| 摘要 |
PCT No. PCT/GB88/00407 Sec. 371 Date Jan. 4, 1990 Sec. 102(e) Date Jan. 4, 1990 PCT Filed May 24, 1988 PCT Pub. No. WO88/09938 PCT Pub. Date Dec. 15, 1988.A method and apparatus of deriving a directional polar diagram from the signals R received by a synthetic-aperture aerial (in direction-finding applications), or P from such an aerial (in radio-beacon applications), these signals including a carrier of frequency omega which is phase-modulated at the scanning frequency omega m of the individual aerials. The method comprises generating an "estimated" signal (26) of frequency omega phase-modulated at frequency omega m, and multiplying (25) the generated signal by the received signal to derive an output which includes a selectable Bessel Function (JO) representing the directional polar diagram. The phase (with circular aerial arrays) (27) or amplitude (with linear aerial arrays) of omega m as applied to phase-modulate the generated signal is controlled to maximize or minimize, as appropriate, the selected Bessel Function and thereby control the bearing direction of the polar diagram. The zero-order Function JO gives a lobe maximum in the bearing direction, the higher orders, J1, J2, etc. a lobe null. The phase difference between omega in the generated and received signals is averaged-out by shifting the frequency of the former by a increment omega x.
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