Mohammed Salhi

Design and Calibration of a Compact Quasi-Optical System for Material Characterization in Millimeter/Submillimeter Wave Domain

A compact quasi-optical setup based on conventional rectangular horn antennas and two symmetrical parabolic mirrors is designed to provide a plane wave on the material under test. To measure the scattering parameters at millimeter/submillimeter wavelengths, a commercial vector network analyzer and waveguide frequency extension units are used. The calibration of the system is performed with a simple practical deembedding process to determine the S-parameters on the material surface without using high-cost micrometer positioners. A reliable extraction method is presented to derive the material permittivity and calculate the errors and uncertainties as direct functions of the sample and setup geometry and their physical characteristics. Several materials are measured and the complex permittivity is presented together with a detailed uncertainty budget.

Traceable measurements of field strength and SAR for the Physical Agents Directive - an update

Due to the pervasive use of broadcasting devices for mobile applications, ambient levels of radio frequency (RF) power, particularly in cities and work places, tend to increase in the EU. The project described here will enable directive EC 2004/40/EC “Physical Agents Directive” to be implemented across Europe by ensuring that the necessary artefact standards and measurement techniques exist to allow compliance with this directive to be tested. It will make the basic restriction for human exposure as specified by International Commission on Non-Ionising Radiation Protection (ICNIRP) accessible comprehensively, which at present is not the case. It also addresses two priority areas of research identified by the World Health Organisation (WHO): child exposure during magnetic resonance imaging (MRI) and techniques for micro-dosimetry of non-ionizing electromagnetic fields (EMF).

Design and calibration of a compact quasi-optical system for material characterization in millimeter/sub-millimeter wave domain

A compact spectrometer setup based on conventional rectangular horn antennas and two symmetrical parabolic mirrors is designed to provide a plane wave on the material-under-test. A commercial Vector Network Analyzer (VNA) and waveguide frequency extension units are used to measure the scattering parameters. A simple practical calibration process is used to determine the S-parameters on the material surface without need of high-cost micrometer positioners. Several materials are measured and the complex permittivity is presented.

A Simple New Method to Calibrate Millimeter-Wave Mixers

This paper presents a novel method to test the conversion loss of fully reciprocal millimeter-wave mixers without measuring the absolute signal power at the radio-frequency port. The authors utilize the reciprocal feature of the mixer and obtain conversion loss based on relative power measured by a network analyzer.

Characterization of 4×4 planar antenna arrays for the frequencies 77 GHz and 94 GHz using an antenna scanning system

Due to the excessive need for bandwidth, a tendency has been noticed towards using higher frequencies up to the millimeter and sub-millimeter wave range. Antennas are essential components in any communication system. Therefore, we present the design and characterization of two 4×4-phased-array patch antennas which work at 77 and 94 GHz. We also present a transition block from the rectangular waveguide source to the planar structure to forward the radiation to the antenna patches. The radiation pattern of the antennas was measured with a new high-precision antenna scanning system. The antennas are designed for applications in communications and for the development of antenna measuring techniques.

Novel method to measure the conversion-losses (C.L.) of microwave and mm-wave mixers

Classic methods to measure the mixer conversion-losses (C.L.) usually need an absolute RF and IF power-measurement at the mixers ports. However, absolute power-measurement cannot be achieved with a low uncertainty level for the higher frequencies and mm-waves because of non-available standards and source & load mismatch problems. A new method is proposed (for reciprocal mixers) based on relative-power measurement at IF-port when the RF-port is fed/measured by VNA. Therefore, the C.L. can be evaluated for the mm-wave mixers by using a suitable VNA and its relevant frequency-converters up to 325GHz. The setup is described and preliminary results are presented for a microwave-mixer and a mm-wave one.

Time-domain evaluation of anechoic environments up to 325 GHz

In this paper we describe measurements performed a) to obtain the broadband attenuation of absorbing material and b) for anechoic chamber performance evaluation up to 325 GHz. The measurements were taken in frequency-domain using the latest vector network analyzer (VNA) technology available. We take advantage of the large dynamic range of a 50 GHz four-port VNA and multiple broadband frequency converters. After a time-domain transform of the measured frequency response data the obtained signal response in time-domain is evaluated for several setups like a metal reflector, anechoic material samples, and several inhomogeneity in anechoic chambers such as edges, doors, light installations etc. Both S11 and S21 measurements are performed in anechoic chambers which give some insight into the imponderabilities of S-VSWR measurements. These have been proposed as a figure of merit of the total chamber performance, but in some laboratories users may have used equipment or setups which do not describe the absorber installation performance adequately. Some, but not all of the drawbacks are addressed by the latest CISPR standards up to 18 GHz. One example is the undersampling due to the given spacing of field strength samples which becomes already obvious below 18 GHz. This sampling procedure may not be useful at higher frequencies at all as the wavelength becomes smaller and smaller. This paper is a contribution to the understanding of how to evaluate anechoic chamber performance up to mm-wave frequencies.