Analysis of broadside coupled strips for filter applications

Coupled transmission lines in inhomogeneous media essentially offer wide bandwidth, tight coupling (3 dB) and low attenuation. This type of structure is very useful for microwave & millimeterwave integrated circuits using planar circuit technologies like Mixers, Oscillators, Multipliers, Filters and Couplers etc. Here a computational method, based on quasi-static spectral domain technique, has been developed for analyzing broadside-coupled suspended stripline structures. The basic parameters of the coupled transmission lines, such as capacitance per unit length, mode characteristic impedance, coupling coefficient and modal phase velocities etc. have been calculated and tabulated. Finally the structure has been utilized to design a suspended stripline filter having broad bandwidth.