Siou Teck Chew

High-efficiency power amplifier integrated with antenna

Two class B GaAs field-effect transistor (FET) power amplifiers integrated with patch antennas have been designed and fabricated at 2.48 GHz. Both amplifiers are integrated with patch antennas, which serve as load and radiator. In one case, a standard patch design was used with random harmonic termination. In another case, a modified patch design was used, which allows the tuning of the second harmonic. In this case the antenna has an additional function of a filter. An increase of 7% in the power-added efficiency (PAE) and 0.5 dB in the output power was achieved through the second harmonic tuning.

A miniaturized dual-mode ring bandpass filter with a new perturbation

A miniaturized dual-mode ring bandpass filter at 1.45 GHz with a bandwidth of 6% is demonstrated. The perturbation of the dual modes is realized by a pair of local ground defects. The miniaturization is achieved by loading the peripheral of the ring with the butterfly radial stub structure. A 41% loading factor has been achieved using this method. The simulated and measured results are in good agreement.

A modified microstrip circular patch resonator filter

Circular holes are etched off a microstrip disk resonator. This results in a size reduction of 30%. By offsetting the positions of some of these holes, a degenerate orthogonal mode is excited, resulting in a split-mode bandpass filter. This filter can be considered as a lattice-type structure. A filter with a bandwidth of 8% centered at 2.0 GHz was designed. The measured insertion loss is 0.6 dB.

Small signal analysis of active circuits using FDTD algorithm

The FDTD method is extended to analyze a microwave amplifier. This amplifier includes matching circuits, DC bias circuits, and an active device. Equivalent current sources are used to model the active element. With the small signal model of the active element, the FDTD full-wave simulations show good agreement with measured results. >

A unilateral injection-locking type active phased array for beam scanning

An active phased array using unilateral injection-locked oscillators was developed. The phase shift is controlled by electronic tuning and the beam scanning is demonstrated. Amplifiers inserted between oscillators eliminate reverse injection locking and control the locking bandwidth. Both theory and experimental results are presented and discussed.<<ETX>>

An active phased array with optical input and beam-scanning capability

An active antenna array with optical input and beam scanning capability was developed. The phase shift between antenna elements is controlled by means of unilateral injection locking. The reference signal for injection locking is launched into an optical fiber by a multiquantum-well InGaAs-InGaAsP distributed feedback laser. The RF signal is recovered by a photodetector at the other end of the link and fed to the RF circuit. Experimental results are presented and discussed.<<ETX>>

PBG-excited split-mode resonator bandpass filter

Photonic bandgap structure is used as a design parameter for the fundamental passband in a split-mode microstrip square resonator. A defect in the PBG cells under the resonator, allows coupling between the two degenerate modes. A filter is designed at 2.2 GHz with good agreement between simulated and measured results.

Application of Volterra series to the problem of self-oscillating mixer

A new approach to the nonlinear problem of self-oscillating mixer has been investigated using Volterra series. The circuit under consideration is first converted into a one-port network. The input and coupling impedances of various ports are represented by Volterra kernels generated by nonlinear current method. Advantage of this approach is that the phase relationships among signals are not required for the analysis. Also, no stability criterion testing is needed to ensure convergence to the correct solution numerically. It is computationally efficient and mathematically simple, yet reasonably accurate. Measured results with respect to RF frequency and power show good agreement with that calculated.

FDTD simulation of a microwave amplifier

This paper presents the application of the Finite-Difference Time-Domain (FDTD) method to microwave circuits. An amplifier with a three-terminal active device is analyzed. The active device is replaced with equivalent current sources to integrate with FDTD simulation. The simulation results are compared with measured data and show good agreement.<<ETX>>

A 2/spl times/2 beam-switching active antenna array

An electronic beam-switching active antenna array is designed. The sum and difference patterns can be switched bi-directionally without additional switching devices. The required phase relationship is obtained through injection-locking. The transmitted power is combined quasi-optically. The measured patterns are in agreement with that of theory.<<ETX>>