Multi- channel microstrip balun-diplexer design

In this thesis, a multi-channel microstrip balun-diplexer design that converts an unbalanced input signal into two balanced output signals is presented by using multi-mode resonators. The unbalanced signal coming from the input port of the designed circuit is converted into balanced signals with a phase difference of 1800 at the center frequencies of 1.8 and 2.0 GHz at the second and third outputs, and at the center frequencies of 3.0 and 3.45 GHz at the fourth and fifth outputs. The designed balun-diplexer is constructed by using co-directional split ring resonators (CDSRR-EYAHR) with two different electrical lengths. These resonators consist of two open ring resonators placed inside each other and an interdigital capacitor placed between the open ends of the inner resonator and can produce two resonant frequencies. By coupling identical resonators to each other at each output, two poles can be obtained in all bands. In order to obtain a phase difference of 180°, the second and third outputs and the fourth and fifth outputs are placed rotationally symmetrically to each other. Two identical CDSRRs were used for the filtering process at each output, thus a total of 8 CDSRRs are used to obtain 4 bipolar channels at the center frequencies of 1.8 GHz, 2.0 GHz, 3.0 GHz, 3.45 GHz. The final dimensions of the designed balun-diplexer were obtained thanks to electromagnetic simulations. A prototype was manufactured on Rogers RO4003C substrate and the measurement results were shown to be in agreement with the simulations. The designed quad-channel balun-diplexer is at a level that can be used in modern communication systems in terms of loss, isolation and amplitude/phase difference performance.