Uniform Aperture Distribution Research Articles

Ka-Band Huygens Antenna Array With Very High Aperture Efficiency and Low Sidelobes

A Ka-band Huygens antenna array with extremely high aperture efficiency (AE) and low sidelobe levels is reported for 5G millimeter-wave (mm-wave) wireless applications. The basic array element is an innovative Huygens subarray consisting of two open rectangular waveguides that form an aperture consisting of a 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 set of orthogonal, tightly coupled electric and magnetic elements separated by a virtual gap that are balanced, in- phase, and radiate Huygens cardioid patterns. A larger 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times16$ </tex-math></inline-formula> element array is then realized with 64 of these 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2 subarrays. With excitations of equal amplitude, the full broadside-radiating array achieves an AE up to 97.5% in the operating bandwidth, which is very close to the 100% limit associated with an ideal uniform aperture distribution. Moreover, a highly efficient and compact feed network with tapered-amplitude and in- phase excitations from the array center to its edges is designed to achieve sidelobe and backlobe levels less than −20 dB. The −10 dB impedance bandwidth covers 26.7–29.65 GHz, and the peak realized AE (RAE) reaches 82%. A full-aluminum array prototype was fabricated with standard machining processes and tested. The measured performance characteristics agree well with their simulated values, confirming the efficacy of their designs.

Reactive synthesis of porous nanolaminate Ti3(Si,Al)C2 intermetallic compound

Ti3SiC2, belongs to MAX phases, usually has the characteristics of low purity and high energy consumption synthesis process. In this work, porous Ti3(Si,Al)C2 quaternary intermetallic compound was fabricated through a reactive synthesis of Ti, Si, Al and graphite elemental powders at relatively low temperature of 1300 °C. The quaternary compound has been characterized by a solid solution based on Ti3SiC2 with the purity of 99.5 vol%. The maximum pore size, open porosity and permeability of porous Ti3(Si,Al)C2 compound were determined to be 7.1 μm, 44.0% and 16.8 m3 m−2 kPa−1·h−1, respectively. The pore size distribution of porous Ti3(Si,Al)C2 exhibits a characteristic of a single main peak with the average pore size of 4.4 μm. Low-cost and easy synthesis method, high purity and uniform aperture distribution impart the new porous material potential applications in purification and separation fields.

60 GHz antenna array for millimeter‐wave wireless sensor devices using silver nanoparticles ink mounted on a flexible polymer substrate

AbstractThis paper demonstrates a mm‐wave high‐gain antenna design that is printed on a flexible polymer substrate using silver nanoparticles ranging from 50 to 200 nm in inkjet printing technology. Specifically, it shows that inkjet technology can leverage to fully fabricated antennas with this technology, where it provides both the characterization and preparation of an antenna. The initial fabrication problem addressed via ink formulation for printing a homogeneous layer with an excellent electrical conductivity. A planar series fed antenna array was analyzed by using the Transmission Line Model with tapering feed line structure. The excitation coefficients in both E and H planes follow a uniform aperture distribution. The realized antenna has 24 dBi gain, the side‐lobe level of elevation direction at the center frequency is lower than −15dB. In combination with the planar antenna structure, polymer substrate, and inkjet printing enables the production of structures with high gain that are widely applicable for mm‐wave wireless sensors and portable communication devices.

Substrate Integrated Horn Antenna With Uniform Aperture Distribution

A new substrate integrated horn antenna with hard side walls combined with a couple of soft surfaces is introduced. The horn takes advantage of the air medium for propagation inside, while having a thickness of dielectric on the walls to realize hard conditions. The covering layers of the air-filled horn are equipped with strip-via arrays, which act as soft surfaces around the horn aperture to reduce the back radiations. The uniform amplitude distribution of the aperture resulting from the hard conditions and the phase correction combined with the profiled horn walls provided a narrow beamwidth and -13 dB sidelobe levels in the frequency of the hard condition, which is validated by the simulated and measured results.

Spongy bilayer dressing composed of chitosan–Ag nanoparticles and chitosan–Bletilla striata polysaccharide for wound healing applications

The purpose of this study was to develop a promising wound dressing. Though chitosan cross-linked with genipin has been widely used as biomaterials, with the addition of partially oxidized Bletilla striata polysaccharide, the newly developed material in this study (coded as CSGB) showed less gelling time, more uniform aperture distribution, higher water retention, demanded mechanical strength and more L929 cell proliferation compared to the chitosan cross-linked only with genipin. Owning to partial blocking of free amino groups of chitosan, CSGB revealed almost no antibacterial activities, thus the bilayer composite of chitosan-silver nanoparticles (CS-AgG) on CSGB was designed to inhibit microbial invasion. The in vivo studies indicated that both CSGB and bilayer wound dressing significantly accelerated the healing rate of cutaneous wounds in mice, and the bilayer exhibited better mature epidermization with less inflammatory cells on Day 7. Therefore, this novel bilayer composite has great potential in wound dressing applications.

Evaluating the effect of internal aperture variability on transport in kilometer scale discrete fracture networks

The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer-scale field–scale fracture networks has been under a matter of debate for a long time because the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling within large-scale fracture networks. We address this question by incorporating internal heterogeneity of individual fractures into flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. A recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time and cumulative retention, are calculated along particles streamlines. It is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture variability than the tails of travel time distributions, where no significant effect of the in-fracture transmissivity variations and spatial correlation length is observed.

Ray tracing technique for shaping a dual reflector antenna system

In radio astronomy applications, antennas having the highest aperture efficiencies are requested. In order to meet this request, a reector shaping program for dual reector antennas has been developed. The design procedure is based on the geometrical optics where differential equations have been formulated to dene the ray trace of the antenna system. Recently, the fourth generation programming language MATLAB has become well known for its numerical computing environment and very useful three-dimensiona data visualization functions. The authors wished to make a dual reector shaping program by a ray tracing method in MATLAB. In this paper, details of the program are explained, and antenna ray tracing results are shown visually by three-dimensiona viewgraphs. The numerical results are compared with the theoretical ones to conrm the correctness of the developed shaping program for a Cassegrain dual reector antenna system. For uniform aperture distribution therst side lobe level is numerically obtained as {17.59 dB, which can be further reduced through shaping to {24.67 dB and {30.65 dB for parabolic and squared parabolic, respectively.

High Efficiency Short Backfire Antenna Using Electromagnetically Hard Walls

This letter presents a high efficiency short backfire antenna (SBFA) using electromagnetically hard walls. A hard surface composed of low permittivity dielectric liner with longitudinal metal surface strips is affixed to the inside walls of a conventional SBFA’s main reflector. The hard-walled SBFA was optimized to operate at L1 and L2 GPS bands with circular polarization using an R2 indicator based evolutionary multiobjective algorithm. A hard-walled SBFA with $2 \lambda $ aperture diameter at L1 achieved 90% and 98% aperture efficiency at L1 and L2, respectively. Also the antenna exhibited more than 90% aperture efficiency over 16% bandwidth around L1. Compared to a conventional SBFA with the same aperture diameter the new antenna achieves 1.25 dB higher directivity at L1 and 0.76 dB at L2, as well as improved cross- polarization due to a more uniform aperture distribution.

A 79-GHz LTCC Patch Array Antenna Using a Laminated Waveguide-Based Vertical Parallel Feed

A microstrip patch array antenna based on a low-temperature co-fired ceramics (LTCC) technology is presented in this letter. The antenna is designed for the 77-81-GHz radar frequency band and uses a high-permittivity material (er = 7.3). A laminated waveguide (LWG) was chosen as transmission line, which minimizes coupling and enables the design of LWG-based vertical power dividers. Three stages of power dividers were combined to realize a vertical parallel feeding network. With this feeding-network, the radiation pattern of the proposed antenna is nearly constant across the whole 4-GHz bandwidth. A uniform aperture distribution was chosen. In total, 12 layers of LTCC tapes were used. The measured half-power beamwidth in the E-plane is ≤ 7° across the whole working frequency bandwidth. This compact LTCC antenna (28.3 × 1.2 mm2) is suitable for short/middle-range radar applications, especially for those with a small channel spacing requirement .

A Post-Wall Waveguide Center-Feed Parallel Plate Slot Array Antenna in the Millimeter-Wave Band

A center-feed structure using cross-junctions is designed for a post-wall waveguide-fed parallel plate slot array antenna. The length of the radiating waveguide in the center-feed antenna is half of that of a conventional end-feed antenna, and the center-feed antenna is expected to enhance bandwidth depending on the long line effect. The symmetrical structure of the antenna can keep the main beam at boresight as the frequency is changed. The cross-junction is analogous to that previously proposed for a single-mode waveguide array, but it excites plane TEM waves in both directions in the oversized parallel plate. The authors have designed and fabricated a slot array with uniform aperture distribution at 61.25 GHz. The bandwidth for 1-dB gain reduction is 1.7 times as wide as that of a conventional end-feed type antenna. The sidelobe level in the E-plane increases to -7.8 dB because of the slot-free area over the center-feed waveguide, which is suppressed to -11.1 dB by introducing a -8.3 dB amplitude tapered distribution in the slot design of the array.

Theoretical Approach of the Assessment of the EM Field in the Vicinity of Aperture Antennas

In this work, an assessment of the influence of the field probes on the uncertainty in the measurements of the electric and magnetic field in the vicinity of aperture antennas is presented. A uniform aperture distribution is considered because the field of a tapered distribution aperture can be reduced to that of a uniform one. Moreover, the effect of probe size and configuration is presented through a comparison between the theoretically calculated and the expected values. Field probes of a single or more perpendicular dipoles are investigated. The maximum permissible length of the dipoles for an accurate field assessment depends on the field's gradient. In the regions where the relative amplitude and phase of the electric field along the measuring device does not exhibit considerable variation, even half-wavelength dipoles can be used. It is also found that probes with sizes less than 0.1lambda ensure measurement uncertainty less than 0.5 dB for field variation up to 7 dB/lambda

Analysis of radial line slot antennas with dielectric layers over the aperture

AbstractThe slot coupling characteristics are analyzed and the aperture distributions are evaluated for several dielectric layers loaded on the upper surface outside the radial line slot antenna. First, for the design of a uniform aperture distribution, mutual coupling is expressed approximately by an infinite array of two‐dimensional slot pairs with equal‐amplitude excitation in a model with periodic boundary walls in the two directions of an external region. Based on this approximation, the slot length and the pair spacing in the radial direction are controlled so as to design an array with a uniform aperture distribution. Next, as a model effective for an arbitrary distribution over a finite aperture, a slot array that is finite in one dimension is analyzed by the spectral domain approach. Also, if the situation with dielectric loading through a gap such as a radome is considered, it is shown that the effect on the aperture distribution can be neglected if a dielectric layer with a thickness reducing the Fresnel reflection coefficient is placed about 1/8 wavelength away. The validity of the analysis and design is confirmed by trial fabrication and measurement at 38 GHz. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(3): 19–27, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10169

Analysis of conical quasi-TEM horn with a hard corrugated section

There is an interest in using electromagnetic bandgap (EBG) surfaces to realize quasi-TEM waveguides and horns. TEM horns will have a uniform aperture distribution and a corresponding high aperture efficiency and low cross polarization. In the present paper a conical quasi-TEM horn with a hard-walled section excited in the TE/sub 11/ mode from a regular waveguide is analyzed. The hard wall is formed by longitudinal dielectric-filled corrugations. The analysis is based on a stepwise cylindrical approximation of the conical surfaces with subsequent application of the mode-matching method in combination with the method of factorization. The modal field expansion of the longitudinally corrugated cylindrical sections is found by using the asymptotic boundary condition of the corrugated surface when the corrugation period approaches zero. The indicated approach refines the data for the limiting aperture efficiency corresponding to the open-ended waveguide, and reveals strong influence of the hard section length as well as the interaction between the aperture and throat on the horn performance. It is shown that in the preferable case when the corrugations occupy the whole inner horn surface, it is possible to provide the crosspolar level below -30 dB and aperture efficiency from 85% to 95% in some frequency band up to 20% depending on the horn parameters.

A self-matching wideband feed network for microstrip arrays

A novel technique for feeding microstrip antenna arrays is proposed. It consists of a microstrip feed network designed to operate in dual standing and traveling-wave modes and provide uniform excitation to its elements with either mode. It, therefore, produces a uniform aperture distribution, regardless of the array element input impedances. The traveling wave propagates when radiating elements are matched, but resonant standing wave prevails if loads become mismatched. Since the feed network resonance does not alter the array excitation, it can be used in combination with the radiating patch resonance to broaden the impedance bandwidth. The physical reasons for such behaviors are explained and experimental verification are provided. The generalization of the concept to large arrays is also discussed.

Radial line planar monopulse antenna

In recent years, mobile satellite communications have been growing rapidly. Monopulse tracking operations for beam pointing to the satellite are often employed for those systems which, in general, require rather severe EIRP and G/T specifications. Thus, the development of a monopulse antenna with a good antenna efficiency is of great interest. A radial line planar monopulse antenna is proposed. An analysis of the probes in a radial line has been carried out which gives an understanding of why the monopulse patterns can be synthesized, and a simple and effective theory is presented about a realization of uniform-aperture field distribution. The antenna has been fabricated and the radiation characteristics have been measured which supports the theory as well as verifies the capability of the antenna for the monopulse tracking operation.

Periodic metal plate-loaded dielectric slab antenna with broadside radiation

Wave guiding properties of a periodic metal plate-loaded dielectric slab structure are investigated for obtaining surface wave antennas with broadside radiation and low voltage standing wave ratio (VSWR) characteristics. A novel technique is proposed in which dielectric phase transformers play an essential role for realizing a uniform phase distribution on the radiating aperture which is required to achieve broadside radiation. A quarter-guided wavelength spacing of the metal plates guarantees the suppression of reflections at the input port. On the basis of the theoretical results obtained, two types of antennas have been designed at 10 GHz, one having the exponential aperture distribution, the other the uniform aperture distribution. The overall antenna efficiency of the latter type has been found to be 53%, exhibiting a practical performance at microwave frequencies. >

A linearly polarized radial line slot antenna

A design for linearly polarized radial line slot antenna (RLSA) is proposed. A novel slot arrangement is presented which couples to the rotationally symmetric guided waves to produce a uniform aperture distribution with linear polarization. Basic characteristics were measured in the 12-GHz band on a model antenna. The radiation patterns indicate a reasonable cross-polarization level more than 15 dB below the copolarization. The poor VSWR response is typical for waveguide broadside arrays. A technique to suppress this reflection is to tilt the beam from the boresight. >

Technical memorandum: Bandwidth of a square hard horn

Horn antennas with dielectrically-filled longitudinal corrugations have recently been presented, and have been referred to as hard horns. Cylindrical hard horns can support a TEM wave at the design frequency, providing uniform aperture distribution and zero cross polarisation: this makes them attractive to use as compact elements in cluster feeds. In the paper the characteristic equation of a square hard waveguide is presented, and the crosspolar bandwidth is determined.

Multiple beams from linear arrays

The problem of devising a passive RF transmission line feed system to provide independent multiple outputs from a linear array is considered. It is shown that a lossless, matched feed network is possible only for uniform aperture distribution. The general feed system for connecting <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2^{n}</tex> inputs to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2^{n}</tex> elements is shown to consist of conventional hybrid junctions with associated phase shifters. In order to increase the possible number of elements in the array, the problem of finding applicable junctions more complex than the hybrid is considered. Junctions with three inputs and three outputs and with four inputs and four outputs are derived for use in multiple feed networks, expanding the number of elements in the array to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2^{l}3^{m}4^{n}</tex> .