| 摘要 |
<p>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 φ which is phase-modulated at the scanning frequency φm of the individual aerials. The method comprises generating an ''estimated'' signal (26) of frequency φ phase-modulated at frequency φm, and multiplying (25) the generated signal by the received signal to derive an output which includes a selectable Bessel Function (J0) representing the directional polar diagram. The phase (with circular aerial arrays) (27) or amplitude (with linear aerial arrays) of φm as applied to phase-modulate the generated signal is controlled to maximise or minimise, as appropriate, the selected Bessel Function and thereby control the bearing direction of the polar diagram. The zero-order Function J0 gives a lobe maximum in the bearing direction, the higher orders, J1, J2, etc. a lobe null. The phase difference between φ in the generated and received signals is averaged-out by shifting the frequency of the former by an increment φx.</p> |
