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In this paper, the impact of amplitude and phase imbalance on a proposed dual differential fed patch antenna is analyzed in the context of system effective reflection coefficient and axial ratio (AR). A single square patch with four ports is used as a solo radiating element and provides absolute symmetry at radiating. An in-depth analysis will be presented to understand the impact of external RF chain components on the performance of the proposed antenna. When fully differential excitations and perfect symmetry can be achieved, all six polarization states exhibit identical system effective reflection coefficients with close to ideal AR for CP. When phase imbalance and amplitude imbalance only exist in between the two differential pairs, the antenna system matching performance is found to be unchanged. In the presence of the feed network, circular polarization (CP) achieves a measured maximum AR of 0.49dB along the antenna pointing angle, while linear polarization (LP) has a measured maximum cross polarization of −30dB. This work monitors the beamwidth over which the AR can be kept below 1dB (BW-AR −1dB ). Based on the optimization of phase imbalance, a novel BW-AR −1dB enhancement technique is introduced. Compared to the case with better AR at the main beam location, an improvement of 14 • beamwidth is measured without significant degradation of AR. Isolation better than 40dB across an operating frequency of 9.27 − 9.4 GHz has been experimentally demonstrated for the proposed dual differential fed technique. The resulting antenna is compact and low profile which is an appealing candidate for phased array applications.INDEX TERMS Dual differential fed, 1dB AR beamwidth, patch antenna, polarization diversity, system effective reflection coefficient, high isolation.

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Adaptability is essential for antenna systems, especially those operating in harsh or unpredictable environments. Adaptable electrically steerable antennas (AESA) provide this flexibility. AESA use in radar systems is expanding due to new technologies that enable higher power and more miniaturized implementations. Polarization diversity is another way of adding adaptability to radar systems.System-level analysis of a typical radar system was performed to determine the specifications for a series of 4x4 switchable polarization AESA arrays meant to operate from 9.4 to 9.5 GHz. These arrays were designed on a multilayer Rogers Duroid PCB.Sub-components such as a microstrip feeding network, patch antennas, switches and hybrid couplers were integrated on the same PCB utilizing both sides of the board.Simple 4x4 linear and 4x4 circular polarized arrays were designed and fabricated on this chosen package. These single-polarization arrays were compacted into a single lowprofile PCB that measures 2.5x2.5 inches. The measurements of both single-polarization arrays closely matched the simulated results, which helped correct issues with the design process before adding more polarization states. Measurements show that these modularly scalable 2.5x2.5-inch PCBs can achieve a gain of between 12 and 21 dB depending on how many boards are tiled together.A technique for increasing the bandwidth of a single patch antenna through resistive loading was also explored. Using commercially packaged resistors to load a single patch resulted in a bandwidth increase of 400 MHz.Once simple single-polarization arrays were verified, two switchable polarization arrays, one linear and one circular, were designed and simulated. These switchable