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In this paper, an antenna gain measurement method for millimeter-wave antennas in an on-wafer probe station environment is studied. The one-antenna gain measurement has been known since the 1940s. However, the authors believe that this extension of their previous work is the first time when the method is systematically studied in the on-wafer probe station environment. The main difference between the original one-antenna gain measurement and our method is that in the probe station environment, the space is limited and, therefore, the reflecting plate dimensions are limited. We have studied the effect of the reflector size limitation through computations using physical optics and through measurements with a standard gain horn (SGH) and with a printed microstrip patch antenna. The necessary size of the reflecting plate naturally depends on the beamwidth of the antenna under test and on the distance. Time gating has been applied in the retrieving calculation to filter out multiple reflections. According to this paper, the one-antenna gain measurement in the $W$ -band results in the correct antenna gain with very high accuracy for the highly directional SGH. For the patch antenna, the gain measured in the on-wafer probe station environment agrees well with the simulated one. [ABSTRACT FROM AUTHOR]

This paper compares three modern and two classical multiobjective optimizers (MOOs) as applied to real-world problems in electromagnetics. The behavior of sophisticated optimizers on simple test functions has been studied exhaustively. In contrast, the algorithms here are tested on practical applications, where the function evaluations are computationally expensive, making the convergence rate a crucial factor. The examples considered include the optimization of a narrowband slot antenna, a mushroom-type electromagnetic bandgap structure, and an ultrawideband Vivaldi antenna. Another popular topic in the literature is in comparing classical MOOs on electromagnetics problems. The modern optimizers chosen in this paper are state of the art and each has a distinct design philosophy. This paper introduces two unique MOOs to the electromagnetics community: BORG, an auto-adaptive genetic algorithm and the Multi-Objective Covariance Matrix Adaptation Evolutionary Strategy (MO-CMA-ES), an extension of the popular single-objective CMA-ES. These algorithms are compared to the Multi-objective Evolutionary Algorithm based on Decomposition (MOEA/D), a Chebysheff scalarization algorithm, and two classical MOOs. This paper will study the behavior of these algorithms on problems in electromagnetics with a limited number of function evaluations using five distinct metrics and will provide useful guidelines and recommended optimizer settings. [ABSTRACT FROM AUTHOR]

Using two electrically long dipoles to estimate the polarizations of impinging sources, this paper pioneers signal-processing algorithms in closed forms. The existing literature on crossed-dipoles polarimetry are restricted to electrically short dipoles with an electrical length of $(L/\lambda) \le (1/10)$ , which have subpar efficiency in radiation and in reception. In contrast, this paper allows electrically long dipoles—two of them here are perpendicularly oriented but may be collocated or may be separated by a known displacement. Using such a pair of electrically long dipoles for polarization estimation, this paper proposes new closed-form formulas and derives the associated Cramér–Rao bounds. [ABSTRACT FROM AUTHOR]

This paper gives a review of the current state-of-the-art in ultrasound parallel acquisition systems for flow imaging using spherical and plane waves emissions. The imaging methods are explained along with the advantages of using these very fast and sensitive velocity estimators. These experimental systems are capable of acquiring thousands of images per second for fast moving flow as well as yielding the estimates of low velocity flow. These emerging techniques allow the vector flow systems to assess highly complex flow with transitory vortices and moving tissue, and they can also be used in functional ultrasound imaging for studying brain function in animals. This paper explains the underlying acquisition and estimation methods for fast 2-D and 3-D velocity imaging and gives a number of examples. Future challenges and the potentials of parallel acquisition systems for flow imaging are also discussed. [ABSTRACT FROM AUTHOR]

This paper offers a new approach for far-field high-resolution imaging of conducting obstacles based on arrays of frequency-multiplexed subwavelength resonant elements. Each resonator is a circular aperture in a metallic screen that is strongly miniaturized by means of loading by a thin epsilon-negative and near-zero metamaterial (MTM) liner. Each MTM-lined aperture exhibits a fano-shape transmission profile, i.e., a peak followed by a minimum, and the resonance frequencies of different apertures are chosen such that the resonance of one lies within/very close to the antiresonance of the other to ensure strong decoupling. This paper shows that blocking an aperture using a conducting disc removes the corresponding resonance peak/minimum from the transmission/far-field amplitude spectrum, enabling far-field detection of any distribution of such obstacles with a spatial resolution determined by the aperture sizes, which measure less than one-sixth of free-space wavelength at their respective resonance frequencies. The proposed imaging mechanism is verified through full-wave HFSS simulations as well as far-field measurements. Some challenges associated with this approach are then discussed. [ABSTRACT FROM AUTHOR]

In this paper, the performance of Fresnel lens antennas is investigated in detail. The performance is evaluated in terms of aperture efficiency and stable radiation pattern over a wide frequency band. This paper proposes an efficient technique for enhancing aperture efficiency by smoothly compensating for the spherical phase front arriving upon the lens surface. The feeder has been optimized to fit an axially symmetric cosn-like radiation pattern. For this, an accurate technological process has been used to manufacture a lens that allows for smooth compensation of the phase shift. The lens is compared with a classic Fresnel lens having the same physical dimensions and feeding system. The improvement is validated by measurement, which has revealed a maximum measured gain of 38.9 dBi corresponding to a maximum measured aperture efficiency of 59% with a −2 dB radiation frequency bandwidth of 29.25 GHz around 90 GHz. This amounts to an aperture efficiency enhancement of 60% and −2 dB radiation frequency bandwidth enhancement of 72% as compared with those of the classic Fresnel lens. [ABSTRACT FROM AUTHOR]

An X-band leaky waveguide antenna (LWA) with high aperture efficiency and high power capacity is investigated in this paper. The antenna is mainly composed of two parts: a sectorial waveguide power divider and an LWA array. First, in the design of the power divider, the magnitude uniformity and phase consistency are ensured by adjusting the channel central angles and introducing phase adjusting structures, respectively. Then, the analysis and design of the LWA array are carried out. New formulas and conditions have been proposed for realizing uniform radiation distribution and maximum aperture efficiency. Five supporting beams are introduced to increase the antenna gain and power capacity. An LWA array as a prototype is fabricated and tested to verify the analysis and simulation. Experimental results agree well with the simulation. The return loss is better than 17 dB at the center frequency 9.7 GHz, the gain is 38.75 dB, and the corresponding aperture efficiency is 80.7%. The power capacity of the LWA array reaches 1.5 GW. These characteristics demonstrate that the proposed LWA array is suitable for radiating high power microwaves. The analysis and design method proposed in this paper is a useful guide for designing the high-aperture efficiency antenna in the future. [ABSTRACT FROM AUTHOR]

In the massive multiple-input multiple-output systems, the antennas should have the ability of beamforming. Under this requirement, the sliding aperture technique is adopted. In this paper, the principle of the sliding aperture technique is first demonstrated. This technique refers to the customization of each beam by part of the aperture, resulting in low scan loss over a wide angular range. Then, with the help of II-shaped transmit element, a linear multibeam transmitarray antenna based on the sliding aperture technique is designed. To the best of the authors’ knowledge, the linear transmitarray is reported for the first time. The fabricated prototype shows that the proposed antenna can generate eight beams simultaneously covering the ±42° azimuth area with low scan loss and the beam intersection level better than −4 dB. The proposed antenna has been simulated, fabricated, and measured, and the experimental results are in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

This paper describes an intuitive approach for synthesizing metal-only, low-profile, high-gain stepped reflector antennas that can aid emerging technologies in the areas of communications and remote sensing. The required reflector aperture is synthesized using a family of confocal parabolic sections, each of which scatters in phase to provide a focused beam in the far field. The parabolic sections provide a distinct advantage over the conventional Fresnel zone plate (FZP) antenna, since the radiation is inherently unidirectional. Furthermore, the metal-only structure avoids the need for dielectric characterization, which is essential for reflectarrays. Using this technique, it is possible to achieve depths of the order of one wavelength while ensuring high efficiencies. Starting from a symmetric stepped reflector synthesis, two distinct approaches to synthesize offset stepped reflectors are explored in this paper. We highlight several interesting tradeoffs between electromagnetic performance and mechanical complexity that arise for each of these approaches. A thorough analysis of the frequency performance of stepped parabolic reflectors is also presented. Comprehensive simulations using both physical optics and multilevel fast multipole method validate our theoretical predictions. The formulations presented in this paper are especially relevant at mmWave frequencies and beyond, which has attracted significant interest for modern technologies. [ABSTRACT FROM AUTHOR]

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the 4 \times 2 elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the {H} -plane and −21.1 dB in the {E}$ -plane. [ABSTRACT FROM AUTHOR]

In certain radar and wireless communication applications, omnidirectional circularly polarized (CP) antennas are desired but existing solutions have complex 3-D structures and are large in size. In this paper, a compact and low profile CP antenna having omnidirectional pattern on azimuthal plane is demonstrated. The CP waveform is synthesized by combining two linearly polarized and omnidirectional antennas with 90° phase difference on their terminals. The most challenging part of the design is the realization of the horizontally polarized antenna with omnidirectional radiation pattern. This antenna is designed using a novel two-faced slot antenna structure capable of emitting in-phase radiation of equal magnitude on both sides of the antenna. The two faces of the low-profile slot antenna are connected by a thin meander parallel plate waveguide to provide antiparallel field distributions over the two faces of the slot radiators. This special design removes radiation nulls on E-plane that exists on conventional slot antennas, the mechanism of which has been carefully discussed in this paper. The other antenna is a compatible pair of planar inverted-F antennas constructed on the sides of the finite-ground plane two-faced slot antenna for the provision of vertically polarized omnidirectional radiation. A feed network with power splitter and phase shifter is also accommodated on the compact CP antenna. The antenna is designed and fabricated, and its performance is measured against numerical simulations. It is shown that the fabricated antenna at 2.4 GHz can provide measured axial ratio of lower than 1.8 and gain variations of less than ±1.5 dB over all azimuth angles. [ABSTRACT FROM PUBLISHER]

It will be shown that “Comments on ‘Stored energies and radiation Q”’ by Capek and Jelinek contains numerous errors, misconceptions, inaccuracies, false assumptions, misunderstandings, and unjustified claims. The analysis of the comment is built on a false assumption that the terminal current of an antenna fed by a waveguide is independent of frequency. This false assumption arises from the misunderstandings on the basic theory of transmission lines and misconceptions of normalization for a linear system. As a result, all the equations obtained from the assumption in the comment are incorrect, and the related discussions are not true. The delta gap source modeling has been abused in the comment, and this is reflected in the numerical results in the comment that give rise to negative stored energy. The main results of the commented paper have been misinterpreted, and the related analysis is established on illogical reasoning. The comment fails to pinpoint any errors in the commented paper. [ABSTRACT FROM PUBLISHER]

A wideband transmitarray antenna based on the magnetoelectric (ME) dipole element and 2-bit phase compensation scheme is presented for vehicular communications in this paper. A wideband 90° phase shifter is proposed and combined with the rotating method to achieve four discrete phase states. Thanks to the polarization-twisting technique and the simple structure of the phase shifter, the proposed element can be easily designed. For the transmitarray design, a multi-frequency phase compensation strategy is applied to guarantee stable performance over the operating band. To validate the design, a 12 × 12 transmitarray antenna simultaneously covering vehicle-to-satellite band (20 GHz), and 5G millimeter-wave (mmWave) bands (24 GHz/28 GHz) is designed, fabricated and measured. The experimental results show that the prototype can achieve high aperture efficiencies (>40%) within a wide bandwidth (34%). The measured peak aperture efficiency is up to 53% at 23 GHz. These results demonstrate that the proposed 2-bit transmitarray antenna enjoys the advantages of wide operating bandwidth, high aperture efficiency and comparatively low design complexity. With these characteristics, the proposed transmitarray antenna can be a promising candidate for vehicular communications that require reliable satellite links and 5G millimeter-wave connections simultaneously. [ABSTRACT FROM AUTHOR]

A full-wave theory of plane wave scattering from rough surfaces called the correction current (CC) method was recently developed. This paper extends the CC method to the more general case of beam wave scattering. Gaussian beams are assumed incident upon a deterministic metal rough surface. Scatter patterns based on the CC method are calculated and compared to scatter patterns determined by the method of moments solution of an electric field integral equation formulation of the scatter problem. It was shown that good agreement between these two solution methods is obtained for scatter surfaces for which the CC method is shown to satisfy conservation of power and an accuracy criterion. [ABSTRACT FROM PUBLISHER]

The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission has been providing L-band brightness temperature (BT) using its instrument, the Microwave Imaging Radiometer using Aperture Synthesis. In the measurements, the negative effect of radio frequency interference (RFI) is clearly present, deteriorating the quality of geophysical parameter retrieval. Detection and geolocation of RFI sources are essential to remove or at least mitigate the RFI impacts and ultimately improve the performance of parameter retrieval. This paper discusses a new approach to SMOS RFI source detection, based on the MUltiple SIgnal Classification (MUSIC) algorithm. Recently, the feasibility of MUSIC direction-of-arrival estimation has been shown for the RFI source detection of the synthetic aperture interferometric radiometer. This paper refines the MUSIC RFI source detection algorithm and tailors it to the SMOS scenario. To consolidate the RFI source detection procedure, several required steps are devised, including the rank estimation of the covariance matrix, local peak detection and thresholds, and multiple-snapshot processing. The developed method is tested using a number of SMOS visibility samples. In the test results, the MUSIC method shows an improvement on the accuracy and precision of the RFI source geolocation, compared with a simple detection method based on the local peaks of BT images. The MUSIC results especially outperform the SMOS BT image on the spatial resolution. [ABSTRACT FROM PUBLISHER]

This paper presents an accurate method for synthesis of true time delay (TTD) reflecting elements to design wideband reflectarray (RA) antennas. In doing so, primarily the conventional phase distribution formulation of RA is modified to accommodate the design of resonant reflecting elements based on TTD technique. An accurate circuit model is then presented to realize the linear reflection coefficient phase of the reflecting elements of the RA antenna using the continued fraction theory. Finally, the equivalent circuit models of reflecting elements are implemented via multilayer frequency selective-surface structures. The RA antenna is designed and fabricated to operate in the X-band frequency. Stable aperture phase efficiency of about 80% and stable radiation patterns throughout the operating frequency band, confirm the accuracy of the proposed method. [ABSTRACT FROM PUBLISHER]

In this paper, we prove experimentally that nondiffractive Bessel beams can be generated by using inward cylindrical traveling wave aperture distributions. An azimuthally invariant inward traveling wave distribution is defined over the aperture of a radial line slot array (RLSA) to launch a Bessel beam whose normal electric-field component assumes a truncated, zeroth-order Bessel function. An optimization procedure based on a holographic approach is used for tuning the position and size of the slots of the RLSA. The antenna is centrally fed by a coaxial probe transition. The final structure operates at 12.5 GHz. Full-wave simulations and measurements of the vertical component of the electric field show that a non-diffractive radiation is obtained within a range larger than 12 wavelengths in front of the antenna. The generated Bessel beam presents a stable half-power beamwidth of about 20 mm within this range. The proposed system may open new opportunities for planar, low-profile Bessel beam generators at millimeter waves, Terahertz, and optics. [ABSTRACT FROM PUBLISHER]

In this paper, a miniaturized circularly polarized (CP) continuous wave Doppler radar system operating at 2.4 GHz is presented. The radar front end consists of one left-handed CP (LHCP) antenna and one right-handed CP (RHCP) antenna, which share a single patch antenna aperture. Orthogonal polarization is achieved through a modified ring-shaped quadrature hybrid coupler (QHC), and the resulting isolation between the two CP antennas is better than 30 dB. With 0 dBm input power to the transmitting antenna, the proposed radar system can accurately detect heartbeat and respiration movements of human test subjects under 1 m and over a wide angular range. The single dual CP antenna achieves 280% size reduction compared to a traditional two linear polarization patch antenna array with the same isolation level. [ABSTRACT FROM AUTHOR]

This paper presents a beam steerable low-profile lens antenna with a flat top wide beam and a high gain operating at 10.10 GHz. It consists of a graded index metasurface (GIMS) lens placed on the top of a microstrip patch antenna (MPA) radiator. An ultrathin linear graded index metasurface (LGIMS) and a radial graded index metasurface (RGIMS) lens were designed for the magnitude and phase transformation of the radiated beam from the microwave radiator. First, an LGIMS lens antenna was designed by placing an LGIMS on the top of an MPA radiator at an optimum height. A maximum measured gain of 16.37 dBi indicating a maximum gain enhancement of 11.50 dB with beam steering in a conical plane with a vertex angle of 84° was observed. Next, a flat top beam (FTB) antenna with a stable gain band was designed by placing an RGIMS on top of an LGIMS lens antenna. The measured peak gain of 14.82 dBi with an FTB pattern having a 1 dB gain variation range of about 96° is observed. Furthermore, the movement of the LGIMS and the RGIMS on top of the radiator results in continuous beam scanning with a maximum gain variation of 1 dB in a conical plane with a vertex angle of about 100°. A maximum gain of 14.82 dBi with a maximum gain enhancement of 10.30 dB at 10.15 GHz was obtained due to the linear and angular movement of the LGIMS and the RGIMS in the FTB antenna. The simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

Radial line slot arrays (RLSAs) are well suited to be used in monopulse radar systems. The excitation of the sum and difference patterns can be achieved by the design of simple feeds as shown in this paper. In this work, a feed system based on the use of a cavity made in groove gap waveguide technology (GGW) is presented. The design is made at 24 GHz but can be easily scaled to higher frequencies as the technology is contact-less and fully made in metal. A good isolation between the sum and difference ports together with a good matching of the two of them is obtained. The radiation patterns of the manufactured antenna are also in good agreement with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper presents the use of terahertz near-field focusing for backscatter side-channel detection. Near-field focusing is done by using a Cassegrain reflector configuration. The focuser is designed to produce the focused beam 28 cm away from the antenna aperture. The focusing is done in the near-field region by axially moving the subreflector from the focal point. It is observed that the subreflector position has to shift approximately 11 wavelengths along the axis to create the focus at the required location. The focused antenna gain is 46 dBi, while the 3 dB focus width and depth of the designed antenna is ~4 mm and 10 cm, respectively. It is found that the focal plane position is sensitive to the subreflector shifts and it is observed that 1 mm change in the subreflector position can shift the focal plane by ~2 cm. The simulations are compared with the measurement results of a fabricated prototype and good agreement is observed. The antenna is fabricated by using 3-D printing technology, which allows rapid prototyping. Finally, we have demonstrated the detection of backscatter side channel from the board placed at 28 cm away from the designed antenna. The received power level of the backscatter signal increases by 6 dB as compared to horn antenna. [ABSTRACT FROM AUTHOR]

This paper describes a new family of all-metallic radiators based on below-cutoff apertures fed by evanescent-mode ridge-waveguide filters. The passband of the filters and the polarization of the apertures are configured to radiate orthogonal signals at a different center frequencies. The simultaneous operation of these radiators in an array configuration results in interleaved apertures producing overlapped fields. This strategy reduces the volume and weight of the antenna system, which is an especially appealing characteristic in satellite antennas. Each isolated evanescent-mode filter ends in a small-size aperture and is designed following a novel synthesis procedure. Next, the radiating elements are combined, and the resulting array is analyzed as a multiplexer from the input ports to the free-space region, thus accounting for all mutual couplings between different apertures. To validate the theoretical formulations, a prototype has also been manufactured. The results obtained show very good agreement between simulation and measurements in terms of reflection coefficient, sidelobe level, and realized gain, thereby fully validating the new family of radiating arrays. [ABSTRACT FROM AUTHOR]

A broadband high-gain low-profile array antenna with a brick structure is presented in this paper. The array antenna is arranged in a $2 \times 4$ configuration, and a printed dipole antenna is taken as the element. Two elements along the E-plane are printed on a substrate as a subarray, and four subarrays along the H-plane are arranged orthogonally to the four-way power divider, meaning that the array is a brick structure. The proposed antenna can provide a relative bandwidth of 40% in the frequency range 1.2–1.8 GHz with return loss (RL) greater than 13 dB, a gain greater than 14 dBi, and a height less than 4/10 of the wavelength of the center frequency. The radiation efficiency of the proposed antenna is between 40% and 80% across the operating bandwidth as well as the horn antenna, and the height is only 1/8 of the horn antenna with the same aperture. Finally, a high-gain low-profile antenna with 17 and 20 dBi is provided, which has the same radiation efficiency as the horn, and this design is verified to be equally applicable to antennas with a higher gain. [ABSTRACT FROM AUTHOR]

This paper deals with the synthesis of monopulse antenna patterns, sum and difference ones, for planar phased array antennas with an elliptical aperture boundary featuring unequal ultra-low peak sidelobe levels (PSLLs) for the two principal planes of its far field. The used synthesis method is the iterative Fourier transform (IFT) approach. The elliptical planar phased array antenna involved in this synthesis contains 3656 open-ended waveguide radiating elements arranged in a triangular element grid and has an aperture width and height of $50\lambda _{\text {o}}$ and $25\lambda _{\text {o}}$ , respectively, where $\lambda _{\text {o}}$ is the wavelength at X-band center frequency 1.0fo. The simulated monopulse pattern results will be compared with those of a 4680-element rectangular planar phased array antenna having the same width, height, radiator type and triangular grid as the elliptical array antenna. The monopulse patterns of the rectangular array antenna meet the same unequal ultra-low PSLL requirements as those of the elliptical array antenna. It will be shown that the elliptical array antenna with a slightly enlarged aperture containing 4170 elements features on receive comparable or even better far-field performance characteristics as that of the rectangular array antenna. All reported far-field pattern simulations take mutual coupling between the array elements into account. [ABSTRACT FROM AUTHOR]

It is necessary, and advantageous, to know the minimum target size (MTS) when assessing fitness between a sensor and a target for the desired application. In the case of micropower impulse radar (MIR) sensor, due to its nature of being wideband, it used to be difficult to estimate the MTS without utilizing complex mathematical modeling or implementing time-consuming direct measurement. This paper addresses the target size estimation task from a system-level approach and presents an alternative method that is simple in computation. This proposed method is based on the physics law of conservation of energy and calls for transmission power, reception power, effective aperture of the receiving antenna, and electronic circuitry of receiver in formulation. The method is cost-and-time effective when compared with direct measurement or mathematical modeling. The proposed method is evidenced to have an accuracy exceeding 90%, verified by a commercially available MIR system. [ABSTRACT FROM AUTHOR]

This paper investigated the possibility of using an $X$ -band traveling-wave antenna for application in synthetic aperture radar (SAR) on a small-satellite platform. A rectangular slotted parallel-plate antenna panel capable of radiating dual polarization over the same physical aperture was selected for this purpose. The design procedure, which provides for an optimal antenna pattern in a SAR application, is described. A meta-heuristic multiobjective optimization algorithm was applied to synthesize an appropriate far-field pattern, which enhances the quality of the SAR image. Subsequently, the optimization results were used to build a more realistic model of the antenna panel in electromagnetic simulation software. An antenna panel was fabricated, and its electrical characteristics were measured. The fabricated prototype weighed 1310 g and measurements showed nearly 50% aperture efficiency for both circular polarizations [34.6-dBic right-hand circular polarized (RHCP), 34.5-dBic left-hand circular polarized (LHCP), and peak gain at 9.65 GHz], with low side-lobes. A beam shift of 2.1° was observed between the RHCP and LHCP beams at the design center frequency and was later analyzed to be the result of an error in the modeling of the adhesive layer. [ABSTRACT FROM PUBLISHER]

In this paper, a reexamined estimate of the test fixture validation factor (TFVF) of fixtures for shielding effectiveness (SE) measurements in a reverberation chamber is shown. The fundamental conditions for the applicability of the model shown here are a large aperture between the chambers, whose transmission cross section is well approximated by the geometrical optics, and an isolation between the chambers greater than or equal to 10 dB, as specified in this paper. The model is applicable for both nonmarginal and marginal SE values; but, in the latter case, the requested isolation between the two chambers has to be met with no sample in the aperture. For nonmarginal SE values, the conditions requested for the applicability of the model are practically the same as those requested in the standard IEC 61000-4-21. The model is applicable to SE measurements of gaskets as well. The results show that the TFVF used in the standard procedure IEC 61000-4-21 has to be updated to achieve more accurate measurements of SE in light of the studies conducted on this topic. We give such an update in this study. [ABSTRACT FROM AUTHOR]

A method to steer the beam of aperture-type antennas is presented in this paper. Beam steering is achieved by transforming phase of the antenna near field using a pair of totally passive metasurfaces, which are located just above and parallel to the antenna. They are rotated independently or synchronously around the antenna axis. A prototype, with a peak gain of 19.4 dBi, demonstrated experimentally that the beam of a resonant cavity antenna can be steered to any direction within a large conical region (with an apex angle of 102°), with less than 3-dB gain variation, by simply turning the two metasurfaces without moving the antenna at all. Measured gain variation within a 92° cone is only 1.9 dBi. Contrary to conventional mechanical steering methods, such as moving reflector antennas with multiaxis rotary joints, the 3-D volume occupied by this antenna system does not change during beam steering. This advantage, together with its low profile, makes it a strong contender for space-limited applications where beam steering with active devices is not desirable due to cost, nonlinear distortion, limited power handling, sensitivity to temperature variations, radio frequency losses, or associated heating. This beam steering method using near-field phase transformation can also be applied to other aperture-type antennas and arrays with medium-to-high gains. [ABSTRACT FROM PUBLISHER]

A novel ultra-wideband (UWB) reflectarray antenna for the Internet of Vehicles (IoV) is introduced in this paper. By simply connecting the neighboring reflectarray elements, the proposed reflectarray antenna achieves a remarkable radiation pattern bandwidth of 20 GHz, ranging from 10 GHz to 30 GHz. To explain the operating principles of the proposed reflectarray antenna, the equivalent circuit (EQC) model of the unit cell is built, which also provides an efficient and rapid way to analyze the performance of the proposed reflectarray element. It is found from the EQC analysis that the connected elements can achieve better reflection phase responses than conventional separated elements, thereby improving the array bandwidth. As a proof of concept, a 503-element reflectarray antenna simultaneously covering the vehicle-to-satellite bands (12.25–12.75 GHz/14.0–14.5 GHz/19.6–21.2 GHz/29.4–31.0 GHz), the 24-GHz short-range vehicle radar band (24.25–26.65 GHz) and the 5G millimeter-wave band (27.5–28.35 GHz) is designed, fabricated, and characterized. The experimental results demonstrate that the presented reflectarray antenna can maintain undistorted beams, high antenna gain, low cross-pol level, and moderate aperture efficiency over a bandwidth of 100%, i.e., from 10 to 30 GHz. With its simple and planar aperture as well as excellent performance, the proposed reflectarray antenna can be a promising candidate for vehicles that require reliable high data-rate satellite links and 5G millimeter-wave connections simultaneously. [ABSTRACT FROM AUTHOR]

We recently proposed a direction-of-arrival (DOA) estimation method for the coexistence of uncorrelated and coherent signals, which is related to the uniform linear antenna arrays with mutual coupling (MC) in the presence of unknown nonuniform noise. This technique, however, relies on the assumption of mixed signals and is not suitable for scenarios with purely coherent signals. This paper extends the mixed signal scenario to the purely coherent signals one on one hand, and on the other hand, allows us to directly adopt the ESPPRIT algorithm to perform DOA estimation in MC environments. To be specific, with the help of the least squares (LS) criterion, the nonuniform noise is first eliminated, and the traditional middle subarray scheme can then be employed to be immune to the influence of MC. Unlike the former operation, following a different line of attack the latter can make full use of the whole array and provide a larger array antenna aperture. Furthermore, we derive a new strategy to directly determine the DOAs without taking MC into account and performing spectral search. This brings substantial benefits to the DOA estimation accuracy and computational cost. The superiority of the proposed approaches is verified by numerical examples. [ABSTRACT FROM AUTHOR]

In this paper, a novel idea to reduce the number of active elements in a large periodic array is presented and demonstrated firstly by an E-plane microstrip array. High aperture efficiency can be achieved by making use of mutual coupling between array elements, and then the total production cost of the array is greatly decreased by reducing the number of active array elements and associated components. A simple way to control the mutual coupling of the microstrip array is given as an example in this paper. Simulations and measurements show that when the active element spacing is as large as 1.6\lambda0 (\lambda0 is the free-space wavelength at the operating frequency), a - 18.3 dB side lobe level (SLL) and an approximately equal aperture efficiency can be achieved. No obvious performance degradations are found compared to a conventional array with half the element spacing (0.8\lambda0) and an identical total size. Then, simulations and measurements of an H-plane sparse array are given based on the same idea, followed by the simulated results of a planar two-dimensional (2-D) one. [ABSTRACT FROM AUTHOR]

For the first time, a liquid crystal (LC) filled lens antenna is investigated for beam steering in this paper. The LC’s anisotropy is applied inside a semicircular shaped parallel-plate waveguide to achieve a deflection of the propagating electromagnetic wave at the interface of lower and higher permittivities. Using an electrode network, the direction of the sector of higher permittivity can be adjusted and, therefore, so can the beam direction. The main advantage of this antenna concept is that neither phase shifters nor switching networks are needed, resulting in a very simple approach for beam steering. Operating at $V$ -band, from 50 to 75 GHz, the first demonstrator proves the antenna concept by reconfiguring the beam in predefined directions of −30°, 0°, and +30° to simplify the electrode biasing network. Furthermore, it is feasible and being demonstrated to adjust the beamwidth and to generate multiple beams. In the measurements, the antenna exhibits a measured input reflection below −10 dB over the complete frequency range. For the unsteered radiation pattern, the sidelobe level is between −8 and −12 dB, whereas these values degrade to −4.5 to −6 dB for the steered radiation pattern at ±30°. The measured gain is between 13 and 15 dBi. [ABSTRACT FROM AUTHOR]

This paper presents new single-ended-fed planar aperture antennas (SPAAs) using low-temperature co-fired ceramics (LTCC) process technology. The SPAA element is proposed first, which not only inherits the merits of the aperture antennas including high gain and wide bandwidth but also exhibits advantages of low profile and compact size. The aperture is excited by a cross-shaped patch, and a loop-shaped balun structure placed below the patch is introduced to convert the single-ended signal into differential one to drive the patch. In this way, the energy can propagate on the patch in a traveling waveform and illuminate the aperture with uniform E-field distributions. Therefore, the antenna achieves good electrical and radiation performances, which are comparable to its balanced-fed counterparts, while processing a simplified structure. Measured results demonstrate that the impedance bandwidth of the antenna covers the 60 GHz license-free band (57–64 GHz), and the maximum gain can reach 11.5 dBi with a cavity area of only about 27 mm2. Furthermore, the element is successfully extended to a $4\,\,\times \,\,4$ element array using a substrate-integrated-waveguide based feeding network to further increase the gain up to 20.4 dBi. The measured results show that the impedance bandwidth of the array is from 57.5 to 65.7 GHz and the radiation performances are very stable over the operating frequency band. [ABSTRACT FROM AUTHOR]

This paper presents the design, development, and measurement results of a low-cost integrated circularly polarized (CP) active phased-array antenna (CP-APAA) technology with sidelobe level (SLL) control, operating at $Ka$ -band, for high throughput land-mobile satellite communication. The proposed CP-APAA is comprised of ($4\times 16$) 64 elements in a rectangular grid array configuration. Eight commercial monolithic monolithic microwave/millimeter-wave integrated circuit. (MMICs) with eight-RF output channels have been used to control the phase and amplitude over the antenna aperture. For simplicity, the array antenna was designed in three metal layers and fabricated by a low-cost printed circuit board (PCB) technology as a proof-of-concept for a modular and scalable $Ka$ -band PAA with a wide steering angle. Measured radiation pattern shows a right-hand CP (RHCP) pattern with an axial-ratio (AR) level < 3 dB and low pointing error ≤1.5° over a scanning angular range of 0° to ±40°. Moreover, the amplitude excitation of the CP-APAA was tapered exponentially to control and reduce the SLL from 11 to 25 dB in boresight direction. Finally, toward a multibeam array implementation, two RHCP beams have been simultaneously generated at −30° and +20° scan angles. [ABSTRACT FROM AUTHOR]

A novel dual-band polarization-independent transmitarray is introduced in this paper for communication systems in Ka-band. Thanks to its unit-cell topology, the transmitarray antenna demonstrates almost complete independent performance at two design frequency bands of 20 GHz and 30 GHz. As a proof-of-concept, a transmitarray antenna prototype having a plate size of $80 $ mm $\times 80$ mm has been fabricated using printed board technology. A dual-band circularly polarized ridged cavity antenna feeds this planar structure and the relative translational displacement between the feed and transmitarray allows beam steering. The antenna performance has been validated via experimental results, which demonstrate good agreement with the theoretical and simulation predictions carried out with commercial software packages. [ABSTRACT FROM AUTHOR]

Fundamental limits on antenna performances are of key interest to the antenna designer, as they allow fast assessment of the feasibility of specific antenna requirements. These limits are defined by the key performance indicators (KPI) of specific antennas, such as the directivity for large aperture antennas or the achievable bandwidth on electrically small antennas. These limits have been obtained considering that the antenna radiates into free space. In this contribution, we develop the fundamental limits for implanted antennas, which thus radiate first into a lossy medium. KPIs assessing the quality of a specific antenna radiating into lossy medium are the total radiated power reaching free space (out of the lossy host medium) and the maximum power density obtained at the surface of the lossy host medium. The fundamental limits for implanted antennas proposed in this paper yield upper bounds for both KPIs and have been obtained considering elementary sources radiating into a spherical phantom. The spherical wave expansion of the electromagnetic fields was used to determine all the fields, and the limits obtained yield a useful upper bound for more complex scenarios. [ABSTRACT FROM AUTHOR]

Focal-plane reflector feeds with shared aperture are a promising solution for the increasing number of beams required in the Ka-band satellite services. Stringent manufacturing tolerances and coupling between feeds tend to penalize performance, which is aggravated for a dual band. This paper proposes a new design of a shared aperture antenna intended for multispot single-feed-per beam satellite applications that allows recovering single-feed performance, minimizing the usual impact of adjacent feeds on the field distribution and ultimately on the antenna directivity and gain. We present a new focal-plane dual-band Fabry–Pérot cavity antenna (FPCA) design, which allows more reliable fabrication, closer agreement with simulations, and larger bandwidth than the reported solutions. It uses only one double-sided printed frequency-selective surface (FSS) to form the dual-band FPCA, and it is fed through a novel arrangement of double-layer slots in the FPCA-printed ground plane. This favors impedance matching and higher isolation between adjacent feeds. The effectiveness of the solution is experimentally demonstrated for a single-feed Ka-band (20 and 30 GHz) prototype. The generalization for a complete multifeed configuration with filters is shown by full-wave simulations. The decoupling slots on the FPCA ground plane enable restoring single-feed performance in the multifeed system, over the bandwidth of interest. [ABSTRACT FROM AUTHOR]

This paper describes the design and realization of a Ku/Ka dual-band shared-aperture beam-scanning antenna array based on the concept of structure reuse. The antenna consists of four Ku-band linear antenna arrays implemented by the substrate-integrated waveguide (SIW) and four Ka-band linear antenna arrays. To increase the aperture utilization efficiency, the Ku-band antenna is employed as some sidewalls of the Ka-band antenna. Thanks to this compact topology, the element spacing at two frequency bands is able to meet the requirement of a wide-angle beam scan. Both feeding networks of these two arrays are designed by proper SIW power dividers through the printed circuit board fabrication process. In addition, the self-filtering characteristic of the antenna, the orthogonal polarization, and the optimal layout of the array are employed to ensure the high channel isolation between the two antennas operating at different frequency bands over the whole beam scan range. The isolation between antennas is better than 28 and 70 dB at the Ku-band and Ka-band, respectively, scanning up to even 40°. The proposed shared-aperture concept and the design results have been validated by the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the combined antenna array is developed to maximize the effective potential gain ($G_{ep}$) within finite aperture area for the high-power ultra-wideband (UWB) radiation. The idea is to make the antenna element as small as possible, so that more elements can be arranged within the prescribed aperture area to maximize $G_{ep}$ of the UWB system. On the other hand, the antenna element should match the pulse excitation. This means that in the frequency domain, the working band of the antenna element should cover the spectrum of the radiated pulse, and in the time domain, critical parameters of the radiated field (e.g., rise time of the monopolar pulse) should not be distorted, and those can be the principles for the UWB antenna to match the pulsed excitation, based on which the minimum size of the antenna element can be determined. With this method, a four-element combined antenna array is designed. Also, an impedance transformer and power divider are designed to feed the antenna array. Also, a big combined antenna is developed with the same aperture dimensions (30 cm $\times30$ cm) as the antenna array. Then, the performances of the antenna array and the big antenna are measured and compared. Compared with the big antenna, $G_{ep}$ of the antenna array is 21% higher under the applied excitation, which indicates that the proposed method can significantly improve $G_{ep}$ of the UWB system within the prescribed aperture area. Finally, the antenna array is furthermore optimized by adjusting the distances between the elements, and $G_{ep}$ is improved by another 11%, the total improvement is 33%, and the corresponding effective potential gain is 1.49. [ABSTRACT FROM AUTHOR]

The operating frequency of future communication systems will cover unlicensed millimeter-wave bands as well as existing microwave bands. Large frequency ratio antennas that can be applied to both frequency bands simultaneously and maintain the high isolation between the two channels are difficult to design. This paper presents a new design of dual-band shared-aperture antenna based on the concept of structure reuse. The antenna consists of a patch antenna working at 3.5 GHz and a $12 \times 12$ substrate integrated waveguide (SIW) slot array antenna working at 60 GHz. The frequency ratio of this shared-aperture antenna is 17. In this design, the overall structure of the SIW slot array antenna is employed as the radiator of the patch antenna. With this new scheme, the high aperture reuse efficiency can be achieved. Meanwhile, the millimeter-wave antenna based on the SIW technology has the high-pass nature to reject the lower frequency signal. A compact microstrip resonant cell that acts as a low-pass filter is connected in series on the feedline of the microwave antenna to suppress the upper frequency signal. Thus, the channel isolation between the patch and the SIW slot array antennas can be more than 130 dB at 3.5 GHz and 65 dB at 60 GHz. [ABSTRACT FROM AUTHOR]

A nonuniform frequency selective surface (FSS)-backed reflectarray with both amplitude and phase controls for beam shaping is presented in this paper. In the process of element design, a dual-resonance reflectarray element backed by a loop FSS is studied. The proposed reflectarray element can achieve a reflection phase range of 570° and an amplitude control range over 10 dB, by tuning the dimensions of the upper reflectarray and lower FSS layers. In the process of reflectarray synthesis, a complex amplitude synthesis technique, based on the modified alternating projection method, is developed to take into account the physically realizable amplitude and phase controls of the FSS-backed element for optimizing the amplitude and phase distributions on the reflectarray aperture. A nonuniform FSS-backed $16\times 16$ -element reflectarray with a sector beam in the azimuth plane and a pencil beam in the elevation plane is designed and fabricated. The simulation and measured results reveal that the proposed reflectarray antenna offers distinguishing features in terms of high-quality pattern with lower sidelobe level, lower cross polarization as well as lower radar cross section, compared to the reflectarray designed by the conventional phase-only synthesis technique. [ABSTRACT FROM AUTHOR]

Current millimeter wave (mm-wave) communications research is focused on large scale antenna with contiguous aperture. On the contrary, in this paper, we present a study of mm-wave communications between transmit and receive antennas based on noncontiguous aperture. Our design aims to form shaped beams with high spatial isolation. We first study the beam shaping feasibility in mm-wave communications with reduced transmit antenna element spacing. We then introduce active scatters, a class of active devices that stimulates scattering effect, to sustain the interference rejection capability of shaped beams. The composition of active scatters forms a (virtual) noncontiguous aperture that is larger than transmit and receive antennas in size. To form multiple orthogonal beam (OB) radiation patterns that have peaks and nulls at designated locations, which enable frequency reuse, we consider slightly increased aperture size of transmit antenna and noncontiguous aperture that is comprised of active scatters. In addition to beamforming via noncontiguous aperture, we also simulated QPSK-modulated signal streams transmitted via OBs and justified the simulated system by inspecting the bit error rate performance at the receiver. [ABSTRACT FROM AUTHOR]

In this paper it is shown that the traditional shunt admittance represented by a rational function yields an accurate wideband equivalent circuit for multi-aperture waveguide irises. The electromagnetic analysis of the structures reveals two different types of resonant phenomena. The first type of resonance is associated with the cutoff frequency of the TE10 mode. The second type or antiresonace corresponds to short-circuit TEM modes. These antiresonances are generated when the asymmetry of the iris allows the excitation of electric fields with opposite phases at contiguous apertures. The proposed equivalent circuit is a shunt admittance represented by a rational function. This rational function is analytically obtained from the singular points (resonances and antiresonances) identified in the full-wave analysis. It is straightforward to obtain the circuit elements from the rational function by following the classical one-port synthesis leading to Foster’s or Cauers’s canonical realizations. One advantage of the proposed equivalent circuit is that it represents the electromagnetic behavior of complicated structures with a minimum number of circuit elements or degrees of freedom. Several examples, with different number of apertures and symmetry, are presented to illustrate the proposed general equivalent circuit. Finally, the proposed procedure is extended to the case of arbitrary shaped irises, such as those used in frequency-selective surfaces. [ABSTRACT FROM PUBLISHER]

Of primary importance for a radio telescope is its receiving sensitivity. The offset Gregorian reflector antennas, as used for the Square Kilometer Array (SKA) radio telescope, can be shaped to make efficient use of the reflector’s aperture and thus to maximize sensitivity for a given sidelobe level. The shape of the reflector is controlled by a mapping function. This paper presents a method to derive the optimum mapping function given a selected set of single pixel feeds. In this case, the feeds were optimized for a geometrically similar classical conic section (unshaped) reflector system. Realistic performance results are given for reflector systems with various subreflector sizes, extensions, and subtended angles. [ABSTRACT FROM PUBLISHER]

State-of-the-art automotive radars have an angular resolution of 1°, which is insufficient for estimating the objects shape and boundaries at long distance. In this paper, we design a novel automotive radar with 1m aperture, which is an order of magnitude larger aperture than state-of-the-art automotive radars, and thus achieves super high angular resolution of 0.1°. The radar is designed to overcomes the major technical challenges of a wide aperture radar, which are: non-robust phase coherency over a wide aperture, spanning a wide aperture with sparse antenna elements, simultaneous non-interfering transmissions from a relatively large number of transmit antennas with unambiguous target speed estimation, and high complexity of near-field beamforming. We demonstrate the super high resolution performance of the radar in automotive scenarios, and show that it attains comparable results to a high resolution LIDAR at short range, and outperforms the LIDAR at long ranges. The wide aperture radar has the potential to enable autonomous driving at higher speed, and also to increase the operation of autonomous driving to more regions and climates. [ABSTRACT FROM AUTHOR]

In this study, we describe the specific features of the near-field distribution of a uniformly illuminated aperture. An analytical method based on physical optics in the time domain is used to calculate the field intensity. The primitive impulse response function makes it possible to calculate the near-field distribution of the antenna. The difference in the amplitudes of the fields during the observation point shift along the X and Y coordinate axes can reach up to 13% of their maximum relative values. This difference should be considered when calculating the antenna radiation patterns. At the end of this paper, we present the results of the comparison obtained using three methods: geometrical theory of diffraction (GTD), plane wave spectrum approach (PWS), and primitive impulse response function (IRF) method. In the near field of relatively small apertures (with respect to wavelength), the results of all three compared methods (GTD, PWS, and IRF) were very similar. The analytical IRF method, the results of which are given in this paper, is much more effective in terms of computer resources than the plane wave spectrum approach, and even more effective than the geometric theory of diffraction method.

Antenna noise temperature calculations of reflector systems is often a slow process and makes direct optimization of the sensitivity of these systems a difficult and time-consuming task. This paper presents an improvement to a recently proposed method to speed up these calculations by several orders of magnitude for large dish systems. The accuracy of the improved method is tested for several types of offset Gregorian systems, and errors are shown to be in the order of a few percent. Comparisons of several layers of simplification to a standard brightness temperature model are also presented to aid the designer in the choice of model complexity to use. [ABSTRACT FROM PUBLISHER]

This paper presents 300-GHz step-profiled corrugated horn antennas, aiming at their integration in low-temperature co-fired ceramic (LTCC) packages. Using substrate integrated waveguide technology, the cavity inside the multi-layer LTCC substrate and a surrounding via fence are used to form a feeding hollow waveguide and horn structure. Owing to the vertical configuration, we were able to design the corrugations and stepped profile of horn antennas to approximate smooth metallic surface. To verify the design experimentally, the LTCC waveguides and horn antennas were fabricated with an LTCC multi-layer process. The LTCC waveguide exhibits insertion loss of 0.6 dB/mm, and the LTCC horn antenna exhibits 18-dBi peak gain and 100-GHz bandwidth with more than 10-dB return loss. The size of the horn antenna is only 5\times 5\times 2.8~mm^3, which makes it easy to integrate it in LTCC transceiver modules. [ABSTRACT FROM PUBLISHER]

In conventional arrays, improving angular resolution requires larger aperture which demands more number of elements. On the other hand, array thinning is an efficient method of achieving narrow beamwidth (high angular resolution) with fewer number of elements. Reducing the number of elements results in reducing weight, cost, hardware complexity, and energy consumption. In this paper, a novel dynamic programming algorithm of array thinning with the objective of reducing sidelobe levels (SLLs), desired for large circular arrays, is proposed. The circular array is partitioned into annular rings, and the objective of the optimization problem is to determine the number of active elements in each ring. Then, active elements of the rings are selected. Although optimal array thinning is an NP-hard problem, converting the problem of selecting active elements into the number of active elements in each ring causes a huge reduction in computational complexity of the proposed algorithm that makes it affordable for large arrays. Moreover, beampatterns with very low SLLs are synthesized. [ABSTRACT FROM AUTHOR]