Novel edge coupled-stripline bandpass filter with significant improvement of attenuation in the stopband

Novel quarter-wavelength coupled pairs of strip transmission-line bandpass filters with attenuation poles are proposed. We propose filters with a novel modification with reference to the edge-coupled structures that consist of the open-circuited stepped impedance stubs or stubs with uniform impedances terminating the first and the last coupled pair of the filter structure. A design method is presented enabling realization of the attenuation poles in filters with symmetrical pairs of coupled TEM transmission lines. Design equations are established from the input reflection coefficient analysis. Imperceptible changes in the passband are possible.