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An “electromagnetic vector sensor” (EMVS) comprises three orthogonal dipoles and three orthogonal loops, all in spatial collocation. The former triplet aims to directly measure the $3 \times 1$ electric-field vector ${\mathbf{e}} $ , whereas the latter triplet aims to directly measure the $3 \times 1$ magnetic-field vector ${\mathbf{h}} $. Their vector cross product $ {\mathbf{e}} \times {\mathbf{h}} $ would yield the incident source’s Poynting vector, which specifies the incident wavefield’s propagation direction. In reality, all these are only an idealization. Instead, a real-world dipole triad’s measurement could equal the incident ${\mathbf{e}} $ , only if the dipoles were electrically short (i.e., with an electrical length of $({L}/{\lambda }) < 0.1$). Likewise, a practical loop triad’s measurement could equal the incident ${\mathbf{h}} $ , only if the loops were electrically small (i.e., with an electrical circumference of $2 \pi ({R}/{\lambda }) < 0.1$). However, such short dipoles and small loops would be electromagnetically inefficient receivers. For a practical dipole that is electrically long, its measurement equals not the incident wavefield’s ${\mathbf{e}} $ but a vector dot product between: 1) the incident wave’s ${\mathbf{e}}$ and 2) that dipole antenna’s “effective length” vector (which depends on that dipole’s $({L}/{\lambda })$ and orientation). An analogous complexity exists for a practical loop that is electrically large. For such practical dipoles and loops, the aforementioned vector-cross-product would fail to yield the Poynting vector, hence it would inaccurately estimate the direction-of-arrival. Instead, this article will advance a new closed-form algorithm to simultaneously estimate an incident source’s direction-of-arrival and polarization, despite the practical dipoles’/ loops’ mathematically complicated gain/phase responses as described earlier, but without any prior knowledge of the dipoles’ electric length $({L}/{\lambda })$ nor the loops’ electric radius $({R}/{\lambda })$. [ABSTRACT FROM AUTHOR]

This paper presents a new estimation technique with $K$ -order expressions for evaluating the maximum electric fields radiated from multiple-antenna transmitters such as those in mobile phones, WiFi access points, and cellphone base stations. The need for $K$ -order estimation to provide precisely estimated electric fields, then develop useful expressions for the estimation and validate the estimation model numerically and experimentally is explained. Fundamental concepts of estimation and detailed electric field formulas, applied to various measurement systems using vector or scalar E-field probes, are presented. Several validations are also illustrated. As a result, it is verified that $K$ -order estimations significantly reduce the differences between the estimated and simulated/measured E-fields [or specific absorption rates (SARs)]. Investigations on the maximum electric fields of two antennas operating at 2.5 GHz in an ordinary room show that the maximum difference between the electric fields obtained by conventional estimations and calculations can be 8.5%, which is suppressed to below 0.24% and 0.02% by 2- and 3-order estimations, respectively. Similarly, in evaluations of the SAR of a three-antenna configuration, the maximum difference between the estimated and calculated SARs of about 5% obtained by conventional estimations is reduced to 0.1% or 0.01% by 2- and 3-order estimations, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel method that utilizes amplitude-only data of the electric field over a completely closed surface for the reconstruction of the spherical electric field, which represents a radiation source or an antenna under test (AUT) in the near-field (NF) region. The electric field exploiting genetic algorithm (GA) for global optimization is originally derived from a random initial estimate of field distribution and will gradually approximate to the exact value during iterations. When GA reaches the convergence criterion, we can calculate the far field (FF) by spherical NF-to-FF (NF-FF) transformation. The simulated and numerical results are in good agreement with each other, which shows that this method is effective over one or two closed surfaces. Furthermore, the related discussions corresponding to GA are given, confirming that the improved GA is feasible and efficient. [ABSTRACT FROM AUTHOR]

A new spherical field transformation approach for near-field measurements above perfectly electrically conducting (PEC) ground planes at arbitrary heights is presented. It provides higher order probe correction and treatment of irregular sample point locations on the measurement surface but has the same low computational complexity as the known fast Fourier transform (FFT) accelerated spherical field transformation with first-order probe correction. The infinite PEC boundary is considered by applying the image principle to the spherical modes of the device under test (DUT). Only the measurements above the ground are required to iteratively solve the inverse problem for the unknown spherical mode coefficients. Due to additional modal translation operators, the scan center of the spherical measurement system does not need to lie in the ground plane. Moreover, if the DUT is positioned at an appropriate height above the ground plane, the free-space sources of the DUT are extractable with good accuracy. By employing the nonequispaced FFT, the near field can be irregularly sampled on the spherical measurement surface. Numerical investigations show the capabilities of the proposed field transformation approach. Its practical relevance and efficiency are demonstrated for simulated automotive antenna measurements and real near-field measurements above a metallic ground. [ABSTRACT FROM PUBLISHER]

We present a nonresonant circular polarization selective structure (CPSS) based on multiple layers of stacked meander line sheets arranged closely after each other. The structure has a total thickness of 13.5 mm (0.68 wavelengths at center frequency 15 GHz) and is realized by cascading printed circuit boards interspaced with a low-permittivity foam material, and the different layers are bonded together with thin layers of adhesive spray. A design procedure is presented that can be used to optimize the proposed structure based on its target band of operation. Based on this method, an optimized design has been simulated, and the structure shows a return loss and an insertion loss better than 0.5 dB, and axial ratio in transmission and reflection better than 0.78 dB, over a fractional bandwidth of 45.8% at normal incidence, fully covering the Ku-band 12–18 GHz. The functionality of the structure has been verified experimentally through measurements, both in reflection and transmission, with a total bandwidth of 42.0%, covering 86.7% of the Ku band. The simulated performance at oblique angles of incidence shows significant improvements when compared to classical resonant CPSSs. [ABSTRACT FROM PUBLISHER]

In this paper, we present a fast technique for estimating the specific absorption rate (SAR) of multiple-antenna transmitting devices such as mobile phones, which utilize two or more antennas in communication. SAR values for arbitrary relative phase combinations of the antennas at an observation point can be estimated from SAR measurements for several known relative phases at the same observation point. Several numerical and experimental validations on different antenna configurations and operating frequencies have been carried out to verify the proposed estimation method. It has been highlighted that the proposed estimation method is simple yet provides highly accurate estimated SAR values. [ABSTRACT FROM PUBLISHER]

A matrix method is developed to calculate the antennas radiation pattern from near-field data measured over arbitrary surfaces. The principle of the matrix method is to determine the modal expansion coefficients by solving a system of linear equations. The number of required measured samples is deduced from the number of modes considering the cylindrical or the spherical wave expansion of antenna radiated fields. Once the modal coefficients are known, the far field of the antenna under test (AUT) is obtained. The matrix method has been implemented, and its potentialities are evaluated using two specific arbitrary surfaces (square section cylinder surrounding the AUT and a closed cylinder). Numerical (dipoles array) and experimental (base station antenna) results are provided to illustrate the efficiency and the stability of the proposed method. [ABSTRACT FROM PUBLISHER]

Measurement results to validate the UTD triple diffraction coefficient are presented. The experimental setup consists of multiple metallic objects, with triangular and rectangular profiles, located inside an anechoic chamber and illuminated by a sector antenna to reproduce a spherical wavefront with a transverse electromagnetic (TEM) incident field. Another sector antenna is moved vertically to collect electromagnetic fields across the second order UTD Incident Shadow Boundaries and in the triple diffraction transition region. The measured and theoretical fields are compared using a free space normalization. Such comparison is also validated by calculating the mean error, the standard deviation, and root mean square error that occur between the theoretical model and the measured field. The results show excellent agreement between the theoretical third order UTD solution, employing the novel triple diffraction coefficient, and the experimental results. [ABSTRACT FROM PUBLISHER]

Radio communication over Earth along mixed-paths in the HF band is a relevant subject today. In this communication, we present measurements of electric field propagating over sea water in HF Band compared to K.A. Norton, R.W.P. King and G. Millington's theories, thanks to a reliable measurement setup. The transmitting antennas are located on the coast while the receiver antenna is installed on a boat steering a constant course. The electric field measurements are carried out with a loop antenna and we measured the field strength attenuation versus distance between the transmitter and the boat along a sea water path. In order to take into account the media change (the coast and the sea water), Millington's solution has been added to King's and Norton's theories with the planar Earth model. The measurements performed at three frequencies (10 MHz, 20 MHz and 30 MHz) and the calculations are in a good agreement. At 10 MHz, the “smoothly” attenuation is shown and is very well correlated with the theory. The EM field decrease as 1/d^2 has been clearly observed at 20 MHz and 30 MHz. [ABSTRACT FROM PUBLISHER]

We present the experimental generation of Bessel beams using a leaky radial waveguide. The radial waveguide consists of a capacitive sheet over a ground plane. The capacitive sheet is composed of patch elements printed on both sides of a dielectric substrate. The radial waveguide is coaxially fed and supports an azimuthally invariant leaky-wave mode whose normal electric-field component is a truncated, zeroth-order Bessel function. Two prototypes are presented with the same propagation constant and lateral extent, but different attenuation constants. 2D electric field measurements and their respective Fourier transforms validate the operation of the prototypes as Bessel-beam launchers at two frequency bands. Cleaner patterns are achieved by the prototype with lower attenuation constant. The dual-band capability and associated frequency dependent resolution can be useful in near-field planar focusing systems. The proposed structure can be used for generating arbitrary zeroth-order propagating Bessel beams at microwave and millimeter-wave frequencies. [ABSTRACT FROM PUBLISHER]

Some focusing properties of Fresnel zone plate (FZP) lens antennas in the near-field region are presented at the ka-band. Simulated and measured results of the FZP antenna show displacement of the maximum intensity of the electric field along the axial direction from the focal point toward the antenna aperture. This displacement increases as the antenna's focal length increases. In addition, the focused beam scanning of the FZP lens antennas in the radiation near-field is examined. [ABSTRACT FROM AUTHOR]