A Bandpass Flter with Combinational Technique

In this letter, a combinational technique to design medium-band bandpass filter (BPF) is presented. The filter is composed of a classical stub bandpass filter with
$\lambda/4$
short-circuited stubs and two short-step impedance transformers. Main part of the filter is designed based on classical stub bandpass filter with higher normalized impedance, which effectively solves the problem that the width of
$\lambda/4$
short-circuited stubs is too large to be realized in design medium- or narrow-band BPF process. And the short-step impedance transformer is used to match higher impedance to 50
$\Omega$
. For demonstration, a bandpass filter with five-poles with a
$\boldsymbol{20}$
-dB-ripple Chebyshev response and fractional bandwidth of 0.25 at a mid-band frequency 2 GHz is simulated, designed and tested. Excellent results between the simulated and measured is achieved.