A broad-band microstrip-to-waveguide transition using quasi-Yagi antenna

A novel microstrip-to-waveguide transition utilizing a coplanar-strip Yagi- like antenna is presented. The compact and single-layered quasi-Yagi antenn a fabricated on high dielectric-constant substrate has end-fire radiation p atterns, This monolithic-microwave Integrated-circuit (MMIC)-compatible ant enna is inserted in the E-plane of the rectangular waveguide to launch the TE10 dominant mode. With this new scheme of excitation, compact design and low-cost fabrication is achieved without requiring multilayered substrate o r backshort hermetic sealing. This transition, in addition, achieves very b road bandwidth and relatively low insertion loss, The transition's broad-ba nd characteristics are analyzed, and optimization guidelines for individual components of the transition are discussed in detail. A tolerance study pr oves that the transition is robust in mechanical alignment, The;X-band tran sition with alumina substrate demonstrates 35% bandwidth with return loss b etter than -12- and -0.3-dB insertion loss at the center frequency, This tr ansition should find wide applications due to its high compatibility with m icrowave integrated-circuit/MMIC technology and very low fabrication cost.