A 4x4 substrate integrated waveguide (SIW) Butler matrix for two‐dimensional (2‐D) beam steering operating at 60 GHz is developed and experimentally evaluated in this article. The SIW beamforming network is a Butler matrix that is implemented with new designs of its constituent components in order to achieve a compact design. Namely, an SIW phase shifter that uses periodic rectangular slots is introduced for the first time at 60 GHz to replace the more area‐consuming meandered SIW. The phase shifter prototype, fabricated and measured as a proof of concept, demonstrates achieving an additional 20.3° of phase shift with using only 3 apertures without increasing the length or meandering the SIW line. The hybrid coupler and crossover sections of the SIW Butler matrix are also optimized to reduce the overall area of Butler matrix by 53.9%. The SIW Butler matrix prototype is fabricated and measured demonstrating achieving the differential output phase values needed to switch the beam of a 2‐D array in four quadrants while keeping the insertion loss magnitude imbalance of below 1.47 dB from simulations and 3.34 dB from measurements.

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A millimeter-wave two-dimensional (2D) beam switching planar microstrip patch antenna array excited by a 4 × 4 substrate-integrated waveguide Butler matrix (BM) is presented in this article. The BM architecture is modified to feed the planar array in a vertically integrated multilayer design to minimize parasitic effects due to junction discontinuity and reduce the radio frequency (RF) front-end footprint. This feed architecture enables the designer to control the phased array inputs to achieve a set of beam directions in four quadrants of radiation space at a desired elevation angle. For verification of beam switching via over-the-air measurements at 60 GHz, a bench-top anechoic chamber with proper transmitter and receiver antenna positioners was designed and fabricated using in-house laboratory resources. 2D beam steering was confirmed in the intended four quadrants of radiation space at ϕ 0 = 50 , 140 , 220 , and 300 and θ 0 = 30 ± 5 , meeting the design specifications with a very good margin. Each switched beam demonstrated between 5 and 6 dBi gain at 60 GHz, which is within 1 dB deviation from the simulated results. K E Y W O R D S60 GHz antennas, butler matrix, over-the-air pattern measurement, planar-phased arrays, SIW

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