On the use of some FMCW transmission schemes for radar angular resolution improvement

A method which uses simultaneous transmission is considered. A two-antenna scheme, simultaneously transmitting FMCW chirps with opposite slopes is analysed. A beamwidth reduction factor of the order of 1.38 with -30dB sidelobe level is shown to be obtainable and a good performance, as shown by the bearing-Doppler ambiguity surface, may be achieved. Three FMCW chirps, slightly shifted in time, are considered for transmission in a three-antenna scheme. The time differences are introduced to provide an adequate means for separation of the signals on reception and these differences are much less than the sweep repetition period. The double simultaneous and the triple near-simultaneous transmission schemes avoid all the inherent disadvantages of sequential transmission methods. A frequency-shifted triple-transmission method is also considered for comparison purposes