Novel Reflective-Type Bandpass Filter with Simultaneously Integrated Tunable Attenuation and Phase Shifting Functions

In this paper, a novel multifunctional bandpass filter with simultaneously integrated amplitude and phase control abilities is proposed. It is constructed by using a filtering rat-race coupler operating in a reflective-type configuration. The phase shifting function is realized by introducing tunable non-resonating nodes at the input/output ports of the filter, while the attenuation function is enabled by tuning the impedances of the reflective loads of the coupler. To validate the proposed techniques, a filter prototype operating at 1.34 GHz with a fractional bandwidth of 4.5% is designed. Measured results demonstrate that the designed multifunctional bandpass filter can simultaneously achieve continuous amplitude control in the range of 0–12.6 dB and insertion phase control in full 360°. Good bandpass filtering and return loss performances can be maintained during the whole tuning process.