René Meys

Measuring the impedance of balanced antennas by an S-parameter method

The input impedance of a balanced antenna is conventionally measured by using a balun that forces opposite currents in each part of the radiator. In this paper, balanced antennas are viewed as two-ports, the S-parameters of which are determined by standard network-analyzer techniques. Simple formulas then lead to the differential input impedance. The method is illustrated by measurements on a dipole antenna, which are compared to the results for monopoles over a ground plane.

A summary of the transmitting and receiving properties of antennas

An expression for the electric field radiated by an arbitrary current distribution is given, which leads to a straightforward characterization of an antenna by a complex vector called the equivalent length. All classical transmitting parameters-such as the radiated power density, power intensity, radiation resistance, directional gain, and gain-are simple functions of the equivalent length. The same is true for the receiving parameters: induced voltage, available power, equivalent surface, and antenna factor. Eliminating the equivalent length between the gain and an equivalent surface provides a simple, direct, and general proof of the fundamental relation for antennas.

Electromagnetic fields estimation using spatial statistics

The spatial statistics formalism is applied to electromagnetic fields analysis. Fields are considered as realizations of a random function. Their spatial structure is studied by a method known as variographic analysis. To infer unknown values of the fields, an interpolation method called kriging is then used. It is shown how kriging can be performed on experimental or numerical data to speed up the fields estimation process.

Statistical Response of Antennas under Uncorrelated Plane Wave Spectrum Illumination

A general formalism is proposed to study the statistical behavior of antennas under uncorrelated plane wave spectrum illumination. It is shown that field statistics are not adequate to understanding antenna responses in such cases and that radiation pattern and polarization must be taken into account. New closed form expressions for correlation functions are derived for the induced voltage and the available power at antenna feeds.

Broadband Noise System Allows Measurements According to Both Standard Methods

A system that completely characterizes the noise temperature of a linear two-port over the 100-MHz-2.9-GHz band is presented. The system is based on a “long” transmission line and frequency variation. It allows measurements through the classical y -factor method or the more recent “cold” method. When applying the y-factor method, the system uses a broadband mismatched noise source and an autocalibration feature. To check the accuracy, a passive device is measured with its noise parameters computed from the S-parameters. The results produced by both methods are compared together and with respect to the values derived from the S-parameters.

Calibrating Broadband Highly Mismatched Noise Sources

Two methods are presented for calibrating broadband highly mismatched noise sources. The first is a reformulation and an extension of the procedure used for very accurately calibrating matched noise sources. It uses isolators and works whatever the source reflection factor. With the second method, the excess noise ratio of the noise source is numerically optimized until the measured reverse noise wave of an attenuator is equal to the theoretical value derived from its S-parameters. It can be applied to sources with reflection factors of about 0.45 to 0.90. Both methods appear to give very consistent results.

Six Easy Steps That Explain the Radiation of the Rectangular Patch Antenna [Education Corner]

This article revisits a classic in antenna theory: the rectangular patch antenna (RPA). The radiated electric field is computed from its physical sources, i.e., the conduction and polarization currents, whose contributions are clearly identified. The symmetrical equivalent of the antenna is first analyzed, and a coordinate system is chosen with the z-axis parallel to the conduction currents. The radiation of these currents appears as close to that of two parallel dipoles carrying opposite currents, which means a very simple and easy-to-understand system. It is further shown that the effect of the polarization currents is typically much smaller. The analysis is fully self-sufficient (no reference specific to the subject is needed). The radiation is summarized by a figure with six parts that graphically explains the topic step by step.

A microprocessor-controlled automatic noise-temperature meter

An automatic noise-temperature or noise-figure meter is presented that combines, to a large extent, both the flexibility and speed of analog automatic meters and the accuracy of manual measurements. This aim is achieved through digital processing of the detected noise by a microprocessor, including offset removal, linearity correction, filtering, and calculation of the results.

The accurate comparison (or calibration) of solid-state noise sources made simple

The accurate comparison (or calibration) of conventional solid-state noise sources is often thought to be a difficult process that only specialized laboratories can perform. In this paper, the uncertainties due to the impedance differences between the sources and their on and off states are emphasized and a simple formula is developed that makes them negligible. It requires an isolator being used in front of the receiver. In the experimental section, the errors associated with common practice are evidenced and compared to what can be achieved through the correction formula.