Novel wiggly-line interdigital microstrip bandpass filter with/sup rd/rd harmonic suppression

In this paper, we present a novel interdigital microstrip bandpass filter with 3/sup rd /harmonic suppression. With this new configuration, which applies a continuous perturbation to the strip width at the inner edges following a sinusoidal law. 3/sup rd /harmonic passband can be suppressed whilst the intrinsic 2/sup nd /harmonic passband free property is retained. In order to demonstrate the characteristics of the proposed filter, 3/sup rd /order Butterworth interdigital bandpass filters centered at 800 MHz with 15% fractional bandwidth of the proposed structure and the conventional ones are designed, respectively. From the EM simulation and experimental results, good agreement is obtained and it is found that no 2/sup nd /harmonic passband as well as more than 10 dB suppression at 3/sup rd /harmonic frequency is achieved by the proposed filter.