An Ultra-wideband Notch Frequency-Adjustable Filter With Improved Band Rejection Performance

In this paper, an ultra-wideband filter with capacitive frequency-adjustable notch is designed. The 3-dB insertion loss bandwidth exceeds 140%. By adding a parallel short branch and an open branch, two transmission zeros are introduced to realize band rejection. The embedded open branch supplies a notch on the output transmission line, and the physical length of the open branch is changed by changing the capacitance of the capacitor attached to the open port, so the notch point moves flexibly within the passband.