Yongxi Qian

Characterization of picosecond pulse crosstalk between coupled microstrip lines with arbitrary conductor width

The propagation and crosstalk properties of picosecond electrical pulses along coupled microstrip lines with arbitrary strip widths are investigated. The current distributions and propagation constants of the dominant c- and pi -modes in these asymmetric coupled striplines are calculated using the spectral domain approach; and the full-wave analysis results obtained are incorporated into a fast Fourier transform (FFT) algorithm to simulate pulse distortion and crosstalk in the coupled transmission lines. Several samples of asymmetric coupled microstrip lines are fabricated and their characteristics are measured. The results of experiments are found to be in good agreement with those of computer simulations. For the first time, rigorous results of picosecond pulse distortion and crosstalk in asymmetric coupled transmission lines are provided. >

Additional approximate formulas and experimental data on micro-coplanar striplines (MMICs)

Approximate design formulas and experimental data of micro-coplanar striplines for high-packing-density MMICs are given. These formulas are applicable to three types of substrate materials: GaAs, plastics, and alumina with different dielectric constants. >

Modal dispersion control and distortion suppression of picosecond pulses in suspended coplanar waveguides

The propagation and dispersion characteristics of picosecond electrical pulses in a suspended coplanar waveguide (SCPW) are investigated, and it is shown that the SCPW is a very promising transmission structure for ultrashort pulses. Numerical results for the modal dispersion of the SCPW are presented and compared to those of the conventional CPW, and a field-coupling theory is used to explain the evolution in the dispersion behavior. An evaluation based on the numerical analysis shows that a SCPW with properly controlled dispersion can exhibit a five times improvement in pulse transmission capability compared to the conventional CPW. Both computer simulations and experimental measurements show a substantial suppression in pulse distortion as well, compared to conventional CPWs. >

Phase compensation and waveform reshaping of picosecond electrical pulses using dispersive microwave transmission lines

The phase compensation effect of microwave transmission line dispersion is studied and a simple effective method for reshaping and compressing picosecond electrical pulses generated from photoconductive switches is proposed. It is shown that a piece of a dispersive strip transmission line can be used as a phase equalizer to compensate the phase distortion included in asymmetric pulses, resulting in effective reshaping and compression of these ultrashort pulses. Initial design formulas of the strip transmission lines for this purpose are presented, together with computer simulation results which confirm the theoretical predictions. Experimental results are presented to show the substantial pulse reshaping effect. A comparison between theory and measurement is given. >

Characterization of A Folded Stepped Impedance Resonator for Miniature Microstrip Bandpass Filter Applications

In this paper we propose a Folded Stepped Impedance Resonator(FSIR) which is effective in realizing extremely compact microstrip bandpass filters. To characterize this new structure we use an FDTD algorithm where all discontinuity effects have been considered. For identical resonant frequencies, the proposed FSIR is found to be approximately 43 percent shorter in total length than conventional half-wavelength microstrip resonators. The accuracy of our FDTD analysis is verified through comparison with results in the open literature, and the effectiveness of the FSIR is also confirmed by experiments with two test resonators we have fabricated.

Optimal design of an offset-fed, twin-slot antenna element for millimeter-wave imaging arrays

The optimal design of an offset-fed, twin-slot antenna suitable for millimeter wave imaging arrays is reported. The dimensions of the antenna and the slot separation for realizing a desirable beam pattern are obtained by using the spectral domain method. The optimal position of the feeding microstrips for perfect impedance matching is determined through a full-wave analysis using the FD-TD method, which takes into consideration both the slot elements and the feeding networks. The input characteristics of an optimally designed antenna is evaluated with a network analyzer, where a reasonable agreement with theoretical predictions is obtained.<<ETX>>

Characterization of picosecond pulse propagation in a microstrip line divider

Many extremely broad bandwidth circuit components have to be newly developed for practical applications of ultrashort electrical pulses. Theoretical and experimental investigations of the transmission properties of picosecond pulses through a microstrip line divider are reported. Full-wave analysis results in the frequency domain are incorporated into a Fourier transform algorithm for computer simulations of pulse propagation through a 3-dB microstrip line divider with a curved-line branching circuit pattern. Excellent agreement has been found between the theoretical predictions and the results of experimental measurements.<<ETX>>

Characterization of the perturbation effect of a probe head using the FD-TD method

The perturbation effect of a probe head in microwave measurement is investigated by using the FD-TD method. A two-simulation approach with improved accuracy is employed to predict the insertion loss caused by the probe head. Depending on the diameter and reclining angle of the probe head, a maximum insertion loss of up to 0.8 dB has been calculated for an example structure. This work provides a rigorous and quantitative estimation of the probe effect. The analysis results may also serve as a guidance for optimal designing and positioning of probe heads so that a minimum field perturbation during measurement can be expected.<<ETX>>

Compression and reshaping of picosecond electrical pulses using dispersive microwave transmission lines

A simple and effective method for reshaping and compressing picosecond electrical pulses generated from photoconductive switches is proposed. A piece of dispersive strip transmission line can be used as a phase equalizer to compensate for the phase distortion included in asymmetric electrical pulses, resulting in effective reshaping and compression of these ultrashort pulses. Initial design formulas of the strip transmission lines for this purpose are presented, together with some computer simulation results showing the pulse reshaping and compression effects.<<ETX>>

Structural Control Of Microstrip Dispersion For Shaping Giga-Hertz-Bandwidth Pulses

Recent optical switching devices are using combinations of very short laser pulses, photoconductors, and strip lines. Since laser pulses have giga-hertz-bandwidth, signal transmission properties of such strip lines in a wide range of frequencies are decisively important. This paper describes the structural control of the dispersion characteristics of microstrip lines by adding ground conductors on both sides of the strip conductor. Some numerical data are shown.