An Ultra-Wideband Stripline Bandpass Filter with a Noise Suppression Level of More than 100 dB

An ultra-wideband bandpass filter formed by cascading of a novel high-pass filter (HPF) and a low-pass filter (LPF) on suspended substrates with a two-sided pattern of strip conductor has been investigated. The high selectivity of the HPF is ensured by the transmission zeros near the passband, the number of which is equal to the filter order. A second-order HPF has been designed on a 0.5-mm-thick substrate with a permittivity of ε = 9.8 using the numerical electrodynamic analysis of a 3D model of the filter. The experimental HPF prototype has a cutoff frequency of fb = 0.25 GHz at a level of –3 dB and a passband that extends to 5 GHz. The ultra-wideband bandpass filter formed by cascading of the LPF and the designed HPF has a fractional bandwidth of Δf/f0 = 150% with a central frequency of f0 = 1 GHz. It has the broad and deep high-frequency stopband, which extends to a frequency of 7.8f0 at a suppression level of –100 dB.