CiteULike: dcastro's Gao

Polarization-agile antennas

S Gao — 2008-07-17T19:46:57-00:00

Antennas and Propagation Magazine, IEEE, Vol. 48, No. 3. (2006), pp. 28-37.

A polarization-agile antenna is a type of antenna the polarization state of which can be changed dynamically, i.e., it can have either linear (vertical or horizontal) or circular polarization (left hand or right hand), depending on the requirements of its specific application. This special characteristic offers great flexibility for antenna systems, because a single antenna could be used to satisfy the different requirements of several systems. This paper gives a comprehensive review of polarization-agile antennas. The basics of polarization in antennas and polarization-agile antennas are explained. Various examples of recent developments are then provided, and the antenna configurations and design principles are illustrated and discussed. Finally, the future development of polarization-agile antennas for wireless systems is discussed.

Broadband high efficiency circularly polarized active integrated antenna

Y Qin — 2008-07-17T19:46:36-00:00

Microwave Conference Proceedings, 2005. APMC 2005. Asia-Pacific Conference Proceedings, Vol. 3 (2005), 4 pp..

This paper presents a broadband high efficiency circularly polarized active antenna integrated with class-E power amplifier (PA) at 2GHz. A single circular microstrip patch fed by a cross slot is employed as not only a broadband circularly polarized radiator but also as a harmonics-termination load network, which is directly connected with the class-E power amplifier output. A low cost PCB technology is employed in the circuit fabrication and a low voltage PHEMT transistor is used. A peak drain efficiency of 71.1% for the class-E amplifier is measured at 2.05GHz, together with a maximum radiated power of 28.2 dBm from the active integrated antenna (AIA). Power added efficiency (PAE) over 50% within a 17% bandwidth from 1.92GHz to 2.28GHz is achieved. Axial ratio below 3 dB is obtained over a 9% bandwidth from 1.99 GHz to 2.18 GHz.

Wideband dual-polarised microstrip patch antenna

SC Gao — 2008-05-09T23:50:34-00:00

Electronics Letters, Vol. 37, No. 20. (2001), pp. 1213-1214.

A dual-polarised microstrip antenna capable of achieving a wide bandwidth, a high isolation, low cross-polarisation levels and low backward radiation levels is presented. The H-shaped coupling aperture is used. For wide bandwidth and easy integration with active circuits, it uses the aperture-coupled stacked microstrip square patches. Measured return loss exhibits a bandwidth of over 20.9%, and isolation is better than 36 dB over the bandwidth. Cross-polarisation levels and the front-to-back ratio are better than 22 and 21 dB, respectively

Dual-polarised wideband microstrip antenna

SC Gao — 2008-05-09T23:49:22-00:00

Electronics Letters, Vol. 37, No. 18. (2001), pp. 1106-1107.

A dual-polarised aperture-coupled microstrip antenna with a wide bandwidth, a high isolation, low cross-polarisation levels and low backward radiation levels is presented. The square patch is fed at two corners via H-shaped apertures. The measured return loss exhibits a bandwidth of over 24.4% and the isolation is better than 30 dB over the bandwidth. The cross-polarisation levels and the front-to-back ratio are better than -23 and 22 dB, respectively

SNR estimation for non-constant modulus constellations

Ping Gao — 2008-05-09T23:49:08-00:00

Wireless Communications and Networking Conference, 2004. WCNC. 2004 IEEE, Vol. 1 (2004), pp. 24-29 Vol.1.

We propose a new technique to estimate the signal-to-noise ratio (SNR) over the flat-fading channel. This is a non-data-aided, envelope-based estimator that can be applied to non-constant modulus constellations which is a feature not found in the existing approaches. We also analyze the performance of our estimators for both PSK and non-PSK constellations by deriving their asymptotic variances and comparing it with the Cramer-Rao bounds (CRBs). Moreover, we discuss how the SNR estimates can be used to approximate the bit error rate (BER) and how the accuracy of the SNR estimate is related to that of the BER estimate, which justifies the necessity for the accurate estimation of SNR. The analytical performance is shown for both PSK and non-PSK constellations, such as 8 QAM. and 16 QAM. Monte Carlo simulation results corroborate our analysis.

High efficiency class-F RF/microwave power amplifiers

S Gao — 2008-05-09T16:11:33-00:00

Microwave Magazine, IEEE, Vol. 7, No. 1. (2006), pp. 40-48.

This article provides a tutorial and review of recent developments in high-efficiency class F RF/ microwave PAs. The principles of class-F RF PAs are explained first. Recent progress in their theory and in design techniques is then presented. Different approaches of class-F PA designs are explained, and some examples of practical designs are illustrated. Finally, an attempt is made to discuss the future developments of class-F RF/microwave PAs.

Novel integrated antenna for LINC power amplifiers

SC Gao — 2008-05-09T15:18:04-00:00

Antennas and Propagation Society International Symposium, 2002. IEEE, Vol. 2 (2002), pp. 508-511 vol.2.

Both theoretical and experimental results of a novel integrated antenna for LINC power amplifiers are presented. The integrated antenna can also serve as a power combiner, ensuring maximum power efficiency. This will be a significant advance on current LINC and CALLIUM systems, where the circuit level power combiner losses degrade overall efficiency. The concept is explained and one example antenna at 1.8 GHz is designed, fabricated and measured. The measured results show that the antenna achieves good impedance matching characteristics under both the common-mode and the differential-mode excitations. Radiation patterns are also presented.

Compact harmonics-suppressed integrated antenna for LINC transmitters

SC Gao — 2008-05-09T15:16:15-00:00

Antennas and Propagation Society International Symposium, 2002. IEEE, Vol. 2 (2002), pp. 280-283 vol.2.

A novel integrated antenna is proposed for LINC (linear amplification using non-linear components) transmitters. In this antenna, the power combiner involved in the conventional LINC is removed, and the power combination is realized within a microstrip antenna. By using a dual-fed H-shaped microstrip patch, the antenna can suppress higher harmonics and occupy a smaller size compared to a rectangular patch. An example antenna is designed at 1.8 GHz. The simulated results based on the moment method are presented, which validate the concept.

Network modeling of an aperture coupling between microstrip line and patch antenna for active array applications

X Gao — 2008-05-06T18:35:45-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 36, No. 3. (1988), pp. 505-513.

An analytical method based on the aperture coupling theory and the derivation of the <e1>S</e1>-parameter matrix has been developed for modeling a microstrip line coupled to a microstrip patch antenna using a circular coupling aperture. Closed-form solutions were derived for scattering parameters of the coupling circuit. Input impedance and matching condition can be calculated from the equivalent six-port network. The theoretical results agree well with the measurements. The analysis should have many applications in active array and spatial power combining systems

Compact power combining patch antenna

ST Chiw — 2008-05-05T14:10:37-00:00

Electronics Letters, Vol. 38, No. 23. (2002), pp. 1413-1414.

A compact two-way power combining antenna is presented which radiates in-phase signals while dissipating the out-of-phase signals in an internal lumped resistor. A transmission line model illustrates the operation and gives first order values for the antenna design. Measured radiation patterns for odd and even mode excitation demonstrate the isolation achieved.

High accuracy frequency offset correction with adjustable acquisition range in OFDM systems

Zhongshan Zhang — 2008-02-25T15:40:02-00:00

Wireless Communications, IEEE Transactions on, Vol. 4, No. 1. (2005), pp. 228-237.

A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) systems is proposed in this paper. Both the carrier frequency offset acquisition and tracking are based on a fixed-length training-symbol-block, which consists of multiple small identical training symbols. When each training symbol is shortened, the number of training symbols in the training-symbol-block should be increased accordingly to keep the total training-symbol-block length fixed. The proposed scheme extends Moose's estimator, where the estimation error is only dependent on total training symbol energy and cannot be reduced any more, once the total training symbol energy is determined. The proposed scheme can shorten each training symbol in a training-symbol block and select an appropriate estimator simultaneously, which can lead to further reduction of estimation error and increase of acquisition range, even with the total training-symbol-block energy being fixed. Performance analyzes for the proposed scheme in both the additive white Gaussian noise channel (AWGN) and the multipath channel are also presented in this paper. All estimators in the proposed scheme are conditionally unbiased, and simulation results demonstrate that they can work well both in the multipath channel and in the AWGN channel.

A soft decision 16-QAM demodulation algorithm for multipath affected DVB-T systems

SL Linfoot — 2008-01-23T08:51:53-00:00

Consumer Electronics, IEEE Transactions on, Vol. 51, No. 4. (2005), pp. 1121-1128.

In 1998, the United Kingdom started the world's first commercial digital terrestrial television service. The system used was the European digital video broadcast-terrestrial (DVB-T) but due to technological constraints at the time, the system chosen was the 2K system - a system that uses 1705 carriers to convey the digital television services through a hostile terrestrial environment. Today, these constraints are no longer applicable but in order to maintain backwards compatibility to the older set top boxes, the 2K system is still used. The 2K system has the disadvantage of excluding the possibility of employing a single frequency network (SFN) - something that can help minimize the required bandwidth for television services. This paper demonstrates an observed phenomenon that explains why DVB-T fails to meet the required BER criteria and also shows how this phenomenon can be used in a computationally inexpensive technique for estimating the relative path attenuation of a multipath signal and how it can be used to estimate the parameters required for a soft decision QAM demapper.

Quick simulation: a review of importance sampling techniques in communications systems

PJ Smith — 2007-01-26T15:19:33-00:00

Selected Areas in Communications, IEEE Journal on, Vol. 15, No. 4. (1997), pp. 597-613.

Importance sampling (IS) is a simulation technique which aims to reduce the variance (or other cost function) of a given simulation estimator. In communication systems, this usually, but not always, means attempting to reduce the variance of the bit error rate (BER) estimator. By reducing the variance, IS estimators can achieve a given precision from shorter simulation runs; hence the term “quick simulation.” The idea behind IS is that certain values of the input random variables in a simulation have more impact on the parameter being estimated than others. If these “important” values are emphasized by sampling more frequently, then the estimator variance can be reduced. Hence, the basic methodology in IS is to choose a distribution which encourages the important values. This use of a “biased” distribution will, of course, result in a biased estimator if applied directly in the simulation. However, there is a simple procedure whereby the simulation outputs are weighted to correct for the use of the biased distribution, and this ensures that the new IS estimator is unbiased. Hence, the “art” of designing quick simulations via IS is entirely dependent on the choice of biased distribution. Over the last 50 years, IS techniques have flourished, but it is only in the last decade that coherent design methods have emerged. The outcome of these developments is that at the expense of increasing technical content, modern techniques can offer substantial run-time saving for a very broad range of problems. We present a comprehensive history and survey of IS methods. In addition, we offer a guide to the strengths and weaknesses of the techniques, and hence indicate which techniques are suitable for various types of communications systems. We stress that simple approaches can still yield useful savings, and so the simulation practitioner as well as the technical researcher should consider IS as a possible simulation tool

Frequency offset estimation with fast acquisition in OFDM system

Zhongshan Zhang — 2007-11-11T15:43:57-00:00

Communications Letters, IEEE, Vol. 8, No. 3. (2004), pp. 171-173.

A new carrier frequency offset estimation scheme in orthogonal frequency-division multiplexing (OFDM) system is proposed. The carrier frequency offset estimation includes acquisition and tracking, and the acquisition range is as large as one half of overall signal bandwidth. The proposed tracking estimator is a maximum-likelihood estimator, and in AWGN channel, the Cramer-Rao lower bound is met at high signal-to-noise ratio (SNR); in multipath channel, the tracking algorithm works well at moderate SNR. Timing synchronization can be also performed during the course of acquisition.

Broadband high-efficiency circularly polarized active antenna and array for RF front-end application

Yin Qin — 2007-11-05T20:47:07-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 54, No. 7. (2006), pp. 2910-2916.

This paper presents a broadband high-efficiency circularly polarized (CP) active integrated antenna, and a broadband CP active array at 2 GHz. To realize the broadband CP antenna, a circular patch is aperture coupled by crossed slots in the ground plane, which are fed by an L-shaped microstrip feed line below the ground. The antenna is designed to serve the functions of both a radiator and a harmonics-terminated load for class-E high-efficiency power-amplifier (PA) integration. The broadband CP active antenna is realized by directly integrating the broadband CP antenna with the class-E PA. It achieves a 9% bandwidth (1.84-2.01 GHz) for axial ratio (AR) below 3 dB, and a 12% bandwidth for power-added efficiency (PAE) over 60%. To form the broadband CP active array, four active antenna elements are sequentially rotated, and each element is directly integrated with broadband class-E PA. A low-cost printed-circuit-board technology is employed in fabrication and a pseudomorphic high electron-mobility transistor is used. A peak drain efficiency of 71.5% for the class-E amplifier is measured at 1.95 GHz. The active array achieves a peak-effective radiated power of 39.7 dBm, and PAE is over 50% within a 22.6% bandwidth (1.72-2.16 GHz). The AR is below 3 dB over a 27% bandwidth (1.72-2.26 GHz).