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A defected ground structure (DGS) on the ground plane of transmission lines, such as microstrips and coplanar waveguides, provides slow-wave characteristics caused by its equivalent inductive and capacitive components. Due to this slow-wave effect, the electrical lengths of the microstrip lines, which are combined by DGS in matching networks, are longer than the original ones. Therefore, the physical length of microstrip line can be shortened by inserting a DGS in order to keep the original electrical length. The resultant lengths of the microstrip lines with DGS are only 54% and 56% of the original lines in input and output matching networks, respectively. Additionally, because the microstrip lines with DGS have rejection characteristics slightly at the harmonic band, while standard transmission lines have a very wide passband only, the magnitude of the second harmonic is less than that of the original amplifier. The technique for size reduction of amplifiers using DGS is also applied to a coplanar waveguide (CPW) amplifier. The resultant lengths of CPW lines combined by DGS in matching networks are only 50% of the original lengths.

Since the manufacturing process does not allow solid ground planes between ceramic layers to isolate the signal lines, the buried ground should be realized as a meshed ground plane. Both characteristic impedances of the signal lines and couplings between different signal layers are influenced by the properties of these meshed planes. In this paper, we propose a new analysis method for coupling behavior between internal transmission lines, which are isolated by the buried meshed-ground planes. The coupling behavior between layers isolated by meshed-ground plane is investigated by the coupled-transmission lines model for the isolated layers. The coupling factors between isolated lines with the meshed-ground are extracted by 2-D FEM calculations.

In this paper, a novel lumped equivalent circuit for a conventional parallel directional coupler is proposed. The equivalent circuit and design formula for the presented lumped element coupler is derived based on the even and odd-mode properties of a parallel-coupled line. By using the derived design formula, we have designed the 3 dB and 10 dB lumped element directional couplers at the center frequency of 100 MHz. Furthermore, a chip type directional coupler has been designed to fabricate with multilayer configurations by employing the Low Temperature Cofired Ceramic (LTCC) process. The designed chip-type directional coupler has a 10 dB coupling value at the center frequency of 2 GHz. Excellent agreements between simulations and measurements on the designed directional couplers show the validity of this paper.

In this paper, a novel equivalent circuit and modeling method for a defected ground structure is proposed to design an optimized DGS lowpass filter circuit. The equivalent circuit presented in this paper has parallel capacitance to explain the fringing fields due to the defects on the metallic ground plane. Several comparisons between the EM-simulations on the DGS circuits and circuit simulations on its equivalent circuits are demonstrated to show the validity of the proposed model. Optimization for the DGS circuit is carried out by using the proposed equivalent circuit. Simulation and measurements on the fabricated DGS lowpass filter show optimized passband and stopband performance.