| 摘要 |
Quadrifilar helix antenna systems for half-duplex communications which are capable of providing a positive gain, quasi-hemispherical antenna pattern over widely separate transmit and receive frequency bands. The antenna systems according to the present invention generally comprise a quadrifilar helix antenna, first and second circuit branches for changing the resonant frequency of the antenna to first and second resonant frequencies corresponding to the transmit and receive frequency bands, and switches or other disconnection means which are used to electrically isolate the first circuit branch from the antenna during periods when the antenna is receiving a signal and to electrically isolate the second circuit branch from the antenna during periods of transmission. In a preferred embodiment, the disconnecting means are implemented as PIN diodes or radio frequency Gallium arsenide field effect transistor switches, the elements of the quadrifilar helix antenna which form each bifilar helix are short-circuited at their distal ends, and energy is fed to and induced from the antenna via receive and transmit 90 DEG hybrid couplers which are electrically connected to the bifilar loops of the quadrifilar helix antenna. Also provided are matching means which are coupled to the elements of the quadrifilar helix antenna for increasing the operating bandwidth of the antenna. |
