Double-sided Parallel Transmission Line (dspsl) Engineering Research

Today, for microwave circuitry, the traditional microstrip line and coplanar waveguide (CPW) still play dominant roles. Recently, the balanced transmission line such as coplanar stripline (CPS) and slot line have been commonly used to construct differential/balanced circuits for improving the circuit performance. The microstrip line (MSL) or coplanar waveguide (CPW) are used in the conventional balanced technology, which usually requires the baluns as the transition between the unbalanced and the balanced circuits so that much space would be occupied, in addition, the extra loss will be introduced. Furthermore, the differential signal will be affected because of the frequency dependence of the baluns; the application in wideband systems is thus not possible. The double-sided parallel-strip line (DSPSL) is investigated, including the performances analysis of DSPSL and their applications in microwave component designs. The DSPSL, as another balanced transmission line, has many important advantages over the CPS and slot line, i.e. easy realization of low or high characteristic impedance.The features of DSPSL are discussed; some novel microwave circuits are designed on the basis of DSPSL, such as wideband bandpass filter, dual-mode dual-band filter, and hybrid coupler.The main works in this thesis are listed below:1) Analyzing the performances of DSPSL. The emphases are focused on how to realize high characteristic impedance and introduce the way to design a transition between DSPSL and other planar transmission lines. At the same time, the effect on circuitry of a ground plane inserted in DSPSL is also discussed. In addition, the basic design theory of conventional hybrid coupler is introduced, while a compact hybrid coupler realized with DSPSL is designed and discussed.2) Based on the DSPSL quarter wavelength couple line and the stepped impedance resonator(SIR) open stubs, a wideband bandpass filter is designed. The transmission zero created by SIR open stubs improves the characteristics of the stopband.3) Based on the slotted equilateral triangle dual-mode bandpass filter, the non-identical resonators on the top and bottom layer, isolated by the inserted conductor plane, generate their respective passband for the construction of the dual-band bandpass filter and diplexer.4) A miniaturized wideband DSPSL hybrid coupler with phase inverter and the open-stubs are also introduced to further reduce the size of the hybrid coupler. The experimental results show that the size of the proposed hybrid is reduced to 11% of the conventional hybrid coupler. Its relative operating bandwidth is greater than 80%.