Search

Abstract This study investigates the possibility of increasing the radiation efficiency of printed antennas and arrays by suppressing their inherent surface waves using a metasurface made of quad-split rings (QSR). A symmetrical resonant microstrip dipole and a four-element series-fed dipole array printed on an infinite grounded dielectric layer (layer thickness: 0.2 mm; relative permittivity: 9.4; tanδ: 0.0005) were simulated with FEKO 2022 software. Conducted at 100–116 GHz, the numerical results revealed extremely low radiation efficiencies of approximately 31% and 40% for the studied dipole and dipole array, respectively, which resulted from the presence of surface waves in the dielectric. However, placing only one QSR near each dipole arm triggered an increase in radiation efficiency by 2.5 times (up to 75%). The use of a metasurface in the form of two small QSR arrays triggered a pronounced improvement in radiation efficiency, reaching 93.6% and 95.8% for the studied dipole and dipole array, respectively. Analysis of the electric field distribution images showed that this enhancement resulted from surface wave suppression.

This paper presents a novel approach for designing a mobile antenna with a Low Specific Absorption Rate (SAR). First, the relationship between the electric field and the SAR value is constructed based on the Poynting Theorem studied in the near-field interaction area. Then, the relationship between the surface current and the magnetic field was examined, establishing a connection between the SAR and the surface current on the ground of the antenna. Next, the interaction mechanism of the radiation fields of the antennas with nearby human tissues was studied using electromagnetic boundary conditions derived from Maxwell’s equations. The approach of reducing the antenna radiated electric field was proposed by directly amending the antenna surface current, thereby reducing the SAR levels in human tissues. Finally, three low-SAR antennas are designed according to the proposed approach. This approach was tested using three different antennas. A 3.6 GHz Planar Inverted-F Antenna (PIFA), 1.8 GHz Meandered Planar Inverted-F Antenna (M-PIFA) and 2.4 GHz M-PIFA. The simulation and measurement results of these low-SAR antennas show good impedance matching in the operating frequency range. The peak values of the 10 g average SAR of these three antennas are reduced by more than 30% without compromising the efficiency, maintaining convenient impedance matching at the operating frequency, and without enlarging the antenna dimensions. The measurement was accomplished using thermal analysis and compared with simulation analysis, which proved the validity of this approach as a guide for low-SAR mobile phone antenna design.

In this paper, a general approach to enhance the beamwidth of microstrip antennas is proposed for wide beam coverage in both E- and H-planes. A microstrip antenna loaded with two arrays of capacitive via fences is propounded and systematically studied. By introducing the vertical currents brought by the capacitive metalized vias, the half-power beamwidth (HPBW) is effectively broadened compared with the regular microstrip antennas. In addition, by utilizing the air medium with low loss, the microstrip antenna can be supported by the two arrays of via fences, maintaining a high radiation efficiency. To validate the proposed design, a prototype is fabricated and tested. The measurement results agree well with the simulated ones, with enhanced HPBWs of 100° and 90° in E- and H-planes, respectively. Compared with the existing 2.4-GHz antennas, the propounded antenna is with the advantages of wide beamwidth and high radiation efficiency, exhibiting the potential applications for space-limited mobile devices with wide coverage requirement.

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]

The human body's absorption of electromagnetic fields from communication enabled devices has consistently been a research topic for both researchers from universities and companies in the mobile communication industry. The absorption of electromagnetic fields could mainly result in two consequences: (a) antenna radiation efficiency of the device could deteriorate dramatically; and (b) a large amount of the radiated power could be dissipated into the human body, such as the hand, ear, scalp and brain, which is defined and described by Specific Absorption Rate (SAR). A comprehensive analysis of electromagnetic field absorption by the human body has been carried out to explain and answer some of the key questions in this area.

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]

A novel method for radiation efficiency measurement of small-size radiators such as mobile phones and other handheld wireless devices is presented. The method is based on the accurate determination of the power which is dissipated in the antenna under test using a calorimetric approach. The principle of the method, some of its variants, and the experimental setup are described. Application of the method is demonstrated for several test objects with different efficiencies. Accuracy is validated by comparison of calorimetric radiation efficiency against numerical estimates and independent measurements using the reflection efficiency method, a generalized variant of the Wheeler cap method, whose basic limitations are briefly discussed. Due to the calorimetric principle employed in the proposed new method, it qualifies equally well as a highly accurate reference method for radiation efficiency measurements and as a low-cost alternative to three-dimensional pattern integration and Wheeler cap type efficiency estimates. [ABSTRACT FROM AUTHOR]

Slot apertures in metallic ground planes are very attractive candidates for conformal antenna applications. However, a low-profile unidirectional antenna requires a backreflector close to the slot aperture and the resulting stripline feed causes strong excitation of parallel-plate modes. In this paper, we investigate unidirectional reflector-backed slot configurations with parallel-plate mode suppression by shorting pins. Starting from a parametric study with respect to shorting pin location and backreflector distance, we present a stripline-fed rectangular slot element with radiation efficiency of more than 80%, a bandwidth of about 5% at a center frequency of 10 GHz. For increased bandwidth applications, a bow-tie slot element with about 8% bandwidth and radiation efficiency of close to 80% is proposed. [ABSTRACT FROM AUTHOR]

A reflector placed near a cellular telephone antenna is proposed to increase its radiation efficiency. In this study, a half wavelength dipole antenna at 900 MHz is treated as a cellular telephone model and a small plate reflector is placed between the antenna and a human head-sized phantom model. By using the finite-difference time-domain (FDTD) method, various kinds of materials, such as a dielectric material, a magnetic material, and a conductive material, are investigated for the reflector composition. Among them, a magnetic reflector having high μr′ and low μr″ (complex relative permeability: μr′-jμr″) is shown to be effective for increasing the radiation efficiency. © 2000 John Wiley & Sons, Inc. Int J RF and Microwave CAE 10: 253–263, 2000. [ABSTRACT FROM AUTHOR]

A resonant feeding loop is used to obtain the desired wideband impedance characteristic. Two implementations are presented and their efficiency characteristics are compared: a low‐admittance resonant feeding loop and a high‐admittance resonant feeding loop. Experimentally it is demonstrated that the low‐admittance feeding loop provides better radiation efficiency than the high‐admittance feeding resonant loop. [ABSTRACT FROM AUTHOR]

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]