A PSO-optimized, compact UWB bandpass filter suppressing the WLAN and the spurious harmonics

An improved small-sized filter is presented for ultra-wideband (UWB) systems. The filter comprises an only one-cell composite right and left handed-transmission line (CRLH-TL) resonator, step impedance (SI), and two spurlines. The one-cell CRLH-TL resonator has a small area and a wide passband. An SI is used to suppress the harmonics of the passband. And the two spurlines nestle the one-cell CRLH-TL resonator to prevent the interference of a wireless local area network (WLAN, 5.15-5.825GHz) band. The optimal design of the proposed filter is enabled by an improved particle swarm optimization (PSO) algorithm removing the ripples in the passband. Applying the improved PSO, the characteristic of the filter is optimized as acceptable results. The proposed filter has the overall size of 14×15mm2(0.63Ig × 0.53λg), a BW of 105% for a return loss > 10 dB, an insertion loss much less than 0.98dB, an acceptable return loss performance, and a stopband at 11.5~22GHz and WLAN band. Particularly, the ripples are removed in the passband.