A Time-Modulated Antenna Array With Continuous Sideband Spectrum Distribution

Traditional time-modulated antenna arrays (TMAs) usually introduce sideband radiations at a multiple of discrete harmonic frequencies. To improve radiation efficiency of TMAs, various evolutionary algorithms become very popular in sideband suppressions. Apparently, the sideband radiation levels highly depend on the performance of these evolutionary algorithms. To achieve robust sideband suppression through physical designs, a novel pseudorandom hybrid phase-amplitude modulation technique is proposed to distribute the sideband radiation power over a continuous spectrum, rather than only at discrete harmonic frequencies. Following the law of energy conservation, sideband levels (SBLs) in this case naturally become extremely low, which eliminates the difficulty arising in TMAs' sideband suppressions. Moreover, the novel modulation technique allows the synthesis of scanning beams with ultralow sidelobe levels, and the corresponding time modulation sequences could be directly calculated from analytical formulations. Therefore, evolutionary optimization algorithms are not necessary in the proposed TMA design procedure, which facilitates the real-time on-board calculation with an field-programmable gate array (FPGA) board. As compared with traditional TMAs, the proposed TMA achieves ultralow SBLs ( $< -35.0$ dB) with much fewer time modulation statuses. Numerical and experimental results are presented to demonstrate the effectiveness of the proposed TMA.