Abstract A bistatic radar system using separate antennas for transmit and receive and taking advantage of the fact that the net radar resolution depends on the product of the two gain patterns. In one illustrated system of the invention, a low resolution transmitter pattern is combined with an ambiguous high resolution receiver pattern formed of a thinned array of phase controlled radiating elements. The elements are separated by a distance greater than the wavelength of the RF signal. In this thinned array approach, the suppressed receive grating lobes may be placed at alternate nulls of the transmit pattern by spacing the receiver array elements to be approximately one-half the transmitted antenna width. The transmit radar forms a conventional sector scanning antenna pattern that illuminates the forward area and the receiving antenna has elements spaced so they form a multilobe pattern that contains selected spacing of grating lobes. In operation only one of these grating lobes is illuminated by the transmit pattern. The transmit and receive antennas are scanned in synchronism either sequentially or in some jump scan sequence to provide the sector scan display. The system is operable substantially without microwave waveguides in the wings of an aircraft by providing a local oscillator signal that is phase shifted to control the antenna pointing. Other systems in accordance with the invention may also utilize a thinned array for transmitting and a single lobe antenna receiving or may utilize thinned array for both transmitting and receiving.
A bistatic radar system comprising: a transmit and a receive antenna, both being electronic scan arrays and each having a plurality of spaced antenna elements such that each forms a thinned array wherEin the spacing between the elements of one array is not equal to the spacing between the elements of the other array thus forming two sets of grating lobes with one set of grating lobes in vernier relationship to the other; means coupled between said transmit and receive antennas for synchronizing the pointing directions thereof and providing thereby position coincidence of a selected grating lobe of one array with a selected grating lobe of the other array; a plurality of radar receiver mixers each responsive to signals received by one of said plurality of receiver antenna elements; a plurality of phase shifters each supplying a phase shifted local oscillator signal to each of said radar receiver mixers; a plurality of intermediate frequency preamplifiers each responsive to signals from said plurality of radar receiver mixers; a corporate feed supplying said local oscillator signal to each of said phase shifters.
Claim 2
Dependent Claim
180 words
A bistatic radar system comprising: a transmit and a receive antenna, both being electronic scan arrays and each having a plurality of spaced antenna elements such that each forms a thinned array wherEin the spacing between the elements of one array is not equal to the spacing between the elements of the other array thus forming two sets of grating lobes with one set of grating lobes in vernier relationship to the other; means coupled between said transmit and receive antennas for synchronizing the pointing directions thereof and providing thereby position coincidence of a selected grating lobe of one array with a selected grating lobe of the other array; a plurality of radar receiver mixers each responsive to signals received by one of said plurality of receiver antenna elements; a plurality of phase shifters each supplying a phase shifted local oscillator signal to each of said radar receiver mixers; a plurality of intermediate frequency preamplifiers each responsive to signals from said plurality of radar receiver mixers; a corporate feed supplying said local oscillator signal to each of said phase shifters.
Claim 3
Dependent Claim
25 words
The combination of claim 1 wherein said corporate feed supplying said local oscillator signal to each of said phase shifters is constructed of coaxial cable.
Claim 4
Dependent Claim
52 words
The combination of claim 1 including local oscillator means and a plurality of phase shifters and mixers with a mixer coupled to each receiver antenna element and a phase shifter coupled between said local oscillator means and each mixer, and including means to control the phase of said plurality of phase shifters.
Claim 5
Dependent Claim
123 words
The combination of claim 1 wherein said thinned array receive antenna elements make up a plurality of sub groups of equal numbers of antenna elements; a plurality of radar receiver mixers each coupled to one of said antenna elements; a plurality of intermediate frequency preamplifiers each coupled between one of said radar receiver mixers and a line common to one of said sub groups; a plurality of phase shifters each coupled to one of said radar receiver mixers; a corporate feed supplying a signal from a local oscillator to each of said plurality of phase shifters; and a plurality of time delay circuits each responsive to signals appearing on a line common to one of said sub groups and the antenna scan angle.
Claim 6
Dependent Claim
29 words
The combination of claim 4 wherein said corporate feed supplying a signal from a local oscillator to each of said plurality of phase shifters is constructed of coaxial cable.
Claim 7
Dependent Claim
37 words
The combination of claim 4 wherein said time delay circuits include a plurality of time delay elements coupled through a plurality of switches, said switches being energized as a function of the scan angle of the antenna.