Wideband Behavior Research Articles

Searching for Nuclear Obscuration in the Infrared Spectra of Nearby FR I Radio Galaxies

Abstract How do active galactic nuclei with low optical luminosities produce powerful radio emission? Recent studies of active galactic nuclei with moderate radio and low optical luminosities (Fanaroff & Riley class I, FR I) searching for broad nuclear emission lines in polarized light, as predicted by some active galactic nucleus unification models, have found heterogeneous results. These models typically consist of a central engine surrounded by a torus of discrete dusty clouds. These clouds would absorb and scatter optical emission, blocking broad nuclear emission lines, and reradiate in mid-infrared. Some scattered broad-line emission may be observable, depending on geometry, which would be polarized. We present a wide-band infrared spectroscopic analysis of 10 nearby FR I radio galaxies to determine whether there is significant emission from a dusty obscuring structure. We used Markov Chain Monte Carlo algorithms to decompose Spitzer/IRS spectra of our sample. We constrained the wide-band behavior of our models with photometry from the Two Micron All Sky Survey, Spitzer/IRAC, Spitzer/MIPS, and Herschel/SPIRE. We find that one galaxy is best fit by a clumpy torus and three others show some thermal mid-infrared component. This suggests that in those three there is likely some obscuring dust structure that is inconsistent with our torus models and there must be some source of photons heating the dust. We conclude that 40% of our FR I radio galaxies show evidence of obscuring dusty material, possibly some other form of hidden broad-line nucleus, but only 10% favor the clumpy torus model specifically.

A Broadband and FSS-Based Transmitarray Antenna for 5G Millimeter-Wave Applications

This letter describes the design of a broadband and FSS-based transmitarray (TA) antenna for 5G millimeter-wave applications. Two different elements are proposed to avoid the issues of the geometrical parameter resizing of the elements to obtain a 2 bit transmission phase of {−π, −π/2, 0, π/2} to achieve a TA antenna with wideband behaviors. Both of the two proposed elements show low insertion loss of below 1 dB from 24 to 38 GHz. Moreover, the two elements can achieve two sets of discrete transmission phases of {– π, 0} and {−π/2, π/2} without resizing their dimensions, respectively. A TA prototype based on the proposed two elements is designed and fabricated. The measured results agree very well with the simulated ones. The measured 1 and 3 dB gain bandwidth is 28.0–37.5 GHz (29.0%) and 25.1–39.1 GHz (43.7%), respectively. A peak aperture efficiency of 44.7% at 30 GHz is experimentally obtained with a realized gain of 26.1 dBi.

Dual-Band Compact Rectenna for UHF and ISM Wireless Power Transfer Systems

A dual-band UHF/industrial, scientific and medical (ISM) compact rectenna with wideband UHF matching (855-935 MHz) covering all, EU, U.S., and Chinese UHF radio frequency identification (RFID), standards is presented. The proposed design consists of a compact single-port, dual-band antenna, a three-port dual-branch matching network, and two voltage doubler rectifiers implemented with Schottky diodes and terminated with a common 10 kΩ load. For each band, the measured RF-to-dc efficiency is around 60% for a -5 dBm unmodulated signal. The wideband behavior of the rectenna supports harvesting of multitone signals. The use of a six-tone signal increases the maximum RF-to-dc efficiency of the dual-band rectifier, from approximately 60% for a single-tone UHF signal (890 MHz) to 80% for a six-tone signal for a received RF power of -5 dBm in both cases. A signal generator is used to generate a six-tone signal of equally weighted and equally spaced (10 MHz separation) monochromatic tones, with a total bandwidth of 50 MHz. The measurement results demonstrate that the dc voltages rectified from the two separate RF signals are effectively superimposed on the load, providing a clear advantage compared to single-band rectennas. The single-layer, compact design with a size of 80×45 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , with a high RF-to-dc efficiency, is an excellent candidate for wirelessly powered RFID tags.

A Bandwidth-Enhanced Cavity-Backed Slot Array Antenna for mmWave Fixed-Beam Applications

A bandwidth-enhanced $8\times 8$ cavity-backed slot array antenna for fixed beam applications is presented. The antenna consists of four $2\times 2$ subarrays fed by ridge gap waveguide and a modified bow-tie coupling slot in the cavity layer. The proposed bow-tie coupling slot provides additional $\text{10}\%$ impedance bandwidth as compared to the traditional rectangular coupling slot. The fabricated prototype demonstrates an $|S_{11}|\leq -10\,$ dB fractional impedance bandwidth and a $3\,$ dB gain-drop bandwidth of approximately $\text{28}\%$ and $\text{25}\%$ , respectively, with peak gain of $26.4\,$ dBi, aperture efficiency $>\text{60}\%$ and cross-polar discrimination $>40\,$ dB. Measurements show good agreement with simulations. Moreover, we show the impact of the dimensions and shape of the cavity coupling slot on the bandwidth enhancement. The bandwidth enhancement is explained by the double-ridge slot behavior of the bow-tie coupling slot, which shows a more wideband behavior than the traditional rectangular coupling slot behaving like a cross section of a waveguide.

Circuit model for curved coupled microstrip line AMC structure based on quasi-static analysis

A novel equivalent circuit model for an artificial magnetic conductor (AMC) made of curved coupled microstrip line (CCML) wideband resonators is presented. In the proposed method, the effects of substrate thickness and permittivity is explicitly accounted in both the ground-terminated line and frequency selective surface of the AMC, which leads to a more accurate model compared to the previous ones. In addition, closed-form formulas predicting the behaviour of the AMC versus geometrical parameters are provided. The dependence of the equivalent circuit parameters on the excitation frequency is discussed and the wideband behaviour of the CCML based AMC is justified. The validity and application of the model is demonstrated via full-wave electromagnetic simulations and design examples.

Modeling of a dual circularly polarized capacitive-coupled slit-loaded truncated microstrip antenna

A slit-loaded truncated-corner suspended rectangular patch antenna is analyzed using the equivalent circuit approach. The proposed antenna shows wideband behavior with dual circular polarization. The antenna provides an impedance bandwidth of 38.80% in the frequency range of 4.47–6.62 GHz. The 3-dB axial ratio bandwidths are 5.18% in the frequency range of 4.89–5.15 GHz and 2.45% in the frequency range of 6.43–6.59 GHz. The theoretical results are validated by method of moments (MoM)-based IE3D simulations and experimental results, revealing good agreement among the theoretical, simulated, and measured results.

A high gain wideband circularly polarized microstrip antenna

AbstractIn this paper, a high gain wideband circularly polarized (CP) microstrip antenna is presented for broadband operation. The proposed structure comprised of a partially grounded printed monopole antenna loaded with a split ring resonator and a metallic reflector. By using the metallic reflector surface underneath the patch radiator results in the reflected waves in the same phase with main lobe radiation, thereby improving the gain and it also acts like a secondary radiator to generate wideband CP behavior in the proposed design. A gain enhancement of 4.3 dBi is achieved in the operating frequency band as compared with the design without a metallic reflector. The maximum gain achieved in the presented method is 8.6 dBic over the entire operating range. The proposed design shows a wideband behavior ranging from 4.30 to 9.10 GHz with the 10-dB impedance bandwidth of 71.64%. In addition, the proposed design yielded a broadside right hand CP radiation with a 3-dB axial ratio bandwidth of 33.88% from 4.98 to 7.01 GHz. The proposed antenna is fabricated and experimental results on reflection coefficient, gain, axial ratio, and radiation patterns concede well with simulation results.

Equivalent Planar Lens Ray-Tracing Model to Design Modulated Geodesic Lenses Using Non-Euclidean Transformation Optics

This article describes a design procedure that enables a time-efficient evaluation of the focusing properties of modulated geodesic lenses using ray tracing on the equivalent gradient-index planar lens. The method uses transformation optics to define the equivalent planar relative permittivity distribution of axially symmetric surfaces and a ray-tracing model to evaluate the phase distribution in the aperture of the lens. This approach is of interest to optimize modulated geodesic lenses having polynomial profiles, reducing their height while preserving their wideband behavior and wide angular focusing properties. The approach is validated with a specific lens design. The profile is optimized at 30 GHz, while the focusing properties are monitored over the complete Ka up-link frequency band allocated to satellite communications (i.e., 27.5–31 GHz). The manufactured prototype produces 21 beams equally spaced every 7.5° over the extended angular range of ±75°. The ray-tracing model results are compared in detail with the corresponding full-wave model results and experimental data. The manufactured design has return loss better than 15 dB over a fractional frequency bandwidth larger than 30%, in line with the predictions. Excellent scanning properties are demonstrated over an angular range of ±60° with scan losses below 1 dB and good pattern stability, including on sidelobe levels. A height reduction by a factor of 4, when compared to a conventional geodesic lens, is demonstrated with this specific design.

Design and analysis of aperture coupled micro strip patch antenna for radar applications

The aperture coupled- Micro strip Patch Antenna (AC-MPA) is designed for long range (≈400 ​km) air Surveillance radars. The design of patch antennas with aperture coupled power feed is crucial and designed for 1 ​GHz–2 ​GHz (D-band) frequency. The proposed aperture coupled feed design gives wideband behavior, better return loss, gain, Voltage Standing Wave Ratio (VSWR), less compatibility and smaller in size by applying aperture feed. The theoretical analysis is done manually and designed using Advanced Design System (ADS). In aperture coupled feeding technique, the input signal couples to the radiating patch through the aperture (slot) that appears on the ground plane of the feed line and with their feeding structure of the radiating patch element it is different from other micro strip patch antenna. In this work, the design and implementation of aperture coupled patch antenna are analyzed in terms of return loss, gain, efficiency, directivity and power parameters and compared with inset line feeding. The proposed design gives 5 ​dB gain, 4.5 ​dB directivity, efficiency of 30%, impedance bandwidth of above 15% higher than inset feed line with 1.5 ​GHz as centre frequency. The maximum return loss of-40dB is achieved compared to −19dB with aperture feed compared to inset feed line micro strip patch antenna with proper impedance matching. The main advantage of this antenna over single layered patch antenna is increased bandwidth and this antenna will act as dual band also with variation in air gap (1 ​mm–5 ​mm) between single and aperture coupled patch antenna.

A Compact Flower‐Shaped Printed Monopole MIMO Antenna for Wideband Applications

AbstractThis paper presents a 2 × 1 flower‐shaped (FS) multiple‐input multiple‐output (MIMO) monopole antenna with enhanced bandwidth and compact dimensions for modern wireless wideband applications. The proposed FS‐MIMO antenna is formed by merging multiple ellipses, each of which has a different value of semimajor axis length and eccentricity. These ellipses are used to obtain resonances at different frequencies, which cumulatively give a wideband behavior. The antenna characteristics such as reflection coefficient (S11), peak gain, surface current distribution at different resonating frequencies, and 2‐D radiation patterns are investigated. The measured impedance bandwidth (for S11 below—10 dB) of the implemented antenna is around 126% (2.52–11.12 GHz). The measured peak gain varies from 2.16 to 6.57 dB in the entire impedance bandwidth. Furthermore, the measured values of diversity performance parameters such as envelope correlation coefficient, diversity gain, total active reflection coefficient, and mutual coupling (S21) are found within their acceptable limit. The more compact dimensions of 22 × 24 mm2 (or about 0.15λ0 × 0.16 λ0) as compared to the latest state‐of‐art along with the good diversity performance makes the proposed antenna a capable contender for antenna structures supporting wide impedance bandwidth wireless applications. The proposed antenna shows the good matching characteristics under various scenarios such as an extended ground plane, USB connector, and device housing (both vertical and horizontal).

A Low-Profile High-Gain and Wideband Log-Periodic Meandered Dipole Array Antenna with a Cascaded Multi-Section Artificial Magnetic Conductor Structure.

This paper presents a low-profile log-periodic meandered dipole array (LPMDA) antenna with wideband and high gain characteristics. The antenna consists of 14 dipole elements. For compactness, a meander line structure is applied to each dipole element to reduce its physical length. As a result, a compact and wideband LPMDA antenna is realized, exhibiting a wide impedance bandwidth of 1.04–5.22 GHz (ratio bandwidth of 5.02:1) for || < −10 dB. To enhance the antenna gain performance while maintaining the wideband behavior, the LPMDA antenna is integrated with a new design of an artificial magnetic conductor (AMC) structure. The designed AMC is realized by combining three AMC structures of different sizes to form a cascaded multi-section AMC structure, of which its overall operating bandwidth can continuously cover the entire impedance bandwidth of the LPMDA antenna. The proposed AMC-backed LPMDA antenna is experimentally verified and its measured −10 dB reflection bandwidth is found to be in the range of 0.84–5.15 GHz (6.13:1). At the main beam direction within the operating frequency bandwidth, the gain of the proposed AMC-backed LPMDA antenna ranges from 7.15–11.43 dBi, which is approximately 4 dBi higher than that of an LPMDA antenna without an AMC. Moreover, the proposed antenna has a low profile of only 0.138. ( is the free-space wavelength at the lowest operating frequency).

Theory and Experiment of UWB Archimedean Conformal Spiral Antennas

A conformal UWB Archimedean spiral antenna on a dielectric hemisphere is theoretically and experimentally investigated. The analysis method, design, and optimization of this type of spherical antennas is performed using an efficient spatial domain method of moments in conjunction with triangular basis functions and asymptotic Green’s functions. A special conformal mapping is used to enhance the impedance bandwidth and axial ratio (AR) bandwidth for a circularly polarized spherical spiral antenna. Emphasis is given to the efficient asymptotic approach in spherical multilayered media. To validate the theory, a UWB leaky-wave conformal spiral antenna was designed, manufactured, and tested. The measured results indicate a pretty wideband behavior for this antenna starting from 1.7 to 6 GHz (1.8 octaves) in its input impedance responses. The circular polarization is maintained over 1.26 octave with less than 3 dB AR.

Defected Ground Based Fractal Antenna for S and C Band Applications

Defected ground based modified rectangular fractal patch antenna for mobile devices communication in Delay Tolerant Networks, Wireless sensor networks and Mobile Adhoc networks is being presented in this paper. In view of the overwhelming demand of small and light weight micro-chip patch antenna in wireless communication in the recent years the size of antenna has been reduced considerably. Wideband behaviour of antenna is achieved with improved values of performance parameters like gain, reflection coefficient (S11), Voltage Standing Wave Ratio (VSWR), radiation pattern and bandwidth. The proposed antenna covers various frequency bands like earth to space communication (2.17–2.2 GHz), satellite communication (2.3 GHz), wireless local area networks (2.4–2.484 GHz), Wi Fi (2.4 GHz for 802.11b and 802.11g), Radio Frequency Identification, Microwave oven, Bluetooth (2.45 GHz), Wireless Computer Networking (2.4 GHz), Mobile Wi-Max (2.5–2.69 GHz), Direct to home services (2.5–2.7 GHz), Wi-Max (3.3–3.6) Satellite Communication for Downlink (3.7–4.2 GHz) at various resonating frequencies. High Frequency Structural Simulator; v13 has been used to simulate the proposed antenna. The antenna has been designed and simulated using FR4 epoxy substrate with relative permittivity 4.4 and having size of 32 mm × 30 mm × 1.6 mm with line feeding technique. Ground plane has also made defective. The antenna shows the bandwidth of 2830 MHz with gain of 6.83 dB, reflection coefficient (S11) − 19.72 dB and VSWR of 1.23 at resonant frequency 2.85 GHz. Size of the antenna stands reduced by 38.73% with deflective ground surface and frequency shifted towards the lower side. The antenna operates from 2.05 to 4.88 GHz covering S and C band applications.

Leaky-Wave Analysis of Wideband Planar Fabry–Pérot Cavity Antennas Formed by a Thick PRS

The radiation properties of wideband Fabry–Perot cavity (FPC) antennas have been investigated by studying the non-Foster behavior of the reflection coefficient phase of the thick partially reflective surface (PRS) forming the cavity. In order to better understand the performance of such cavities, we show for the first time that the wideband behavior can be explained via a unique dispersion characteristic of the dominant excited leaky-waves (LWs) inside such cavities. We derive new formulas that demonstrate the role of the LWs in forming wideband FPC antennas when the reflective phase of the PRS exhibits an increase with frequency within the band of operation.

Investigation of Enhanced Gain Miniaturized Patch Antenna Using Near Zero Index Metamaterial Structure Characteristics

This paper presents a novel miniaturized patch antenna with enhanced gain characteristics using a Near Zero Index Metamaterial Structure (NZIMS). The proposed antenna consists of a ground plane, rectangular radiating patch and inverted metamaterial structure, which provides wideband behavior, high gain and relatively good matching around 534 MHz. Moreover, the effects of high permittivity and permeability on Hilbert fractals reduced the size of the antenna. The antenna has a small area (44 mm × 58 mm) and offers an impedance bandwidth of 2.11% in 534 MHz. The gain of proposed antenna is better than similar previous works. An NZIMS material with Electric-LC Resonators (ELCR) is used to attain better gain performance and acceptable near-zero permittivity in superstrate. The simulation and optimization process was accelerated using equivalent material parameters for simulation of materials in substrate and superstrate. The simulation and measurement results of the antenna showed a gain of 7.27 dB and a miniaturization factor of 4.8. Both simulated and experimental results obtained for this antenna, validate better radiation performance at 534 MHz frequency range.

A wideband rectifier array on dual‐polarized differential‐feed fractal slotted ground antenna for RF energy harvesting

This article reports a novel wideband rectenna for RF energy harvesting applications. A wideband fractal slotted ground antenna (SGA) is adopted. The operating frequency bands of the antenna are GSM, UMTS, Wi-Fi, and LTE2600/4G bands. The antenna is fed by a dual-polarized and differential-feed (DP-DF) microstrip lines disposed with an angle of 90° each relative to the other. The feed lines are etched on the bottom side of the substrate and connected to an array of four wideband RF-to-DC rectifiers. A nonuniform transmission lines filter ensures wideband behavior for each rectifier. The rectenna performances are simulated and measured. The experiments show an output DC voltage of 1 V at a power density of 26.6 μW/cm2 over the frequency band of operation with a peak efficiency of 50%. The proposed rectenna is suitable for energy harvesting applications in urban environments.

Corrugated fractal monopole antenna with enhanced bandwidth for ultrawideband applications

A very compact coplanar waveguide (CPW)-fed fractal monopole antenna with a modified ground plane is presented. The main objective is to obtain ultra wideband (UWB) characteristics from a simple microstrip monopole antenna. A wideband behaviour and good impedance matching are obtained by modifying the ground plane to semi-trapezoidal shape. Further, the self-similar fractal nature is introduced in the radiating element to enhance the bandwidth. The proposed antenna shows a wider impedance bandwidth from 3 GHz to 11.2 GHz for S11 &–10 dB. A fractional bandwidth of about 115.5% (impedance bandwidth ratio 3.73:1) is achieved for the third fractal iteration. The total volume of the presented antenna is 18×12×1.6 mm³. The measurements are carried out to validate the simulations and the performance of the proposed antenna is analysed.

Application of New Hybrid Jaya Grey Wolf Optimizer to Antenna Design for 5G Communications Systems

The new expected fifth generation (5G) communication systems will serve users with data rates of several Gbps and will allow running new applications in mobile devices. In order to do so, several design challenges have to be met. One of these is the antenna design and fabrication for the 5G mobile devices, especially in the millimeter wave frequencies. In this paper, we address the above issue by designing two different antennas for 3.7 and 26 GHz. We apply a design procedure based on a new proposed evolutionary algorithm, the Grey Wolf Optimizer-Jaya (GWO-Jaya), which combines features from both GWO and Jaya. We evaluate the new algorithm on a set of widely exploited benchmark functions. We design both antennas using the new proposed algorithm. Moreover, we evaluate their performance characteristics through fabrication and measurements. Both antennas are circularly polarized at an acceptable bandwidth and also exhibit wide-band behavior. In both cases, simulation and measurement results are in good agreement.

A Wideband Resonant Cavity Antenna Assembled Using a Micromachined CPW-Fed Patch Source and a Two-Layer Metamaterial Superstrate

This paper reports the development of a wideband resonant cavity antenna (RCA). The RCA device was obtained by using an optimized aperture-coupled coplanar waveguide fed wideband patch antenna and a metamaterial-based superstrate design. The wideband behavior is based on the effects of Fabry–Perot cavity on either side of the resonant frequency of the metamaterial superstrate and the finite size of the superstrate to obtain enhanced gain around this frequency. In addition, the metamaterial superstrate in this paper contains two identical layers of a frequency selective surface (FSS) based on a 2-D patch array rather than dissimilar arrays as used in the previous studies. Two such FSS layers are assembled using a laser micromachined polymethyl methacrylate rim and an SU8-based bonding method. The air spacer based metamaterial design offers better performance by minimizing the dielectric loss between the metallic patch arrays and also offers flexibility in the control of the separation between the two FSS layers as well as resulting in a lightweight RCA device. The RCA device was designed to operate in the X-band. The dimensions of the compact RCA device are $45\times 45\times24$ mm3. The gain of the device was measured to be ~13 dBi with a 3-dB bandwidth of 46% and a corresponding 1-dBi-ripple bandwidth as wide as 40%. The measured impedance bandwidth was 44%.

Planar Antenna Design for Omnidirectional Conical Radiation Through Cylindrical Leaky Waves

An annular periodic leaky-wave antenna (LWA) fed by a simple azimuth-symmetric source is designed to generate a high-gain omnidirectional conical-beam pattern, which scans with frequency over a wide angular range. The proposed structure is defined by a finite metallic radial strip grating printed on a grounded dielectric slab, which supports an $n=0$ cylindrical leaky wave (CLW). The distinctive features of CLWs supported by such a truncated structure are also highlighted and discussed. The directional far-field pattern generated by the proposed LWA, in conjunction with its nondiffracting and wideband behavior in the near field (as previously reported by the authors), defines an original dual-operational LWA. Possible applications include next-generation wireless power transfer systems that provide functionality in both the near and far field, vehicle roof-mounted antennas for base-station data connectivity as well as future short-range near-field communications, and object tracking by ceiling-mounting devices for indoor localization.