at the bottom of the wave transmission stack and the said bottom shaped to form a waveguide lens collimating in the direction perpendicular to the waveguide walls. Alternatively the bottom of the transmission stack may be cut to form a lens in two dimensions so that when directly fed from the dipole system it replaces the paraboloidal reflector of Fig. 1 and the waveguide steps can be made linear (Fig. 6, not shown). As described, all the stacked stepped waveguides, of which there may be thirty to fifty in a practical embodiment, are the same except for the possible shaping of their bottom edges to form a lens, they may, however, vary about a median plane. The stepped waveguide units may be constructed by making the unit as wide as its greatest width throughout and then laminating to the walls thin metal sheets of the required shape to form the necessary steps.