A Study on Subarray Design for Performance Optimization of Active Phased Array Antenna

Abstract

Active array antennas are widely used in radar application due to good signal-to-noise ratio and graceful degradation. The active array antennas use hundreds or thousands of transmit- receive modules, so even if some get failed, the antennas can still operate. These active array antennas are currently in the transition period from analog to digital array. Compared to the analog array with proven technology, the digital array gets good performances, such as enhanced dynamic range and highly simultaneous beam-forming coverage, but gives rise to high cost and complex hardware structure. In this respect, the digitized subarray can be an alternative array architecture. In this dissertation, two types of digitized subarray configuration are discussed, namely, irregular and partially thinned digitized subarray configuration. First, the irregular subarray configuration to be optimized by using random search method for large-scale active array antenna is presented to maximize G/T and minimize MPSL. To accomplish this objective, mathematical formulation is done for G/T and multi- beam analysis with respect to proposed active array antenna. The formulation gives insight that G/T depends on the subarray configuration presenting the number of array elements and shape of subarrays. To form the subarrays in the optimization scheme, a set to select the number of array elements of each subarray is generated, then each subarray has different number of array elements. In the set S, it is possible to choose same number of array elements repeatedly in the set S to form 20 subarrays. By random search method, the reference and optimized subarray configuration are designed. Compared to the reference subarray configuration, the optimized subarray configuration obtains 1.38, 0.68 and 1.18 dB higher G/T, MPSL and average PSL, respectively. Higher G/T results from similar value of G/T at each subarray at the expense of higher SLL characteristic due to shape and size of subarrays. Next, the partially thinned digitized subarray configuration to be optimized by using 2-stage random search method is presented. The goal is to maximize SLB performance and minimize MPSL in the constraint that decrease of G/T is minimized. For this goal, mathematical formulation is described for G/T, multi-beams and SLB cover rate. In the optimization scheme, 2-stage random search method is specified. To form the subarrays in the 1st stage, a seed TRM assembly consisting of 2ⅹ2 array elements are selected at nearest position from origin and expanded to fill 32 TRM assemblies which are constituting a subarray. In the 2nd stage, two subarrays at the outer boundary in the quadrant are randomly selected, then 16 array elements of those subarrays are eliminated randomly to generate partially thinned subarrays. Although the G/T of the optimized subarray configuration is lower by 0.07 dB/K than the reference subarray configuration, the false alarm rate related to the SLB cover rate decreases to one-sixth and the MPSL decreases by 1.6 dB. These results indicated that both irregular and partially thinned digitized subarray configurations offer good performance in G/T, the SLB capability and MPSL, and so the digitized subarray configuration can be applied in various large-scale active phased array antennas as an alternative architecture between analog and digital array for versatile radar systems.