Ultrabroadband Diplexers for Next-Generation High-Frequency Measurement Applications

This article presents a novel methodology of realizing a broadband diplexer that could be integrated into an on-wafer probe to create dual-band probes. Such a dual-band probe is capable to capture different frequency bands within a single measurement. A contiguous diplexer in suspended stripline technology with ultrawideband channels from dc to 110 GHz and 110 to 170 GHz is presented. The design of the diplexer is based on equivalent circuit models for the low-pass filter (LPF) and high-pass filter (HPF) separately. This design procedure requires no susceptance annulling networks and no introduction of unit elements, which could limit the diplexer's operation bandwidth. The realized diplexer is extremely compact (4.1 mm x 1.5 mm) and features very low channel insertion losses of typically less than 2 dB for the LPF and 2.5 dB for the HPF after proper optimization.