| 摘要 |
<p>1475319 Aerials HARRIS CORP 23 May 1974 [23 May 1973] 23186/74 Heading H4A A passive antenna element for use in a phased array, and which can reflect incident circularly polarized electromagnetic radiation with a relative phase shift of 0, 90, 180 or 270 degrees comprises four concentred spiral arms rotationally displaced by 90 degrees relative to each other, and central switching diodes and D.C. bias controls 120-126 for connected selected inner arm ends together according to the desired phase shift, the arms being so formed, or terminated at their outer ends, that currents travelling outwardly along the arms are reflected into the active region (that where waves of length # are received or transmitted and constituted by an annular region of mean radius #/2#) with 0 degrees relative phase shift for one opposed pair of arms and by 180 degrees for the other opposed pair of arms. As shown, the latter phase shifts are introduced by reactances X 1 and X 2 . Alternatively the length of the arms may be varied or the spirals may have different sizes, Figs. 2 and 3 respectively (not shown). In operation, in the embodiment of Fig. 1, it is said that received right circularly polarized radiation produces currents which are in phase along any radius in the active region, and which propagates to the terminal ends T 1 -T 4 , but after reflection to the active region, do not cause radiation due to 0, 180, 0, 180 degrees relative phasing. On reaching inner terminals 1-4, current swapping or reflection occurs as described in copending Specification 1,469,156. The outwardly propagating waves reaching the active region the second time still have a 0, 180, 0, 180 degrees relation and do not cause radiation, until they have undergone a further phase shift by reflection at the ends T 1 -T 4 and reappear in phase in the active region.</p> |
