CiteULike: dcastro's Chen

Broad-bandwidth and low-loss metamaterials: Theory, design and realization

Le-Wei Li — 2008-06-29T18:25:25-00:00

Journal of Zhejiang University - Science A, Vol. 7, No. 1. (23 January 2006), pp. 5-23.

Abstract In this paper, we summarize some recent activities in the field of metamaterial research at the National University of Singapore (NUS). Integral equations are applied for electromagnetic modelling of supernatural materials. Some special characteristics of the metamaterials are shown. Moreover, quasi-static Lorentz theory and numerical method (i.e., the method of moments for solving the electric field integral equation) and the transmission line theory are both presented to obtain the effective constitutive relations of metamaterials, respectively. Finally, feasibility of fabricating metamaterials based on analysis of equivalent transmission line model in the microwave spectrum and even higher is also shown and correspondingly some broad-bandwidth and low-loss metamaterial structures are designed and synthesized.

Properties of left-handed metamaterials: transmission, backward phase, negative refraction, and focusing

TM Grzegorczyk — 2008-06-15T13:49:49-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 53, No. 9. (2005), pp. 2956-2967.

Four properties related to left-handed metamaterials are studied numerically: transmission within a stop-band, backward phase, negative refraction, and partial focusing. The unit cell of the metamaterial under study is composed of a rod and a ring originally proposed at infrared frequencies and redesigned here at microwave frequencies. We show that this ring, because of its symmetry, exhibits a better transmission in a parallel-plate waveguide than the original concentric split-ring resonator. Negative refraction is studied from a prism-shaped metamaterial, while all of the other properties are studied from a slab-shaped metamaterial. In particular, transmission and backward phase are studied on a slab where rings naturally couple with the incident wave, while partial focusing is studied on a slab of rings perpendicular to the direction of propagation. The numerical simulations are based on a two-dimensional periodic method of moments, whose Green's function is computed via Ewald's method, and a three-dimensional finite-difference time-domain technique.

The overview of synchronization in DS-UWB

Jun Chen — 2008-06-11T20:26:39-00:00

Communications and Information Technology, 2005. ISCIT 2005. IEEE International Symposium on, Vol. 2 (2005), pp. 983-986.

Ultra-Wide band (UWB) radio, transmits data using nanosecond level impulses, is gaining increasing attention own to its attractive features that include low-complexity hardware and high transmission rate. However, UWB system has to cope with great design challenges, including synchronization, multi-path energy combining. A review of acquisition methods in direct sequence-spread spectrum (DS-SS) communication system is given in detail at first and analysis of their performance with evaluating parameters, which is the essential reference to DS-SS acquisition algorithm is shown next. Then, several acquisition scheme used specially in DS-UWB system is analyzed. Hardware complexity and acquisition performance in DS-UWB is still the two sides of one contradiction needed to be tradeoff.

An electrically small impedance-matched microstrip antenna design

MC Liang — 2008-06-11T20:15:13-00:00

Antennas and Propagation Society International Symposium, 2002. IEEE, Vol. 4 (2002), pp. 38-41 vol.4.

In traditional antenna design, a rule of thumb is that an impedance-matched antenna has to be wavelength compatible in size. It is not possible to design an electrically small antenna with matched impedance. In our previous studies, it was found that the operating frequency of a patch antenna could be reduced to 1/3 or even 1/4 of the original operating frequency using a loaded capacitor. By making use of dual capacitor loading, the operating frequency of the patch antenna could be reduced further. With proper choice of the loaded capacitors and the feed location, an electrically small microstrip antenna with matched impedance is found. This electrically small microstrip antenna design is presented. Like the previous capacitor loaded patch antenna, the operating frequency of this electrically small microstrip antenna could be tuned according to customer requirement. Simulated as well as measured result of the electrically small antenna are shown.

PHY 23-1 - Iterative Unequal Length Search Syndrome Decoding for Product Codes

Yantao Qiao — 2008-06-11T20:11:07-00:00

Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE (2008), pp. 593-598.

In this paper, Iterative Unequal Length Search (ULS) Syndrome Decoding for Product Codes is proposed by introducing an idea of unequal length search space. The principle and realization of the algorithm is presented. Moreover, a mathematical performance and decoding complexity analysis is illustrated. Compared to the conventional Equal Length Search (ELS) Syndrome algorithm, experimental results indicate that the iterative ULS syndrome decoding algorithm, not only significantly reduces the decoding complexity, but also improves the error-correcting performance. Because of the balance between the odd and even circuits, the speed of parallel processing is increased and hardware resources are saved accordingly. Simulations results have shown that the proposed algorithm leads to a decrease of 25%~30% of search complexity and a gain of 0.3 dB in the BER performance for various subcodes.

OFDM timing synchronisation under multi-path channels

N Chen — 2008-06-03T14:51:21-00:00

Vehicular Technology Conference, 2003. VTC 2003-Spring. The 57th IEEE Semiannual, Vol. 1 (2003), pp. 378-382 vol.1.

Wireless OFDM signals typically have a prefixed guard interval. The FFT timing synchronisation at the receiver is traditionally based on the peak point of correlation output between the guard interval and its corresponding duplicate at the OFDM symbol's tail. This approach does not in general find the optimum timing position for the FFT when the channel contains more than one path. This is particularly true when the first arriving replica of the signal is not the strongest, potentially resulting in the timing position that is outside the acceptable range, causing ISI. In this paper, the OFDM FFT timing synchronisation problem under multi-path channel conditions is studied. Algorithms that produce improved FFT timing synchronisation are developed, which exploit either the channel information obtained, say, through scattered pilots or the characteristics exhibited by combining a modified correlation scheme with a special filtering process. Results from simulation study are presented which have shown a noticeable performance improvement.

A transmission line model for high-frequency power line communication channel

H Meng — 2008-05-16T12:02:03-00:00

Power System Technology, 2002. Proceedings. PowerCon 2002. International Conference on, Vol. 2 (2002), pp. 1290-1295 vol.2.

This paper presents a novel approach to modelling the transfer function of the broadband power line communication channel. In the approach, the power line is firstly approximated as a two-wire transmission line. The two intrinsic line parameters, the characteristic impedance and the propagation constant, are derived based on the transmission line theory. Then from the derived line parameters, an echo-based model is used to determine the transfer function for communication signals in the frequency range of 1 MHz-30 MHz. This approach reaps the advantages of accuracy and simplicity of the conventional modeling approaches.

A PN Code Acquisition Scheme in the Presence of Data Modulation and Doppler Shift

Zhi-Jun Chen — 2008-05-15T18:22:16-00:00

Machine Learning and Cybernetics, 2007 International Conference on, Vol. 5 (2007), pp. 2653-2656.

A PN (pseudo noise) code acquisition scheme for direct sequence spread spectrum (DSSS) systems is developed in this paper, which is especially suitable for the simultaneous presence of various rate data modulation and wide Doppler shift range at low signal-to-noise ratio. The technique is based on FFT and noncoherent integration, and can be implemented easily with less hardware cost. Some computer simulation results are given, which show that the technique can achieve fast PN acquisition and obtain carrier Doppler frequency estimation.

A periodic microstrip radial antenna array with a conical beam

Kuo-Cheng Chen — 2008-05-15T12:14:36-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 51, No. 4. (2003), pp. 756-765.

We present the analysis and design of a microstrip antenna array with a conical beam. The antenna array employs a periodic structure derived from a microstrip on a perforated ground plane. The microstrip antenna array consists of eight leaky lines evenly distributed around a circle. Each line radiates mainly a pair of forward and backward beams, forming a conical beam. The new leaky line design employs the concept of space-harmonic modulation on the EH/sub 0/ mode launched at the common joint of the antenna array. The scattering and dispersion characteristics of the leaky line are thoroughly investigated. It is theoretically and experimentally validated that the perturbation of the photolithographically etched antisymmetric holes excites the leaky EH/sub 1/ mode. Scattering analyses of the surface currents on the microstrip reveal in detail the physical operation of the leaky line. The dispersion characteristics are, thus, established and shown in a Brillouin diagram, indicating the role of each space harmonic, denoted by its complex propagation constant, /spl gamma//sub m,n//sup /spl plusmn//. Constant /spl gamma//sub m,n//sup /spl plusmn// represents a traveling-wave component of the nth higher-order spatial component in association with the EH/sub m/ mode: the superscript, + (-), signifies a forward (backward) traveling wave. For the particular leaky line design, /spl gamma//sub 0,-1//sup +/ and /spl gamma//sub 1,0//sup +/ space harmonics, both showing odd-symmetric field polarization, and both outside the triangular Brillouin region, form the backward and forward leaky waves, respectively. When the leaky lines are evenly and collinearly tied, an 11.5 GHz radial antenna array prototype is formed, and emits a conical beam, showing a 3 dB beamwidth of 24/spl deg/ at the flare angle of 31/spl deg/.

Global time-domain full-wave analysis of microwave FET oscillators and self-oscillating mixers

Min Chen — 2008-05-15T12:12:47-00:00

Microwave Symposium Digest, 1998 IEEE MTT-S International, Vol. 2 (1998), pp. 1135-1138 vol.2.

The global time-domain nonlinear analysis of microwave FET oscillators and self-oscillating mixers using the extended FDTD technique is presented. Employing the concept of equivalent current/voltage sources, the device-wave interaction is characterized and incorporated into the FDTD time-stepping algorithm. Consequently, investigation of highly nonlinear phenomena, such as injection locking and intermodulation, can be accomplished by utilizing a large-signal device circuit model. Theoretical results are validated by experiments

FDTD analysis of a metal-strip-loaded dielectric leaky-wave antenna

M Chen — 2008-05-15T12:11:18-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 45, No. 8. (1997), pp. 1294-1301.

The finite-difference time-domain (FDTD) method is used to analyze a dielectric leaky-wave antenna comprising metal strips etched on a rectangular dielectric rod. The radiation patterns of the leaky-wave antenna with and without the transition are determined by using FDTD. The effects of the launching discontinuity on the performance of the antenna are discussed. In addition, the application of the perfectly matched layer (PML) technique to the three-dimensional (3-D) dielectric waveguide and its performance, compared to those of the Mur's (1981) first-order and super-absorbing Mur's first-order absorbing boundary conditions (ABCs) are described. In addition, the effects caused by perturbation on the wave propagation characteristics of dielectric waveguide are also discussed. The FDTD results are verified by a W-band experiment and found to be in good agreement

Effective electromagnetic parameters of novel distributed left-handed microstrip lines

Shau-Gang Mao — 2008-05-09T23:56:00-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 53, No. 4. (2005), pp. 1515-1521.

The novel one-dimensional left-handed microstrip lines (LHMLs) consisting of the arrays of thin wires and two-layer split-ring resonators are investigated theoretically and experimentally in this paper. Unlike the conventional left-handed metamaterials for waveguides or microstrip lines, which are bulky three-dimensional constructions or require the lumped elements for high-pass configuration, this distributed structure can be directly implemented on a substrate by photolithographic techniques without soldering any chip inductors or capacitors. Moreover, it can also be easily realized at a higher frequency region by scaling the dimensions of the structure, making it highly efficient and flexible in millimeter-wave applications. To characterize the inhomogeneous LHML, the effective medium description is developed for extracting the effective electromagnetic parameters, i.e., the complex effective permittivity and permeability, as well as the refractive index. Results show that not only the simultaneously negative real permittivity and permeability, but also the antiparallel phase and group velocities may be achieved in the design passband region. In contrast to the antenna array using the conventional microstrip delay line, the LHML is incorporated in the series-fed microstrip combline array to exhibit the leading phase between the successive elements.

Propagation characteristics of finite-width conductor-backed coplanar waveguides with periodic electromagnetic bandgap cells

Shau-Gang Mao — 2008-05-09T23:55:59-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 50, No. 11. (2002), pp. 2624-2628.

Wave propagation along the finite-width conductor-backed coplanar waveguide (FW-CBCPW) with periodically loaded one-dimensional electromagnetic bandgap (EBG) cells proposed earlier by the authors is investigated theoretically and experimentally in this paper. The full-wave simulation in conjunction with Floquet's theorem is employed to find the dispersion diagram for characterizing the guided and leaky waves over a wide frequency range. For examining the guided-wave mode, the equivalent-circuit model is established to obtain the analytical formula of the Bloch impedance. The remarkable slow-wave factor 1.9-2.9 times higher than that of a conventional FW-CBCPW is presented. When operating frequency is sufficiently high, the leaky-wave mode is emitted so that the structure radiates in the backward direction. Good agreement among the results of the full-wave simulation, equivalent-circuit model, published data, and measurement supports the usefulness of the proposed full-wave simulation and also validates the analytical formula. By properly adjusting the circuit configuration, the periodic EBG structure with controllable propagation characteristics, which include the bandgap zone, the slow-wave factor, and the Bloch impedance for the guided wave, as well as the radiation main beam for the leaky wave, may be achieved.

A novel periodic electromagnetic bandgap structure for finite-width conductor-backed coplanar waveguides

Shau-Gang Mao — 2008-05-09T23:55:57-00:00

Microwave and Wireless Components Letters, IEEE, Vol. 11, No. 6. (2001), pp. 261-263.

The one-dimensional (1-D) periodic electromagnetic bandgap (EBG) structure for the finite-width conductor-backed coplanar waveguide (FW-CBCPW) is proposed. Unlike the conventional EBG structures for the microstrip line and the coplanar waveguide (CPW), which are typically placed on one of the signal strips and the ground plane, this EBG cell is etched on both the signal strip and the upper ground plane of FW-CBCPW resulting in a novel circuit element. The equivalent circuit is also used to model the EBG cell. Measured and full-wave simulated results show that the cell exhibits remarkable stopband effect. The low-pass filter with lower cutoff frequency and wider rejection bandwidth is constructed from a serial connection of the EBG cells. The effect of back metallization on the guiding characteristic is also discussed. Compared to the published EBG cells, the proposed structure has the advantages of relative flexibility, higher compactness, lower radiation loss, and easier integration with the uniplanar circuits

Effects of output harmonic termination on PAE and output power of AlGaN/GaN HEMT power amplifier

Y Chung — 2008-05-09T23:49:18-00:00

Microwave and Wireless Components Letters, IEEE, Vol. 12, No. 11. (2002), pp. 421-423.

The authors experimentally investigate and discuss the effects of output harmonic termination on power added efficiency (PAE) and output power of an AlGaN/GaN high electron mobility transistor (HEMT) power amplifier (PA). The AlGaN/GaN HEMT PA with gate periphery of 1 mm was built and tested at L-band. Large-signal measurements and comparisons of the PAE and output power were carried out at different DC bias conditions from 50% of saturated drain current (I/sub dss/) to 1% of Id., for the PA with and without output harmonic termination. For class-AB operation at 25% of I/sub dss/, an increase of about 10% in peak PAE and 1 dBm in output power were observed in saturated output power range. Improvements of up to 9% in PAE and 1.2 dBm in output power were achieved over the measured DC bias conditions provided the output harmonics are properly terminated.

Dual-band bandpass filter using coupled resonator pairs

Cheng-Chung Chen — 2008-05-09T23:46:53-00:00

Microwave and Wireless Components Letters, IEEE, Vol. 15, No. 4. (2005), pp. 259-261.

This letter proposes and fabricates a novel dual-band bandpass filter topology. The proposed topology facilitates the split resonating frequencies of coupled resonator pairs in realizing the dual-band response and introduces transmission zeros for improving the stopband attenuation. The semi-lumped prototype enables the integration of the filter in a multilayer circuit for miniaturized implementation. Finally, a design example fabricated with low temperature co-fired ceramic (LTCC) technology is presented for validating the filter configuration.

Cavity-backed active slot loop antenna

M Zheng — 2008-05-09T16:13:48-00:00

Antennas and Propagation Society International Symposium, 1998. IEEE, Vol. 3 (1998), pp. 1620-1623 vol.3.

A rectangular cavity-backed active slot loop antenna has been investigated and the experimental results show that a 30 dB oscillator noise reduction can be achieved for the active slot loop antenna at a carrier frequency of 3.42 GHz and an offset frequency of 40 kHz. The advantage of the active slot loop antenna is that it is easy to fabricate and compatible with the micromachining process. The authors build a cavity-backed active slot loop antenna for the K band using silicon micromachining techniques, and it is believed that this novel active slot loop silicon micromachined antenna should be well suited to short range radars and communication systems

Study of a printed circular disc monopole antenna for UWB systems

Jianxin Liang — 2008-05-09T08:23:41-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 53, No. 11. (2005), pp. 3500-3504.

This paper presents a study of a novel monopole antenna for ultrawide-band (UWB) applications. Printed on a dielectric substrate and fed by a 50 /spl Omega/ microstrip line, a planar circular disc monopole has been demonstrated to provide an ultra wide 10 dB return loss bandwidth with satisfactory radiation properties. The parameters which affect the performance of the antenna in terms of its frequency domain characteristics are investigated. A good agreement is achieved between the simulation and the experiment. In addition, the time domain performance of the proposed antenna is also evaluated in simulations.

Active phase array using injection-locked oscillators

Yen-Horng Chen — 2008-05-09T06:48:30-00:00

Microwave Conference, 2001. APMC 2001. 2001 Asia-Pacific (2001), pp. 819-822 vol.2.

This paper presents the design and measurement results of an active phase array using injection-locked oscillators. The required phase relation for each array element is obtained by electronic tuning through the injection-locked technique, and the beam-scanning capability is demonstrated

Single-feed dual-band circularly polarised microstrip antenna

Gui-Bin Hsieh — 2008-05-09T06:38:11-00:00

Electronics Letters, Vol. 34, No. 12. (1998), pp. 1170-1171.

A novel technique for obtaining dual-band circular polarisation (CP) radiation of a single-feed circular microstrip antenna is proposed and demonstrated. By embedding two pairs of arc-shaped slots of proper lengths close to the boundary of a circular patch, and protruding one of the arc-shaped slots with a narrow slot, the circular microstrip antenna can perform dual-band CP radiation using a single probe feed. Details of the antenna design and experimental results are presented

Integration of a self-oscillating mixer and an active antenna

Jiazong Zhang — 2008-05-09T06:37:33-00:00

Microwave and Guided Wave Letters, IEEE [see also IEEE Microwave and Wireless Components Letters], Vol. 9, No. 3. (1999), pp. 117-119.

Current trends in commercial communication system developments have called for small-size and low-cost radio frequency (RF)/microwave circuits. One of the solutions is to design a circuit element such that it possesses multiple functionality. In other words, different parts of a circuit are integrated into a single element, and consequently fewer elements are required. In this work, a C-band self-oscillating mixer (SOM) integrated with an active antenna is presented. A dual-gate field-effect transistor (FET) is employed to facilitate the integration. The resultant unit was tested and experimental results are shown to demonstrate the feasibility of the design

Adaptive minimum-BER linear multiuser detection for DS-CDMA signals in multipath channels

Sheng Chen — 2008-05-08T08:33:40-00:00

Signal Processing, IEEE Transactions on [see also Acoustics, Speech, and Signal Processing, IEEE Transactions on], Vol. 49, No. 6. (2001), pp. 1240-1247.

The problem of constructing adaptive minimum bit error rate (MBER) linear multiuser detectors is considered for direct-sequence code division multiple access (DS-CDMA) signals transmitted through multipath channels. Based on the approach of kernel density estimation for approximating the bit error rate (BER) from training data, a least mean squares (LMS) style stochastic gradient adaptive algorithm is developed for training linear multiuser detectors. Computer simulation is used to study the convergence speed and steady-state BER misadjustment of this adaptive MBER linear multiuser detector, and the results show that it outperforms an existing LMS-style adaptive MBER algorithm presented by Yeh et al. (see Proc. Globecom, Sydney, Australia, p.3590-95, 1998)

Design of an LTCC tri-band transceiver module for GPRS mobile applications

Yo-Shen Lin — 2008-05-08T06:40:28-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 52, No. 12. (2004), pp. 2718-2724.

This paper presents the design and results of a low-temperature co-fired ceramic (LTCC) module for tri-band general packet radio service (GPRS) mobile applications. The proposed transceiver module integrates the tri-band (EGSM900/DCS1800/PCS1900) antenna switch, the surface-acoustic-wave filters for band selection, and a fully integrated tri-band transceiver integrated circuit into one LTCC package. By taking advantages of the three-dimensional layout capability of the LTCC substrate, the embedded circuit elements can be arranged vertically for size reduction. In addition, the utilization of mutual coupling leads to a novel design of miniature lumped-element realization of the transmission line. By combining these miniature passive component designs, the proposed module features a compact size of 13.8 mm /spl times/ 8.1 mm, with a packaged height of 1.8 mm. The module is compliant with the European Telecommunications Standards Institute regulations for GPRS mobile applications and is currently in use in commercially available mobile phones.

Planar diplexer for microwave integrated circuits

ZC Hao — 2008-05-08T06:40:24-00:00

Microwaves, Antennas and Propagation, IEE Proceedings - (2005), pp. 455-459.

A planar microwave diplexer based on the substrate integrated waveguide (SIW) technique is presented in the paper. The SIW-microstrip transition and SIW filter are experimentally investigated, and then a C-band SIW diplexer is designed and fabricated using a standard PCB process. The relative bandwidths of up and down channels are 3% and 4.8% at 5.96 GHz and 5.42 GHz, respectively. The measured results show good channel isolation, moderate insert losses and small return losses in pass-bands. The diplexer takes a planar form and can be easily integrated in microwave integrated circuits (MICs).

A novel microstrip diplexer design using defected ground structure

Haiwen Liu — 2008-05-08T06:28:47-00:00

Communications, Circuits and Systems, 2005. Proceedings. 2005 International Conference on, Vol. 2 (2005)

A simple microstrip diplexer using defected ground structure (DGS) is described in this letter. The diplexer has been designed, fabricated, and measured. Results show the new diplexer exhibits an isolation of greater than 26 dB between channels.

Broadband monolithic passive baluns and monolithic double-balanced mixer

Chen — 2008-05-06T18:33:19-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 39, No. 12. (1991), pp. 1980-1986.

The design and fabrication of four broadband monolithic passive baluns including CPW Marchand, multilayer MS Marchand, planar-transformer and broadside-coupled line baluns are presented. Operational frequencies range from 1.5 GHz to 24 GHz. Maximum relative bandwidths in excess of 3:1 are achieved. Simulated performances using full wave electromagnetic analysis are shown to agree with the measured results. Two accurate equivalent circuit models constructed from either electromagnetic simulated or measured S-parameters are developed for the MS Marchand and transformer baluns making the optimization of baluns and circuit design using the baluns much more efficient. The design of monolithic double-balanced diode mixer using two planar-transformer baluns is also presented. Without DC bias, the mixer shows a minimum conversion loss of 6 dB with the RF at 5 GHz and a LO drive of 15 dBm at 4 GHz. The measured input IP3 of this mixer is better than 15 dBm over the 4 to 5.75 GHz frequency band

Device and circuit approaches for improved linearity and efficiency in microwave transmitters

PM Asbeck — 2008-05-06T18:30:58-00:00

Microwave Symposium Digest, 1998 IEEE MTT-S International, Vol. 1 (1998), pp. 327-330 vol.1.

This paper presents several power amplifier approaches that promise to significantly improve efficiency, while meeting the linearity requirements of advanced, spectrally efficient wireless systems. The approaches include: a) use of active integrated antenna structures that provide harmonic terminations for high efficiency Class F amplifiers; b) integrated dc-dc converters for power conditioning and envelope restoration; c) switching mode amplifiers based on bipolar transistors with controlled saturation; and d) the use of band-pass delta-sigma modulators to tailor input signals

High efficiency and broadband excitation of leaky mode in microstrip structures

Y Qian — 2008-05-06T18:28:46-00:00

Microwave Symposium Digest, 1999 IEEE MTT-S International, Vol. 4 (1999), pp. 1419-1422 vol.4.

This paper reports a novel technique for high efficiency and broadband excitation of the first higher order leaky mode in microstrips. A uniplanar microstrip-to-CPS transition is employed to launch the odd leaky mode, and the mode purity is enhanced by suppressing the even fundamental mode using an optimized mode suppressor. An X-band prototype demonstrates excellent mode conversion efficiency as predicted by simulations. A record bandwidth of 20.2% is achieved for a microstrip leaky-wave source based on this newly proposed structure

Microwave power amplifier efficiency improvement with a 10 MHz HBT DC-DC converter

G Hanington — 2008-05-06T17:42:50-00:00

Microwave Symposium Digest, 1998 IEEE MTT-S International, Vol. 2 (1998), pp. 589-592 vol.2.

This paper presents a technique for raising power efficiency in portable wireless transmitters by integrating a variable voltage output DC-DC converter together with a MESFET RF power amplifier. Significant increases in power efficiency are obtainable over a large range of output power levels. The system includes an envelope detector, a closed feedback loop, and a pulse width modulator operating at 10 MHz. A 300 mW transmitter is shown for which battery life can be extended by over 1.4 times

Cavity induced polarisation switching in a slot-loop active antenna

Q Chen — 2008-05-06T17:16:12-00:00

Microwave Symposium Digest, 1998 IEEE MTT-S International, Vol. 3 (1998), pp. 1899-1902 vol.3.

The new features of a cavity backed active slot-loop antenna are discussed in this paper. By using a high Q cavity, 35 dBc phase noise level reduction at 200 kHz from the carrier has been achieved. Once in resonance, the established TE110 cavity fields rotate the principle E-plane of the slot-loop antenna through 90°. This results in an exchange of E- and H-plane locations in the radiation pattern together with reduced cross-polarisation levels. Thus the presence of the cavity tuned into and out of resonance allows the antenna to have its polarisation properties orthogonally switched

Broadband microstrip patch antenna on micromachined silicon substrates

M Zheng — 2008-05-06T17:16:11-00:00

Electronics Letters, Vol. 34, No. 1. (1998), pp. 3-4.

A micromachined rectangular cavity-backed microstrip patch antenna has been developed on high resistivity silicon wafers. This novel path antenna has a much reduced effective dielectric constant and wide bandwidth

Cavity control of active integrated antenna oscillators

M Zheng — 2008-05-06T17:15:59-00:00

Microwaves, Antennas and Propagation, IEE Proceedings -, Vol. 148, No. 1. (2001), pp. 15-20.

The use of a cavity coupled to an active integrated antenna oscillator is described. The cavity increases the loaded Q factor of the oscillator, thus improving stability and reducing the phase noise. Cavity stabilisation of a microstrip patch and slot ring oscillators is described. In both cases, phase noise at a frequency offset of 10 kHz is reduced by the order of 20 dB. A first-order analysis based on measured and simulated cavity Q factors is shown to give similar results. A Van der Pol analysis of a two-element array of patch oscillators, with a single extended coupled cavity, indicates that the likelihood of mutual locking in an array which has oscillators with slightly different free running frequencies is enhanced albeit at the expense of increased start-up time

Active integrated antenna oscillator stability and phase noise reduction

M Zheng — 2008-05-05T20:24:15-00:00

Microwave and Millimeter Wave Technology Proceedings, 1998. ICMMT '98. 1998 International Conference on (1998), pp. 285-288.

Active microstrip patch antennas have been stabilised using cavity-backed and phase-locked-loop (PLL) controlled techniques. Experimental results show that phase noise reductions of up to 25 and 26 dB respectively can be realised

Joint Channel Estimation for WiMAX by Preamble and Uneven Pilots

Xuetao Dong — 2008-04-23T17:53:34-00:00

Wireless Communications, Networking and Mobile Computing, 2007. WiCom 2007. International Conference on (2007), pp. 1104-1107.

Miniaturized uniplanar 180° hybrid-ring couplers with 0.8 λg and 0.67 λg circumferences

Chih-Wai Kao — 2008-04-16T19:41:43-00:00

Microwave Conference, 2000 Asia-Pacific (2000), pp. 217-220.

Two miniaturized uniplanar 180° hybrid-rings with 0.8 λ g and 0.67 λg circumferences, respectively, are proposed. These hybrid-rings are implemented using the finite ground coplanar waveguide (FGCPW) structure. The sizes of these hybrid-rings are effectively reduced, and broadband performances are also achieved

Maximum likelihood channel estimation and signal detection for OFDM systems

Pei Chen — 2008-03-07T11:07:49-00:00

Communications, 2002. ICC 2002. IEEE International Conference on, Vol. 3 (2002), pp. 1640-1645 vol.3.

We apply joint maximum likelihood (ML) estimation to orthogonal frequency division multiplexing (OFDM) systems and develop a simple receiver structure that gives joint ML estimates of a multipath channel and the transmitted data sequence. Simulation results have confirmed good performance of our algorithm. For a two-path or three-path slow fading channel, our algorithm converges to the case with known channel parameters.

Decision feedback equaliser design using support vector machines

S Chen — 2008-02-26T18:59:57-00:00

Vision, Image and Signal Processing, IEE Proceedings -, Vol. 147, No. 3. (2000), pp. 213-219.

The conventional decision feedback equaliser (DFE) that employs a linear combination of channel observations and past decisions is considered. The design of this class of DFE is to construct a hyperplane that separates the different signal classes. It is well known that the popular minimum mean square error (MMSE) design is generally not the optimal minimum bit error rate (MBER) solution. A strategy is proposed for designing the DFE based on support vector machines (SVMs). The SVM design achieves asymptotically the MBER solution and is superior in performance to the usual MMSE solution. Unlike the exact MBER solution, this SVM solution can be computed very efficiently

Performance Analysis of Adaptive Threshold Acquisition Algorithm in DS-UWB with Multi-path Environment

Jun Chen — 2008-02-25T15:00:17-00:00

Communications and Networking in China, 2006. ChinaCom '06. First International Conference on (2006), pp. 1-5.

Synchronization process is essential especially in UWB communication system owes to its extremely short transmitted pulse shape and the ultra dense multi-path interference. Acquisition performance decreased rapidly own to serious inter-symbol interference (ISI) caused by those complex channel with relatively large delay spread. An interference resistant adaptive threshold acquisition algorithm (IR-ATAA) for DS-UWB systems proposed here has the feature that the decision threshold changes automatically adapting to the signal to noise ratio (SNR) at time of comparison. The performance analysis mainly focus on the probability of correct acquisition (PACQ) and estimation error of timing delay (MSE) with IEEE defined standard channel models and in the presents of multi-access interference (MAI) which is assumed as an additive white Gaussian noise. The simulation results also indicate the superiority of IR-ATAA over the fixed threshold acquisition algorithm

Signal processing techniques in network-aided positioning: a survey of state-of-the-art positioning designs

Guolin Sun — 2007-01-08T07:26:34-00:00

Signal Processing Magazine, IEEE, Vol. 22, No. 4. (2005), pp. 12-23.

Wireless positioning has attracted much research attention and has become increasingly important in recent years. Wireless positioning has been found very useful for other applications besides E911 service, ranging from vehicle navigation and network optimization to resource management and automated billing. Although many positioning devices and services are currently available, it is necessary to develop an integrated and seamless positioning platform to provide a uniform solution for different network configurations. This article surveys the state-of-the-art positioning designs, focusing specifically on signal processing techniques in network-aided positioning. It serves as a tutorial for researchers and engineers interested in this rapidly growing field. It also provides new directions for future research for those who have been working in this field for many years.

A New Planar Dual-Band GPS Antenna Designed for Reduced Susceptibility to Low-Angle Multipath

LI Basilio — 2008-01-02T12:17:22-00:00

Antennas and Propagation, IEEE Transactions on, Vol. 55, No. 8. (2007), pp. 2358-2366.

A new Global Positioning System (GPS) microstrip patch antenna designed for dual-band (LI /L2) operation is introduced. The antenna design is based on the reduced-surface-wave (RSW) concept and, as a result, is much less susceptible to low-angle multipath interference effects than some of the more commonly-used high-precision GPS antennas. In this paper, the radiation characteristics of this new design was compared to a dual- band choke-ring and a dual-band pinwheel antenna. In addition to having the advantages typically associated with microstrip patch antennas, this planar dual-band antenna lacks the design complications associated with the frequently-used stacked-patch method for realizing dual-band microstrip antenna performance. Thus, the simplicity of the design, together with the reduced horizon and backside radiation levels and excellent circular polarization characteristics indicate that this new antenna design is a promising candidate for dual-band, high-precision applications.

Compact microstrip antenna with dual-frequency operation

Kin-Lu Wong — 2007-12-31T18:19:16-00:00

Electronics Letters, Vol. 33, No. 8. (1997), pp. 646-647.

The characteristics of a single-feed dual-frequency compact microstrip antenna with a shorting pin are studied experimentally. Besides the compactness of the antenna, this dual-frequency design can provide a high frequency ratio of >3.0 between the two operating frequencies. Typical experimental results of the proposed antenna are presented and discussed

ML estimation of timing and frequency offset using multiple OFDM symbols in OFDM systems

Tiejun Lv — 2007-12-07T09:52:57-00:00

Global Telecommunications Conference, 2003. GLOBECOM '03. IEEE, Vol. 4 (2003), pp. 2280-2284 vol.4.

An approach of joint blind estimation of the symbol timing offset and carrier frequency offset using multiple orthogonal frequency-division multiplexing (OFDM) symbols is proposed for OFDM systems in frequency selective fading environments. The proposed approach greatly improves the estimation accuracy of the synchronization parameters, more than the ML estimation of N. Lashkarian and S. Kiaei (see IEEE Trans. Commun., vol.48, p.2139-49, 2000). This conclusion is derived from analyzing their performances. Meanwhile, simulation shows that estimation of symbol timing is completely correct for signal-to-noise ratio (SNR) as low as 0 dB, and the variance of the frequency offset estimator is nearly close to its Cramer-Rao bound (CRB) with varying SNR.

Synthesizing Microstrip Branch-Line Couplers With Predetermined Compact Size and Bandwidth

CW Tang — 2007-12-06T16:52:53-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 55, No. 9. (2007), pp. 1926-1934.

<para> A new method for designing the microstrip branch-line couplers with predetermined compact size and bandwidth is proposed in this paper. With the proposed approach, the size of the quarter-wavelength transmission line in the branch-line coupler can be reduced greatly. In addition, the proposed couplers can be easily fabricated on the printed circuit board without any lumped element. A chart concludes the relationship between bandwidth and size reduction rate. It shows that open stubs with low impedance perform better than those with high impedance; moreover, the more open stubs with low impedance utilized, the broader the bandwidth will be. Furthermore, the measured frequency responses show good agreement with the theoretical results. </para>

What is the price paid for superimposed training in OFDM?

Ning Chen — 2007-11-28T11:36:26-00:00

Acoustics, Speech, and Signal Processing, 2004. Proceedings. (ICASSP '04). IEEE International Conference on, Vol. 4 (2004), pp. iv-421-iv-424 vol.4.

Orthogonal frequency division multiplexing (OFDM) transmission with superimposed training is considered in this paper. The superimposed training scheme is promoted for its high bandwidth efficiency, low computational complexity, and possibly improved power amplifier (PA) efficiency. Channel equalization is also straightforward thanks to the OFDM structure. By analyzing the peak-to-average power ratio (PAR) of the superimposed OFDM signal and utilizing a peak power constraint, we demonstrate that it is possible to lose a little in the information signal power, but gain a lot in the power that is devoted to channel sounding.

Minimax microstrip filter design using direct EM field simulation

JW Bandler — 2007-11-27T10:27:34-00:00

Microwave Symposium Digest, 1993., IEEE MTT-S International (1993), pp. 889-892 vol.2.

A comprehensive approach to microwave filter design which exploits accurate filed simulations driven directly by a gradient-based minimax optimizer is presented. Challenges of efficiency, discretization of geometrical dimensions, and continuity of optimization variables are reconciled by a three-stage attack: (1) efficient response interpolation; (2) smooth gradient estimation; and (3) dynamic database updating. The design optimization of two microstrip filters illustrates the technique described.<<ETX>>

Novel lumped-element uniplanar transitions

Yo-Shen Lin — 2007-11-27T10:26:14-00:00

Microwave Theory and Techniques, IEEE Transactions on, Vol. 49, No. 12. (2001), pp. 2322-2330.

Novel reduced-size lumped-element uniplanar transitions are proposed, using the planar parallel and series inductor-capacitor (LC) circuits to realize the effective open and short circuits, respectively. In this study, various compact lumped-element coplanar waveguide-to-slotline and finite-ground coplanar waveguide-to-coplanar stripline transition structures are developed and carefully examined. Specifically, the performance of proposed basic lumped-element transitions can easily be adjusted through the control of L and C values, while the design of lumped-element Marchand-balun-type transitions may be accomplished by the use of conventional filter synthesis techniques. Simple equivalent-circuit models are also established, from which the passband behavior of the lumped-element transition structures may be characterized

Review of Electromagnetic Theory in Left-handed Materials

Chen — 2007-01-03T08:37:21-00:00

Journal of Electromagnetic Waves and Applications, Vol. 20, No. 15. (2006), pp. 2137-2151.

Broadband wireless access with WiMax/802.16: current performance benchmarks and future potential

A Ghosh — 2006-06-30T20:09:07-00:00

Communications Magazine, IEEE, Vol. 43, No. 2. (2005), pp. 129-136.

The IEEE 802.16 family of standards and its associated industry consortium, WiMax, promise to deliver high data rates over large areas to a large number of users in the near future. This exciting addition to current broadband options such as DSL, cable, and WiFi promises to rapidly provide broadband access to locations in the world's rural and developing areas where broadband is currently unavailable, as well as competing for urban market share. WiMax's competitiveness in the marketplace largely depends on the actual data rates and ranges that are achieved, but this has been difficult to judge due to the large number of possible options and competing marketing claims. This article first provides a tutorial overview of 802.16. Then, based on extensive recent studies, this article presents the realistic attainable throughput and performance of expected WiMax compatible systems based on the 802.16d standard approved in June 2004 (now named 802.16-2004). We also suggest future enhancements to the standard that could at least quadruple the achievable data rate, while also increasing the robustness and coverage, with only moderate complexity increases.

On importance sampling in digital communications. II. Trellis-coded modulation

JC Chen — 2007-11-14T09:23:58-00:00

Selected Areas in Communications, IEEE Journal on, Vol. 11, No. 3. (1993), pp. 300-308.

For Pt.I see ibid., vol.11, no.3, p.289-99 (1993). A simulation algorithm design strategy based on event simulation, conditional importance sampling, and mean translation biasing of Gaussian noise distribution is applied to systems with trellis-coded modulation using the error event simulation. Suboptimal Viterbi decoding in the presence of weak intersymbol interference (ISI) is discussed. To illustrate the utility of the technique, some numerical results for a nonlinear channel model with intersymbol interference (ISI) are presented

Sequential Monte Carlo Methods for Dynamic Systems

Jun Liu — 2006-07-12T10:58:25-00:00

Journal of the American Statistical Association, Vol. 93, No. 443. (1998), pp. 1032-1044.

We provide a general framework for using Monte Carlo methods in dynamic systems and discuss its wide applications. Under this framework, several currently available techniques are studied and generalized to accommodate more complex features. All of these methods are partial combinations of three ingredients: importance sampling and resampling, rejection sampling, and Markov chain iterations. We provide guidelines on how they should be used and under what circumstance each method is most suitable. Through the analysis of differences and connections, we consolidate these methods into a generic algorithm by combining desirable features. In addition, we propose a general use of Rao-Blackwellization to improve performance. Examples from econometrics and engineering are presented to demonstrate the importance of Rao-Blackwellization and to compare different Monte Carlo procedures.