compact and tunable microstrip bandpass filter using a disk resonator and a u-shaped waveguide for wi-max and wlan applications

In this paper, a microstrip dual-band bandpass filter containing a disk resonator and a u-shaped waveguide is designed. the proposed structure generates two pass-bands with resonance frequencies of 3.7 and 5.7 ghz which can be used for wi-max and wlan applications, respectively. it is worth mentioning that two resonance frequencies are located in a relatively wide frequency range of 0 to 10 ghz. the simulation results show that the insertion losses and return losses of two pass-bands are better than 0.62, 0.75 db, and 21.9, 20.1 db, respectively. furthermore, its total size is equal to 12.9×9.5 mm2. in addition to the simple structure of the proposed filter, its second resonance frequency can be tuned by changing only the radius of the disk resonator, without the need to change the overall structure or add another element to the filter structure. furthermore, this filter's symmetrical structure has caused no distinction between the input and output ports, which facilitates the mass production of this structure. the other remarkable features of the suggested filter are its compact size, low insertion loss, high return loss, sharp transition bands, high attenuation level in the stop-bands, wide upper stop-band bandwidth, and sharpness of transient bands.