Performance Analysis of Cross Beam Correlation Microwave Radiometers Using Two Orthogonal Subarrays

A cross beam correlation microwave radiometer (CBCR) using two orthogonal subarrays is introduced. It consists of two spatially orthogonal subarrays and a correlation receiver, where a pencil beam is realized by the coherence of two orthogonal fan beams. However, the differences between the two orthogonal fan beam patterns lead to gain loss and negative sidelobes. The gain loss (effective aperture reduction) of cross arrays has been proven to lead to deterioration in radiometric resolution. However, the properties of negative sidelobes and their impact on observations have not been fully investigated. In this article, the performance of the cross array is comprehensively analyzed, and the systematic expressions of beam characteristics and radiometric resolution are proposed. The main beam efficiency (MBE) is redefined to prevent it from exceeding unity. Two novel factors, namely the spatial sparsity factor and phase influence factor, are introduced to quantitatively assess the influence of the cross array on radiometric resolution. In addition, a planar cross-antenna array is proposed to remedy the shortcomings of Mills cross in small radiometer applications, and the performance of the two cross arrays is evaluated based on the above methods. Finally, the numerical simulations and hardware experiments with an L-band prototype are conducted to verify the theoretical results.