Antenna Substrate Research Articles

Moisture-Resistant Polyimide Aerogels Containing Propylene Oxide Links in the Backbone.

Polyimide aerogels made using anhydride-capped oligomers from 4,4'-oxydianiline (ODA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) cross-linked with 1,3,5-tri(aminophenoxy)benzene (TAB) have been reported with very good mechanical properties but poor resistance to moisture. Replacing 50 mol % of the ODA with poly(propylene glycol)bis(2-aminopropyl ether) (PPG) with an average molecular weight of 230 g/mol in the oligomer backbone gives aerogels with water contact angles of 80°. The aerogels also absorb very little moisture on soaking in water. The aerogels also shrink less with increasing PPG concentration and therefore have significantly lower density and higher porosity than those made without PPG. Mechanical properties of the aerogels increased with increasing density, regardless of the polymer backbone. Brunauer-Emmett-Teller (BET) surface area of the aerogels studied ranged from 300 to 400 m2/g, depending mainly on PPG concentration. The high moisture resistance makes them promising materials for substrates for lightweight antennas as well as insulation for a variety of applications.

High gain, directive and miniaturized metamaterial C-band antenna

AbstractIn this paper, design and analysis of U–T-shaped metamaterial antenna have been presented. It shows negative permittivity and permeability characteristics. The metamaterial array is embedded inside the substrate of rectangular microstrip patch antenna. Upon incorporation, directivity increases by 24% and gain increases by 18%. Results were compared with equivalent circuit analysis of patch antenna and are well in coherence with FEM (finite-element method)-based Ansoft HFSS (high-frequency structure simulator) simulation with around 1% error. Using fractal metamaterial antenna of first and second order iterative mathematics, antenna is miniaturized by 58 and 75% along with improvement in bandwidth.

A Comparative Study of the Effects of Substrate Composite Materials on External and Internal Handset Antenna EM Absorption

Cellular phones are used in the vicinity of a human head, which absorbs power from antenna radiation. This investigation analyzes the effects of antenna substrate materials on electromagnetic (EM) absorption in a human head. Antennas are used in analysis with four different dielectric substrate materials, which are Bakelite, FR4 glass epoxy, Rogers R04003, and Taconic TLC. Moreover, two different thicknesses of each substrate are considered in the experimental setup. The EM absorption associated with two types of cell phone antennas is evaluated in the closed vicinity of the human head model. One of them is planar inverted-F antenna (PIFA), which is used as the internal handset antenna and another one is helical antenna, which is used as external handset antenna. This investigation consists of two different operating frequency bands, GSM 900 MHz and DCS 1800 MHz. The EM absorption in the human head is presented using the peak specific absorption rate (SAR) and total absorbed power (TAP) by the user. The finite-difference time-domain (FDTD) method based on Computer Simulation Technology (CST) Microwave studio is utilized in this investigation. The obtained results show that the substrate materials do not effect SAR and TAP values considerably for both antennas, but substrate thickness affects the SAR and TAP values significantly. In addition, the substrate thickness affects the SAR and TAP values significantly in most of the cases Moreover, PIFA produces lower SAR than that of a helical antenna significantly for both GSM and DCS frequency band. DOI: http://dx.doi.org/10.5755/j01.ms.22.3.8889

Single End-Fire Antenna for Dual-Beam and Broad Beamwidth Operation at 60 GHz by Artificially Modifying the Permittivity of the Antenna Substrate

A technique is proposed to generate a dual-beam and broad beamwidth radiation in the $E$ -plane of a printed bow-tie antenna operating over 57–64 GHz. This is achieved by artificially modifying the dielectric constant of the antenna substrate using arrays of metamaterial inclusions realized using stub-loaded H-shaped unit cells to provide a high index of refraction. The H-shaped inclusions are tilted with respect to the axis of the antenna and embedded in the direction of the end-fire radiation. The resulting dual-beam radiation in the $E$ -plane has maxima at +60° and 120° with respect to the end-fire direction (90°), with a maximum peak gain of 9 dBi at 60 GHz.

Gain Enhancement of Planar Antenna Enabled by Array of Split-Ring Resonators

This communication proposes a high-gain bow-tie antenna operating over the frequency band of 5.5–8 GHz. The proposed antenna is comprised of a microstrip-to-slot transition line connected to bow-tie radiators. Seven slabs of split-ring resonator (SRR) unit cells are integrated into the orthogonal plane of antenna substrate to enhance its gain. Each slab consists of $2 \times 7$ double-sided SRR unit cells. A prototype of the antenna is fabricated and measured. The results indicate that the reflection coefficient is better than −10 dB over the frequency band of 3.5–8 GHz. The measured antenna gain varies from 10.2 to 13.8 dBi over a frequency range of 5.65–7.8 GHz. The measured radiation efficiency corresponds to 90% at 7 GHz. The cross polarization is better than −30 dB in the $E$ -plane at 6.5 GHz.

Substrate-Integrated Two-Port Dual-Frequency Antenna

A two-port dual-frequency substrate-integrated antenna with a large frequency difference is presented. It consists of a differentially fed slot antenna and a substrate-integrated dielectric resonator antenna for low- and high-frequency radiation, respectively. The former is loaded by a hollow patch, whereas the latter is fabricated inside the hollow region of the patch by using air holes and metalized vias. Beneath the antenna substrate is a second substrate on which slot-coupled sources are printed to feed the two antennas. For demonstration, a two-port dual-frequency antenna working at 5.2-GHz WLAN band and 24-GHz ISM band was designed, fabricated, and measured. The S-parameters, radiation patterns, and antenna gains of the two antenna parts are reported. Reasonable agreement between the measured and simulated results is observed. Very good isolation of over 35 dB between the two antenna parts is observed.

Broadband compact microstrip patch antenna design loaded by multiple split ring resonator superstrate and substrate

We present microstrip patch antenna loaded with multiple split ring resonator substrate and superstrate. We analyze how the loading of split ring resonator superstrate and substrate can improve the bandwidth compared to the simple microstrip patch antenna and microstrip patch antenna loaded with split ring resonator superstrate. Another important observation is made for multiple split ring resonator loading in superstrate and substrate of microstrip patch antenna. The design is compared for two, three, and four-ring split ring resonator loading. The designs are also compared for different gap spacing between the rings. All three designs are compared for small gap and large gap between the rings. The design results in the form of reflection coefficient and bandwidth is presented in this manuscript. The design results are also compared with previously published designs.

RETRACTED: Miniaturization of body worn antenna using nano magneto-dielectric composite as substrate in C-band

Abstract It is preferable to have small size conformal microstrip patch antenna for body worn applications. Size reduction is generally carried out by using magneto-dielectric material. Nanosized Ni 1− x Zn x Fe 2 O 4 ( x =0.25, 0.50 and 0.75) of crystallite size ~32 nm is synthesized as magnetic filler and dispersed in flexible linear low density polyethylene (LLDPE) matrix. The filler concentrations are varied as 1, 3, 5 and 7 wt% in the composite. The developed composite is tested for suitability to be used as substrate for microstrip antenna by determining its permittivity, permeability and losses in the C-band (4–8 GHz). Other relevant parameters like, tensile strength, water absorbance and decomposition temperature of the composite are also determined. The real part of complex permittivity of the composite varies from 2.23 to 2.38 and complex permeability from 1.25 to 1.46 for different filler concentrations. Verification of the composites as potential substrates for body worn antenna is carried out by fabricating simple rectangular patch antenna at 6 GHz on it using transmission line model. Rectangular patch for x =0.50 for 7 wt% shows S 11 of −30.44 dB and −10 dB bandwidth of 8.30% at 6.02 GHz. Directivity of 10.14 dBi and negligible side lobe level for both E and H plane radiation pattern is observed. A size reduction of 27.09% as compared to patch on LLDPE and tensile strength of 50 MPa is observed.

UWB and directive E-shaped metamaterial patch antenna

Left-handed materials, which have both negative permittivity and permeability, have been the area of potential research over a decade. This paper elucidates the design of a double-negative group (DNG) THz metamaterial, namely, E-shaped, having negative refraction ranging from 34.5 to 37.5 THz. Rectangular microstrip patch antenna (RMPA) with microstrip feed has been designed using Ansoft HFSS with RT Duroid (ϵr = 2.33) as substrate and having the same frequency range as that of the metamaterial's negative region. Upon incorporation of proposed metamaterial's array inside the antenna substrate, bandwidth of antenna increases by 4 THz and directivity of antenna increases by about 43% with E-shaped metamaterial.

Effects of structural parameters of textile substrates on the novel textile conformal half-wave dipole antenna

In the smart textile area, textile antennas integrated into people’s clothing functioning as the wireless signal transmission devices have gained increasing attention in recent decades. In this study, a textile conformal dipole antenna was designed to work at the frequency of 915 MHz. The radiation elements of the antenna were adhered directly onto the stitched polyester fabric substrate to get the conformal effect. The measured results showed that the antenna had good performance with the return loss value and typical omnidirectional radiation patterns. To investigate the effect of textile substrate on the antenna performance, models for stitched and plain weave structures were built and the value of root mean square (RMS) surface error was calculated using integration methods. Then an acceptable range of operation frequencies versus RMS was marked out for estimating the reliability of textile substrate. The calculated RMS of our designed antenna was 0.25 mm, which was in the acceptable range area indicating the proper antenna design. Finally, the relationships between the critical frequencies and fabric parameters such as yarn thickness and density were studied, which gives the direct guideline for selecting the fabric as the substrate for textile antennas.

Antenna with three dimensional 3D printed substrates

ABSTRACTIn this letter, 3D printing technology is used to modify the substrate shape with the aim of modifying the antenna's performance. The antenna substrate is made using a 3D printer and commercially available materials. A ridge near the center of the patch has been used to downshift the resonant frequency of the antenna. The effect of the ridge shape has been investigated via simulations and measurements. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:741–744, 2016

Improvement of terahertz field effect transistor detectors by substrate thinning and radiation losses reduction.

Phenomena of the radiation coupling to the field effect transistors based terahertz (THz) detectors are studied. We show that in the case of planar metal antennas a significant portion of incoming radiation, instead of being coupled to the transistors, is coupled to an antenna substrate leading to responsivity losses and/or cross-talk effects in the field effect based THz detector arrays. Experimental and theoretical investigations of the responsivity versus substrate thickness are performed. They clearly show how to minimize the losses by the detector/ array substrate thinning. In conclusion simple quantitative rules of losses minimization by choosing a proper substrate thickness of field effect transistor THz detectors are presented for common materials (Si, GaAs, InP, GaN) used in semiconductor technologies.

Flexible Ultra Wide Band Antenna for WBAN Applications

This paper introduces a small-sized, low-profile, planar and flexible ultra-wide band (UWB) antenna using natural rubber as the substrate. It is the primary approach in using natural rubber as the substrate for UWB antenna. The UWB antenna is designed for applications in WBAN, which is the current revolution in wireless sensor networks. The antenna operates from 3.1-10.6GHz, which is a candidate for WBAN operation. The flexible nature of the antenna makes it convenient for the use as a body worn antenna for WBAN. This paper is a case study of whether rubber can be used as a substrate for UWB antenna and compares the performance using FR4 substrate.

Half-Mode Substrate-Integrated-Waveguide Cavity-Backed Slot Antenna on Cork Substrate

A wideband half-mode substrate-integrated-waveguide cavity-backed slot antenna covering all Unlicensed National Information Infrastructure (U-NII) radio bands (5.15-5.85 GHz) is designed, fabricated, and validated. By a half-mode implementation of a multimoded cavity with nonresonant slot, a compact ultrawideband antenna is obtained with very stable radiation characteristics, owing to the excellent antenna/platform isolation. Cork material is applied as antenna substrate, making the proposed antenna suitable for integration into floors or walls. In free-space conditions, an impedance bandwidth of 1.30 GHz (23.7%), a radiation efficiency of 85%, a front-to-back ratio of 15.0 dB, and a maximum gain of 4.3 dBi at 5.50 GHz are measured. Performance is also validated when the antenna is deployed on various dielectric or conducting platforms and underneath different dielectric superstrates. Only the latter slightly detunes the antenna's impedance bandwidth. Yet, the complete frequency band of interest remains covered, owing to additional design margins incorporated in the requirements. Its compactness, unobtrusive integration potential, and stable high performance in different environments make this antenna topology an ideal candidate for Internet of Things applications.

Echo-Less Photoconductive Antenna Sources for High-Resolution Terahertz Time-Domain Spectroscopy

Interdigitated photoconductive antennas are powerful and easy-to-use sources of terahertz radiation for time-resolved spectroscopy. However, the emission of unwanted echoes, resulting from reflections of the emitted pulse in the antenna substrate, inherently limits the spectroscopic frequency resolution. A novel interdigitated photoconductive antenna that suppresses unwanted echoes from the substrate, without power losses, is proposed and demonstrated. This is realized through a buried metal geometry where a metal plane is placed at a sub-wavelength thickness below the surface antenna structure and GaAs active layer. In a reflection geometry this effectively eliminates echoes, permitting high resolution spectroscopy to be performed. As a proof-of-principle, the 1 01 -2 12 and the 2 12 -3 03 rotational lines of water vapor have been spectrally resolved with the new buried metal antenna, which are unresolvable with a standard antenna. In addition, as no THz field is lost to the substrate and reflections, the THz peak electric field amplitude is enhanced by a factor of three compared to a standard design in the equivalent reflection geometry.

A Reconfigurable Substrate–Superstrate Graphene-Based Leaky-Wave THz Antenna

A planar substrate-superstrate configuration loaded by a graphene sheet is proposed as a novel reconfigurable antenna for terahertz applications. The effects of the introduction of graphene on the dispersion and radiation properties of the fundamental leaky modes supported by the structure are analyzed in detail, with the aim of investigating the possibility of beam scanning at a fixed frequency by varying the graphene chemical potential via an electrostatic bias. After optimizing the graphene position inside the antenna substrate for achieving maximum directivity at broadside, large scanning ranges are obtained in which the normalized attenuation constants of the fundamental TE/TM leaky-mode pair exhibit small values and reduced variation, thus producing a scanning process with an essentially constant narrow beamwidth. In the same ranges, the phase constants of the TE/TM-mode pair are shown to be equalized, thus opening the possibility of designing fixed-frequency scanning antennas with conical beams and reconfigurable dual polarization.

Response to “Comments on ‘SIW Hybrid Feeding Network-Integrated 2D DRA Array: Simulations and Experiments’”

The prototypes were built in a very advanced industrial fabrication lab, where the process steps were closely followed. These steps include drilling, via electroplating, surface finishing, and milling the dielectric superstrate. The fabrication cost can be high, mainly because of the DRA milling on board. An obvious solution for larger arrays is to form smaller antenna substrate, which leads to less milling (or even no milling). The large-scale 2D SIW-DRA array in the paper. To significantly lower the fabrication cost, the process is somewhat simplified without losing its generality. Process step can be ignored when the DRA elements are formed (milled) off the SIW board precisely, then glued (bonded). This process was used to fabricate the 2D array at a university lab. The DRA blocks were glued to their positions with the help of an aligning board. Sometimes, DRAs fall off the board during radiation pattern measurement and have to be glued back to their positions.

Microwave dielectric properties of Mn x Zn(1−x)Fe2O4 ceramics and their compatibility with patch antenna

Nanocrystalline spinel mixed ferrites are well known for their sensing application. However, they have not been explored much for microwave applications. The microwave dielectric properties of Mn x Zn(1−x)Fe2O4 were studied to find their utilization as an antenna substrate for microwave wave applications. The sol–gel method was employed to synthesize these ceramics. The formation of spinel structure and crystalline size were confirmed using X-ray diffraction method. Morphology of the samples was studied using the scanning electron microscopy. Relative permittivity (e r) and quality factor (Q × f) of the samples were measured using LCR spectrometer. Based on the material investigation and microwave antenna theory, patch antennas were fabricated and then their performances were studied using return loss analysis. The patch antenna, fabricated from Mn0.2Zn0.8Fe2O4 ceramics showed excellent performances with relative permittivity of 5.76, Q × f of 442, return loss of −41.2 dB and wide bandwidth of 2 GHz.

Y-type hexagonal ferrites for microwave absorber and antenna applications

This article examines the potential of the Y-type hexagonal ferrites, BaSrCo2−xNixFe12O22, as passive microwave absorbing materials and magneto-dielectric antenna substrates. To this effect, we investigated the electromagnetic properties of the fabricated samples up to 18GHz, in conjunction with the composition, microstructure and static magnetic characteristics. It was found that the Ni substitution yields the increase of permeability μ* and permittivity ε* as a consequence of the weaker magnetocrystalline anisotropy and enhanced dielectric orientation polarization. By virtue of their different ε* and μ* spectra, the Co-rich hexagonal ferrites appear as appropriate for narrowband-yet tunable-reflection reduction in the 2.6–18GHz range (>20dB), whereas with Ni addition wideband attenuation of the transmitted waves (>20dB) is attained in the 7–18GHz band. In addition, the persistence of high refractive index up to 1GHz enables the utilization of these hexagonal ferrites in UHF antenna designs with smaller dimensions. Among them, designs with Co2-Y compound are liable to higher radiation efficiency, while Ni2-Y favours the achievement of wider bandwidth. On this basis, the performance of the produced materials in high frequency applications is evaluated and certain improvement directions are indicated.

A Wide-angle Multi-Octave Broadband Waveplate Based on Field Transformation Approach.

Transformation optics (TO) offers a geometrical approach in designing optical components of any shapes. Although it has been proven to be a versatile and robust mathematical tool, TO has, however, limited control over electromagnetic (EM) field polarization in the process of coordinate transformation. Such a technique can be extended to a so-called “Field transformation (FT)” which provides direct control over the impedance and polarization signature of an arbitrary object. In this work, we demonstrate a FT application by designing and manufacturing a novel waveplate, which defies the fundamental limit of bandwidth and incident angles and has the ability of converting between TE (transverse electric) and TM (transverse magnetic) as well as LCP (left-handed circular polarization) and RCP (right-handed circular polarization). Such a waveplate can also be applied to different operating modes for both transmitted and reflected waves by adjusting its thickness and adding an optional metallic ground plane. The proposed design approach presents a remarkable degree of advance for designing future devices with arbitrary polarization controls, artificial waveguides or antenna substrates and polarization-enabled resonators with angle-insensitive functionalities. Our approach has far reaching implications applicable from radio to optical frequencies.