Marc Piette

Antenna radiation efficiency measurements in a reverberation chamber

In severe multipath environments, the relevant antenna parameter for mobile radiofrequency system performance is not its radiation pattern, but rather its radiation efficiency. Unfortunately, this feature is seldom known from the antenna manufacturer and is also difficult to calculate accurately for practical antennas. The determination of the radiation efficiency of an antenna from measurements carried out in the stochastic fields of a mode stirred reverberation chamber is described and discussed. Using a thin monopole antenna on a circular ground plane as a reference antenna, the efficiency of a horn antenna is measured at 1800 MHz. The influence on the measured radiation efficiency of any direct coupling between the antenna under test (AUT) and the source antenna is discussed.

Laboratory UWB GPR system for land mine detection

In this paper, the design and the modeling of an indoor impulse UWB GPR systems (1 GHz - 5 GHz), built in the scope of the HUDEM project, is presented. For an impulse UWB system, a time-domain modeling is an obvious choice. We explain how the antennas can be characterized by their normalized impulse response. By considering the antenna as a convolution operator, we get a mechanism for modeling the whole radar system as a cascade of linear responses, which gives a lot of advantages and possible application. In our research it is used to express the radar range equation in the time-domain, to optimize the antenna configuration and to tune signal- processing algorithms. The deconvolution of the signal source and antenna impulse responses is an ill posed operation. In this paper we present a method for decomposing an A-scan in a linear combination of wavelets, using the Continuous Wavelet Transformations -- by properly choosing the mother wavelet. This technique can also be used to reduce the amount of data for further processing. Finally results obtained by our UWB GPR system are shown. Advantages and shortcomings are discussed.

Demonstration of a Low-Cost Ultrawideband Transmitter in the 3.1–10.6-GHz Band

An architecture for the generation of short pulses based on a filter step response technique is described. One uses the transient response of a passive circuit to an input square signal. This approach is experimentally demonstrated by the generation of subnanosecond pulses compatible with the indoor frequency mask authorized by the Federal Communications Commission for ultrawideband applications. It is shown that a pulse repetition frequency of 1 GHz can be achieved. The effect of the transition time of the source is analyzed and is shown not to be a limitation.

IEC 61000-4-21 testing : Selective source-mode tuning with two orthogonal antennas scanning system

An important issue for laboratories that perform tests according both parties accepted standards is the testing time. Comparison between the IEC 61000-4-21 and the IEC 61000-4-3 shows that the testing time of the first is relatively high. So, a new method is presented here that uses a selective source-mode tuning in a reverberation chamber in order to reduce the difference of testing time. The work has been made in the perspective of making immunity testing according the IEC 61000-4-21 standard at HIRF (High Intensity Radiated Fields) in the frequency band of mobile phone and GPS systems (800-2500 MHz). The three components of the E-field, the forward and reverse output powers and the displacement of the two LPDA (Log Periodic Dipole Array) antennas have been measured for each of the 24 tuner positions, at eight locations of the working volume and at twenty two frequencies within the frequency range of interest. The measurements are organized in function of the requirements of the standard, i.e., the field uniformity. The results show that with this low number of samples, the compromise to have low testing time with compliance with the standard is achieved.

A low-cost UWB pulse generator for medical imaging, through-wall imaging and surveillance systems

This paper describes a low-cost architecture for the generation of subnanosecond pulses based on the transient response of passive filters. Two prototypes are developed to demonstrate experimentally this approach. The first one covers the band 1.61 GHz to 10.6 GHz for medical imaging systems and the second one the band 1.99 GHz to 10.6 GHz for through-wall imaging and surveillance systems. In both cases, we obtain pulses with spectral densities well adapted to the FCC rules.

Complete space - time validation of a single mode stirrer reverberation chamber for immunity testing

Summary form only given. This paper gives an overview of the validation measurements in a small cubic reverberation chamber (15 m3) equiped with a single mode stirrer and two TEM horns set in cross-polarization in order to enhance the unpolarized character of the stochastic fields. Frequencies of interest are between 900 MHz and 2.5 GHz. The set of results points out that what could be firstly seen as a drawback - the cubic shape - can be effectively overcome by the design quality of the stirrer. Space homogeneity, quality factor, chamber gain, stirring ratio and CDF at 900 MHz and 1800 MHz (GSM, DECT and DCS mobile radio systems) are presented and critically commented

Anisotropy & polarization analysis in a cubic mode-stirred chamber

Summary form only given. Anisotropy and polarization are two important aspects of stochastic field generation in reverberation chambers. Yet they are seldom directly measured but rather indirectly demonstrated from field homogeneity and CDF validation. In this paper, anisotropy and random polarization are experimentally addressed in a small cubic mode stirred chamber by means of field anisotropy and cross-correlation coefficients. Those are directly calculated from field component measurements carried out in the frequency band of 900 MHz - 2.5 GHz by means of a broadband triaxial E-field probe. The effect of cavity wall proximity on polarization is also demonstrated

UWB pulse generator switched by the PSK modulation based on a band pass filter with two zeros transmissions

This paper describes a simple and original method to generate short UWB pulses, obtained by the transient response of a notch filter. Whose the first principle is based on a technique On-Off Keying signal with a carrier frequency centered at the rejection frequency (requires a very fast switch and a sinusoidal carrier). Now, we propose an all-digital solution, using a Phase-Shift Keying modulation to produce short pulses. We compare the both methods and show that pulses with a spectrum satisfying the FCC indoor regulatory mask in USA. The second method (without fast switch) which can be applied to the generation of pulses matched to any type of available spectrum mask (European, Asia, imaging, medical, outdoor, radar, ...). In both cases, circuits are realized at FCC to demonstrate these principles. It is shown that the measurements are in good agreement with the theory.

Ultra-wideband duplexers for low and high peak power applications

Two different duplexers have been conceived, designed and tested that allow for using an impulse ultra-wideband (UWB) radar in a monostatic configuration. The first one, which is based on a fast GaAs SPDT switch, is usable with a low peak power transmitter (<100 mW), while the second one, completely passive, is intended for high peak power applications (up to 50 kW). Both exhibit an instantaneous bandwidth covering the frequency range (400 MHz-4 GHz) which is the most suitable frequency band for detecting buried antipersonnel landmines by means of UWB radar. These duplexers contribute to a gain of space, weight and cost, three important factors in the design of portable detection systems for humanitarian operations.

A UWB generator based on a ECL Monostable one-shot for ETSI communications and Military radar applications

This paper describes circuits for pulse generation based on an ECL Monostable one-shot. The first one produces pulses between 0.8 and 1.5 ns for the European communications in the band [6 to 8.5] GHz. The second one produces pulses between 0.6 and 1.1ns for Military radar applications in the band [22 to 29] GHz. The measurements comply with ETSI/FCC regulations.