Analysis and design of broadside and overlap microstrip line couplers by finite element method

The general configuration of coupled microstrip lines on different dielectric interfaces is analyzed, and their design parameters are derived in terms of the system capacitances which are computed by using the finite element method. Design curves are calculated for edge coupled lines, broadside coupled lines and overlap coupled lines. The computed results are compared whenever possible with the available published data and prove to be very accurate. The design and performance of the broadside overlap coupler are presented. A broadside coupler is realized experimentally on Teflon substrates using thin-film technology and photolithographic techniques. The performance of the coupler, which has been evaluated by its scattering parameters, is in good agreement with the theoretical calculation in the considered range of frequency