Radio Frequency by Steve Winder and Joe Carr - HTML preview
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19.9 Antenna multi-coupling
The sharing of antennas and feeders between a number of co-sited services is not only a precise method of controlling frequency isolation, it is an economic solution to the problems of antenna and tower management. An antenna may be shared between a number of receivers or transmitters, or shared simultaneously by both receivers and transmitters. Receiver sharing requires a splitter, i.e. a filter, to separate the frequencies for each receiver and an amplifier to make up the filter losses. Transmitters can share an antenna through circulator/isolators and filters. To obtain the required selectivity, stability
Txsystem RxsystemSpectrum dividing Ferrite
filter Cavity 0 dBisolator resonator−1 dB TxTx1 band
− 50 dB Spectrum dividing
filter0 dB −1 dB Rx band
− 50 dB
Receiver splitter amplifier
0 dB 3 dB gain Tx3Rx band −50 dB
Loss 0.7 dB 0 dB
−1 dB
−20 dB
−30 dB
Figure 19.4 Typical sub-band transmitter/receiver sharing (é Crown Copyright 1991, Radiocommunications Agency)
and power handling capability the filters are often solidly constructed cavity resonators with an insertion loss of 1 dB and a bandwidth of 0.1% to the −20 dB points. Figure 19.4 shows the layout of a transmitter/receiver sharing system.