Compact and low‐insertion‐loss dual‐mode patch filter with spur‐lines

A compact microstrip dual‐mode bandpass filter with inserted spur‐lines at the edge of the patch is proposed. In order to obtain a low insertion loss, the proposed filter has no coupling gaps. Also, it has a size reduction of about 45% at the same resonant frequency as compared conventional dual‐mode bandpass filters. Feed lines with offset are applied to ensure a minimal mismatch. From the measured results, the dual‐mode filter has a 0.58‐dB insertion loss at 1.27 GHz with 12% bandwidth.