| 摘要 |
A quadrifilar helix antenna system capable of providing a positive gain, quasi-hemispherical antenna pattern over widely separate transmit and receive frequency bands. This new antenna system comprises concentrically arranged, but electrically isolated, transmit and receive quadrifilar helix antennas, each of which comprises two bifilar helices arranged orthogonally and excited in phase quadrature. In the preferred embodiment, the antenna elements forming each bifilar helix are short-circuited at their distal ends, and energy is induced from the receive antenna and coupled to the transmit antenna via receive and transmit 90 DEG hybrid couplers which are electrically connected to the bifilar loops of the respective receive and transmit antennas. Also provided are switches or other disconnection means which are used to electrically isolate the transmit antenna during periods when the antenna is receiving a signal and to electrically isolate the receive antenna during periods of transmission. In the preferred embodiments, these disconnecting means are implemented as PIN diodes or radio frequency Gallium arsenide field effect transistor switches.
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