A Novel Type of Broadband Radial Stub

We report on a new type of broadband radial stub. It consists of two inclined half-stubs, which are separated by a small gap at their vertices. This radial stub can provide −15 dB rejection over almost 29% fractional bandwidth, which is an 86% improvement over the conventional radial stub. Using this stub in a double-sided (butterfly) configuration results in a −15 dB rejection bandwidth of about 61%, higher by a factor of two than in the case of a conventional butterfly stub. This stub was utilized in the DC-bias paths of a GaN power amplifier, which can provide more than 10 dB of gain between 60 and 110 GHz, resulting in the first-ever GaN power amplifier able to cover the whole W-band (75–110 GHz).