Very Concise Eight-Port Coupler for Two-Dimensional Beamforming Application
Compact and concise scheme of eight-port couplers without junctions discontinuities, vias, high or low characteristic impedance transmission lines are proposed. The structure is based on a back-to-back double layer microstrip configuration with a common ground in between. Only two half-wavelength microstrips on both layers with two half-wavelength slots in the ground form the complete configurations of the coupler. Remarkably, the property of the coupler at the central frequency is barely sensitive to the width of either the strips or the slots. The satisfying matching, isolation, and directional couplings with equal amplitude can be achieved within a more than 24% fractional bandwidth. An experimental example is fabricated and tested for verification and demonstration, and a satisfying correspondence can be observed between the results of simulated and measured. Besides, another functional example, a two-dimensional beamforming network for a 2×2 array is exemplified to exhibit the application of the eight-port coupler for beamforming.