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This paper presents a simple and effective way to increase the scan range of phased array antennas by using a metasurface (MTS) curved dome. The technique is based on a phase-gradient passive MTS that deflects the incident rays coming from the array aperture, and on a predistortion of amplitude and phase applied to the original phased array. We assume, therefore, to have at disposal an array capable of electronic beam scanning over a limited angular range with control of amplitude and phase. Geometrical optics ray tracing is used for the design of the metadome and physical optics for the analysis. For the sake of simplicity, the idea is illustrated here for a 2-D scan case; however, the extension to full 3-D scanning appears to be straightforward. [ABSTRACT FROM AUTHOR]

This paper studies the concept of a new waveguide feeding technique for wideband application of an $X$ -band deployable rectangular parallel-plate slot-array antenna panel network with the vertical polarization for a synthetic aperture radar onboard a 100 kg class microsatellite. The antenna design procedure in high-frequency structure simulator followed by its fabrication and measurement results are explained. Simulations and antenna array measurement results confirmed that the corporate feeding technique achieved wide-beam antenna gain within permissible reflection limit in the desired bandwidth, thereby ensuring wideband operation. The fabricated center antenna panel achieved 35.3 dBi peak gain and 75% peak aperture efficiency, and the four-panel antenna array network achieved 40.8 dBi peak gain and 68% peak aperture efficiency in designed 300 MHz bandwidth. Although there was some mismatch in the measured reflection profile of each panel compared to the simulation results, this discrepancy was subsequently analyzed to be due to the imperfect modeling of the adhesive layer thickness and further analysis revealed that increasing the slot length of all coupling slots in the waveguide feeders by 0.2 mm can nullify this undesired effect. [ABSTRACT FROM AUTHOR]

Characteristic mode analysis (CMA) is a promising method that has been used in antenna design. However, CMA of aperture antennas is cumbersome as the equivalent magnetic current is rarely available in main stream method of moments solvers. Based on the duality principle, an equivalent CMA of aperture antennas is proposed, by which the characteristic values and characteristic magnetic currents are calculated through its complementary form. A rigorous proof for such equivalence is provided. Lumped loads are very useful for the manipulation of certain modes, and in this paper, the relationship between the loads for an aperture and its complementary plate is built. The duality CMA is applied to reduce the mutual coupling between aperture antennas etched on a finite plate. Interdigital capacitors are adopted to suppress the out-of-band mutual coupling while an H-shaped aperture for the reduction of in-band one for narrow slots. Numerical and experimental results show that over 10 dB reduction of mutual coupling is achieved for both examples. [ABSTRACT FROM AUTHOR]

In this paper, the design of an ultracompact cavity-backed waveguide aperture antenna operating at C-band with 14% fractional bandwidth at 5.8 GHz is discussed. The measured results demonstrated a 96% antenna efficiency, greater than 78% aperture efficiency, 18 dB return loss, and 15 dBi gain with 0.6 dB flatness over the entire desired bandwidth (5.4–6.2 GHz). Measurements were found to be in excellent agreement with the simulation results. With a size of 126 mm (length) $\times86$ mm (width) $\times48$ mm (height), the proposed antenna is also ultracompact in comparison with other reported antennas with the same aperture size and electromagnetic features. The compactness of the proposed antenna was accomplished by employing a novel approach to excite the output aperture. This approach was achieved by incorporating the cavity-backed waveguide apertures and waveguide steps. The antenna structure is composed of three aluminum layers firmly screwed to each other. Each layer is manufactured by using the computer numerical control milling machine. The proposed antenna is an appropriate candidate for high-power applications due to its metallic structure and high radiation efficiency. The proposed structure is very robust and has carefully been designed to exhibit low sensitive to manufacturing tolerances. [ABSTRACT FROM PUBLISHER]

The intensity of a Sentinel-1 Terrain Observation with Progressive Scans synthetic aperture radar image is disturbed by additive thermal noise, particularly in the crosspolarization channel. Although the European Space Agency provides calibrated noise vectors for noise power subtraction, residual noise contributions are significant when considering the relatively narrow backscattering distribution of the crosspolarization channel. In this paper, we investigate the characteristics of noise and propose an efficient method for noise reduction based on a three-step correction process comprised of azimuth descalloping, noise scaling and interswath power balancing, and local residual noise power compensation. The core idea is to find the optimal correction coefficients resulting in the most noise-uncorrelated gentle backscatter profile over a homogeneous region and to combine them with the scalloping gain for a reconstruction of the complete 2-D noise field. Denoising is accomplished by subtracting the reconstructed noise field from the original image. The performance improvement in some applications by adopting the denoising procedure shows the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents the complete design of a wideband transmit-array (TA) antenna with high gain and high efficiency for D-band applications based on the low-temperature co-fired ceramic technology. The proposed unit cell is composed of a pair of wideband magnetoelectric dipoles as the receive/transmit elements, together with a substrate-integrated waveguide (SIW) aperture-coupling transmission structure for independent phase adjustability. A 360° phase coverage is obtained by the proposed phasing element, and its phase response curves are nearly parallel within a broad frequency band, which indicates a wideband performance. To verify the design, the fabricated prototype is measured by using a vector network analyzer in a terahertz compact-range anechoic chamber. The measured peak gain is 33.45 dBi at 150 GHz with the aperture efficiency of 44.03%, and the measured 3 dB gain bandwidth is 124–158 GHz (24.29%). The good radiation performance ensures that the proposed SIW aperture-coupling TA antenna is a promising candidate for D-band applications. [ABSTRACT FROM AUTHOR]

In order to improve the operating bandwidth and achieve a compact design of the combined antenna, the Klopfenstein impedance taper method is adopted to implement the structure of the combined antenna in this paper. The effects of Klopfenstein taper with different parameters are compared and analyzed with simulation method. Also, the quantity of the magnetic moment of the combined antenna is optimized to improve the low-frequency performance. The relationship between the performance and the structural parameters for the combined antenna is concluded based on the research results. Finally, an optimized combined antenna with length of 30 cm is designed and measured. The impedance bandwidth [voltage standing wave ratio (VSWR) <; 2] of the antenna is 180 MHz to 7 GHz, which means that the band ratio is about 40. The ratio between the antenna length and the wavelength of the lower cut-off frequency, L/λ, is reduced to 0.18. The weighted radiation efficiency within 0-7 GHz is 93.7%. Both numerical and experimental results show that the antenna exhibits unidirectional patterns within the frequency range of 0.5-7 GHz. With a short ultra-wideband pulse excitation, gain of the antenna is measured and derived within the spectrum of the excitation, i.e., 0-3 GHz. The corner frequency of the antenna gain is about 200 MHz, which is close to that of VSWR. Moreover, the radiation efficiency is 76.1%, and the pulse fidelity factor is 0.82 with the applied excitation. [ABSTRACT FROM PUBLISHER]

In this paper, a 94 GHz substrate integrated waveguide (SIW) parallel-plate long-slot array antenna is presented, which is able to generate dual-circular-polarization (CP) low sidelobe level (SLL) beams from a single radiating aperture. This antenna consists of two layers of substrates. One is used to construct the unequal feeding network and the other is used to construct a $15 \times 15$ shared-aperture parallel-plate long-slot array antenna. This multilayer topology has a smaller size compared with the single-layer design. A simple and feasible method is applied to control the radiation pattern, which is able to realize dual-CP low SLL beams without a complicated feeding network. Two 1-D sixteen-way unequal dividers are employed to suppress the SLL in two planes of a CP array. Then, a 90° coupler is employed in the feeding network to switch the polarization modes between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). Finally, a prototype of SIW parallel-plate long-slot array antenna is fabricated. Simulation and measured results show that SLLs of the fabricated antenna are under −18.5 dB in two planes. [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.

This paper compares the capacity improvement capability of spatial multiplexing and beamforming techniques for 60 GHz spatial transmissions in a multi-carrier radio system such as orthogonal frequency division multiplexing. The term beamforming in this paper refers to the conventional gain focusing, for the strongest propagation path, by narrow antenna beams. Our channel capacity metric depends only on the multipath richness of the propagation channel and the antenna aperture size, but is otherwise independent of the realization of antenna elements on the aperture. Our analysis also reveals the spatial degrees-of-freedom (SDoF) of the radio channel, which is the maximum number of antenna elements on the aperture for efficient spatial multiplexing. We evaluate the capacity and SDoF of single-polarized 60 GHz radio channels measured in an office environment. Our results show that the radio channel offers multiple SDoFs both in line-of-sight (LOS) and non-LOS (NLOS) scenarios such that spatial multiplexing can improve the channel capacity, provided that the receive signal-to-noise ratio (SNR) is sufficiently high to utilize them. Under -10 dBm of the transmit power, the high receive SNR is guaranteed when the antenna aperture size is larger than 1\lambda^2 in LOS and 9\lambda^2 in NLOS scenarios, respectively. [ABSTRACT FROM PUBLISHER]

We present the experimental validation of the dual-mode, polarization-agile parallel-fed continuous transverse stub (CTS) antenna architecture introduced in Part I of this two-part paper. The Ka-band dual-mode CTS array described in Part I is characterized when it radiates in horizontal and vertical polarization. To this end, it is combined with two different quasi-optical beamformers operating in a quasi-transverse electromagnetic (quasi-TEM) and in a quasi-transverse electric (quasi-TE1) mode, respectively. The scanning capabilities of both multibeam antenna systems are demonstrated. The CTS array and its feed network comprising corrugated parallel-plate waveguides (CPPWs) are fabricated by additive manufacturing. Measurements show that the dual-polarized CTS antenna works between 29 and 32 GHz in a field of view of about 45°, achieving a peak gain of 31.3 dBi and very low cross polarization. These promising results pave the way for the realization of dual-circularly polarized beam-scanning antennas with application to broadband and compact Ka-band ground terminals. [ABSTRACT FROM AUTHOR]

This paper proposes a compact dual-polarized cross-dipole antenna with low-pass filtering radiation response. The antenna consists of two pairs of orthogonally placed cross-dipoles, a circular patch, a filtering balun and a folded ground plane. Shape of the dipoles and installation of the patch are designed collaboratively to realize wideband and high efficiency in a compact size. The balun, which also contributes a resonance, simultaneously realizes low-pass filtering response at wide stop-band and low loss in passband, with a simple structure. For demonstration, the proposed antenna is implemented. Size of the radiator is 0.28*0.28*0.29 λ3. The measured 15-dB return-loss bandwidth of the prototype is 32.7%, which covers the 4G bands (from 690 MHz to 960 MHz). In the passband, efficiencies beyond 90% and peak gains of 9.05 ± 0.55 dBi are measured. The half-power beamwidth at passband is maintained 65° ± 5°. At frequencies ranging from 1.7 GHz to 4.0 GHz, the prototype can provide beyond 13 dB gain suppression. The proposed antenna can be a good candidate to integrate with elements operating at higher frequencies to form an aperture-shared array for shore-to-ship communication. [ABSTRACT FROM AUTHOR]

Nano-photonic antennas are one of the key components in integrated photonic transmitter and receiver systems. Conventionally, grating couplers, designed to couple into an optical fiber, suffering from limitations such as large footprint and small field-of-view (FOV) have been used as on-chip antennas. The challenge of the antenna design is more pronounced for the receiver systems, where both the collected power by the antenna and its FOV often need to be maximized. While some novel solutions have been demonstrated recently, identifying fundamental limits and trade-offs in nano-photonic antenna design is essential for devising compact antenna structures with improved performance. In this paper, the fundamental electromagnetic limits, as well as fabrication imposed constraints on improving antenna effective aperture and FOV are studied, and approximated performance upper limits are derived and quantified. By deviating from the conventional assumptions leading to these limits, high-performance multi-mode antenna structures with performance characteristics beyond the conventional perceived limits are demonstrated. Finally, the application of a pillar multi-mode antenna in a dense array is discussed, an antenna array with more than 95% collection efficiency and 170 $^\circ$ FOV is demonstrated, and a coherent receiving system utilizing such an aperture is presented. [ABSTRACT FROM AUTHOR]

In this paper, a wideband $2 \times 2$ multilayer substrate integrated waveguide (SIW)-based cavity-backed slot array is proposed. The array element is constructed by stacking five layers of SIW cavity-backed slots and has a wide impedance bandwidth from 18 to 30 GHz. Two different feed networks based on probe coupling and slot coupling are introduced to maintain the wideband characteristic of the proposed element when employed in an array. Two $2 \times 2$ arrays fed by the proposed feed networks are designed, fabricated, and tested. The measured results show that both the arrays employing probe coupling and slot coupling feed networks have a wide impedance bandwidth over 30%. Within the obtained operation bands, good radiation performance is achieved. Moreover, advantages and disadvantages of the proposed two feed networks are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a novel tri-band (X/Ku/Ka-band) planar antenna array with dual polarizations and shared aperture. Compared with traditional dual-polarized arrays, the proposed array has advantages of low cost, low profile, and high integration. Three types of antennas resonating at different frequencies, including the perforated patch, stacked patch, and slim crosspatch, are innovatively interleaved in the same aperture. The crosspatch fed by proximity coupling is presented as Ku-band element for its advantages of compact size, high isolation, and pure polarization. The techniques such as series feed and reverse feed are utilized to implement the six feed networks in a compact size with reduced cross polarizations. Measured results agree well with the simulations, showing three operation bands at X-, Ku-, and Ka-bands with the bandwidths of 3.6%, 6.7%, and 5.3%, respectively. The antenna also exhibits excellent radiation performance with the cross-polarization discrimination over 25 dB at the three bands. To the best of the author’s knowledge, this is the first shared-aperture X/Ku/Ka-band dual-polarized antenna array reported, which is useful for potential synthetic aperture radar applications. [ABSTRACT FROM AUTHOR]

In this paper, a systematic method to design a quasi-optimum lens profile based on quasi-conformal transformation optics technique for a given excitation is presented. This method is applied to a number of conventional antennas, such as an aperture and a log-spiral slot. In all these configurations, an increase of the directivity is observed. Furthermore, using this method, a quasi-optimum graded index lens for a broadband enhanced leaky slot excitation is designed and the results are compared with a hyperhemispherical lens with and without matching layers. Our proposed methodology demonstrates to be able to increase the directivity, to reduce the sidelobes and the cross polarization in a broad bandwidth from 20 to 70 GHz. Due to the continuously changed dielectric constant of the lens profile, reflections are also reduced considerably inside the lens. [ABSTRACT FROM PUBLISHER]

In this paper, a general formula for the half-power beamwidth of one-dimensional leaky-wave antennas (1-D LWAs) is presented. With respect to previous beamwidth formulas found in the literature, the new formula allows for both arbitrary propagation wavenumber and length of the antenna. The pointing angle of the beam is allowed to be arbitrary, and may be near broadside or endfire, or any angle in between. The beamwidth is also allowed to be arbitrary, though a simpler approximate expression is obtained under the assumption of a narrow beam. Numerical results confirm the accuracy of the new beamwidth formula. Furthermore, it is shown that the previous existing formulas are approximate limiting cases of this more general result. This new formula will provide a very useful tool for obtaining more reliable results for the beamwidth of any type of 1-D LWA. [ABSTRACT FROM PUBLISHER]

Many aspects of the Atacama Large Millimeter Array (ALMA) instrument are still unknown due to its young age. One such aspect is the true nature of the primary beam of each baseline, and how changes to the individual primary beams affect astronomical observations when said changes are ignored during imaging. This paper aims to create a more thorough understanding of the strengths and weaknesses of ALMA through realistic modeling of the primary beams and simulated observations, which in turn can inform the user of the necessity of implementing more computationally costly algorithms, such as A-Projection, and when simpler, quicker algorithms will suffice. We quantify our results by examining the dynamic range of each observation, along with the ability to reconstruct the Stokes I amplitude of the test sources. These tests conclude that for the dynamic ranges of less than 1000, for point sources and sources much smaller than the main lobe of the primary beam, the accuracy of the primary beam model beyond the physical size of the aperture simply does not matter. In the observations of large extended sources, deconvolution errors dominate the reconstructed images and the individual primary beam errors were indistinguishable from each other. [ABSTRACT FROM PUBLISHER]

This paper presents a novel dual polarized planar aperture antenna using the low-temperature cofired ceramics technology to realize a novel antenna-in-package for a 60-GHz CMOS differential transceiver chip. Planar aperture antenna technology ensures high gain and wide bandwidth. Differential feeding is adopted to be compatible with the chip. Dual polarization makes the antenna function as a pair of single polarized antennas but occupies much less area. The antenna is ±45° dual polarized, and each polarization acts as either a transmitting (TX) or receiving (RX) antenna. This improves the signal-to-noise ratio of the wireless channel in a point-to-point communication, because the TX/RX polarization of one antenna is naturally copolarized with the RX/TX polarization of the other antenna. A prototype of the proposed antenna is designed, fabricated, and measured, whose size is 12 mm $\times $ 12 mm \times1.128$ mm ( 2.4\lambda _{0}\times 2.4\lambda _{0}\times 0.226\lambda _{0} ). The measurement shows that the −10 dB impedance bandwidth covers the entire 60 GHz unlicensed band (57–64 GHz) for both polarizations. Within the bandwidth, the isolation between the ports of the two polarizations is better than 26 dB, and the gain is higher than 10 dBi with a peak of around 12 dBi for both polarizations. [ABSTRACT FROM AUTHOR]

This paper proposes a reconfigurable polarization converter based on a p-i-n diode controlled active metasurface (AMS). The AMS consists of a thin dielectric substrate and is tuned by two identical layers of elliptic split rings loaded with p-i-n diodes. The p-i-n diodes are positioned between the split gaps and biased through the interconnected elliptic split rings without extra bias network. The active design achieves conversion from linear to circular polarization when the p-i-n diodes are OFF, whereas no conversion takes place when the diodes are ON. A prototype of the proposed design is fabricated, and the operational characteristics are measured. Both the simulated and the experimental results verify the viability of the design. Subsequently, the converter is applied to a linearly polarized horn antenna as a superstrate, making the polarization of the antenna reconfigurable. [ABSTRACT FROM PUBLISHER]

A wideband THz H-plane dielectric horn antenna based on silicon (Si) technology is proposed in this paper. The antenna can be integrated with the planar structure circuit and the dielectric ridge waveguide. To fabricate the proposed antenna, the deep reactive ion etching high-resistivity Si fabrication process is used. The size of the proposed antenna is $3.13 \times 4 \times 0.1$ mm3. The operating frequency of the antenna ranges from 750 to 1000 GHz, which corresponds to a fractional impedance bandwidth of 28.6%. The antenna has a narrow beamwidth in the H-plane and a high gain. To test this antenna, the characterization of the metal waveguide diagonal horn for measurement is analyzed. Then the non-contact measurement method is applied to measure the designed dielectric horn. The simulated radiation efficiency of the antenna is higher than 80% while the measured gain of the antenna is larger than 8 dBi. Measured H-plane radiation patterns from the proposed antenna are presented and show reasonable agreement with the simulated results. [ABSTRACT FROM PUBLISHER]

The manipulation of the near-field (NF) is a challenging topic in electromagnetics, carrying essential importance for several applications. In this paper, we develop an algorithm capable of shaping the NF in 3-D domains according to given specifications. The algorithm is based on a set theoretic approach and a front-and-back iterative propagation scheme. The latter is realized using fast Fourier transforms (FFT), reducing the required computational time. The algorithm is applied on a focal shaping scenario. In this case, a full control of the depth of focus, spot diameter, and sidelobe level of the generated radiation is achieved. In particular, the proposed procedure is successfully adopted to control the normal component of a radiating aperture over a range of 12 \lambda at 30 GHz. The derived aperture field distribution is then synthesized by a radial line slot antenna (RLSA) by means of an in-house method of moments (MoM) code. NF measurements have validated the proposed approach and prototype. [ABSTRACT FROM PUBLISHER]

The incorporation of gallium nitride (GaN) power amplifiers (PAs) into future high-power aperture radar systems is certain; however, the introduction of this technology into multifunction radar systems will present new challenges to radar engineers. This paper describes a broad investigation into amplitude and phase transients produced by GaN PAs when they are excited with multifunction radar waveforms. These transients are the result of self-heating electrothermal memory effects and are manifested as interpulse instabilities that can negatively impact the coherent processing of multiple pulses. A behavioral model based on a Foster network topology has been developed to replicate the measured amplitude and phase transients accurately. This model has been used to develop a digital predistortion technique that successfully mitigates the impact of the transients. The moving target indicator improvement factor and the root mean square pulse-to-pulse stability are used as a metric to assess the impact of transients on radar system performance and to test the effectiveness of a novel digital predistortion concept. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a beam forming approach capable of synthesizing versatile, pre-specified beam shapes using concentric excitations satisfying multiple weighted sinc or Bessel function distribution. We show by both theoretical calculation and full wave simulation that by tuning different weights of a sinc or Bessel function distribution, not only radiation beams with pencil, flat-topped and bimodal shapes can be synthesized, but also the beam-width and the side lobe level can be independently adjusted. An example is provided to demonstrate how an isoflux beam aiming at a better coverage of the earth surface is synthesized, and how an optimized continuous distribution is properly discretized for a physical realization of a satellite aperture array antenna. The approach proposed in this paper can be applied to a wide range of applications that require performance optimization of concentric ring array antennas. [ABSTRACT FROM PUBLISHER]

This paper reports on the detailed design and experimental demonstration of a metamaterial-enabled low-sidelobe horn antenna (metahorn) based on principles similar to those of earlier soft horn antennas. The target application is a linearly polarized feed horn in the super-extended C-band (3.4–6.725 GHz) for communication satellite reflector antennas. The paper describes the detailed design and manufacturing of the E-plane metamaterial liner (metaliner) based on a freestanding wire grid without the need for a dielectric substrate material. The measured copolarized and cross-polarized antenna patterns from the feed horn demonstrate over an octave pattern bandwidth with negligible loss. The results show similar bandwidth with lower sidelobes and backlobes than those of the trifurcated horn that is currently used as the standard C-band feed for single linear polarization. This demonstration shows promise for lightweight metamaterial horns to replace heavy and expensive C-band corrugated horns. [ABSTRACT FROM PUBLISHER]

This paper presents a synthetic aperture radar (SAR) imaging system using a stepped frequency waveform. The main problem in stepped frequency SAR is the range difference in one sequence of pulses. This paper analyzes the influence of range difference in one sequence of pulses in detail and proposes a method to compensate this influence in the Doppler domain. A Stolt interpolation for the stepped frequency signal is used to focus the data accurately. The parameters for the stepped frequency SAR are analyzed, and some criteria are proposed for system design. Finally, simulation and experimental results are presented to demonstrate the validity of the proposed method. The experimental data are collected by using a stepped frequency radar mounted on a rail. [ABSTRACT FROM AUTHOR]

The shooting and bouncing ray (SBR) method may give rise to a divergence problem when ray tubes intersect discontinuous parts of the target, such as the boundary, and this affects the accuracy to some extent. This paper proposes an adaptive aperture partition algorithm to solve this problem. The proposed algorithm adaptively splits the virtual aperture into continuous irregular beams instead of discrete uniform ray tubes according to the geometry of the target during the recursive beam tracing. These beams form a beam tree, the level of which represents the number of reflections. Geometric optics is applied to the representative propagation path of each leaf beam to obtain the exit field, and then physical optics is used to evaluate each leaf beam's scattered field. The proposed algorithm could generate the convergent solution of the SBR method when the ray-tube size tends toward infinitesimal. Additionally, this paper describes the beam-triangle intersection in detail and utilizes the kd-tree to accelerate the beam-target intersection. Numerical experiments demonstrate that adaptive aperture partition can greatly improve the accuracy of the SBR method, and the computational efficiency can be also significantly enhanced in several applications, such as the RCS prediction in the THz band. [ABSTRACT FROM AUTHOR]

Wide frequency band antenna systems are required for many now and future applications, such as in radio astronomy and ultrawideband (UWB) technology. Constant radiation characteristics over a decade bandwidth are required for some of wide band applications, for example, feeds for reflector antennas in radio telescope. The log-periodic array antenna is one of the technologies for wideband antennas. In the present paper, an analysis on condition for constant radiation characteristics over wide bandwidth for a log-periodic array antenna is presented. From this condition, a guide rule for designing a wideband log-periodic array antenna is obtained. The Eleven antenna, a decade bandwidth log-periodic array antenna, is selected to illustrate the condition and verify the analysis in the paper. [ABSTRACT FROM AUTHOR]

With the increasing interest in the applications of large deployable reflector antennas operating at high frequencies, the requirement on the reflector surface accuracy becomes more demanding. Thermal effects inevitably cause certain reflector surface distortions, thus degrading the overall antenna performance. This paper introduces a novel reflector surface distortion compensation technique using a subreflectarray and presents detailed discussions. A microstrip reflectarray is used as a subreflector, illuminated by a primary feed. By properly adjusting the additional phase shift provided by the subreflectarray, the aperture phase errors caused by the main reflector surface distortions are compensated, resulting in a considerably improved antenna performance. As an example, a distorted 20-m offset parabolic reflector antenna operating at X-band is successfully compensated by a subreflectarray, and the simulation results are compared with those obtained by array feed and shaped subreflector compensation techniques. The microstrip subreflectarray is low-profile, lightweight, and cost-effective. Only one primary feed is required, and a reconfigurable design can be achieved if electronically reconfigurable reflectarray elements are adopted. [ABSTRACT FROM AUTHOR]

This paper introduces a probe-correction method for near-field antenna measurements. The proposed technique is intended to be used jointly with a sources reconstruction method for antenna diagnosis and near-field-to-far-field (NF-FF) transformation. The method is based on the introduction of the probe antenna's pattern as a weighting function into the field integral equations relating the measured near field and the antenna's equivalent sources. In this way, the equivalent currents are reconstructed without distortion due to the probe's pattern, as well as the fields calculated from those currents. The theoretical formulation and practical examples based on antenna measurements are presented in this paper. [ABSTRACT FROM AUTHOR]

The performance of multibeam focal plane arrays feeding a single aperture is usually reduced due to conflicting requirements on the feed elements. Dense packing is usually required to minimize the beam separation, while typically large feed apertures are needed to provide the high feed directivity to reduce spillover losses from the reflector. In this paper the use of dielectric super-layers to shape the radiation pattern of each feed is demonstrated. The shaping is obtained by exciting, according to design, a pair of TE/TM leaky waves. The spillover from the reflector is reduced without physically increasing the dimensions of each single element aperture. A prototype of a feed array composed of 19 waveguides arranged in a hexagonal lattice was designed, manufactured and tested. The measured embedded patterns provided an increase of the edge of coverage gain, with respect to the free space case, of at least 0.6 dB in an operating bandwidth (BW) of ≈ 12%. Moreover when reactive loading of adjacent feeds is adopted the increase in the edge of coverage with respect to the free space case was demonstrated to be larger than 1.6 dB over a 3% BW. [ABSTRACT FROM AUTHOR]

Antenna arrays based on aperiodic tilings have been shown to exhibit low sidelobe levels and modest bandwidths over which grating lobes are suppressed. In addition, compared to conventional periodic arrays, these arrays are naturally thinned (i.e., mean interelement spacing is greater than λ/2). The generation of these arrays involves placing array elements at the locations of the vertices of an aperiodic tiling. To obtain a realizable design, the entire array is then scaled and truncated to achieve a desired minimum element spacing and aperture size. This paper demonstrates that it is possible to greatly extend the bandwidth of these arrays by incorporating a simple perturbation scheme into the basic array generation process. The implementation of this perturbation scheme is straightforward and it lends itself well to being combined with an optimization technique such as the genetic algorithm. It is successfully used to generate arrays that have large bandwidths (peak sidelobe level ≤ -10 dB with no grating lobes) of up to a minimum element spacing of 5λ. Moreover, the flexibility of this technique will be further demonstrated by introducing a slight variation of the basic scheme that is capable of generating arrays with extremely wide bandwidths. An example will be presented for an array design that has a bandwidth corresponding to a minimum element spacing of up to 11λ. [ABSTRACT FROM AUTHOR]

This paper presents a novel anisotropic metasurface (AMS)-based integrated antenna system to facilitate dual-polarized fan-beam patterns with independent beam-scanning ability. In the proposed configuration, the antenna subsystem comprises a specially designed differentially fed microstrip patch antenna (source antenna) along with a polarization rotator (PR). The differential antenna arrangement is realized using a square shaped microstrip patch capacitively coupled with two metallic strips, which are connected to a specially designed wideband hybrid coupler using two metallic vias for the microstrip feeding. This source antenna is loaded with a PR by placing it at a height of $0.35\lambda _{0}$ from the radiating aperture. The PR comprised two identical metallic layer patterns, separated by two substrates. Depending upon the relative orientation of these layers, the polarization of the linearly polarized impinging spherical electromagnetic (EM) waves (originating from the source antenna) either remains preserved or gets rotated by 90° while transmitting through this PR. After realizing the antenna subsystem, a novel AMS lens is designed and placed above the PR. The proposed AMS lens is realized by integrating two cylindrical MS (CMS) lenses, $\text {CMS}_{Y}$ and $\text {CMS}_{X}$. This integration provides a unique phase profile to the AMS lens, thus introducing appropriate phase correction to the incident orthogonally polarized spherical EM waves along their respective polarization direction. The proposed configuration of AMS lens, thus, results into formation of the independent dual-polarized fan-beam radiation beams. Finally, the steering of the generated fan-beams along the direction of their respective polarization is facilitated using the proposed system by translating the AMS lens parallel to the source antenna. [ABSTRACT FROM AUTHOR]

Frequency-reconfigurable antennas seem a viable solution to achieve better performance and increased flexibility for integrated mobile phone antennas. Due to the lossy nature of many tunable components, the use of multiple combined tuning components in a single design seems attractive, as it can distribute the current over the components. However, many combinations of individual tuning component settings can result in an acceptable input match, while they will significantly vary in terms of radiation efficiency. It is challenging to distinguish between these radiating and nonradiating tuning component settings during the design procedure. In this paper, we propose a method to determine the component settings with the highest efficiency at a desired operating frequency. The method uses a single full-wave simulation, which is combined with circuit-level calculations. We discuss how to apply the method in detail and demonstrate its functionality with an inverted-L antenna sporting three tunable barium-strontium titanate capacitors. It is shown that the method can successfully predict tuning component settings for high antenna efficiency over a 1.4–2.8 GHz tuning band, with total efficiencies up to 35% and radiation efficiencies up to 50%. The method can easily be applied to any desired antenna geometry. [ABSTRACT FROM AUTHOR]

The feasibility of using stacked microstrip-patch arrays as feeds for offset reflector antennas is investigated in this paper. It is shown that patch arrays can be used as alternatives to the conventionally used horn feeds, which tend to be bulky. In particular, patch arrays can be of interest for spacecraft applications where reduced size and light-weight feeds are highly desirable. In this paper, patch arrays were tailored to provide radiation characteristics similar to those of horn feeds by varying the element spacing and excitation. A reduction in weight was mainly realized by the planar construction of the patch arrays. A full-wave analysis of the feed array, using finite-difference time-domain (FDTD) and PO-based UCLA reflector-analysis codes, was used to test the results of the proposed feed, operating at 1.413 GHz for radiometer applications, and 1.26 GHz for radar applications. A dual-polarized and dual-frequency stacked microstrip-patch element was fabricated and tested. It was then demonstrated that a seven-element hexagonal array design seemed to be the best match to the horn feeds for a 12 m offset-reflector antenna. [ABSTRACT FROM AUTHOR]

Here, we propose a low-profile polarizing technique integrated in a parallel plate waveguide (PPW) configuration, compatible with fully metallic geodesic lens antennas. The geodesic shape of the antenna is chosen to resemble the operation of a Luneburg lens. The lens is fed with 11 waveguide ports with 10° separation producing 11 switchable beams in an angular range of $\pm \mathrm{50}^{\circ }$. Two metallic polarizing screens are loaded into the aperture of the antenna to rotate the electric field from a vertical linear polarization, which is the polarization of the transverse electromagnetic (TEM) mode supported in the lens, to a $+ \mathrm{45}^{\circ }$ linear polarization. Since the polarizing unit cells are integrated into the aperture of the antenna, the final design is compact. In addition, the size of the polarizing unit cells is about $0.55\lambda $ at the central frequency of operation making the antenna suitable to produce an array formed of stacked lenses. A prototype of the antenna in the $\text{K}_{\text {a}}$ -band was manufactured and tested, verifying the performance obtained in simulations. [ABSTRACT FROM AUTHOR]

An effective synthesis procedure for planar antennas realized with nonuniform metasurfaces (MTSs) excited by a point source is presented. This synthesis potentiates previous formulations by introducing a control of the amplitude of the aperture field while improving the polarization and phase performances. The class of MTS antennas we are dealing with is realized by using subwavelength patches of different dimensions printed on a grounded slab, illuminated by a transverse magnetic point source. These antennas are based on the interaction between a cylindrical surface-wave and the periodic modulation of the MTS, which leads to radiation through a leaky-wave (LW) effect. This new design method permits a systematic and simple synthesis of amplitude, phase, and polarization of the aperture field by designing the boundary conditions imposed by the MTS. The polarization control is based on the local value of the MTS anisotropy, the phase is controlled by the shape and periodicity of the modulation, and the amplitude is controlled by the local leakage attenuation parameter of the LW. The synthesis is based on analytical formulas derived by an adiabatic Floquet-wave expansion of currents and fields over the surface, which are simultaneously published in this journal issue. The effectiveness of the procedure is tested through several numerical examples involving realistic structures. [ABSTRACT FROM AUTHOR]

This paper deals with the exploitation of Doppler centroid measurements for ship velocity estimation from focused single-look complex synthetic aperture radar (SAR) images. An algorithm is presented, which can be used as a discrimination tool to reduce the false alarm rate of standard adaptive threshold detectors and to complement the ship detection task with velocity estimation. The outputs are the indication of the presence of a moving target and the estimate of its slant range velocity. After a review of its theoretical background, algorithm features and performance are verified by application to TerraSAR-X data. The proposed method performs robust Doppler spectrum derivation for candidate ship targets and background pixels. The presented results show that the estimated radial velocity is in very good agreement (5% root-mean-square deviation) with that resulting from the azimuth offset method. Rejection of bright sea features and azimuth ambiguities is also demonstrated, taking advantage of the performed velocity analysis. [ABSTRACT FROM AUTHOR]

This paper numerically validates a simple formula to calculate the aperture efficiency reduction due to grating lobes in planar phased arrays. Array antennas with element spacing greater than one wavelength will produce grating lobes. Grating lobes are not a big problem in most new millimeter-wave applications, except for the fact that they reduce the aperture efficiency and thereby normally the directivity. When the element pattern is known, the simple formula can be used to calculate the aperture efficiency in the presence of grating lobes. The formula is verified by the simulations of a large uniformly excited planar slot array. The agreement is good for both broadside radiation and a phased main beam, even if we use the far field of an isolated slot. Using the far field of the embedded slot element gives almost the same results, except when a grating lobe radiates along the ground plane and the isolated element pattern is nonzero in this direction. [ABSTRACT FROM PUBLISHER]

This paper presents a new approach to designing an indoor Wi-Fi energy harvester with a bridgeless converter that operates at low incident power. The design approach started with the analysis of the incident power available at a point of the harvester with certain harvesting distance, dimension, position, and height from the ground plane. Then, a simple single-plane antenna was proposed. Finally, a bridgeless converter circuit was proposed to boost the voltage at very low input power. The analysis showed typical calculated incident power at the antenna on the pathway of the transmitter is approximately 15\; \mu \textW/\textm^2 and in the case of non-line-of-sight, the values dropped down to about 2\; \mu\textW/\textm^2. The proposed system has been tested in an indoor environment where the measured signal strength is between -60\;\textdBm to -50\;\textdBm; and the output voltage and power at the output of the converter were measured as 3.86 mV and 0.15 nW, respectively, a 100 \text k\Omega resistive load is connected for testing. An additional boost-buffer module was connected to the converter circuit for further voltage boost. It was found that the energy harvester stabilizes after 38 hours of operation and 1.8 V was measured at the output supercapacitor (1000 uF), meaning 1.67 J of energy has been stored for driving external low power devices. [ABSTRACT FROM AUTHOR]

This paper presents a novel circularly polarized (CP) planar aperture antenna for cost-sensitive millimeter-wave, particularly fifth generation (5G), applications. The proposed antenna, which is a differential one, has high gain and wide bandwidth and can be built on a single-layer laminate using standard printed-circuit board (PCB) technology. This makes the antenna both low cost and easy to integrate with common differential circuits. The antenna consists of an opening cavity formed by metalized vias, which encloses a set of loop-like strips that are fed differentially. The strips carry traveling wave current which together with the aperture’s E-fields distribution give rise to CP radiation. The aperture size of the antenna can be extended for higher gain by adopting a dual- or quadruple-loop-like strips configuration enclosed by a larger opening cavity. The fabricated quadruple-loop-like strips-based antenna prototype designed to operate at 60-GHz band could achieve 3-dB axial ratio (AR) bandwidth of 16.7% (56–66.2 GHz) within its $-10$-dB impedance bandwidth and stable right-handed CP (RHCP) gain throughout the operating bandwidth with a peak of 14.6 dBi. [ABSTRACT FROM AUTHOR]

This paper presents a novel differentially driven planar aperture antenna with circularly polarized (CP) radiation. The proposed antenna is simple in structure yet can achieve high gain and wide bandwidth, and is constructed using only a single layer laminate via standard printed-circuit-board (PCB) technology. Circular polarization is realized by a rotationally symmetric windmill-shaped patch-aperture formation with travelling wave distribution. The physical aperture of the antenna is constituted by an opening cavity structure formed by metalized vias, which offers high-gain unidirectional radiation pattern. Measurement results of a prototype operating at 60 GHz band show a 3-dB axial ratio (AR) bandwidth of 17.9% (56.5–67.5 GHz), which is within its - 10\ - dB impedance bandwidth. Meanwhile, the left-handed CP (LHCP) gain is stable throughout the operating bandwidth with a peak gain of 13.4 dBi. The proposed antenna is a promising candidate for various consumer level millimeter-wave (mmWave) band applications due to its merits of wideband, high gain, simple structure, low cost, and easy integration with differential circuits. [ABSTRACT FROM PUBLISHER]

In this paper, a compact building block composed of a slot antenna and a loop antenna is proposed. The slot antenna and the loop antenna share a rectangular clearance, which improves the compactness of the building block effectively. Although the slot and the loop have overlapped completely, the proposed building block exhibits good isolation (better than 19 dB) without any external decoupling structure. Four such building blocks are used to implement a compact eight-port multiple-input multiple-output (MIMO) array operating at 3.5 GHz band (3.4–3.6 GHz) for fifth-generation (5G) metal-rimmed smartphone applications. The proposed eight-antenna MIMO array exhibits good isolation of better than 16 dB across the whole operating band. The measured efficiencies of the proposed MIMO array were between 59% and 73%, and its corresponding measured envelope correlation coefficients (ECCs) were better than 0.05. Furthermore, the calculated channel capacity of the proposed MIMO array with 20 dB signal-to-noise ratio (SNR) was about 38.2–39.8 bps/Hz across the desired bands (3.4–3.6 GHz). The measured results confirm that the proposed MIMO array is a good candidate for 5G terminals. [ABSTRACT FROM AUTHOR]

In this paper, we provide a detailed three-dimensional numerical analysis of the optical properties of common and modified bowtie aperture antennas integrated onto a silicon waveguide platform, to discuss the influence of geometrical parameters on the electric field enhancement factor and waveguide transmission when such antennas are excited by the evanescent field of the Si waveguide mode. We demonstrate that waveguide transmission is severely affected by the interference between Si waveguide modes and surface plasmon polariton modes excited in the antenna, while the antenna's field enhancement factor is mainly determined by the localized surface plasmon resonance occurring in its nano-gap. These mechanisms lead to a mismatch between the wavelength at which the antenna's field enhancement factor is maximized, and the wavelength at which transmission through the Si waveguide is minimized, suggesting that in some multi-mode cases, the optical properties of integrated nanoantennas determined through direct measurement of Si waveguide transmission may be misleading. Methods for improving the electric field enhancement (such that it has a bigger modulation depth) that have minimal impact on the resonant wavelength, and for improving the shape and location of the corresponding hot spot of the bowtie aperture antennas, are also discussed and analyzed. We believe that this analysis will be helpful in design of on-chip bowtie-type optical antennas for surface enhanced Raman spectroscopy, near-field optical microscopy, high sensitivity detection, and plasmonic optical tweezers. [ABSTRACT FROM AUTHOR]

A circular aperture box-horn array antenna operating in W-band, with sum and difference radiation beams, is presented in this paper. The circular aperture provides maximum usage efficiency of the area, which is well suited for a rotational platform. Nonuniform power distribution is applied for the radiating elements, contributing to a radiation pattern with suppressed sidelobe. In order to fit into the circular aperture, the feed networks are optimally arranged on a compact two-planar layer with four quadrants fed by the sum–difference network. The antenna array, along with its full-corporate feed networks, has a low profile and is easy to be machined. Measured results show that the peak gain is over 35.6 dBi from 92 to 94 GHz, with up to −21 dBi sidelobe level. In addition, the sum–difference contradictions are less than 4 dB, and the nulls of difference beams are below −25 dB. [ABSTRACT FROM AUTHOR]

The problem of optimum sparse array configuration to maximize the beamformer output signal-to-interference plus noise ratio (MaxSINR) in the presence of multiple sources of interest (SOI) has been recently addressed in the literature. In this paper, we consider a shared aperture system where optimum sparse subarrays are allocated to individual SOIs and collectively span the entire full array receiver aperture. Each subarray may have its own antenna type and can comprise a different number of antennas. The optimum joint sparse subarray design for shared aperture based on maximizing the sum of the subarray beamformer SINRs is considered with and without SINR threshold constraints. We utilize Taylor series approximation and sequential convex programming techniques to render the initial nonconvex optimization a convex problem. The simulation results validate the shared aperture design solutions for MaxSINR for both cases where the number of sparse subarray antennas is predefined or left to constitute an optimization variable. [ABSTRACT FROM AUTHOR]

This paper investigates the generation of Laguerre–Gaussian (LG) modes at radio frequencies (RFs) by utilizing either a continuous aperture or a discrete array. The mode generation can be performed with or without sidelobe control, and superdirectivity is avoided by properly selecting the system geometry and regularizing the associated inverse problem. For an individual mode, a continuous aperture source is first determined based on the singular value decomposition of the wave system. This continuous source is subsequently discretized following the construction of a 2-D quadrature rule, which, in the two extreme cases of no and maximum sidelobe suppression, results in an array grid that inherently requires a minimum number of antenna elements. A tradeoff can be made between the adopted array element number and the realized sidelobe level. A method to use a single array with a conserved number of elements to generate and multiplex multiple modes simultaneously is also developed. Full-wave simulations are used to demonstrate the application of the developed theories to arrays of realistic antennas with mutual coupling included. The study shows that, despite their origin in optics, LG modes can be accurately generated in the RF regime, and therefore still play a crucial role in orbital angular momentum (OAM)-based radio. [ABSTRACT FROM AUTHOR]

This paper presents the phase error analysis of a single-layer discrete dielectric lens that uses nonresonant unit cell and can be fabricated using low-cost PCB technology. An extensive detailed study of the nonresonant unit cell is performed to understand the phase error loss mechanism and to find the best periodicity (unit cell size or interelement spacing) that produces almost the same phase response not only at different frequencies but also for both normal and oblique incidence which leads to lower oblique phase error (OPE) loss across the lens aperture and higher aperture efficiency. Unit cells of $0.47{{\lambda }_{{94}\;{\text{GHz}}}} \leq {\rm periodicity} \leq 0.68{{\lambda }_{{94}\;{\text{GHz}}}} are studied and the optimum periodicity is addressed. Based on this study, three lenses of identical aperture area (100 \times 100 \times 6.35\;\textm\text m^3) but different unit cell sizes (0.5\lambda 94\,\text{GHz}, 0.53\lambda {94\;{\text{GHz}}}, and 0.62\lambda {94\;{\text{GHz}}}) are designed, fabricated, and tested. It is found that the maximum OPE is reduced from about 65° to less than 25°, aperture efficiency is improved by about 13.4% at 94 GHz, and the total number of unit cells is reduced by about 42.6% when periodicity changed from 0.47\lambda {94\;{\text{GHz}}} to 0.62\lambda {94\;{\text{GHz}}}, respectively. Furthermore, lens of 0.62\lambda {94\;{\text{GHz}}} periodicity will have the highest aperture efficiency of 48.7%, \textgain = 37. 8\;\textdB at 94 GHz, beamwidth \approx 1.2^\circ , {\text F}/{\text B}\;{\text{ratio}} \approx \;37.5\,\text{dB}, measured \vert{{\text S}_{11}}\vert < - 10\,\text{dB}, \textcross-pol\; < - 27\,\textdB and offers \textSLL{\text H} < - 24.3\,\textdB, and \textSLL{\text E} < \; - 18.5\,\text{dB}. [ABSTRACT FROM PUBLISHER]

This paper presents a spiraphase-type reflectarray based on reactively loaded ring slot resonators. The infinite array approach was used to optimize the unit cell geometry to obtain high aperture efficiencies and low cross-polarization levels at large reflection elevation angles \theta_0. The results of the optimization were used to design four 367-element reflectarrays for \theta_0 of 0°, 20°, 40°, and 60° operating at 36.5 GHz. The designed reflectarrays were then fabricated and tested. The experimental investigation of the fabricated reflectarrays revealed that aperture efficiencies of 0.60, 0.51, 0.42, and 0.21 along with cross-polarization levels of -25.8, -24.0, -17.8 were obtained for the reflectarrays with reflection elevation angles of 0°, 20°, 40°, and 60°, respectively, at 36.5 GHz. Additionally, it was experimentally demonstrated that for certain planes of scanning the cross-polarization level can be reduced to -19\;\textdB even for reflection elevation angles \theta_0 as high as 60°. [ABSTRACT FROM PUBLISHER]