Tunable substrate integrated waveguide (SİW) balun filter design for S and C bands

In this thesis, microstrip multimode bandpass filter designs, substrate integrated waveguide (SIW) bandpass filter circuits and SIW balun filter circuit designs and applications in S and C bands for balun circuits are presented. Coupling matrix synthesis and even-odd mode impedance analysis methods are used in filter design and analysis. Square patch resonator and square ring resonator are used for multimode dual band microstrip bandpass filter circuit. It has been shown that the filter designed using a ring resonator instead of a patch resonator is more advantageous in terms of size. Also, it has been shown that two types of filtering characteristics (linear and quasi-elliptical) can be obtained depending on the placement of the resonators in both filter circuits. The structure and properties of the substrate integrated waveguide, which has been widely used in microwave circuit design in recent years, are explained in detail. A square DBD resonator is proposed for the tunable DBD balun filter circuit, which is one of the final goals of the thesis. In order to provide mode excitation in the DBD resonator, a ground-to-plane transition conductor (via) is used at any of the four corners of the resonator. It has been shown that depending on the position of this via used for perturbation, two types of filtering characteristics (linear and quasi-elliptical) can be obtained. In addition, it has been shown that transmission zeros can be controlled thanks to the in different lengths of slots used at the input and output for coupling in the designed filter. The coupling matrix synthesis method is used to obtain the theoretical responses of the filter circuits with linear and quasi-elliptic characteristics. Based on the proposed DBD resonator, the DBD balun filter circuit is designed. In the DBD balun circuit, transmission zeros can be controlled as in the DBD filter. Also, it has been shown that the center frequency can be adjusted in the S and C band region by placing a varactor diode in the slits opened from the corners in the DBD balun filter circuit. The filter circuits have been manufactured and measured to show the validity of the proposed designs, and it has been observed that the measured results are in a good agreement with the theoretical and simulated results. The proposed circuits are suitable for use in applications covering frequency regions below 6 GHz in 5G technology.