A compact multilayer liquid crystal polymer VHF bandpass filter

This paper presents a novel compact VHF bandpass filter with a superb performance in the upper stopband. For the first time, to the authors' knowledge, such a bandpass filter with moderate bandwidth is designed and manufactured using multilayer liquid crystal polymer (LCP) technology. Unlike coupled distributed-resonators based filters, this design has a very wide spurious free upper stopband and the 2nd harmonic only appears at about 9.4 times the center frequency. Measured on a HP8510B network analyzer, the design shows a better than - 70dB upper stopband attenuation, which is limited by the noise floor. Implemented as a 5-metal-layer LCP module, the VHF-band filter has a size of 56.7mm x 13.75mm x 0.4mm, which is only 0.074 lambda(g) x 0.018 lambda(g) x 0.00052 lambda(g), where lambda(g) is the guided wavelength at the center frequency 250 MHz. Both simulated and measured responses are presented and a good agreement between them has been observed.