A wideband dual‐polarized microstrip antenna is presented. By designing the coplanar parasitic patches and modified feed probes, antenna profile is decreased significantly. Shorted pins are used and 34 dB isolation between input ports is then achieved. A phase difference feed network is introduced to suppress higher‐order modes and reduce the cross polarization to −27 dB. To verify the design, a prototype of the antenna is fabricated and experimentally studied. Measured results show that 30.3% operating bandwidth (VSWR < 1.5) and good dual linear polarization characteristics with a profile height as low as 0.08λ are achieved. Due to the very compact configuration, the proposed antenna is suitable for micro‐base‐station applications.

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A novel pattern synthesis approach for circularly polarised (CP) four‐dimensional (4D) antenna arrays with microstrip patch elements is presented. Sequential rotation method is used to reduce the cross‐polarisation component of the CP antenna array and good circular polarisation purity is achieved. Moreover, the time modulation technique of 4D antenna arrays is adopted for the realisation of low sidelobe levels (SLLs), thus forming a CP 4D antenna array. The differential evolution (DE) algorithm is used to optimise the time sequences, and hence low SLLs and sideband levels (SBLs) are obtained. To achieve low SLLs and low SBLs simultaneously, both of the static amplitude excitations and time sequences are optimised by the DE algorithm. Simulation results show that the CP 4D patch arrays can be used to achieve lower SLLs, while the dynamic‐range ratios of the amplitude excitations can be very small or even uniform.

A direction-finding technique based on time-modulated arrays (TMAs) is presented. Signals radiated/received by the TMAs with moving phase centre suffer from the Doppler effect and the shifted frequency is direction-dependent. This interesting property allows TMAs to be used for direction finding. A radar bearing system using the TMA is proposed. Performance of the new direction-finding technique is discussed and compared with conventional techniques. Numerical results show that this method is effective and provides reconfigurable angle-searching range and bearing accuracy. It is proved to be a flexible bearing method qualified for different detection requirements just by changing the time schemes of the TMAs.

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