Approximate minimum phase equivalent networks of quasi-TEM uniform coupled lines used for VHF-UHF band pass filter

Miniaturized VHF-UHF filters for communication are usually made of coupled uniform lines in high dielectric material. The coupling is sometimes achieved by air holes between neighboring lines, resulting in quasi-TEM- rather than TEM-mode coupling. An approximate minimum-phase equivalent network that facilitates understanding of such quasi-TEM coupled lines is presented. Practical examples are given together with the practical coupling coefficient for corresponding structures