A Steerable DC-1 GHz all-pass filter-Sum RF space-time 2-D beam filter in 65 nm CMOS

An electronically steerable broadband radio frequency (RF) filter-sum beamforming filter using 1^st-order all-pass filters is proposed. The beamforming filter has the 2-D transfer function Ha (z_x, s_ct), which uses M-section cascaded 1^st-order all-pass filters and analog combiners as building blocks. Beam steering is achieved by tuning the group delay of the all-pass filters via a control voltage. For beam directions ψ ≤ 20^o from array broadside, M = 1 provides close to ideal broadband response, and 1 <; M ≤ 4 is shown to provide nearly ideal broadband response for beam directions ψ > 20°. The array factor of the beamformer is evaluated using 65 nm CMOS BSIM 4 simulations of the all-pass filters and a 4-channel RF combiner for a linear antenna array of 4 antennas and is shown to provide steerable beams at 1 GHz. The CMOS simulations verify a broadband response from DC to 1 GHz.