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This article presents a millimetre‐wave (MMW) wideband multibeam antenna array with a pillbox transition using multilayer low‐temperature cofired ceramic (LTCC) technology. The mushroom structure with dual resonant modes offers wideband performance for radiating array, while an integrated pillbox reflector achieves multibeam scheme. To reduce the design complexity of electrically large pillbox system, two popular pillbox transitions are investigated with a unit model method. The proposed unit model can be used to predict the transmission performance of pillbox reflector in any incident angle. Moreover, the mushroom antenna array and power divider fed by quasi‐TEM wave are also designed using unit model, greatly simplifying the design of electrically large pillbox antenna array. In the final design, the long‐slot pillbox transition, rather than multi‐slot transition, is selected due to its ultrawideband performance and simple structure. The proposed LTCC prototype is analysed and fabricated, obtaining a good agreement between simulation and measurement. The measured results show a −10 dB impedance bandwidth of 17.6% from 31 to 37 GHz, and five beams with ±45° scanning range is achieved with sidelobe level lower than −10 dB. [ABSTRACT FROM AUTHOR]

A comprehensive theoretical analysis of two‐plane waveguide coupler with arbitrary coupling ratios in the H‐plane and E‐plane directions is provided and a design of the two‐plane coupler with 1:2 $\mathbf{1}:\sqrt{\mathbf{2}}$ coupling ratio in the H‐plane direction and 2:1 $\sqrt{\mathbf{2}}:\mathbf{1}$ coupling ratio in the E‐plane direction is reported. The analysis of the two‐plane waveguide coupler is fully refined and accomplished by the authors. To realise an arbitrary and different coupling ratio in the two directions, it is crucial to specifically constrain the transition phase of the quarter model of the two‐plane coupler for different boundaries as necessitated by mode polarity. A prototype of the proposed two‐plane coupler is manufactured and measured to verify the concept. Its performance is observed from 27.0 to 29.5 GHz (8.85% fractional bandwidth). The measurement results are basically in accord with the simulation results, demonstrating the reliability of the theoretical analysis. Finally, samples of designed conventional H‐plane and E‐plane couplers are provided, cascading of which can realise the same functionality as the proposed two‐plane coupler. Compared with one‐plane couplers, the two‐plane coupler reported realises overall miniaturisation rates in terms of length and volume around 58.4% and 50.1%, respectively. According to the demonstration and verification of the two‐plane couplers having arbitrary coupling ratios, the employment of the two‐plane couplers to replace the conventional one‐plane couplers to realise miniaturisation of 2‐D beam switching matrices will be promoted in future applications. [ABSTRACT FROM AUTHOR]

A spherical Luneburg lens made of parallel planar layers of lightweight foam with embedded conducting cylindrical inserts on a uniform hexagonal grid centered in each layer is presented. This work draws on the authors’ previous paper (Ansari et al., 2020) describing a Luneburg lens that uses cubic conducting inserts on a uniform cubic grid. This previous lens, while being of lightweight and economical construction, suffered from anisotropy resulting in a focal length that varied with the inclination of the beam relative to the orientation of the cubic grid. The lens described here largely overcomes this problem and allows for simpler and more economical construction. A prototype lens designed for the 3.3–3.8 GHz band with a diameter of 400 mm and a beamwidth of 14° was tested. Radiation patterns at wide scanning angles were nearly identical, and cross-polarization for slant incident polarization was below −25 dB on boresight and below −18 dB for all angles. A characteristic of this lens construction is its extremely high efficiency. The measured gain at the mid-band was 21.6 dBi, agreeing with simulated gain based on lossless materials to within measurement error. It is shown that wider bandwidths are obtainable if the thickness of the layers is reduced. [ABSTRACT FROM AUTHOR]

A method based on beam tracking in an underwater acoustic (UWA) time-varying channel was proposed to improve the performance of UWA spread spectrum communication systems using arrays. In the ocean, the acoustic signal reaches the receiver through various paths, and the signal on each path has its own propagation delay and incidence angle. To effectively use the time and space characteristics of the received signal in a typical timevarying or all types of UWA channels of mobile communication scenarios, the multiple signal classification (MUSIC) algorithm constantly updates the beam orientation. In addition, the receiving signal beamforming and maximum ratio combination can solve the severe inter-symbol interference in a sea channel and significantly improve the signalto-noise ratio of the received signal; the UWA spread spectrum communication system is more reliable. Through computer simulation and an actual pool experiment, a space-- time receiver for an UWA spread spectrum communication system with beam tracking was successfully implemented. [ABSTRACT FROM AUTHOR]

This article presents the design, fabrication, and testing of a modulated metasurface (MTS) antenna for monopulse radar tracking at Ka-band. The antenna consists of a circular, thin grounded dielectric layer printed by a texture of metallic patches modulated in shape and size. The patch layer can be modeled as a spatially variable capacitive impedance sheet, which together with the grounded slab contribution provides an overall, modulated, inductive boundary condition (BC). The antenna aperture is divided into four identical angular quadrants each of them radiating independent broadside beams when excited by an individual monopole launcher. Each of the four launchers excites a TM cylindrical surface wave (SW), which is progressively converted into a leaky-wave (LW) by the MTS. The four subapertures are virtually separated by properly designing the MTS modulation. To this end, the LW attenuation constant is calibrated for dumping sufficiently each individual SW, thus preventing the interaction between the adjacent regions. Therefore, the printed structure is not delimited by any physical separation, but only by a continuous change of the equivalent BCs. The monopulse-type linearly polarized $\Sigma $ , $\Delta \Delta $ , $\Delta _{\mathrm{ E}}$ , $\Delta _{\mathrm{ H}}$ beams are obtained by combining the source excitation with a simple phasing scheme. Notably, this solution does not affect the overall lightness, low profile, feed simplicity, and low fabrication cost of the structure, which constitutes an inherent advantage with respect to more traditional waveguide-based solutions. [ABSTRACT FROM AUTHOR]

Broadband satellite systems rely on multibeam antennas for reusing the spectrum and, despite the numerous beam layout options, they have persistently adopted regular patterns to ease the antenna design. Regular beam patterns, however, ultimately undermine the system’s competitiveness as they limit the achievable throughput and prevent the full exploitation of the payload’s resources. The reason behind these limitations is the inherent mismatch between the uniform way regular beam patterns provide capacity and the nonuniform distribution of the traffic which results in underloaded beams with surplus capacity and overloaded beams with insufficient capacity to meet the demand. This compels the system to face the paradox of leaving capacity unused while there is still unmet demand. In this contribution, we propose to overcome these limitations by using nonregular beam patterns specifically designed to balance the traffic among beams and match the demand to the supply. We also present a methodology for designing such patterns with excellent results in satellite communications that can be broadly adopted in multiuser/multibeam wireless systems. [ABSTRACT FROM AUTHOR]

A broadband stepped tapered slots’ endfire circularly polarized (CP) antenna and a multibeam antenna array are proposed for millimeter-wave (mmWave) applications. First, a modified tapered slot endfire antenna element is designed. Compared with the normal antipodal linearly tapered slot (ALTSA) endfire antenna, the performance of the stepped tapered slots’ antenna shows remarkable improvement, and the size of the antenna reduces effectively. The simulation and measurement results of the proposed endfire antenna show that an impedance bandwidth of 63.5% (75.1–145 GHz), an AR < 3 dB bandwidth of 50% (75.9–125.3 GHz), and a max gain of 8.8 dBic are realized, respectively. Second, to reduce fabrication and assembly requirements, a groove gap waveguide (GWG) feeding network is designed for multibeam array applications. The broadband 2 $\times $ 2 GWG network, interconnections, and transitions are designed and applied in the antenna array. Finally, a multibeam array based on the proposed endfire antenna is designed, fabricated, and measured. An impedance bandwidth up to 37.7% and a wide axial ratio bandwidth of 38.7% with a max LHCP gain of 12.8 dBic are achieved by the proposed 2 $\times $ 2 multibeam antenna array. The proposed multibeam endfire CP antenna array would be an attractive candidate for mmWave wireless applications. [ABSTRACT FROM AUTHOR]

This communication presents a Ka-band multibeam substrate-integrated waveguide (SIW) horn array implemented in a single-layer planar substrate. By conforming the array into a circular shape, the horn array covers full 360° azimuth range with 12 beams. Every adjacent beam overlaps each other at the half-power beam shoulders. A wideband matching is obtained with −10 dB reflection coefficients from 27.5 to 38 GHz. By suppressing the side-lobe levels to be lower than −20 dB, the mutual coupling between each SIW horn is less than −45 dB from 28 to 38 GHz. With a thin radiating aperture of 0.1 $6\lambda$ , a stable realized gain of each beam is achieved around 9.5 dBi, whereas it increases to 12.9 dBi when there is a conducting reflector closely beneath it. Due to the reflector, the main radiation directions tilt 30°, which enables the proposed multibeam antenna to be mounted on the ceiling while maintaining the communication for multiple users below. Results with a manufactured prototype well demonstrate the multibeam performance both in simulation and measurement with good agreement. In addition, it is compact and easy to be fabricated with common printed circuit board (PCB) techniques, also suitable to be integrated into microwave systems. It is promising for the application in beam-switched, multiple-input multiple-output (MIMO), and omnidirectional systems. [ABSTRACT FROM AUTHOR]

We present a cylindrical, multibeam, modified Luneburg lens antenna. The proposed antenna features low-profile, good impedance match, high gain, and wide angle scanning capability. We tapered the thickness of a dielectric disk along its radius to achieve the required refractive index profile of the lens in a nondispersive fashion. Seventeen dielectric-filled waveguide feeds, arranged circumferentially around the focal arc of the lens, provide almost invariant azimuthal scanning in the range of ±60° from broadside direction. The lens and the interior of the waveguide feeds are made of the same dielectric material, offering a smooth impedance transition from the feed antenna to the lens. A prototype of the antenna was fabricated and characterized. Measured reflection coefficient is better than −10 dB from 14 to 16 GHz. The isolations between feeds remain higher than 24 dB over the entire operational frequency range. We measured a maximum antenna gain of 20.5 dB with only 1.5 dB gain loss near the maximum 60° scanning angle. The proposed high-gain, multibeam antenna design can be used in a wide range of applications including automotive and surveillance radars. [ABSTRACT FROM AUTHOR]

This contribution describes the design of a multibeam parabolic reflectarray to produce two adjacent beams per feed in orthogonal circular polarization (CP) simultaneously at the transmission (Tx) and reception (Rx) frequencies in the Ka-band. The variable rotation technique (VRT) has been applied to the reflectarray cells based on two types of resonant elements, which makes it possible to provide orthogonal beams at Tx and Rx, as well as to implement an in-band optimization procedure to reduce the cross-polarization. A 90 cm parabolic reflectarray has been designed, manufactured, and tested to produce multiple adjacent beams in RHCP and LHCP at both 20 and 30 GHz. The results are satisfactory and validate the concept of generating two spaced beams in the orthogonal CP by a single feed, changing the polarization of the beam between Tx and Rx. This concept can be suitable for multispot satellites in the Ka-band, enabling to halve the number of onboard antennas and feeds. [ABSTRACT FROM AUTHOR]

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]

An alternative approach for the design of feeding networks designated for two-beam antenna arrays that ensure similar radiation patterns in a very broad frequency range has been proposed. The presented concept is based on directional filters that are utilized for smooth change of excitation signals of two broadband radiating elements and a broadband directional coupler used for ensuring quadrature excitations between two identical parts of the antenna arrays. The proposed concept has been confirmed by measurements of two-beams antenna arrays operating in frequency ratio fH/fL ≈ 2 :1 and 3:1. [ABSTRACT FROM AUTHOR]

This contribution describes the design of a reflectarray to produce two adjacent beams per feed in orthogonal circular polarization (CP) simultaneously at transmit (Tx) and receive (Rx) frequencies in the Ka band. The discrimination in CP is achieved by the variable rotation technique (VRT), whose dual band operation is validated for the first time by the manufacture and measurement of a 25 cm $\times \,\, 25$ cm reflectarray demonstrator. Moreover, an optimization procedure has been implemented to improve the narrowband performance of the VRT (which leads to high cross-polar levels when the VRT is applied). The reflectarray prototype has been designed to deviate by ±5° the beams radiated by a dual-CP feed-horn at Tx and Rx frequencies in the $Ka$ band (20/30 GHz). The results are satisfactory and validate the concept of generating two spaced beams in orthogonal CP and dual band by the VRT with a single feed. This concept can be suitable for multiple spot satellites in the $Ka$ band, enabling a reduction in the number of antennas and feeds needed to provide the multispot coverage. [ABSTRACT FROM AUTHOR]

In order to fulfill the exponential increase in the demand of high-speed wireless links, future XG wireless networks will be developed at higher carrier signal frequencies, reaching the hundreds of gigahertz. In this contribution, a leaky-wave-fed HDPE lens antenna working at ${G}$ -band which can be useful for future XG communications is presented. The proposed lens design enables the generation of up to 40 beams, with gains higher than 30 dB. Analytical tools have been applied to optimize the lens aperture efficiency, validating the results via full-wave simulations. The reached aperture efficiency for the broadside beam is higher than 80% over a 44% relative bandwidth. The measurement results for a fabricated prototype show excellent agreement with the simulated performance. [ABSTRACT FROM AUTHOR]

With sum throughputs exceeding 1 Tb/s, next-generation high throughput satellite will play a key role in 5G networks for applications including backhauling or broadband in-flight connectivity. Such satellites require the deployment of tens of $Q/V$ -band feeder links to support the data traffic in their uplink. Meanwhile, geographical restrictions and cost considerations significantly constrain the search for gateway deployment sites. Diversity strategies are, furthermore, necessary to cope with strong rain fades. In this paper, multiple-input-multiple-output (MIMO) feeder links are proposed to address these challenges. Using two active gateway antennas per feeder link, a MIMO-based solution enables to support twice the user link bandwidth per link compared to the state-of-the-art. On-ground and onboard processing strategies for such MIMO links are introduced, and the link outage probabilities are determined. An extension of smart diversity schemes to MIMO-based architectures is also presented to guarantee a sufficient robustness against rain fades. An analysis of the achieved uplink CINR demonstrates the superiority of the proposed concept and provides guidelines for an efficient design. [ABSTRACT FROM AUTHOR]

This paper proposes a compact continuous transverse stub (CTS) array that utilizes substrate integrated waveguide (SIW) technology. The CTS array includes six radiation slots and is powered by a novel linear source generator (LSG) with a parabolic reflector located on the bottom layer. The LSG converts the input wave into a planar wave that is subsequently coupled to the parallel-plate waveguide (PPW) of the CTS array through a coupling slot. By utilizing different input ports, the CTS array can produce planar waves in various directions, allowing for the production of beams with different pointing. The CTS array comprises four-layer substrates with a total thickness of only 0.24 λ 0. The measurement results show that the reflection coefficient of the array is below -10.9 dB in the operating range of 33-37 GHz. The array scanning angle theta can be up to about ±38°at the center frequency of 35 GHz, with a maximum gain of 20.9 dBi. When using the middle port feed, the measurement gain is superior to 20.1dBi and the radiation efficiency is above 87.1% in the 33-37 GHz range. Simulation and measurement results are in agreement, demonstrating that the proposed CTS array is suitable for multibeam applications in the K a -band. [ABSTRACT FROM AUTHOR]

A multibeam antenna with a single input port using a cavity‐based waveguide structure is implemented. The proposed structure uses a cylindrical cavity and a higher‐order TM21 mode is excited in it. The higher‐order mode is to divide the incoming power in three different directions. The beam in three different directions is confined by using a 3D‐printed extended hemispherical lens integrated at three openings at the cylindrical cavity. The proposed structure has measured an impedance bandwidth of 1.7 GHz from 56.9 to 58.6 GHz. The achieved beam directions for the proposed antenna structure is 0, 87 and 270°. The measured gain of the antenna for each beam directions is better than 12 dBi. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The sidelobe noise is eliminated in a specific direction. • The algorithm effectively improves the utilization of data. • The target details are effectively preserved by adjusting the soft threshold. Abstract Recording abundant back scatter information in the water, multibeam sonar water column imaging (WCI) has become one of the most effective means for the acoustic remote sensing investigation of water targets and has been applied and developed rapidly for sounding, fishery, oceanography and archaeology applications as well as in other industries in recent years. Due to the signal interference caused by the sidelobes, there is a great deal of noise in non-target areas of WCI, which reduces the accuracy and efficiency of interpretation of WCI and hinders the automatic detection and recognition of underwater objects. In this paper, an adaptive soft threshold denoising algorithm for WCI is proposed. The WCI data are divided into background areas and target-noise mixing areas by analysing the mathematical features of all angle sequences; thus, the target, noise, and sidelobe artefacts are separated using adjustable threshold parameters and by suppressing noise and sidelobe artefacts to obtain a clearer image. Lastly, the measured data are used for verification. The results indicate that the algorithm has a certain reference value for sidelobe suppression of multibeam WCI. [ABSTRACT FROM AUTHOR]

A heterogeneous medium access control (MAC) scheme (with both scheduled and random communications) is proposed for airborne networks. These networks have a hierarchical topology with a small number of powerful aircraft nodes with multibeam antennas and long-distance links at the higher level, and high-density unmanned aerial vehicle (UAV) nodes with single-beam directional antennas at the lower level. Our proposed MAC scheme has the following three parts: First, multibeam, long-distance MAC for aircraft to aircraft links: a dynamic, scheduled MAC is proposed to take advantage of the multibeam features to achieve high-throughput transmissions, and the beam locking/synchronization issues are solved; second, uplink MAC for UAV to aircraft communication: conventional IEEE 802.11n MAC is enhanced with fame aggregation and compressive-sensing-based request polling; and third, MAC for UAV to UAV links: IEEE 802.11e DCF MAC is enhanced through parameter adjustment for channel access. Our simulation results show the significant performance improvement over conventional MAC protocols. [ABSTRACT FROM AUTHOR]

This contribution describes a design concept of a reflectarray antenna to produce four adjacent beams per feed through the simultaneous use of polarization and frequency discrimination. The feed position is computed to produce two adjacent beams in different frequencies accounting for the beam squint effect, which ensures a minimum phase variation between the phase distributions at the two frequencies. The other two beams in orthogonal polarization are generated by implementing in the reflectarray a different phase shift for each polarization. This contribution presents the design, manufacturing, and measurement of a 43 cm demonstrator that operates at transmit frequencies in the Ka-band. The proposed concept can be suitable for multiple spot-beam satellites in the Ka-band, enabling a reduction in the number of antennas and feeds needed to provide the multispot coverage. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are millisecond pulses of radio emission of seemingly extragalactic origin. More than 50 FRBs have now been detected, with only one seen to repeat. Here we present a new FRB discovery, FRB 110214, which was detected in the high-latitude portion of the High Time Resolution Universe South survey at the Parkes telescope. FRB 110214 has one of the lowest dispersion measures of any known FRB (DM  = 168.8 ± 0.5 pc cm−3), and was detected in two beams of the Parkes multibeam receiver. A triangulation of the burst origin on the sky identified three possible regions in the beam pattern where it may have originated, all in sidelobes of the primary detection beam. Depending on the true location of the burst the intrinsic fluence is estimated to fall in the range of 50–2000 Jy ms, making FRB 110214 one of the highest fluence FRBs detected with the Parkes telescope. No repeating pulses were seen in almost 100 h of follow-up observations with the Parkes telescope down to a limiting fluence of 0.3 Jy ms for a 2 ms pulse. Similar low DM, ultrabright FRBs may be detected in telescope sidelobes in the future, making careful modelling of multibeam instrument beam patterns of utmost importance for upcoming FRB surveys. [ABSTRACT FROM AUTHOR]

It is difficult to effectively rectify or convert low power in the circuit stage of harvesters. The high-gain antenna can offer a higher level of power and is beneficial to RF power harvesting in a low power density environment. To extend the narrow beam of the conventional high-gain rectenna, the multiport and multibeam antenna is promising. To pursue a simple configuration and avoid extra beamforming networks, a traveling-wave grid-array antenna (GAA) with two isolated ports and two symmetrically tilted beams is proposed. A prototype is designed and fabricated after a detailed analysis of the GAA with tilted beams and the coplanar stripline-based rectifier. The measured results show that the proposed rectenna is sensitive and effective in a wide-angle range. The harvesting angle range is extended by combining two tilted beams and can be greater than 70°, where the level of dc power exceeds $100~\mu \text{W}$ when the power density is as low as $1~\mu \text{W}$ /cm2. A maximum dc output of 3.6– $203.8~\mu \text{W}$ and a maximum RF-to-dc conversion efficiency of 16.3%–45.3% are available at 2.45 GHz, under the condition that the power density ranges from 0.052 to $1~\mu \text{W}$ /cm2. [ABSTRACT FROM AUTHOR]

This paper describes a 3-D bifocal design technique for offset dual-reflectarray antennas (DRAAs) with application to multibeam satellite antennas in Ka-band. The bifocal technique has been used to obtain beams closer than those obtained with a single-focus antenna and, at the same time, to improve the performance of the extreme beams. The technique has been applied to design a multibeam DRAA in an offset compact range configuration to provide 1.12° separation between adjacent beams at 19.7 GHz. A small-scale bifocal DRAA demonstrator has been designed, fabricated, and tested. The demonstrator generates 10 beams alternating in dual-linear polarization when the antenna is illuminated by five adjacent feeds, but the technique can be extended to circular polarization. The results are in a good agreement with the design requirements in the frequency band from 19.2 to 20.2 GHz. [ABSTRACT FROM AUTHOR]

We fabricated silicon (100) membranes of 3 mm in diameter on the surface of silicon-on-insulator (SOI) substrates and investigated the characteristics of the membranes. The handle layer of one SOI substrate was etched using deep reactive ion etching process with the buried oxide (BOX) layer that remained together with the device layer. The BOX layer of the other SOI substrate was removed using C4F8-based plasma etching after the handle layer etching. The surfaces of both silicon (100) membranes were observed using the scanning white light interferometer system at room temperature. Both silicon (100) membranes have dome-like deformations. The silicon (100) membranes are effectively flattened by etching the BOX layer under the device layer. Both silicon (100) membranes were cooled from room temperature to 4 K by a Gifford-McMahon refrigerator. Wrinkles appeared on the surfaces of both silicon (100) membranes when the temperature dropped to about 200 K. However, the wrinkles disappeared below about 180 K. This phenomenon indicates the wrinkles at low temperature would depend on the properties of the silicon (100) of the device layers and independent of the properties of the BOX layers under the silicon (100) membranes. [ABSTRACT FROM AUTHOR]

A standing-wave slot array covered with a two-layer dielectric slab based on substrate integrated waveguide (SIW) technology, which is circumferentially conformed to a cylinder, is designed, fabricated and measured at Ka-band. The radiating part consists of seven slotted cylindrical SIWs, each of which has four-element longitudinal slots. Several such slot arrays fed by Rotman lenses are grouped on a cylinder along the circumferential direction to cover a 2D field of view. The microstrip Rotman lens is employed as the beamforming network with seven input ports, which can generate a corresponding number of beams to cover -35° to 35° along 1D (E-plane). Another dimension (H-plane) is covered from -52° to 52° with four beams generated by the slot arrays group. A prototype antenna is fabricated, the measured results demonstrate its ability of scanning over a 2D field of view with multiple beams. This type of multibeam conformal antenna is a good candidate for high-speed vehicles or communication base stations requiring electronic beam-scanning capabilities and considering conformal reasons. [ABSTRACT FROM AUTHOR]

This paper proposes a fast far-field estimation method of electrically long antenna in compact measurement space. The presented method estimates a far-field pattern on an orthogonal cut plane from the linear equivalent electric current and circular current distribution. The equivalent electric current data is measured in a reactive near-field region using a small loop probe. In the proposed method, the linear equivalent current distribution is extended by a simple numerical extrapolation formula for improving the accuracy of the estimated far field in the broadside direction. In the horizontal plane, the far-field pattern is calculated from both the circular equivalent electric and the magnetic distribution approximating equivalent magnetic current with equivalent electric current. We confirmed the validity of the proposed method from the numerical simulation and measurements results. The method allows accurate directivity measurement in a small space in about a few minutes. [ABSTRACT FROM AUTHOR]

A novel full-digital multibeam array with wide scanning angle and enhanced beam gain is proposed for millimeter-wave massive multiple-input multiple-output applications. The array consists of 16 dual exponentially tapered slot antenna (DETSA) elements. Each element is integrated with a radio frequency receiver, an intermediate frequency chain, and an analog-to-digital converter (ADC). The H-plane radiation pattern of the proposed DETSA is very wide to enable the beam scanning in the azimuth plane. The beam gain is further enhanced by employing a 1-D multilayered planar lens that transforms the spherical wave into a plane wave in the E-plane for increasing the beam gain and keeping the phase compensation unaltered in the H-plane. Meanwhile, the planar lens is optimized to guarantee the wide scanning angle. In addition, all the signals received by the 16 independent channels are converted to a digital signal via ADC simultaneously and then used for synthesizing the multibeam patterns in the digital domain. Furthermore, the calibration and the verification of the synthesizing weights are discussed in detail. The measured results show that a scanning coverage of ±40° in the H-plane (or in horizontal plane) and an estimated maximum gain of 24.8 dBi with a gain tolerance of 3 dB can be achieved by the proposed 16-element array with a 1-D lens. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to formulate an aggressively thinned sparse antenna array suitable for orthogonal multibeam receiver applications. The power patterns of $M \times N$ element planar rectangular array are first reduced to orthogonally placed cross multiplicative subarrays. These arrays are then redistributed using a compressive sensing (CS) approach in order to achieve array thinning along two 1-D subarrays for a fixed steered beam projection. A multibeam synthesis approach is then implemented which permits efficient beam maxima as well as a null placement of multiple interlaced far-field patterns. Numerical examples are presented to show the implementation of the proposed approach. [ABSTRACT FROM AUTHOR]

This communication presents a shaped reflector antenna for radiating five quasi-orthogonal beams for radio coverage of mobile communication at 38 GHz. The feeds are miniaturized by replacing the horn section of the waveguide with a lens structure to avoid an over-crowded accommodation. This configuration has the advantages of subdividing the coverage area and radiating dual-polarized fields to enhance the communication capacity by using a single set of antennas. The overlapped pattern spans an angular coverage of 51° with an efficiency of 88%, which is particularly suitable for mobile cell networks. The numerical and measurement results in terms of radiation patterns and the subsequent results of network modeling are discussed to demonstrate the characteristics of radiation and beam orthogonality. [ABSTRACT FROM AUTHOR]

We demonstrate a method for obtaining optical coefficients over a broad terahertz spectral range from 1.5 THz to 16 THz at room temperature. Based on the interferograms directly acquired by a Fourier transform infrared spectrometer (FTIR), multi-beam interference principle combining Fresnel’s formula is employed to extract the refraction index and the extinction coefficient, giving the basis for calculating dielectric coefficients. It avoids the uncertainty and phase instability while using Kramers–Kronig (KK) relations and overcomes the limited frequency range of terahertz time-domain spectroscopy (TDS). Moreover, this method has better stability and is needless of cutting useful information between neighboring interference peaks for thin samples compared with TDS, making it a general processing method for interferograms and a good alternative for terahertz dielectric measurement. [ABSTRACT FROM AUTHOR]

A multibeam antenna consisting of a set of four L-shaped microstrip line sections is presented for pattern switchable applications. A planar electromagnetic band gap substrate is implemented to reduce the antenna profile to λ2.45/35, where λ2.45 is the free space wavelength at a design frequency of 2.45 GHz. An impedance matching network is integrated on the lowest layer below a ground plane. The microstrip lines have a resonant frequency of 2.45 GHz and are excited separately. When one of the strips is excited, the antenna generates a tilted beam with a gain of 8.6 dBi. By switching the excitation strip sequentially, a full azimuth beam steering is achieved. When the antenna is located above a large conducting reflector, the antenna maintains its performance. Thus, the antenna is a candidate for moving objects with high speed internet and vehicular tracking. [ABSTRACT FROM AUTHOR]

This paper presents an automatic, rigorous, and robust method to determine a Multi-Beam Echo Sounder (MBES) and Inertial Measurement Unit/Inertial Navigation System (IMU/INS) latency calibration. The latency may be due to the IMU/INS itself, but also to the time-tagging configuration, which is generally left to the survey systems user. One survey strip over a flat seafloor is the required configuration of line for using this approach, called Multibeam IMU/INS Latency Automatic Calibration (MILAC), standing for MBES to IMU/INS Latency Automatic Calibration. The algorithm considers only data with maximum latency effects and integrates an automatic data selection for this purpose. The latency estimation procedure is based on an iterative Least Square adjustment method followed by a statistical analysis. Our process can deal with beam acoustic refraction caused by the speed of sound in sea water. The accuracy of MILAC is about 2 ms (millisecond) and its average precision of 0.15 ms. MILAC is able to determine the latency with an average resolution of 5 ms. However, the morphology of the survey line is restricted to smooth and regular seafloor and the survey platform should have a relatively high attitude rate. [ABSTRACT FROM AUTHOR]

A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband $4\times 4$ SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications. [ABSTRACT FROM AUTHOR]

The western continental margin of India and the adjacent deep ocean basins were formed by break-up and separation among India, Seychelles and Madagascar since the Late Cretaceous. The initial India-Madagascar separation and the subsequent India-Seychelles separation are believed to have been caused by the Marion hotspot at ~90 Ma and the Réunion hotspot at ~68.5 Ma, respectively. These geodynamic events resulted in the formation of several bathymetric highs that probably represent imprints of these volcanic events. In the present study these bathymetric high features were mapped comprehensively to understand their morphotectonic characteristics, using a fresh set of multibeam bathymetry, sea-surface gravity and magnetic anomalies, complemented by the available multichannel seismic reflection sections. A high-resolution bathymetric map of the southwestern continental margin of India and the adjoining deep offshore regions has been generated to decipher detailed morphological configuration and distribution of prominent undersea bathymetric features. We also carried out detailed morphometric analysis of these features to deduce the morphological parameters. A total of 33 individual bathymetric high features were identified and classified as seamounts, hills, knolls, guyots and plateaus based on the standardization of undersea feature names published by Intergovernmental Oceanographic Commission (IOC) and International Hydrographic Organization (IHO) in 2013. Multichannel seismic reflection, sea-surface gravity and magnetic data were used to describe the sub-seafloor configuration and qualitative interpretation of the geophysical signatures associated with the bathymetric highs. Interpretation of the multichannel seismic reflection sections suggest that some of these identified features are extrusive in nature, while others are intrusive. These features are associated with characteristic gravity highs superimposed over regional negative anomalies and complex negative and positive magnetic anomalies. The study results suggest that the genesis of the bathymetric highs mapped in the study area could be attributed to the hotspot volcanism, caused by the Marion or Réunion hotspots. We infer that the features in the southwestern continental margin of India closer to the Alleppey-Trivandrum Terrace Complex might have been created by the Marion hotspot volcanism, while those in the Laccadive Basin and eastern sector of the Laccadive Plateau might have been formed by Réunion hotspot volcanism. [ABSTRACT FROM AUTHOR]

Linear random antenna arrays are usually studied in conjunction with uniform excitations with, at most, a linear phase shift in order to steer the main beam. This offers some advantages in terms of the feeding network but puts limitations on the array factor that can be obtained. The authors introduce unequally excited random arrays whose excitation currents are obtained by suitable transformations of the random variables related to the element positions. Besides, the first- and secondorder statistic characterisation, the uniform norm (i.e. the supremum) of difference between the mean (the desired one) and the actual array factors is estimated. In particular, while in the general case, this is achieved only via a Monte Carlo study, for the case of symmetric arrays (where the elements are randomly deployed symmetrically with respect to the array aperture centre) that norm is analytically estimated using the up-crossing theory for random processes. It is shown that the proposed unequally excited random arrays, unlike some other previous approaches, allow shaping the mean radiation pattern. However, the procedure in general yields reduced achievable performance. Therefore, the theoretical findings are checked through some numerical examples only for the important class of multi-beam array factors. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is emerging as a key technology for the minimization and integration of microwave antenna systems. Among the several AM processes, selective laser melting (SLM) is rather convenient for waveguide components, since it allows for all-metal parts with a mechanical accuracy within 30–60 $\mu \text{m}$ and an equivalent surface electrical resistivity in the range of 10–20 $\mu \Omega \text {cm}$. This paper reports on the assessment of the SLM applicability to the manufacturing of dual-polarization waveguide components operating in Ka-band, namely, a septum polarizer, a smooth-wall feed horn integrated with the septum polarizer, and an orthomode transducer (OMT). In order to achieve high electromagnetic performance in the Ka-band, the architectures have been optimized for the manufacturing process, above all in terms of orientation on the building platform and minimization of supporting structures. As a consequence, the corresponding prototypes exhibit measured performances in significant agreement with the predicted values. As an example, the return loss of all the components has been measured to be as high as 25 dB, while the measured isolation between the rectangular waveguide ports of the OMT is better than 47 dB. [ABSTRACT FROM AUTHOR]

A dual-beam filtering patch antenna consisting of a slotted patch, a metal strip underneath the patch, two pins, and a ground plane is proposed for wireless communication application. A wide operation band with stable symmetrical dual-beam far-field radiation pattern is obtained, and two radiation nulls at the lower and the upper band edges, respectively, are controlled to ensure a sharp rolloff rate at the band edges for both reflection coefficient and realize gain. Undesired higher modes can be suppressed over the stopband by changing the spacing between the patch and ground pane With entire height of $0.058~\lambda _{0}$ , the proposed antenna is implemented to show a −10 dB bandwidth of 3.0–3.8 GHz, a consistent realized gain of about 6.8 dBi within the passband for both two radiation beams directed at ±30°, out-of-band radiation suppression level of higher than 17 dBi, and good band-edge selectivity. [ABSTRACT FROM AUTHOR]

A dual-layer multibeam conformal slot array antenna operating at a center frequency of 10 GHz is proposed in this paper. The antenna consists of a microstrip Rotman lens and a substrate-integrated waveguide (SIW) array of $10{\times} 10$ radiating slots, which is axially mounted onto a cylindrical surface with a radius of 90 mm, i.e., $3\lambda _{0}$. The Rotman lens feeds the slot array through the coupling slots in the broad sides of the SIWs. An improved design process is introduced for realizing a conformal Rotman lens for cylindrically conformal arrays. There are unique requirements for the phase distribution and phase compensation in cylindrically conformal applications. The Rotman lens and slot antenna are built and optimized in full-wave simulation software. To validate the proposed concepts, a conformal antenna prototype is implemented and measured. The experimental results demonstrate a scanning range of ±46°, with a −3 dB crossover level between adjacent radiation beams in the E-plane and a −20 dB sidelobe level in the H-plane. The measured and simulated radiation patterns of all the scanned beams are in good agreement. This type of multibeam conformal slot array has been theoretically and experimentally studied, and it demonstrated the potential for applications in aircraft, missiles, and high-speed vehicles. [ABSTRACT FROM AUTHOR]

An amplitude-comparison monopulse slotted waveguide antenna array with a pillbox parabolic quasi-optical beamforming network is proposed in substrate integrated waveguide (SIW) technology in the 24 GHz band. The beamformer is illuminated by a cluster of horn pairs located in the focal plane of the pillbox reflector. Each horn pair is composed of two H-plane sectorial horns connected to a coupler. In-phase and out-of-phase operations of each horn pair allow radiation of the $\Sigma $ and $\Delta $ beams along the antenna scanning plane (E-plane). At the design frequency of 24.15 GHz, the experimental results demonstrate an antenna field of view of ± 26°, with null depth better than −20 dB for all the measured $\Delta $ beams. The antenna gain varies between 21.6 and 20.5 dBi for the $\Sigma $ beams and the measured input reflection bandwidth is about 2.4% for VSWR < 2. [ABSTRACT FROM PUBLISHER]

Multi-Beam Smart Antennas (MBSAs) achieve concurrent communications in multiple beams, thereby providing higher throughput compared to regular directional antennas. Most of the transport control schemes used today are based on TCP, which is too conservative since it indiscriminately reduces the window size upon any packet loss. The other extremity is the de-congestion control strategy, which abandons both window size control and retransmission, aggressively saturates the network, and compensates packet loss via network coding. To adapt to the features of the MBSA-based networks, this paper proposes a balanced transport control strategy between the above two categories, which is based on the idea of Adaptive Batch Coding (ABC). The proposed ABC scheme resists random loss through redundant coding and copes with congestion via window shrink and retransmission. Using a cross-layer design (between transport and routing layer), both the coding scheme and the traffic allocation are adaptively adjusted according to network conditions. A customized simulation system has been developed to comprehensively evaluate the performance of the proposed ABC protocol. Experimental results show that the proposed scheme overcomes the drawbacks of those two extremities. It achieves both high throughput and high throughput (under packet loss) in MBSA-based networks. [ABSTRACT FROM PUBLISHER]

A slot array in substrate-integrated waveguide (SIW) technology fed by a microstrip Rotman lens is proposed. This compact multibeam antenna is designed in two layers using a novel transition based on double-stepped coupling slots on the broad wall of SIWs. Compared with a rectangular transverse coupling slot, this transition is broadband and its coupling power can be controlled for low-sidelobe applications. The radiating part is a 10 × 10 slot array and the beam-forming network can generate seven beams with good coverage from −30° to 30° in the azimuthal plane. To validate the proposed concept, an antenna prototype is implemented at 10 GHz. The frequency response and measured radiation patterns are in good agreement with simulated results provided by full wave simulation software. Experimental results show that the sidelobe level is lower than −21 dB for the central beam in both H and E planes and better than −18 dB for the edge beams. [ABSTRACT FROM AUTHOR]

A planar millimeter-wave 2-D beam-scanning multibeam array antenna fed by compact 16-way beam-forming network (BFN) in multilayered substrate integrated waveguide (SIW) technology is addressed. The BFN is formed by connecting two stacks of sub-BFNs, the E-plane sub-BFN and the H-plane sub-BFN. The H-plane sub-BFN is realized by a traditional H-plane $4 \times 4$ Butler matrix (BM). The key point of this design is to propose an E-plane $4 \times 4$ BM which realizes a planar E-plane sub-BFN. These two sets of sub-BFNs can joint directly without resorting to any connectors or connecting networks to form such a compact 16-way BFN with a reduced area of merely $3\lambda \times 12\lambda $ . After that, to be compatible with the proposed BFN, a ladder-type $4 \times 4$ slot antenna array is employed, which is comprised of four linear $1 \times 4$ slot antenna arrays. Different from traditional array, the four subarrays are distributed in separate layers for the purpose of jointing to the BFN more conveniently. Transition network are also required to connect the BFN with the antenna array. Finally, a compact 2-D scanning multibeam array antenna based on the planar SIW BFN are fabricated and measured, which would be an attractive candidate for 5G application. [ABSTRACT FROM PUBLISHER]

A compact UWB (6–18 GHz) multibeam antenna system is proposed. Design procedures comprising of ridged coaxial waveguide, radome with lens properties, and biconical antenna are presented. A novel UWB feed network consisting of a ridged coaxial waveguide with eight inputs has been designed and optimized to achieve minimum reflections as well as desired radiation pattern over the frequency range of operation. The radiating element is a biconical antenna, redesigned and optimized to meet the requirements for radiation characteristics. Another notable improvement made by our design is to employ a radome, which not only enhances the mechanical stability of the biconical antenna and protects the structure, but also it acts as a lens that improves the directivity of the radiating element. Extensive optimization procedures have been applied to all parts of the antenna system to achieve the desired performance. The whole system has been simulated using HFSS full-wave simulator. The measurement results of the fabricated system are in good agreement with simulations. [ABSTRACT FROM AUTHOR]

A novel wide-angle beam-scanning phase synthesis method, namely, multibeam phase matching method is introduced in this paper. It takes full advantage of angle sensitivity characteristic of reflectarray elements to improve the beam-scanning performance of reflectarrays. In the process of reflectarray aperture synthesis, the beam deviation factors and reference phases are optimized to minimize the total phase error, and the geometries of each element are optimized to match the desired phase shifts at multiple beam-scanning angles after taking into account the real incident angles. Then, a $16 \times 16$ -element reflectarray antenna with square patch elements operating at 12 GHz has been designed, simulated, and fabricated. The measured results show that a gain variation less than 1.7 dB across the scan coverage from −45° to +45° can be achieved by mechanically rotating the feed antenna, which shows a considerable improvement in beam-scanning performance as compared to the reflectarrays designed using conventional single-focus and bifocal methods. [ABSTRACT FROM AUTHOR]

A novel class of circular polarization selective surfaces (CPSSs) consisting of a pair of planar split-ring resonator arrays is proposed. A significant advantage of the proposed structure over existing designs is its manufacturing simplicity compatible with standard printed technology processes. Its operating principle is reviewed alongside that of the Pierrot cell and in light of the linear polarization reflection and transmission characteristics of CPSSs. Guidelines for the initial design of the proposed CPSS concept are thus derived. Further design considerations and tradeoffs are also discussed. The validity of the concept is confirmed by means of a design example entailing a right-hand CPSS at 20 GHz. Full-wave simulation results and experimental testing on a fabricated prototype are presented and agree well with the theoretical predictions. [ABSTRACT FROM AUTHOR]

A novel concept of multibeam antenna arrays operating in an octave frequency band has been presented. To achieve multiple beams in such a wide bandwidth N-element antenna arrays are fed by frequency-dependent Butler matrices which smoothly change their properties across the bandwidth. The proposed Butler matrices are designed in such a way that for the selected inputs their amplitude and differential phase characteristics feature the ones obtained for N \times N Butler matrices at f_{0} , whereas at 2f_{0}$ they feature the properties of $N/2 \times N/2$ Butler matrices. The proposed concept has been verified by measurements of a multibeam antenna array operating in 1.75–3.5 GHz frequency range and extended showing the possibility of designing antenna arrays with higher number of beams. [ABSTRACT FROM AUTHOR]

In this paper, a power allocation in multibeam satellite (MBS) communication based on heuristic particle swarm optimization (PSO) is proposed. The PSO algorithm is evocated to solve the problem of power allocation in the multiple narrow spotbeams aiming to provide the minimum signal-to-noise plus interference ratio (SNIR) required by Earth station users to establish reliable communication. In the developed model it is considered the multibeam interference and the different channel conditions of each beam by rain attenuation. The numerical results have been generated taking into account different sky situations, including clear and rainy scenarios; such results have revealed the viability and accuracy of the PSO algorithm deployment in solving the power allocation problem. In addition, with the proposed scheme it is observed the decrement of transmitted power for non-rainy beams with guarantee of the minimum SNIR at the Earth receivers input, while increase the power availability to the rainy beams; as a consequence, the overall energy efficiency of the MBS system has been improved substantially. Moreover, the convergence of the proposed heuristic PSO-based algorithm is discussed while such heuristic approach comes with computational complexity reduction when compared with others efficient power allocation schemes. [ABSTRACT FROM AUTHOR]

This communication presents a compact 94-GHz 2-D multibeam antenna using the low-temperature co-fired ceramic (LTCC) technology. A good 2-D substrate integrated waveguide (SIW) beam-forming network (BFN) for eight beams is proposed, where four-phase shifters are properly introduced to increase the flexibility of the beams. Benefiting from multilayer LTCC, the BFN is compactly implemented in a completely symmetrical structure by using two multifolded SIW Butler matrixes with 50% reduction of the longitudinal size, and four couplers placed on different layers with interlaced signal routes to avoid overlaps or crossovers. Combined with a $2 \times 4$ SIW slot antenna array, the multibeam antenna can realize eight symmetric scanning beams on 2-D with stable gains for a wide coverage. For demonstration, the two single-port antennas with different pitch-angle beams are fabricated and measured, and good agreements with the expectations are observed. The differences of the beam orientations are less than 5°, while the measured peak gains of the beams are about 8.5 dBi. [ABSTRACT FROM PUBLISHER]

A novel triple-layer dual-mode meta-atom wherein an H-shaped structure is combined with a pair of symmetric patches is proposed. The composite structure substantially lowered the operation frequency, and balanced phase agility with transmission magnitude bandwidth. The transmission phase limit of the proposed composite structure approaches the theoretical limit. Because this structure has appealing features, we employed a set of these ultrathin meta-atoms to implement the phase distribution of an optimized array using the alternating projection method. An X-band single-feed quad-beam transmitarray consisting of $25 \times 25$ elements, each carefully designed to exhibit the desired transmission phase, was designed, simulated, physically implemented, and measured. Feeding the meta-array using a horn at its focus, four-beam radiation patterns with satisfactory sidelobe levels and gain were numerically and experimentally demonstrated. The peak gain was found to be 18.8 dB at 9.6 GHz, and the aperture efficiency was calculated as 38.3%. Moreover, the half-power beamwidth of the array antenna was approximately 7°, which was 50° narrower than that of a bare feed horn. Moreover, the gain of each beam was higher than 17 dB in all studied cases, which was at least 7 dB higher than that of a bare feed horn. [ABSTRACT FROM PUBLISHER]

This paper presents a novel surface-wave (SW)-based high-impedance surface (HIS) multibeam antenna with 360° scanning capability in azimuth. The proposed antenna consists of four rotationally symmetric beamforming networks (BFNs) and a microstrip patch array-based HIS. Regarding to the BFN, it is formed by a planar offset parabolic reflector fed by multiple substrate integrated waveguides. Through proper design, the proposed BFN can efficiently launch guided SWs with TM0 mode. With the perturbation of the HIS structure, the bounded SWs can be transformed to $m=-1$ space harmonic mode leaky-wave radiation. Combining the feature of the leaky-wave radiation in the elevation plane and the manipulation of the propagation direction of the SWs by switching the feeding ports, beam scanning in the azimuth direction with a tilted elevation angle can be realized. As the HIS is shared by the four BFNs, the size of the antenna can be reduced and a broadened antenna scanning range is achieved. In this paper, a prototype of the proposed antenna with 28 feeding ports, 7 in each BFN, is numerically analyzed and experimentally demonstrated. The proposed antenna features low-cost, low-profile, and single layer configuration. [ABSTRACT FROM PUBLISHER]