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This article presents a contactless measurement method for antenna radiation efficiency estimation within reverberation chambers (RCs). This method does not require to connect any analyzer to the antenna under test (AUT). The AUT radiation efficiency is obtained from the differential measurement of the RC composite ${Q}$ -factor estimated for two AUT load conditions, namely an open circuit and a 50 $\Omega$ load. Remotely controlled RF switches are used in order to keep the setup identical for both measurements. The method is experimentally validated in two RCs of different volumes (1 m $\mathbf {^3}$ and 19 m $\mathbf {^3}$) with a wideband patch antenna in the 1.8 GHz to 2.8 GHz frequency range. The estimated efficiency is found to be in a very good agreement with the one obtained through a conventional invasive RC measurement technique. This new method is suitable for miniature and buried antenna characterization without access to its port. [ABSTRACT FROM AUTHOR]

This letter presents a possibility of increasing the radiation efficiency of double-sided leaky-wave antennas (LWAs) by using the substrate integrated slab waveguide (SISW). The idea originates from the fact that double-sided LWAs usually operate on the second mode, and the attenuation constant of the second mode in the SISW is smaller than that in the standard substrate integrated waveguide (SIW). This inherently leads to an increase of antenna radiation efficiency, as less power is dissipated by the traveling wave. In order to prove this concept, two antennas have been designed with the same characteristics (central frequency of 28 GHz, pointing angle of 50°, and beamwidth of 10°), one based on SIW and the other based on SISW. Our experimental verification yields 64% radiation efficiency for the SIW LWA and 80% radiation efficiency for the SISW LWA, thus proving the theoretical and simulated predictions. [ABSTRACT FROM AUTHOR]

We provide results of antenna radiation and total radiation efficiency at millimeter-wave frequencies gathered with a new open-ended waveguide-plate method that is compared to a well-known two-antenna method. The new method yields improved uncertainty in antenna efficiency measurements. Both methods are based on use of a reverberation chamber. Measurement results are compared to numerical simulations and good agreement (~3% maximum difference) is achieved. Before performing the efficiency measurements, the chamber configuration was assessed with respect to the Rician $K$ -factor, number of uncorrelated paddle orientations, and coherence bandwidth. We calculated the uncertainty using the NIST microwave uncertainty framework capable of performing parallel sensitivity and Monte Carlo analyses. The framework enables us to capture and propagate the uncertainties in the S-parameter measurements to the final efficiency result. The expanded uncertainty that we achieved for these antenna efficiency measurements is 2.60%. [ABSTRACT FROM PUBLISHER]

Average ACS can be measured in a reverberation chamber; however, the existing technique determines a value that includes the effects of the radiation efficiencies of the antennas used in the measurement. Correcting for these necessitates further complex measurements. Here, we present the theory of an alternative measurement methodology using two nested or contiguous reverberation chambers which is free from errors caused by the radiation efficiencies of the antennas. The new method is based on the theoretical average transmission cross sections (TCS) of circular holes in a metal plate between the two chambers. In fact, the method can be viewed as an accurate transfer calibration measurement between TCS and ACS that is independent of both the chamber and antenna characteristics. Further, since the existing method of measuring ACS includes the effects of the radiation efficiencies of the antennas, a comparison of the ACS of a reference object, measured using both the existing and new methods, also provides an alternative method of determining radiation antenna efficiency. Measurement uncertainties for both alternative measurement methods—ACS and antenna radiation efficiency—are also derived. [ABSTRACT FROM AUTHOR]

The time reversal (TR) technique is applied in a reverberation chamber (RC) to perform an analysis of antenna efficiency. RC are mainly used for electromagnetic compatibility measurements. They provide through a stirring process the total radiated power from any electromagnetic source placed inside these overmoded cavities with a reasonable statistical uncertainty. Performances of TR techniques also increase with the number of modes or path densities, inherently high in RCs. In this paper, we show how a RC may be used in combination with the TR technique to measure ultra wide band (UWB) antenna efficiency with simple operation all over the frequency band. Principles of this new method called time reversal efficiency measurement (TREM) are provided together with experimental validations. Results are discussed and compared with simulations or other measurement methods. [ABSTRACT FROM PUBLISHER]

Reverberation chambers are becoming a popular alternative testing facility for a wide range of electromagnetic applications. Because of the statistical environment created inside a reverberation chamber, they offer a unique test facility. In particular, these chambers are ideally suited for performing radiated power measurements of either an antenna or device under test, and as such, it is possible to determine the efficiency of antennas. There have been several reverberation chamber techniques proposed over the years for measuring the antenna efficiency; however, these techniques require either the use of a reference antenna (i.e., an antenna with a known efficiency) and/or require the assumption that the two antennas used in the test have identical efficiencies. In this paper, we present three different approaches for determining both the radiation and total efficiencies of an unknown antenna that overcome these limitations and assumptions. We present a one-antenna approach, a two-antenna approach, and a three-antenna approach. We present measured data for three different antennas in order to compare these three approaches. We also discuss the uncertainties related to these types of measurements. [ABSTRACT FROM AUTHOR]

This paper proposes an effective and efficient technique for the evaluation and optimization of the specific absorption rate for multiantenna wireless systems. This technique is based on a decomposition/superposition procedure with two different measurement scenarios. Using this proposed approach, we can estimate the lower and upper bounds of specific absorption rate within anatomically correct human head models as well as minimize the specific absorption rate within selected tissues in the head models. Furthermore, this technique can be combined with a beamforming technique to maximize the overall system reception and minimize peak spatial specific absorption rate. Numerical examples are used to demonstrate the effectiveness of this proposed approach. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the performance of an electrically small genetic antenna, immersed in several different powders having relative dielectric constants as large as 12. Placing the antenna in a dielectric reduces its electrical size from about 1/20th of a wavelength in free space to less than 1/50th of a wavelength, in a powder having a dielectric constant of 12, even for a dielectric volume just slightly larger than the antenna. Although the bandwidth decreases as the electrical size of the antenna becomes smaller, it is shown that for each dielectric powder, there is a set of frequencies for which the antenna is operational. It is thus possible to efficiently operate the antenna at specific frequencies within a wide band. [ABSTRACT FROM PUBLISHER]