Design of broadband microstrip three-way directional coupler for multibeam antenna application

In this letter, a design of broadband microstrip three-way directional coupler (TWDC) is presented. The broadband performance of the microstrip TWDC is realized by the method of cascading multi-section. The broadband TWDC is designed to achieve equal power division and −120°, 0°, and +120° phase differences between output signals. To verify the broadband design, a prototype of three-section microstrip TWDC operating at C-band is designed, fabricated and measured. The measured results show that the power division error of the designed broadband TWDC is less than ±0.7 dB and phase error is less than ±12° at a relative bandwidth of 16%. To verify its performance in multibeam application, the designed TWDC is used as a beamforming network for multibeam antenna array to generate three orthogonal beams.