Design of X-Band Bandpass Filter Using Hairpin Resonators and Tapped Feeding Line

Based on theory of micro strip filter, the letter adopts the structure of half-wave width hairpin resonator and tapped feeding line in designing a six-order X-band band pass filter. The centre frequency is 8.75 GHz, ranging from 8.1 to 9.4 GHz. The filter has characteristics of wide stop-band and good sideband suppression. By tapping feeding line and controlling the position of two transmission zeros, it makes the stop band suppression lower than 30 dB when in 1 to 8 GHz and 9 to 15 GHz. A compact micro strip band pass filter is simulated, fabricated and measured. The simulated and measured results are in good agreement, showing validity of the proposed method. The proposed filter has a wider restraint outside the band and the relatively small demission in size. With the easy design, it has a practical application value in engineering field.