A Simple Planar Microstrip Dual-Band Bandpass Filter with Multiple Transmission Zeros

This thesis proposes a planar microstrip dual-band bandpass filter (BPF), which consists of four coupled-lines and a short-circuited stub. Scattering parameters of the presented dual-band BPF were discussed according to the even-and odd-mode network analysis theory and transmission line theory. Moreover, all of the transmission poles and transmission zeros were calculated mathematically. Two prototypes with different center frequency ratios (CFRs) were designed, fabricated, simulated, and measured. Finally, two dual-band BPFs with return loss higher than 15 dB in passbands and insertion loss higher than 10 dB in stopbands were obtained, which also had different CFRs as 1.96 and 2.38 respectively.