An adaptive nulling system digital microwave radio

An adaptive antenna preprocessor for an equalized demodulator is described. The adaptive antenna preprocessor is used to spatially null undesired directional interference by linearly combining the signal received by two antennas. A 64-tap adaptive equalizer contained within the digital demodulator is used to remove adjacent channel and intersymbol interference. The adaptive algorithms do not require knowledge of antenna calibration nor prearranged training signals. Instead blind adaptation is used during initial acquisition and decision-directed adaptation is used during tracking. Experimental results have shown that the system is capable of forming a 30-dB null over a 40-MHz-wide interference bandwidth. Time constants overall system in tracking mode have been measured and are of the order of 100 ms