Beamwidth-Invariant and Independent Multibeam Time-Modulated Antenna Arrays With Stepped Amplitude–Phase Modulation

Pseudorandom time-modulated array (TMA) offers high design degrees of freedom for low-complexity beamforming. However, existing pseudorandom modulation schemes usually rely on subarray partitioning to generate multiple independent beams, resulting in a tradeoff between beamwidth, array size, and the number of beams. This article proposes a novel pseudorandom modulation technique, named stepped amplitude–phase (SAP) modulation, for beamwidth-invariant and independent harmonic beamforming. By superimposing and discretizing only the complex-weighted carrier signals of the wanted harmonic orders, the proposed technique allows independent control of multiple harmonic beams under a single radio frequency (RF) chain. Since each antenna element in this case produces multiharmonic spectra with arbitrary amplitude and phase weightings, the beamwidth is decoupled from the number of beams for a fixed array size. A pattern synthesis approach is then developed to analytically determine the instantaneous modulation statuses for a specified number of beams, beam-scanning angles, and sidelobe levels (SLLs). It benefits the real-time design of modulation waveforms based on a field-programmable gate array (FPGA). The effectiveness of the proposed approach is verified through a Ku-band 16-element U-slot microstrip linear array.