A constant absolute bandwidth tunable band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling

In this paper, a constant absolute bandwidth (CABW) band-pass filter based on magnetic dominated mixed coupling and source–load electric coupling is proposed. Specially, a novel mixed electric and magnetic coupling structure is presented to control the coupling coefficient variation and thus realize a narrow CABW width. Two transmission zeros are added to the filter response using a source–load coupling technique, leading to a better selectivity. The measurement shows that the –1 dB absolute and fractional bandwidth is 29 ± 3 MHz and 1.8–2.6%, respectively, while the central frequency of the passband varies from 1.11 to 1.51 GHz.