Design of parallel 4-cavity helical filter with cross-coupled structure

Against the structure and the coupling method of helical filters,the parallel 4-cavity helical filter with cross-coupled structure by adding control parts between the 1st and the 4th non-adjacent cavities to introduce transmission zeroes to increase out band rejection was proposed.A helical filter with the size of 150 mm × 60 mm × 70 mm and the center frequency of 380 MHz was designed by Ansoft HFSS and fabricated.The test result shows thatin-band return loss of the filter is higher than 20 dB and the insertion loss is lower than 2dB,the feasibility and practicability of the method are verified.