Compact quasi-elliptic microstrip bandpass filter using terminated anti-parallel coupled-line

A compact quasi-elliptic microstrip bandpass filter with lower and upper stopband zeros is presented. The bandpass filter consists of terminated anti-parallel coupled-line and the stopband zero is generated and controlled by the reactive termination. In comparison to the traditional parallel coupled-line bandpass filter, the proposed filter achieves simultaneous size reduction and sharp filter skirt. The usefulness of the proposed filter is validated by a simultaneously miniature and selective quasi-elliptic bandpass filter centred at 2.4 GHz with 4.6 fractional bandwidth as well as two transmission zeros at 2 and 3.2 GHz.