Abstract
We report rigorous approach for the design of differential coupled-line directional couplers in multilayer dielectric structures. In the proposed procedure numerically calculated per-unit-length parameters of coupled transmission lines are utilized for derivation of differential couplers’ properties. The known description technique with multimode scattering parameters has been extended to the eight-ports considered in the paper and the properties resulting from symmetry of the considered networks have been shown. Exemplary 3-dB and 8-dB coupled-line directional couplers have been designed and experimentally evaluated. Nodal to mixed-mode conversion of scattering parameters has been applied to allow for measurements of the physically realized models. Results of measurements are shown to confirm the presented theoretical considerations.
Highlights
Directional couplers have been for years utilized as basic components in high-frequency electronics in different technologies including monolithic or dielectric-substrate-embedded1–9
To verify experimentally the proposed design method, a 3-dB differential coupler described in Section III has been manufactured and measured
The entire differential directional coupler has been analyzed electromagnetically to confirm the influence of the transitions between coupled lines and coplanar waveguides
Summary
Directional couplers have been for years utilized as basic components in high-frequency electronics in different technologies including monolithic or dielectric-substrate-embedded. The design of coupled-line directional couplers having strong coupling requires, a multilayer technology to allow for sufficient mutual coupling of the coupler’s conductors The realization of such couplers has been widely described in a number of papers, where different dielectric structures as well as different topologies have been considered. The majority of the reported work focuses on the development of directional couplers operating with nodal excitations of their coupled conductors2,8 Nowadays it is common, to design analog electronic circuits having differential inputs and outputs due to their superior interference rejection. The presented in this paper approach has not been reported so far with respect to the differential couplers’ design, in only a simplified design approach has been proposed, where the existence of a ground-plane has been neglected Such a simplification was justified by the geometry of the considered coupled lines where the distance between coupled strips and a ground plane was relatively large. The nodal measurements of the developed couplers have been made and the obtained results have been converted with the described procedure into differential and common mode S parameters
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