Broadband Passive Two-Feed-Per-Beam Pillbox Architecture for High Beam Crossover Level

Multi-beam antennas based on quasi-optical systems feeding a single radiating aperture generate orthogonal beams with a low crossover level between adjacent beams (around -13 dB at most). To circumvent this limitation, we present a circuit architecture allowing the excitation of a quasi-optical system (pillbox system) with two feeds per beam to reach much higher beam crossover levels. To this end, a specific eight-beam passive circuit is designed to cover the 76-86 GHz frequency band. It is based on a single-layer substrate integrated waveguide (SIW) coupler followed by equiphase SIW lines. The maximum phase and amplitude imbalance between the sources are only 35 (λ_g/1g, with λ_g the wavelength in the SIW lines at the design frequency) and 1.3 dB, respectively, and the isolation is better than -19 dB. The measured beam crossover level of the corresponding antenna is better than -3.2 dB, corresponding to an improvement of 16 dB with respect to single-feed-per-beam pillbox systems. The proposed passive architecture offers beam crossover levels suitable for low-cost electronically controlled multi-beam applications, as for next-generation 5G backhauling systems.