Compact UHF 5th-Order bandpass filter with sharp skirt

We propose a bandpass filter miniaturized by the composite right-handed and left-handed(CRLH) zeroth order resonators(ZORs). A 5th-order bandpass filter form a cascaded triplet(CT) to have a significantly sharp skirt for high frequency selectivity. First, we design an in-line ZOR bandpass filter whose total size is nearly 0.2 of the parallel-edge coupled filter. Second, we create multiple transmission zeros(TZs) by changing the three innermost ZORs of the in-line filter to a CT. As a result, the proposed filter has the insertion loss less than 1.5dB and the return loss less than −15dB. The simulation and measurement validate the proposed design method, and the CRLH ZOR properties are proven by the no-phase variation electric field and dispersion diagram.