Absolute Bandwidth-stabilized S-band Tunable Bandpass Filter

This paper reports on a frequency tunable bandpass filter with a constant absolute bandwidth that operates in the s-band. Two half-wavelength resonators loaded with varactor diodes are controlled by the same bias. Hence, the control circuit is user-friendly and has high engineering applicability. In addition, the use of a coupling structure to feed the resonator reduces insertion loss. The coupling coefficient between the two resonators is determined by a combination of electrical and magnetic coupling to achieve the requirement that the absolute bandwidth of the passband remains constant during frequency tuning. According to the measured data, the filter achieves -3dB absolute bandwidth of 140MHz ± 3MHz in the passband. adjustable range is 2.49GHz~1.99GH. in the tuning process, the insertion loss is better than 2.82db and the return loss is greater than 10db.