Flexible millimeter‐wave Butler matrix based on the low‐loss substrate integrated suspended line patch hybrid coupler with arbitrary phase difference and coupling coefficient

In this paper, a millimeter-wave Butler matrix with flexible phase differences is proposed using the substrate integrated suspended line technology. To begin with, a low-loss substrate integrated suspended line (SISL) circular patch coupler consisting of four circular sectors is presented, achieving arbitrary phase difference and coupling coefficient by adjusting the angle and radii of the sectors. Based on the proposed coupler, two prototypes of the SISL Butler matrix are designed, fabricated and measured for the demonstration. In prototype I, the crossovers are removed and a flexible phase difference is obtained with an area size of 2.5 lambda(g) x 2.8 lambda(g). In prototype II, both the crossovers and 45 degrees phase shifters are removed and the phase differences of +/- 45 degrees and +/- 135 degrees are obtained with an area size of 1.86 lambda(g) x 2.24 lambda(g). Low crosstalk between components and minimal radiation loss can be achieved by the SISL self-packaged characteristic and electromagnetic shielding. For both prototypes, the measured insertion losses are less than 2 dB at 26 GHz, including the loss of transitions and connectors, and the measured phase errors are less than +/- 10 degrees within a bandwidth of more than 10%. The proposed Butler matrix shows the advantages of compact size, low loss and high integration.