Effects of Parasitic Elements on LC/CL Matching Circuits

L-type LC/CL matching circuits are well known for their simple analytical solutions, and have been applied to many RF circuits. In the actual circuit, parasitic elements are added to inductors and capacitors. Therefore, each $L$ and $C$ element has a self-resonant frequency, which affects the characteristics of the matching circuit. In this paper, the parallel parasitic capacitance to the inductor and the series parasitic inductor to the capacitance are taken up as parasitic elements, and the details of the effects of the self-resonant frequency of each element on the $S_{11}$, VSWR (voltage standing wave ratio) and $S_{21}$ characteristics are reported. When a parasitic element is added, each characteristic basically tends to deteriorate as the self-resonant frequency decreases. However, as an interesting feature, we found that the combination of resonant frequencies determines the VSWR and passband characteristics, regardless of whether it is the inductor or the capacitor.