This paper presents a theoretical analysis of a tunable resonator using a coupled line and switches for the first time. The tunable resonator has the capability to tune its resonant frequency and bandwidth. The resonator has two suitable features on its tunable capability. The first feature is that the resonator retains its resonant frequency during bandwidth tuning. The second feature is that the on-state switch for tuning the bandwidth does not affect the insertion loss at the resonant frequency. These features are theoretically confirmed by its mathematically derived input impedance. The results from electromagnetic simulation and measurement of the fabricated tunable resonator also confirm these features. The fabricated tunable resonator changes the resonant frequency from 2.6 GHz to 6.4 GHz and bandwidth between 9% and 55%.

This paper presents a theoretical analysis and experimental confirmation of a tunable ring resonator that can independently change its resonant frequency and bandwidth. The tunable ring resonator comprises a ring resonator, three tunable capacitors, and switches. The resonant frequency changes according to the capacitance of tunable capacitors, and the bandwidth varies by changing the state of the switches. The unique feature of the resonator is that the resonant frequency remains steady when the bandwidth is changed. The fundamental characteristics are shown based on linear circuit simulation and electromagnetic simulation results. The resonator is fabricated using GaAs FET single-pole single-throw switches. The fabricated resonator changes the resonant frequency from 1.5 GHz to 2.0 GHz and the fractional bandwidth from 5% to 30%.

This paper presents a simple-structured tunable resonator employing semiconductor switches that can change its resonant frequency discretely but precisely. The tunable resonator comprises a transmission line with a comb-shaped pattern and multiple single-pole single-throw (SPST) switches placed between the teeth of the comb-shaped pattern. The resonator changes its resonant frequency according to the switch states, by controlling the path length carrying a high frequency current. The characteristics of the proposed resonator are evaluated through both method of moment electromagnetic simulation and fabrication, using GaAs FET SPST switches. The fabricated resonator changes its resonant frequency from 1.63,GHz to 1.85,GHz. This paper also introduces two circuit designs based on the proposed resonator that expands the tuning range of the resonant frequency or the number of resonant frequencies to be obtained.

A nonreciprocal left-handed transmission line is proposed and investigated, which is composed of a normally magnetized ferrite microstrip line periodically loaded with inductive stubs but without capacitive loading. The circuit configuration becomes simpler than that of a nonreciprocal left-handed transmission line with both shunt inductive and series capacitive loadings. In the proposed structure, ferrite medium is employed as the substrate not only for the nonreciprocal characteristics but also for negative effective permeability that is essential to establish the left-handedness. After calculations of dispersion curves using equivalent circuit model, scattering parameters along with field patterns are estimated numerically with the help of electromagnetic simulation, and the experiments are also carried out. It is found that the band width of the proposed left-handed transmission line is relatively narrow but the structure still has the high isolation ratio of more than 30 dB.

This paper presents an analytical model for the electromagnetic radiation in multi-microstrip lines covering the frequency range from 30 MHz to 1 GHz. The radiated emissions of multi-microstrip structure can be divided into the summation of radiated emissions of multi-individual microstrip structures. It is done by modelling the imperfect ground effect of the PCBs. Here we present a circuit model based on traditional transmission lines (TMLs) model. For more accurate analysis of the imperfect ground effect in multi-microstrip lines, we will divide the equivalent circuit model into N sections, based on transverse electromagnetic (TEM) assumption, to estimate the electromagnetic interference (EMI) of multi-microstrip lines. The quantitative value of induced current distribution along the ground return path depends on the physical size, geometry and length of ground trace. Measured data are presented to confirm the results of numerical analysis and the computer simulations with a software package based on the Finite Element Method. A knowledge of EMI source mechanism and their relationship to layout geometries is necessary to determine the essential features that must be modelled to estimate emissions in PCBs design.

Novel microstrip lowpass filters are developed with reduced size and significantly improved stopband characteristics. After introducing quarter-wavelength open stubs, we get one or two transmission zeros in the stopband. By folding the high impedance microstrip lines, we reduce the size of the filter. Three-pole and five-pole lowpass filters are designed, and their measured frequency responses agree well with theoretical predictions.

In transient analyzing of a crosstalk, the crosstalk waveform can be obtained with a commercial simulator such as SPICE simulation or FDTD (Finite Difference Time Domain) simulation. In case of using a simple model, a CMOS-IC load is considered as a constant capacitance load in crosstalk simulation. However, the semiconductor devices, such as CMOS-IC, have a characteristic of nonlinear impedance depending on the input voltage. We measured the far-end crosstalk of two parallel microstrip lines for a CMOS inverter (74HC04) load by changing the magnitude of the input step voltage. As the result, we found that the far-end crosstalk for the CMOS inverter load dose not necessarily depend on the input capacitance of the CMOS inverter.

A combined mode-matching and moment method is proposed to calculate the capacitance matrix of wedge-supported cylindrical microstrip lines with an indented ground. Each indent is modeled as a multilayered medium in which the potential distribution is systematically derived by defining reflection matrices. An integral equation is derived in terms of the charge distribution on the strip surfaces. Galerkin's method is then applied to solve the integral equation for the charge distribution. The effects of strip width, strip separation, indent depth, and indent shape are analyzed.

The dispersion characteristics of two nonidentical coupled microstrip lines and N identical coupled microstrip lines are analyzed using the coupled-mode theory combined with Galerkin's moment method in spectral domain. In this approach, the solutions to the original coupled microstrips are approximated by a linear combination of eigenmode solutions associated with the isolated single microstrip, and the reciprocity relation is used to derive the coupled-mode equations. The coupling coefficients are given by the simple overlap integrals in spectral domain between the eigenmode fields and currents of the individual microstrips. It is shown that the numerical results are in very good agreement with those obtained by the direct Galerkin's moment method over a broad range of weak to moderately strong coupling.

For a method to control the microwave coupled lines with optically induced plasma effectively, we propose the selective mode-control method, which restricts controlled modes to a selected one. We analyzed the basic characteristics of coupled microstrip lines theoretically by using the spectral domain technique and indicated the effectiveness of this method with the aid of numerical results. Further, we designed an optically controlled change-over switch as an application of this method.