A miniature dual-mode microstrip bandpass filter at 15.5GHz

A miniature dual-mode microstrip bandpass filter at the central frequency of 15.5GHz is proposed using a half-wavelength (λ/2) stepped-impedance resonator (SIR) with a pair of symmetrical T-type tap-connected open-ended stubs. Such paired stubs with total length of about λ/2 constructs an equivalent line resonator. Distinct characteristics of this new type of dual-mode filter are investigated using full-wave electro-magnetic simulations. Two transmission poles can be achieved inside the passband. Meanwhile, the T-type stubs are adjusted slightly to realize a transmission zero at high-rejection band. Good agreements are obtained between its measured and simulated S-parameters.