Research On Localized Electromagnetic Bandgap Structures

In recent years, Localized electromagnetic band-gap structures (LEBGs) have been widely used in research and application fields of communication because of their remarkable slow wave effect, resonant bandgap characteristics, and non-periodic structures. This dissertation focuses on two kinds of LEBGs: Defected Ground Structure (DGS) and Resonator Loaded Coupled-Line Cell (RCLC). Main works include modeling of LEBGs and their applications to the filters, power dividers (PDs) and harmonic suppressing:First, a four-order equivalent circuit model of the spiral shaped defected ground structures (SP-DGS) and a simplified three-order equivalent circuit model of SP-DGS are developed, which can be applied directly to improve designs of microwave circuits. An even-/odd- mode equivalent circuit model of the coupled-lines on a defected ground is also investigated, which is important to develop multi-port network applications based on DGSs.Second, a compact Quasi-Elliptic lowpass filter (QE-LPF) is proposed, whose lumped topology is derived from the Chebyshev prototype circuits by introducing an attenuation pole. Inductances in series branch circuits of QE-LPF are realized by dumb-bell shaped defected ground structures (DB-DGSs), while the high external quality factor of LC parallel resonance circuits in series branch circuits are achieved by SP-DGSs. And shunt capacitances are implemented by broadened microstrip lines.Then, a novel compact coupled microstrip PD with harmonic suppression is designed, which consists of a pair of coupled-lines on a defected ground. Two outputs of the PD are connected by a resistor and a capacitor. The non-Ï€/2 phase-shifts between the input and outputs are also discussed. A novel dual-band PD is further developed, which consists of a multi-section impedance transformer integrated with a SP-DGS. By properly utilizing SP-DGS, a PD has been implemented with desirable characteristics such as an equal power split, impedance matching at all ports, and a good isolation between output ports at two arbitrary given frequencies simultaneously.Furthermore, an even-/odd- mode equivalent circuit model of the Open Stub Resonator Loaded Coupled-Line Cell (OS-RCLC) is proposed and used to analyze the bandgap effect of OS-RCLC. Utilizing this configuration, Butterworth response and Chebyshev response LPFs are designed.Finally, a compact narrow band-pass filter using OS-RCLC and short stubs is presented. The passbands are determined by the short stubs, and the multi-harmonic suppression is achieved with introducing transmission zeros of OS-RCLC.