Development of Integration HTSC Linear Phase Filter With External Equalization

A variety of miniature half-wave multizigzag resonators was given, and an eight-pole high-temperature superconductor (HTSC) quasi-elliptic filter with no cross-line was developed with these resonators. In this paper, a novel single-pole group delay equalizer was also given to flatten a nonlinear phase quasi-elliptic filter's phase, which solves the tuning difficulty of the HTSC linear phase filter. Moreover, it cannot only ensure that the finished HTSC filter has a good linear phase characteristic but also solve the integration of the linear phase filter with external equalization. Finally, on
$\hbox{YBCO/LaAlO}_{3} \hbox{/YBCO}$
substrate with the dimension of 31.6 mm
$\times$
29.2 mm, a miniature eight-pole HTSC quasi-elliptic linear phase filter using external equalization is developed, where the center frequency is 2250.84 MHz, the bandwidth is 14 MHz, the best insertion loss in passband is 2.09 dB, and the return loss is better than 18.97 dB, as per measurements. In passband, the measured group delay response has a good agreement with the simulated response, and its variation is less than 50 ns over 78.5% of the filter bandwidth.