Reconfigurable uniform impedance active bandpass filter using coupled lines for l-band satellite communication

Abstract

—This work presents the design and implementation of a four-section reconfigurable uniform impedance resonator (UIR) active filter. UIR active filter consists of λg /4 microstrip line resonators cascaded in series with parallel coupled lines (PCLs). An additional quarter wavelength section is added to the coupled line quarter wave resonator section and gives flexibility in the coupling length. The proposed active filter provides a gain as a means of compensation to loss incurred by passive circuitry. In addition, it gives high selectivity (−70 dB) and wide stopband. The wide stopband is the result of suppression of spurious frequencies which is accomplished by using shunt stub resonators at appropriate locations in the active filter. The bandwidth reconfigurability is achieved by varying the bias currents of the active devices as well as by tuning the varactor diodes. The UIR concept with active matching is implemented on an FR4 substrate (εr =4.4), with passband gain of around 15 dB at 1.3 GHz, and out of band rejection is better than −35 dB at twice the centre frequency of 1.3 GHz.