Design of Compact Bandpass Filter with Stub-Loaded to The Closed Loop Resonator

In this paper, a compact 3-order Band-pass filter (BPF) is proposed using a resonator that adds stub-loaded to the closed loop resonator. In consideration of coupled with 50$\Omega$ feeding line, the first and last resonator of $\lambda_{0}/4$ is folded type. The proposed filter is designed and fabricated with a fractional bandwidth of 8% at 1GHz center frequency. As compared to the area of the conventional interdigital BPF, a decrease of 50.04% is verified. Experimental results have shown good agreement with simulated ones.