A Novel Compact Dual-band Filter Based on SICL Structure

A compact dual-band filter based on substrate integrated coaxial line (SICL) is introduced in this letter. There are two pairs of microstrip-based uniform impedance resonators (UIRs) etched between two SIW cavities. Both of the UIRs consist of two quarter-wavelength short-circuited resonators, and the center frequencies of the two resonators are 5.1 GHz and 6.8 GHz which are also the center frequency of two passbands of the filter. Compared with a normal microstrip filter, the SICL structure can reduce the radiation loss, so the filter has a higher quality factor. Besides, in order to improve the frequency selectivity of the filter by generating transmission zeros (TZs), the source-load coupling is created by adjusting the structure of two feedlines, the gap between feedlines can influence the position of TZs. In addition, by folding the microstrip properly, this filter has a compact size (2cm*2cm) and the thickness of the substrate is 0.508mm. Finally, this filter is simulated, fabricated and measured, the measured result shows a good agreement with simulation result.