Topology Design, Analysis, and Optimization for a Bandpass Baw Filter

In this paper, the effect of topology structures on filter out-of-band (OoB) rejection is analyzed and the approximate expressions for OoB rejection of different structures are provided. Using the Mason model, the optimal synthesis topology of
$\pi$
-type and L-type is applied for designing a Band39(1880 MHz-1920 MHz) filter to achieve good performance of low OoB rejection exceeding -70 dB as well as a return loss less than -15 dB according to the simulation results.