Optimal Design of a Compact Filter for UWB Applications Using an Improved Particle Swarm Optimization

This paper proposes an improved particle swarm optimization (PSO) process to design a high-performance compact ultrawideband (UWB) filter. The filter consists of one-cell composite right- and left-handed-transmission line (CRLH-TL) resonator, a stepped impedance (SI), and two spurlines. The one-cell CRLH-TL resonator has compact size but performs wide passband filtering. One SI and two spurlines are employed to reject both the harmonics outside the UWB and the wireless local area network (WLAN) (5.15-5.825 GHz) band. The improved PSO consists of the conventional PSO with the sensitivity analysis, and the process for checking the ripple. The improved PSO suppresses the ripple and accelerates the optimization. During the improved PSO, the objective function converges from the 116th iteration. In addition, the characteristic of the filter is optimized to get acceptable results. The proposed filter has the overall size of 14×15 mm
²
(0.63λg ×0.53λg) only, a 105% bandwidth for a return loss >10 dB, a flat insertion loss <;1.4 dB, and stopbands on 11.5~22 GHz and WLAN band. In particular, the ripple in the passband is minimized significantly by the improved PSO.