An ultra-wideband stripline bandpass filter with a noise suppression level of more than 100 dB

An ultra-wideband bandpass filter formed by a cascade connection of a new high-pass filter (HPF) and a low-pass filter (LPF), which are made on suspended substrates with a double-sided pattern of strip conductors, is under investigation. The high selectivity of the HPF is observed due to the presence of zero poles at the frequency response near the passband, which number is equal to the order of the filter. A second-order HPF, designed on a 0.5 mm thick substrate with a relative permittivity $\varepsilon$ = 9.8, was synthesized using numerical electrodynamic analysis of its 3D model. The experimental HPF has the 3 dB cut-off frequency at $f_b$ = 0.25 GHz and it's passband extends up to 5 GHz. An ultra-wideband bandpass filter made by cascade connection of the low-pass filter and developed high-pass filter has a relative bandwidth $\Delta f/f_0$ = 150% with a central frequency $f_0$ = 1 GHz. It has a wide and deep high-frequency stopband, which extends up to a frequency of 7.8$f_0$ for the suppression level -100 dB.