Millimeter-wave microstrip-to-waveguide transition operating over broad frequency bandwidth

A broadband microstrip-to-waveguide transition is developed in the millimeter-wave band. Since novel geometrical features are applied in the printed pattern on the substrate, the proposed transition operates over a quite broad frequency bandwidth due to its double resonance. The two resonant frequencies can be controlled independently according to dimensions of the structure for required bandwidth and reflection level. Two versions of transition are designed and reliability is confirmed by measurements in the millimeter-wave band. The design frequency is 76.5 GHz. The bandwidth 12.9 GHz (16.8 %) is obtained for reflection level lower than -30 dB. In the other design for broadband, the bandwidth for reflection level lower than -20 dB results in 24.9 GHz (32.5%).

I. Introduction

Millimeter-wave technologies have been developed for applications of broadband high-speed wireless communication systems and high angular resolution microwave sensors such as wireless LAN, inter-vehicle communications, automotive radars and home security systems in these days. They are suitable applications for millimeter-wave technologies because high-gain and narrow-beam antenna can be developed readily even though the physical size of the aperture is small.