own T/R module and the entire array is made up of thousands of such modules, limited failures in these components would not significantly affect the performance of the radar. A theoretical example of the expected degradation in the antenna pattern for randomly located T/R failures is shown in Figure 4.4. The top panels provide three examples of failure scenarios (no failures, 20% failure, and 40% failure). The bottom panel shows the one-way antenna patterns for the three cases, with uniform weighting assumed. As the number of failed T/R modules increases, the main lobe decreases, the nulls in the pattern are filled, and the sidelobe envelope is retained. T/R module failures could also have a serious effect on polarization capabilities and should be addressed in the MPAR R&D process. Nevertheless, the general shape of the pattern is retained. Non-random locations of the failed modules, or complete failures in larger groupings or subarrays, could have a more significant effect on the pattern; the overall aperture performance of the array is retained under this simplified scenario.

FIGURE 4.4. One-way phased array antenna pattern for varying number of T/R module failures. The top panels provide the locations of the operational T/R modules, with failures randomly dispersed across the array. The bottom panel gives the antenna pattern for the three different failure ratios (no failure, 20% failure, 40% failure).

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