Reduction of microstrip FEXT plays an important role in microwave engineering, as microstrip coupled line backward couplers suffer from poor directivity when not compensated. Techniques to improve directivity are similar to those for high-speed digital design and include dielectric overlays, the use of wiggly lines and capacitive compensation. In this article, Henning Mextorf presents a general approach which does not require a modification of the dimensions of the coupled line structure and provides closed form solutions for optimum capacitor values.
