A Novel Compact Coaxial Bandpass Filter for T/R Module Harmonic Rejection

摘要

A novel compact coaxial bandpass filter with wide upper stopband is proposed. To reduce the circuit size and up move the parasitic harmonic passband, the stepped impedance resonator (SIR) is applied. By properly adjusting the characteristic impedance ratio of SIR, the spurious resonance frequency can be adjusted to the desired frequency. The end-coupled technique providing a weak coupling for the small coupling area is employed to minimize the radial dimension of the coaxial structure. For the wideband requirement, AL(2)O(3) with epsilon(r) = 9.8 with certain thickness is used to fill the gap between the adjacent SIR resonators to enhance the coupling. Based on the above analysis, a three-pole ended-coupled coaxial bandpass filter with the size of 4.5x36.8 mm covering 3.81 similar to 6.9 GHz is designed. The insert loss is less than 0.5 dB in the operating band, while the rejection level around 2f(0) and 3f(0) are more than 41 dB and 53 dB respectively.

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