GB1405241A - High resolution radar apparatus - Google Patents

Abstract

1405241 Radar; aerials HUGHES AIRCRAFT CO 14 Feb 1973 [14 Feb 1972 (2)] 7312/73 Headings H4D and H4A A radar system comprises a transmit and a receive antenna, at least one of the antennas having a radiation pattern with a number of substantial sidelobes, and a scan control means for maintaining a single lobe of the other antenna in substantial alignment with only one of the lobes of the said one antenna, the substantial lobes appearing substantially at alternate pulls of the other antenna pattern. A transmit antenna has a single substantial lobe 14, Fig. 1. The antenna is driven by servo 13 which also controls device 28 so that the electronically steered receive antenna 12 is steered in synchronism with the transmit antenna. Elements, e.g. 18, 20, of the receive antenna are spaced at a distance greater than the wavelength of the radar signal. As a result the receive antenna has a number of substantial lobes, e.g. 42, 44, 46. The transmit and receive antenna synchronization is such that only one lobe 42 of the receive antenna is always illuminated by echo energy from the main lobe 40 of the transmit antenna. The radar system therefore has a narrow azimuth pattern. To reduce the effects of lobes, e.g. 44, 46, the patterns of the transmit and receive antennas are arranged so that the lobes of the receive antenna other than lobe 42, coincide with nulls of the transmit pattern. Several antenna arrangements are possible, e.g. the transmit and receive antenna may be interchanged or both may use electronically scanned antennas of the type 12. The electronic scanning may be by phase or frequency variation. Antenna 12 is preferably scanned such that the unwanted receive grating lobes do not point in directions capable of picking up energy from previous trasmitted pulses until after a specific delay. This suppresses reception of second go around return. Details of phase and frequency scanned antennas are given. Figs. 6a, 6b, illustrate scanned arrays. Transmit antenna 90 (Fig. 6b) includes phase shifters 94 coupled to feed 96 carrying pulses from transmitter 100. Controller 102 provides the phase control signals to both antenna 90 and receive antenna 92 (Fig. 6a). The thinned array antenna 92 comprises sub groups 106 to 109 with, e.g. elements 110 to 113. Mixers, e.g. 117 to 120 feed pre-amps 121 to 124 and common line 126. Phase shifters, e.g. 128 to 131 feed the mixers so that the received signals are phase shifted and mixed and then summed at I.F. in common line 126 (for the group 106). The other groups are similarly connected. Oscillator 140 feeds the phase shifters which is controlled by the transmitter. The signals in the common lines are passed on to further processing circuitry and then displayed (Fig. 6c, not shown). Fig. 7a illustrates transmit antenna 240 which may be mechanically, frequency or phase scanned. Receiving antenna 242 is of the frequency scan type and comprises sub groups 250 to 253. Sub group 250 comprises elements 246 to 249 feeding mixers 260 to 263. The mixers are provided with signals from ramp oscillator 290 and the I.F. signals are fed to line 276 and summed. The signals from the other sub groups are similarly processed and passed on to further circuitry and finally displayed (Fig. 76, not shown). The serpentine feed 292 is of such length that the frequency variation from the oscillator 290 provides a phase variation to vary the reception direction. Fig. 14 illustrates a radiating element comprising a dielectric plastics wedge 440 connected to a section of waveguide 442 through a matching section. The signal output is taken from connector 446 having a waveguide to coaxial stub.