Fig. 2 A simple metal rim model
Matching circuits of separate feeding ports can just change its
amplitude or curve depth of S21 and have a little effect on S21 notch
frequency. So, we can sweep parameters Cp and Lp to obtain a good
isolation without matching circuits. Simulations are done by applying
CST Studio Suit 2022, a full wave simulation software. Firstly, Lp is
fixed to 1nH, and Cp increases from 0.2pF to 6.2pF, with empty matching
circuits of Port1 and Port2. Secondly, Cp is fixed to 0.8pF, and Lp
increases from 0.6nH to 3nH. Fig.3 shows S21 notch frequency decreases
with the increasement of Cp and Lp. Low bands have a large range and
broad bandwidth with Cp while Lp mainly influences on high bands. A
combination of Cp=0.7pF, Lp=1.6nH consists of well decoupled elements.