A Vertical Transition Between Rectangular Waveguide and Coupled Microstrip Lines

In this letter, a novel transition between a rectangular waveguide and coupled microstrip lines is presented. A differential microstrip patch antenna (DMPA) inside the waveguide acts as a radiation element. The antenna is composed of the main patch, the short-end parasitic patch, and the matching network. By implementing the short-end parasitic patch, the bandwidth of differential mode signals is greatly increased, while transmission of common mode signals is strongly suppressed. Back-to-back arrangements of such a transition were fabricated and measured. The results show that the 10 dB return loss bandwidth reaches 14.5 GHz, and the insertion loss at the center frequency (96 GHz) is 0.5 dB. Such a transition is suitable for numerous millimeter-wave applications.