A 2-Bit Beam-Steering Coding Array With High Beam Pointing Accuracy and Side Lobe Level for Wide-Angle Beam Scanning

We present a 2-bit coding array that features high beam-pointing accuracy and side-lobe-level (SLL) performance for wide-angle beam scanning. By symmetrically exciting a circular ring patch antenna and integrating a 90° phase shifter into the feeding line, a 2-bit characteristic is obtained. Four positive-intrinsic-negative (PIN) diodes are deployed in each antenna element and are controlled by a field-programmable gate array (FPGA) for switching the states of PINs. The 2-bit circular ring patch element is subsequently used for building a $1\times 12$ array. Apart from introducing a set of initial phases, we add initial amplitudes to the array for the first time to further improve the array performance. Both initial phases and amplitudes are obtained from the invasive weed optimization (IWO) algorithm by setting the goals of desired beam pointing accuracy and SLL performance. In addition, the active element pattern (AEP) that accounts for the mutual coupling between elements is used in the optimization process to provide an accurate array response. The simulated and measured results agree well, and both show that the proposed array can achieve a scanning range of ±50° with a beam pointing error (BPE) within ±1°, yet the simulated maximum SLL (MSLL), 9.2 dB, deteriorates to 8.3 dB in the measurement. The measured peak aperture efficiency is 43.2% with a peak gain as 13.2 dBi. The proposed array, which features low cost, low profile, and low power consumption, is well suited for intelligent Internet of Things (IoT) applications where space and power are limited.