Van Yem Vu

Novel reconfigurable 8 - shape PIFA antenna using PIN diode

A frequency reconfigurable Planar Inverted-F Antenna (RPIFA) antenna is proposed. From an initial 8-shape patch antenna by connecting or disconnecting one or more PIN diode, ten different structures are obtained. Corresponding to ten different geometries such as I-shape patch, U-shape patch, E-shape patch, etc, the antenna can be tuned in two frequency bands from 2GHz to 3GHz and from 4GHz to 7GHz. The novel RPIFA antenna is designed and optimized using Genetic Algorithm (GA) and then it is implemented on FR4 substrate. The simulation and measurement results of antenna parameters are compared to show the performance of the developed antenna.

Measurement of direction-of-arrival of coherent signals using five-port reflectometers and quasi-Yagi antennas

The measurement results of detection-of-arrival (DoA) of coherent signals using five-port reflectometers and quasi Yagi antennas are presented. The receiver operating at 2.4GHz consists of eight five-port reflectometers and a uniform linear array (ULA) of eight 2.4GHz quasi-Yagi antennas. The DoA is estimated by measuring the phase difference of signals pitched by the antenna array and by using the MUSIC algorithm associated with Spatial Smoothing Pre-processing (SSP). The phase difference is determined using the five-port technique. The measurement results show that the DoA of coherent signals are well estimated with a maximum error of 2/spl deg/. In addition, we also show that it is capable of estimating the time delay and direction of arrival simultaneously using the five-port technique.

Joint TOA/DOA measurements for spatio-temporal characteristics of 2.4 GHz indoor propagation channel

The aim of this paper is to present a new system based on five-port reflectometers, which measures direction of arrival (DOA) in azimuth plane and propagation time of arrival (TOA) of incoherent signals and coherent signals simultaneously for indoor communication applications. The receiver operating at 2.4 GHz consists of seven five-ports and a uniform linear array (ULA) of seven quasi-Yagi antennas. The spatio-temporal signal processing method is also proposed. Estimation procedure for joint DOA and TOA is based on the multiple signal classification (MUSIC) algorithm associated with spatial smoothing pre-processing (SSP) and the frequency domain sounding technique. It is clear from the simulation results and measurement results that it is possible to measure simultaneously TOA and DOA using five-port technique

Simulation and implementation of improved chaotic Colpitts circuit for UWB communications

In this paper, we develop an improved chaotic Colpitts oscillator applied to ultra wide band wireless communication system. We design, simulate and implement the improved chaotic Colpitts oscillator using Philips wideband transistor BJT BFG425W. The numerical simulation using Matlab and circuit simulation using Advanced Design System (ADS) are also presented. The oscillator is designed based on micro-strip substrate and the simulation result of the layout approves the possibility for UWB wireless communication applications.

Optimization Of PIFA antenna using an auto-embedded Genetic Algorithm

We propose in this paper single and dual polarization PIFA antenna optimization using a Genetic Algorithm (GA) embedded in CST environment. At first, we investigate an embedded GA for simultaneous multiple parameter optimization and then we design, optimize and implement a single polarization Planar Inverted F Antenna (PIFA) using the developed algorithm. With an L-shape microstrip patch antenna, the change of microstrip patch length as well as shorting pin position leads several antenna configurations. A dual polarization PIFA antenna is also proposed and optimized using the GA. Simulation and measurement results of the input reflection coefficient of the two antennas are shown for the performance of our joint developed model.

Improving Opto-Electronic Oscillator stability by controlling the Electro-Optic Modulator

This paper presents a study concerning the improvement of the stability of an Opto-Electronic Oscillator (OEO). It seems to be the first publication about this subject. An advanced method for controlling the optical bias point of the Electro-Optic Modulator (EOM) has been developed. The evolution of the modulator characteristics can be followed through its non-linear behavior by detecting the second harmonic of a low-frequency modulating signal. The control system implemented with PSoC microcontrollers is designed in order to keep the bias point at the quadrature position for minimizing the second order non-linear component. By this way the medium term stability can be greatly improved. Without bias point position control the OEO operates only for a few hours (2 or 3 h) but with the control it can operate for at least a working day (8 h).

A new technique to monitor the long-term stability of an optoelectronic oscillator.

The main advantage of an optoelectronic oscillator (OEO) is the ability to synthesize directly very high spectral purity frequency in microwave domain. Beside applications in radar, telecommunication and satellite systems, OEO can also be used in sensor applications such as refractive index or distance measurements. However, the long-term stability of the OEO is easily affected by ambient environment variations. The optical fiber loop effective refractive index varies corresponding to its surrounding temperature changes. Consequently, it makes the optical transmission path inside the fiber loop differ from the initial state, leading to oscillation frequency changes. To stabilize the single loop OEO, it is essential to keep its high Q elements in a well-controlled thermal box as much as possible. Unfortunately, in the real implementation condition, this requirement is difficult to be satisfied. In this paper, we present a new technique to estimate the oscillation frequency variation under the room temperature by using a vector network analyzer (VNA). Experimental results show a good correlation between OEO oscillation frequency drift and the phase measured by the VNA. This technique can be implemented to apply corrections when using the OEO as a distance variation or a refractive index measurement tool. We also tracked the temperature of the fiber loop at the same time with the VNAbased experiment to compare two correlations of temperature and phase with OEO oscillation frequency.

Improving the operation of optoelectronic oscillator by stabilizing the electrooptic modulator

In an optoelectronic oscillator (OEO) system, it is crucial to keep the frequency as constant as possible. Electrooptic modulator (EOM) is a key component in this system having a big influence on OEO stabilization. The EOM is characterized by its voltage to optical output transfer function which unfortunately undergoes a drift during time leading to changes of the EOM characteristics and finally to a drift of the oscillation frequency. A twofold instrumentation system has been developed for controlling the EOM. Its first part is dedicated to the EOM temperature control. By using this part, the OEO frequency drift can be reduced by a factor 1.39 for one hour duration. The second part of the instrumentation system is used for compensating the drift of the EOM transfer function. With these two parts operating simultaneously, the frequency drift reduction can reach a factor up to 3.44 for one hour. These results demonstrate the efficiency of the compensation method.

Genetic algorithm for optimization of L-shaped PIFA antennas

Two new designs of the L-shaped Planar Inverted-F Antenna (PIFA) antennas with single and dual polarization operating at the frequency band for IEEE 802.11b/g standard with satisfactory radiation characteristics are presented. We further propose a genetic algorithm (GA) embedded in CST Microwave Studio for optimizing these antenna parameters. The agreement of simulation and measurement results shows the performance of our joint model. Also, they show that our dual-polarization antenna is suitable for indoor Multiple Input Multiple Output (MIMO) wireless environment applications.

New receiver architecture for localisation system

We propose in this paper a simple receiver structure in which the radio frequency signal is directly digitized by the analog-to-digital converters (ADC) with a sampling frequency smaller than signal frequency. This structure is used for a direction finding system by means of an antenna array. The direction of arrival (DOA) of RF signal is estimated using the proposed receiver architecture and the high resolution method MUSIC (multiple signal classification). The measurement system composed of a 4 quasi-Yagi antenna element uniform linear array and of 4 parallel digital receivers using a digital oscilloscope is built for validating this idea. The simulation results using ADS (advanced design system) software and the measurement results in anechoic chamber show that the DOA is accurately determined by this structure