One-channel adaptive antenna for troposhere microwave relay lines

Adaptive antennas improve the performance of troposphere microwave relay lines (TMRL) by reducing fading and eliminating competing signals. The signal steadiness gain is equivalent to an increase in the number of channels and grows with antenna aperture. A horn system containing adjustable gaps is considered with regulation by microprocessor control of the input signal, which is digitized and compared with reference values. The signal processing algorithm uses a linear relation for the criteria which is not always satisfied and can lead to errors. In April 1981 experiments were made with a one-channel antenna coupled to a TMRL with a relay path of 389 km, an antenna power of 43 dB and an aperture of 20 x 20 m2. The horn contained 64 controllable elements. The results showed that with low signal levels the gain was a factor of 2, the noise reduction for a one-component signal in comparison with a simple relay was 5-7 dB, the gain for a three-component signal was 3-4 dB, and interference elimination amounted to 4-8 dB. It is concluded that adaptive antennas should be used on TMRL. Protection of control elements against high transmitter power levels should be studied.