An optically-switched transmit/receive lens array for beam-space adaptive communication systems

With the growth in today's modern communication world, multiple user and multi-path environments are becoming an ever increasing problem. These environments reduce the quality of the communication link through multiple users interfering with each other or self interference in multi-path environments. A common technique used to combat these environments, is to use a planar antenna array that steers its receptivity pattern in the direction of the desired user. The receptivity patterns for the arrays are controlled through adaptive algorithms that adjust the magnitude and phase of each received signal at each element in the planar array before coherently combining the signals. The magnitude and phase adjustments (complex weights) reverse the phase shifts induced in the signals as they propagate across the surface of the planar array. The disadvantage of this technique is that it requires significant amounts of computational processing power for large arrays containing many antenna elements. By using a microwave lens array instead of a planar array in the communication system, the received signals are transformed from a phase-space representation to a beam-space representation, which can reduce the processing load for the algorithm and may increase the overall signal to noise ratio (SNR) through partial beam-forming before the noise is added to the system. For these reasons, an optically controlled transmit/receive lens array is developed. The optical control of the lens array allows the array to switch between transmit and receive modes rapidly with negligible interference to the microwave signals. A low optical power single pole double throw switch is developed for routing the transmit and receiving signals in the array that has insertion loss of 0.3 dB and isolation of 36 dB. To model the performance of lens arrays for wireless communication systems, code is developed that calculates the imaging properties of lens arrays under different design conditions. The lens array modeling code is used in conjunction with a modified Least Mean Square (LMS) algorithm that turns off small valued complex weights, to improve the overall SNR and adaptation rate for the communication system.