Wideband Hybrid Couplers With Unequal Power Division/Arbitrary Output Phases and Applications to Miniaturized Nolen Matrices

In this article, a new design approach for developing hybrid couplers with arbitrary power division and the phase difference is presented. The design is based on a transformer-based coupler with high isolation between sum and difference ports. Based on this model, a modified coupler is developed by including two L-shaped networks to produce constant phase differences at two output ports. Slotlines and microstrip-to-slotline transitions are used for expanding the bandwidth and introducing a 180° phase difference at the difference port. Two prototypes with equal and unequal power division are designed and verified. Experimental results reveal that the proposed designs can achieve constant phase difference, low insertion loss, and satisfactory matching across a broad bandwidth of more than 40%. Based on the proposed designs, a simplified multibeam Nolen matrix is also designed utilizing only three hybrid couplers and no phase shifters. The compact beamforming network demonstrates that the proposed component is very useful for size reduction in wireless communication systems.