Stripline Bandpass Filter with Variable Physical Dimensions

A theory for the design of coupled-line bandpass filters has been derived. The filter comprises cascaded sections of two-port stepped coupled-line sections of length ¿/4 and with individual wave impedance parameters within each ¿/8 section. The design includes the possibility of altering the band-pass center frequency for a given length of the resonators. Narrow-band maximally flat or equal-ripple filter can be designed. The flexibility in filter length can be exploited for reducing space at low frequencies or for increasing the transmission line length-width ratio at high frequencies where the effect of end capacitance can be troublesome.