The goal of the project is to research the designing methods of multi-conductor coupled-line sections, in which the selected pairs of differentially excited conductors constitute a circuit having the properties of an ideal coupled-line section. Such sections, which feature theoretically broad operational bandwidth, ideal isolation between respective ports and a given coupling coefficient, can be utilized for realization of microwave directional couplers with differential ports. The major research task within the project is to derive the conditions of ideal differential coupled-line section realization in inhomogeneous dielectric media in which the inductive and capacitive coupling coefficients are equalized (or alternatively phase velocities of propagating modes are equalized). One of the important aspects, to be investigated within the project, is the design of differential coupled-line sections in which high attenuations between common and differential modes is ensured.
Therefore, the following research hypotheses can be outlined:
- It is possible to realize multi-conductor coupled-line sections, in which the selected pairs of conductors are differentially excited, and feature the properties corresponding to the properties of well-known coupled-line sections with common excitation,
- the utilization of appropriate compensation technique, allowing for equalization of the inductive and capacitive coupling coefficients, results in differential coupled-line section featuring ideal isolation, impedance match with respect to the chosen terminating impedance; moreover, by appropriate design of coupled-line geometry high conversion losses between common and differential modes can be achieved,
- appropriately designed differentially excited coupled-line sections allow for realization of broadband multi-section directional couplers with differential excitations having the properties corresponding to the well-known multi-section directional couplers with common excitation,
- the application of appropriately designed differentially excited coupled-line sections allow for realization of microwave filters having differential input/output ports.