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 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.