Design for a Self-Packaged All-PCB Wideband Filter With Good Stopband Performance
B. А. Belyaev, А. М. Сержантов, Yaroslav F. Bal'va, R. G. Galeev, A.A. Leksikov
Abstract
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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {30~dB}}/\Delta f_{\mathrm {3~dB}}$ </tex-math></inline-formula> ) is 1.21, and the 40-dB stopband width is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.16f_{0}$ </tex-math></inline-formula> .