Comparison of Butler Matrix and Rotman Lens Beam-Switching Networks at K-Band

This paper presents a comparative study between an $8\times 8$ Butler matrix and an $8\times 8$ Rotman lens operating over K-band (24.25 GHz to 27.5 GHz). The Butler matrix is designed based on aperture hybrid coupler and Schiffman phase shifter and printed on a multilayer stack-up to eliminate all the cross-overs and therefore, reduces the size and the insertion loss of the system. The Rotman lens has 8 inputs, 8 outputs, and 2 dummy ports and is designed to provide $\pm 45^{{\circ}}$ scanning range over the desired frequency band. Both beam-switching networks show less than −10 dB return loss over 24.25 GHz to 27.5 GHz. The designed $8\times 8$ Butler Matrix presents less insertion loss and a more compact size compare to the $8\times 8$ Rotman lens. However, the plotted Array Factor (AF) using the achieved output phase of each network proves that the Rotman lens is True Time Delay (TTD) while beam squint is an inherent characteristic of Butler Matrix.