X-Band Waveguide Coupler with Low Ripple and Losses

A novel wideband coupler operating in the frequency bandwidth from 10.7 GHz to 12.8 GHz is presented. The coupler consists of two crossed rectangular waveguides coupled through four circular apertures with different diameters. In order to improve the operating bandwidth and reduce the coupling ripple across the frequency bandwidth, a Chebyshev distribution is used to determine the radius and distance between the apertures. The coupling coefficient in the operating bandwidth is below -30 dB with less than 0.6 dB ripple. The return loss of all the ports is under -15 dB, and the maximum isolation between ports is below -60 dB. The proposed coupler has the advantage of having small size and low losses, which make it appropriate for high-power applications. The whole structure is simulated and optimized using CST microwave studio software and then fabricated and measured. Excellent agreement between measured and simulated results was achieved.