Compact Wide-Frequency Tunable Filter With Switchable Bandpass and Bandstop Frequency Response

In this paper, a novel compact wide-frequency tunable filter with switchable bandpass and bandstop frequency response is presented. By employing two PIN diodes between the source and load port, the bandpass and bandstop filtering response can be switched, respectively. Three varactor diodes have been used to tuning the operating frequency of the tunable filter at bandpass and bandstop frequency response. The even- and odd-mode method is applied to analyze the presented tunable filter. When PIN diode is forward-biased, the filter has the bandstop response, and the filter has bandpass response while it is reversed. To verify the proposed tunable filter circuits, the tunable bandpass filter and bandstop filter are designed, fabricated, and measured. It is demonstrated that the center frequency of the fabricated tunable filter is tuned from 0.95 to 1.35 GHz. The measured insertion loss in the band is greater than 13 and 11 dB for bandstop mode and bandpass mode, respectively. Moreover, the fabricated tunable filter has a compact size of 0.24λ _g × 0.24λ _g (λ _g is the wavelength of the center frequency during the tunable frequency range).