Spatially coherent array technology for wide-band infrared heterodyne receivers
The feasibility of a 3 by 3 (nine-element) coherent receiver array operating at 10.6 μm with 1.5-GHz instantaneous IF bandwidth and near theoretical quantum-noise limited operation has been demonstrated. An analysis of the complex amplitudes of received signal and local oscillator was performed to yield high signal conversion efficiences and controlled optical beam crossovers. Experimental results are presented that include mixer frequency response, mixer sensitivity, and far-field "receiving antenna" patterns for the array showing -3-dB optical crossovers between adjacent array elements. It is concluded that infrared heterodyne arrays provide a multiplicity of coherent resolution elements analogous to multifeed microwave antennas.