A 10–50-GHz UWB BPF With GSG Probe Transition Using Micromachined Rectangular Microcoaxial Line

This article presents a millimeter-wave (mmW) ultrawideband (UWB) bandpass filter (BPF) using micromachined rectangular microcoaxial line ( $\text{R}\mu $ CL). The tightly coupled stepped-impedance stub loaded resonator (TC-SISLR) exhibiting multiple-mode resonator (MMR) property, which has nine controllable transmission poles (TPs) and two controllable transmission zeros (TZs), is proposed to achieve the design goal. Nine controllable TPs of TC-SISLR can support a 10–50-GHz UWB passband, while two controllable TZs of TC-SISLR can provide a sharp rejection passband. Step-to-step design process is given to guide the 10–50-GHz UWB BPF design, and the vertical broadside coupling configuration and the defected ground structure (DGS) are introduced to strengthen the tight coupling. Moreover, the $\text{R}\mu $ CL-to-ground–signal–ground (GSG) probe transition is also proposed and designed for on-chip measurement. As examples, the back-to-back GSG probe transition is fabricated, which has a low loss of 0.19 dB within 10–50-GHz passband, and a low loss of 0.6 dB up to 110 GHz. A 10–50-GHz UWB BPF with GSG probe transition is also fabricated, which has a minimum insertion loss of 0.44 dB within 10–50-GHz passband.