Design for a Self-Packaged All-PCB Wideband Filter With Good Stopband Performance

A new design of a self-packaged all-printed circuit board (PCB) wideband filter based on the cascade connection of high-pass filter (HPF) and low-pass filter (LPF) is presented. The novel low- and high-pass quasi-lumped filter structure differs from the known ones by the existence of cross coupling between elements producing transmission zeroes (TZs) at the desired frequency. It is shown that high-order structures make it possible to design a wideband filter having the number of TZs in the low-frequency stopband equal to the order of the applied HPF and the number of TZs in the high-frequency stopband equal to half the order of the LPF. An implementation of two-layer metallization of the capacitor plates made it possible to manufacture all three types of filters using the common technology of multilayer PCBs with a good coincidence of the characteristics of the model and the fabricated filters. The filter fabricated using materials with a rather low quality factor (F4BM/RO4450B/RO4003C) has demonstrated a good performance: the central frequency is 0.99 GHz, the 1-dB fractional bandwidth is 152%, the minimum in-band loss is 0.3 dB, the selectivity ( $\Delta f_{\mathrm {30~dB}}/\Delta f_{\mathrm {3~dB}}$ ) is 1.21, and the 40-dB stopband width is $6.16f_{0}$ .