Tah-Hsiung Chu

A Study of Loosely Coupled Coils for Wireless Power Transfer

Nonradiative wireless power transfer using magnetically coupled coils is studied in order to transfer a predetermined amount of power at the maximum efficiency. Accordingly, a conceptual wireless power transfer system and a tuning method are presented. Such a study is essential for effectively exploiting the inherent ability of a given pair of coupled coils. With the equations for inductance and resistance calculations, the system performance is evaluated and verified with well-known experimental results and circuit simulations.

A Low-Cost 60-GHz Switched-Beam Patch Antenna Array With Butler Matrix Network

In this letter, a low-cost 60-GHz switched-beam patch antenna array with Butler matrix network is developed and experimentally demonstrated. In order to improve integration with the patch elements, a 4 times 4 planar Butler matrix is implemented in a low-dielectric substrate. The four rectangular patches fed by inset microstrip lines are connected to the outputs of the Butler matrix for the 60-GHz operation. Because of the fabrication tolerances, the operating frequency of the fabricated antenna shifts to 62 GHz. The radiation patterns measured at 62 GHz are in good agreement with the theoretical array factors. The antenna developed in this letter provides a cost-effective approach to implement an adaptive antenna for 60-GHz wireless communications.

Port reduction methods for scattering matrix measurement of an n-port network

The port reduction method (PRM) is a method to acquire the scattering matrix of an n-port network from the scattering matrix measured at a reduced port order by terminating certain ports. This then relaxes the instrumentation requirement and calibration procedure. As the port order is reduced to two, the scattering matrix of an n-port network can be obtained from the measurement using a conventional two-port vector network analyzer. In this paper, we describe two novel PRMs, which can reduce the order of measured ports to two. The experimental results show good accuracy. These two PRMs can provide a simpler calibration procedure and instrumentation than those directly using an n-port network analyzer. In addition, they give more accurate results than those measured by a two-port network analyzer with the assumption of using ideal terminators.

Multiport scattering matrix measurement using a reduced-port network analyzer

A novel method to acquire the scattering matrix of an n-port network from the measurements using a reduced-port network analyzer is developed. This method can obtain the scattering matrix of a nonreciprocal or reciprocal n-port network with the use of a three-port or two-port network analyzer. The formulation of this method considers the imperfection of terminators used in the measurement, and only two of the terminators are required to be known. Experimental results of a four-port microstrip circuit show the good accuracy using the developed method.

Measurement of frequency-dependent equivalent width of substrate integrated waveguide

In this paper, a method is developed to measure the frequency-dependent equivalent width (FDEW) of the substrate integrated waveguide (SIW). Based on the deembedding concept, the formulas of the measurement procedures are derived, and then the measured equivalent width corresponding to each frequency is applied to the transmission/reflection method to acquire the substrate dielectric constant. The measurement method is experimentally verified over the frequency range from 26 to 40 GHz. The measured FDEW of the SIW is compared with that calculated by the empirical equation. Furthermore, the results of the measured dielectric constant are shown to be in reasonable agreement with those measured by the ring resonator method. It demonstrates that the developed method is an effective measurement approach to characterizing the SIW.

An Nth-harmonic oscillator using an N-push coupled oscillator array with voltage-clamping circuits

The push-push oscillator is commonly used for implementing a second-harmonic oscillator. By combining two out-of-phase oscillators, their fundamental frequency components are canceled and the second-harmonic components are enhanced. This structure can be extended to triple-push, quadruple-push and hence N-push harmonic oscillators. From the oscillator injection-locking phenomenon, the relative phase between coupled oscillators can be controlled by the oscillator free-running frequency. As the output phase-shifted version signals are properly shaped and combined, the desired harmonic components are constructively added and lower-order harmonic components are canceled. This structure can be viewed as the general case of push-push oscillators. Since the output power is combined in a passive circuit, it does not suffer from the power limit of the output device in the cascade structure. The desired harmonic component can be selected by tuning the relative phase of the coupled oscillators and the conductive angle of the voltage-clamping circuit. Second-harmonic, third-harmonic and fourth-harmonic oscillators are designed and verified experimentally.

Design of a 60-GHz Substrate Integrated Waveguide Butler Matrix—A Systematic Approach

A 60-GHz substrate integrated waveguide Butler matrix designed based on a systematic approach is fabricated by a standard single-layer print circuit board process, which is more economical for mass production than are the advanced processes such as low-temperature co-fired ceramic, thick-film process, etc. The systematic approach involves design equations, simulations, and measurements. Starting with a set of explicit design equations for the short-slot couplers, one calculates the structure dimensions. The calculated dimensions are then optimized with full-wave simulation to finalize the design of the key components, including the couplers and phase shifters. With the use of a noncoaxial multiport measurement technique, the characteristics of the components are acquired through a probe station and a two-port vector network analyzer. Measurement technique plays a critical role in the systematic design approach. By measuring at the intrinsic ports or the wave ports defined in the full-wave simulations, the components are unambiguously verified and then integrated to complete the design of the Butler matrix. The resulting Butler matrix is also verified by the measured eight-port S -matrix, which is shown in good agreement with the simulated one. As the measured results of the Butler matrix show, for the operating bandwidth from 58 to 62 GHz, the reflections and isolations are lower than -13.5 dB and the insertion losses are below 2.5 dB. Much like the measured results of the components, the measured eight-port S -matrix not only verifies the design of the Butler matrix, but also will facilitate the follow-on design of a switched-beam antenna array.

Analysis of wire scatterers with nonlinear or time-harmonic loads in the frequency domain

The time-harmonic scattering properties of wire scatterers with nonlinear or time-harmonic loads are analyzed in the frequency domain. First, the scattering problem is treated as a network problem that is analyzed by the method of moments. Then, the harmonic balance technique is applied in the nonlinear load case, and the conversion matrix technique is applied in the time-harmonic load case. The analysis is shown to be efficient for the calculation of steady-state response compared with the conventional time-domain approach. Numerical simulation shows the effect of nonlinear loads on changing the scatterer radar cross section (RCS), the intermodulation phenomenon as the incident wave containing two different frequencies, and the effect of time-harmonic loads on modulating the scattered field of wire scatterer. >

A new calibration algorithm of wide-band polarimetric measurement system

The principle and experimental results of a new self-consistent calibration algorithm for a wideband polarimetric scattering measurement system are presented. The calibration targets include a flat plate, a dihedral corner reflector, and a rotated dihedral corner reflector. The rotation angle of the third calibrator can be derived in the calibration process and used to verify the calibration performance. Experimental results show that the calculated rotation angle of the third calibrator over the operation bandwidth is in good agreement with its actual angle, hence it provides a self-consistent parameter of the calibration algorithm. Based on the signal-to-noise consideration, an optimal rotation angle for a dihedral corner reflector is found to be 22.5 degrees . This calibration technique is also useful in characterizing the frequency and polarization responses of dual-polarization antennas. >

A W-band subharmonically pumped monolithic GaAs-based HEMT gate mixer

A W-band high electron mobility transistor (HEMT) subharmonically pumped (SHP) gate mixer is designed with fixed LO frequency operation. it is fabricated on a 4-mil substrate using 0.15-/spl mu/m GaAs pHEMT monolithic microwave integrated circuit (MMIC) process. the on-wafer measurement results show that the best conversion loss is about 4.7 dB in the W-band, as a 11-dbm 42-GHz low observable (LO) signal is pumped. To our knowledge, this is the first result on low conversion-loss W-band MMIC SHP HEMT gate mixer.