Fabrication of an X-Band Dual Mode Bandpass Filter Using Low Cost FR4 Substrate

Abstract

SUMMARY The investigation presents a low cost and low insertionloss X-band dual mode bandpass filter (BPF) based on inexpensive com-mercial FR4 substrate. The proposed filter at a central frequency f 0 of11.3GHz has high filter performance filter with a fractional bandwidth of14%, the insertion loss of −2.7dB, and two transmission zeros. The de-signed procedures are presented in this letter and the fabricated filter veri-fies the proposed designed concept. key words: dual-mode, transmission zero, ring resonator, FR4 1. Introduction Miocrowave communication systems are expanding rapidlyto higher frequency such as C-band or X-band since they canprovide many advantages over conventional wireless links,for example the larger bandwidth and smaller device size.Waveguide components are widely used at these frequenciesand offer very good performance. However, they result inhigh production costs and bulky systems. Conventional pla-nar filter structures suffer from radiation from the resonatorsinto the substrate and from high ohmic loss, and there-fore give high insertion loss and poor filter rejection. Re-cently, the micromachined techniques have been providedand shown to enhance filter performance by removing thedielectric material up to a thin membrane that suspends theplanar filters, therefore reducing of the radiation, ohmic,and dielectric losses of resonators [1],[2]. However, thereis still a challenge in cost down of the commercial RF mi-cromachined device since the devices are fabricated in thesemiconductor-like process.In this letter, we have succeeded to fabricate an lowcost and low loss X band dual mode BPF by using inex-pensive commercial FR4 GD (Glass-Epoxy Double Sided)substrates with thickness of 0.4mm and original relative di-electric constant e