Bandwidth Radiation Research Articles

Fully Printed 3-D Antennas With Wideband Radiation Isotropy Based on Annular Currents Models

Fully Printed 3-D Antennas With Wideband Radiation Isotropy Based on Annular Currents Models

High power balanced TEM horn antenna for ultra wide band radiator

AbstractA balanced transverse electromagnetic (TEM) horn type antenna is designed and developed for a 120 kV, 66 Ω high power ultra wideband (UWB) radiator. This antenna consists of a coaxial to parallel plate unzipper BALUN followed by an exponentially tapered TEM horn structure. Analysis of this antenna in time and frequency domain is performed using CST Microwave Studio. This antenna is having a power handling capacity of 1000 MW, with percentage bandwidth of 167%. This antenna has a gain of ~10 dB at 1 GHz frequency. Return loss performance of better than −10 dB is observed in 150 MHz to 1 GHz frequency range. Effective radiation of short pulses (<5 ns) with very fast rise time (300–500 ps) has been demonstrated using this high‐power antenna. Practical results at 220 MW power are presented in this article. Directional performance of this antenna is practically established through peak power patterns in horizontal and vertical plane.

Materials for Optical Sensors of X-ray Irradiation Based on (GaxIn1 – x)2Se3 Films

(GaxIn1-x)2Se3 films with 0.1 ≤ x ≤ 0.4 were deposited by the thermal evaporation technique. As-deposited (GaxIn1-x)2Se3 films were irradiated using the wideband radiation of a Cu-anode X-ray tube at different exposure times. The spectral dependences of the refractive index and extinction coefficient are measured by the spectral ellipsometry technique. The optical transmission spectra of X-ray irradiated (GaxIn1-x)2Se3 films are studied for various irradiation times. Parameters of the Urbach absorption edge for X-ray-irradiated (GaxIn1-x)2Se3 thin films are determined and compared with those of non-irradiated films. The spectral dependences of the refractive indices of non-irradiated and X-ray-irradiated (GaxIn1-x)2Se3 films are described in the framework of the model developed by Cauchy, Sellmeier, Wemple, and DiDomenico, as well as by the optical-refractometric relation. The detailed variation of the parameters of the Wemple–DiDomenico model for non-irradiated and X-ray-irradiated (GaxIn1-x)2Se3 films has been analyzed. The perspective of applications of (GaxIn1-x)2Se3 films as the materials for optical sensors of X-rays is discussed.

Plasmonic grating assisted photo‐absorption enhancement in terahertz photoconductive antenna

AbstractA large aperture photoconductive antenna (PCA) with a plasmonic grating structure was fabricated and characterized. The intensity of the terahertz radiation from the plasmonic PCA was enhanced two‐fold compared with that from the conventional PCA without the plasmonic grating structure. By using an electrically isolated nano‐grating structure, the performance enhancement was found to be due to the plasmonic effect other than bias field enhancement. The photo‐absorption enhancement near the GaAs surface and the plasmonic grating interface was investigated to elucidate the terahertz radiation enhancement mechanism in the plasmonic PCA. The highly localized electric field near the nanoscale grating shows optical absorption at the GaAs surface was enhanced. The enhanced optical absorption increased the photo‐generated carrier density at the device surface, leading to enhanced intensity and bandwidth of the terahertz radiation from the plasmonic PCA.

Dual Circularly Polarized Broadband Antenna Array for Millimeter-Wave Applications

A planar dual circularly polarized (CP) broadband array is proposed in this letter. The antenna consists of two semicircular patches and two suspended metal posts. According to the investigation of our previous work, the circularly polarized mode generated by combining the patches and the metal posts can achieve very wideband CP radiation. In order to achieve dual CP radiation with similar performance, a new antenna element is proposed with a centrally symmetrical configuration. The orthogonally crossed slot etched on the substrate-integrated waveguide cavity is used to excite the antenna element. A 4×4 array is designed, fabricated, and tested. Measured results show that a 3 dB AR bandwidth of 28.28% (26–34.6 GHz) and 30.61% (26–35.4GHz) is achieved for left-handed CP (LHCP) and right-handed CP (RHCP) radiation, respectively. The 3 dB gain bandwidth of 22.81% (26.4–33.2 GHz) and 24.50% (26–33.26 GHz) for these two polarizations is obtained. The proposed array demonstrates the feasibility of dual-polarized radiation. It features the advantage of wide bandwidth, easy integration, and low cost, which is very suitable for millimeter-Wave system applications.

Integrated silicon-based spectral reshaping intermediate structures for high performance solar thermophotovoltaics

Solar thermophotovoltaics (STPV) system is a technique that uses absorber and emitter to remold wide-band solar radiation into narrowband infrared emission and then convert it into electric energy in order to get high energy conversion efficiency. In this study, we fabricated an integrated silicon-based intermediate structure to enable the spectral reshaping. The absorber is a hierarchical Si NW structure, which exhibits excellent absorption performance of over 95 % in the spectral range of 220–1100 nm and a low heat loss in the long-wavelength band. The emitter is planar Si-W-SiN/SiNO structure, exhibiting a selective narrowband absorption (i.e., emission) peak in the target wavelength. When the emission peak of emitter is at 1800 nm, the overall efficiency of the STPV system based on this silicon-based intermediate structure can theoretically exceed 29 % with an achievable solar concentration of 1000 and an emitter-to-absorber area ratio of 4. We also test the prepared spectral reshaping intermediate structures on real systems and discuss further optimizations.

Metasurface-Loaded Off-Center Monopoles With Wideband Radiation Performance Using Characteristic Mode Analysis

A metasurface (MTS)-based reactive impedance surface (RIS) is proposed to load an eccentrically placed monopole above a ground plane for controllable wideband omnidirectional radiation. With the off-center placement, the radiation pattern of the monopole is not omnidirectional anymore, with ripples in the H-plane measured by un-roundness. The RIS is introduced above and in parallel with the finite ground plane and the monopole is placed in the center of the RIS. Characteristic mode analysis (CMA) is used to analyze the RIS-loaded monopole and to reveal the mechanism. It is found that two desired modes determine the bandwidth of the omnidirectional radiation together. The resonant frequency of the RIS mode can be easily tuned by changing the sheet impedance of the RIS. A metal-dielectric-metal constructed MTS is proposed to realize the RIS. The grid impedance of the MTS can be tuned easily by changing the size of the patch in the unit cell. For a single monopole placed off-center above a rectangular ground plane (150 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times300$ </tex-math></inline-formula> mm), the impedance bandwidth is increased from 19.6% to 32.4% with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert &lt; -10$ </tex-math></inline-formula> dB at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0} =2.5$ </tex-math></inline-formula> GHz. And the maximum un-roundness is reduced by 66.7% from 4.8 to 1.6 dB over the frequency band of 2.2–2.8 GHz. For a two-monopole antenna system with the same ground plane mentioned above, the loading MTS increases the impedance bandwidth of the monopole from 19.2% to 32.4% with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert &lt; -10$ </tex-math></inline-formula> dB at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0} =2.5$ </tex-math></inline-formula> GHz. When only one monopole is loaded with MTS in the system, the maximum un-roundness is reduced by 65.5% from 5.5 to 1.9 dB in the frequency band of 2.2–2.8 GHz. When both monopoles are loaded with MTS in the system, the maximum un-roundness is reduced by 40% from 5.5 to 3.3 dB in the frequency band of 2.2–2.8 GHz. The antenna prototypes are fabricated and measured.

Miniaturized wideband implantable slotted loop antenna for biotelemetry applications

Abstract Small size of the implantable antenna is the major concern in Implantable Medical Devices. A compact implantable wideband radiator working at the ISM band is proposed for biotelemetry applications. The overall dimension of the proposed radiator is 10 mm ⁎ 15 mm ⁎ 0.8 mm and the thickness includes substrate and superstrate thickness. The Coaxial feeding method is employed here. The inner and outer diameter of the coaxial feed is 1 and 1.5 mm respectively. The design process starts with a creation of rectangular patch of size 10 mm ⁎ 15 mm and the coaxial feed is located at (2.5, 7). Then slot like loops are introduced on a rectangular patch. This compact size is achieved by introducing small loops on a rectangular patch along with triangular cuts at the bottom right and top-left of the patch. The antenna is simulated with a tissue model (Skin, Fat, Muscle, Bone) and measured with a Body Equivalent Fluid (phantom). The −10 dB bandwidth is obtained over 1340 MHz (1.66–3 GHz) and the fractional bandwidth of 54.7% at the ISM band. The simulated gain and radiation efficiency of the radiator are −13.5 dBi and 3.15% respectively. The measured return loss of the proposed antenna is −30.53 dB and the SAR value averaged over 1 g tissue is 302.6 W/kg with 1 W input power. When compared to the previous works mentioned in the literature the proposed antenna displays wider bandwidth, high gain, low SAR and high radiation efficiency.

Wideband low-RCS circularly polarized antenna with metasurface combining wave diffusion and polarization conversion

A novel and simple low-profile high-gain wideband circularly polarized (CP) slot antenna with low radar cross section (RCS) is presented. The proposed antenna is composed of a traditional linearly polarized (LP) slot antenna and an integrated metasurface-based superstrate. The superstrate consists of a center array with metasurface (MS) unit cells and four surrounding arrays with 4×4 MS unit cells. On the one hand, a wideband and high-gain CP radiation in the frequency band of 5.27-6.18 GHz (a relative bandwidth of 15.9%) is achieved by the polarization conversion property of the MS and four surrounding arrays. On the other hand, a broadband RCS reduction in the frequency band of 4.5-20 GHz (a relative bandwidth of 126.5%) is obtained by the combination of two electromagnetic wave diffusion principles. Inspired by C-band, X-band and Ku-band radar applications, a low-cost stealthy prototype with broadband low RCS and CP radiation is realized.

A Unified Synthesis Method for Series-Fed Networks Under Equal/Unequal Distributions With Bandwidth Enhancement

Aiming to realize series-fed antenna array with good return loss, low sidelobe level (SLL), and small gain variation over a wide bandwidth, this article presents a unified synthesis method of designing series-fed networks (SFNs) under the equal/unequal distributions with the bandwidth enhancement. We find that the return loss and current distribution bandwidths of SFN are dominated by its input reactance slope. The ratio of SFN main line impedance Z0 and antenna impedance ZL plays an important role in it. When the optimal Z0/ZL makes the input reactance slope equal to zero at the center frequency, the bandwidth of SFN can be highly extended by 2–4 times compared with nonoptimal solutions. In this context, four classical types of SFNs are investigated and synthesized. The closed-form optimal formulas for these SFNs are further deduced under the specified element number N and current distributions I1, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{I}_{2}, \ldots $ </tex-math></inline-formula> , and IN. For experimental verification, an eight-element series-fed antenna array driven by the SFN with Dolph–Chebyshev current distribution is designed and fabricated based on the proposed design method. By virtue of the improved SFN, the designed series-fed array exhibits enhanced impedance and radiation bandwidths as predicted. The measured results show designed array achieves an impedance bandwidth of 52.2% (3.34–5.70 GHz) with S11 ≤ −10 dB and the radiation bandwidth with SLL ≤ −20 dB is 20.9% (3.85–4.75 GHz). The measured antenna gain is 11.3 dBi with a small variation of 1.3 dB and the efficiency of array is better than 82% over the operational bandwidth of 18.7% (3.88–4.68 GHz).

A Broadband Metasurface Antenna Array With Ultrawideband RCS Reduction

In this communication, a metasurface-based antenna array with wideband radiation and broadband radar cross section (RCS) reduction is constructed. Without introducing additional radiators, the broadband radiation performance of the antenna array is achieved by inspiring the metasurface itself. In addition, the characteristic mode theory is introduced to analyze the radiation mechanism of the radiator elements and the proposed antenna array. Both simulations and measurements are carried out to verify the performance of the proposed antenna array. The results show that the impedance bandwidth and 3 dB gain bandwidth of the proposed antenna array are 5.1–9.0 and 5.1–8.0 GHz, respectively, with a peak gain of 12.1 dBi. Monostatic RCS reduction more than 10 dB is achieved within the frequency band of 6.0–26.2 GHz.

Improving the Patch-Based Crossovers by Parasitic Modes and a Sub-Element Technique

This brief introduces new methodologies to design microstrip line crossovers on a high-speed interconnection circuit. The crossover is based on a simple square patch, which employs TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">001</sub> to achieve mode orthogonality so that two sets of intersecting signals can transmit along microstrip lines with a high isolation. Compared with rectangular waveguide crossovers that employ high modes, namely TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">102</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> , it shows advantages like a smaller size and easier manufacturing. Then, the relevant techniques for performance improvement, including radiation suppression and bandwidth widening, are studied for practical circuit designs. Finally, based on the sub-element technique, the study designs a controllable frequency response for two intersecting signals and miniaturization of patch based crossovers. Two examples are implemented, manufactured and measured to justify the validity of the sub-element technology. In addition, the design steps of this method are simplified compared with relying on full-wave simulations entirely.

Generation of primary photons through inverse Compton scattering using a Monte Carlo simulation code

Photon sources based on inverse Compton scattering, namely, the interaction between relativistic electrons and laser photons, are emerging as quasimonochromatic energy-tunable sources either as compact alternatives to synchrotron facilities for the production of low-energy (10--100 keV) x rays or to reach the 1--100 MeV photon energy range, which is inaccessible at synchrotrons. Different interaction layouts are possible for electron and laser beams, and several applications are being studied, ranging from fundamental research in nuclear physics to advanced x-ray imaging in the biomedical field, depending on the radiation energy range, intensity, and bandwidth. Regardless of the specific application, a reliable tool for the simulation of the radiation produced is essential for the design, the commissioning, and, subsequently, the study and optimization of this kind of source. Different computational tools have been developed for this task, based on both a purely analytical treatment and Monte Carlo simulation codes. Each of these tools has strengths and weaknesses. Here, we present a novel Monte Carlo code based on geant4 for the simulation of inverse Compton scattering in the linear regime. The code produces results in agreement with cain, one of the most used Monte Carlo tools, for a wide range of interaction conditions at a computational time reduced by 2 orders of magnitude. Furthermore, the developed tool can be easily embedded in a geant4 user application for the tracking of photons generated through inverse Compton scattering in a given experimental setup.

Bias-free terahertz generation from a silicon-compatible photoconductive emitter operating at telecommunication wavelengths

We present a telecommunication-compatible bias-free photoconductive terahertz emitter composed of a bilayer InAs structure directly grown on a high-resistivity silicon substrate. The bilayer InAs structure includes p+-doped and undoped InAs layers, inducing a strong built-in electric field that enables terahertz generation without requiring any external bias voltage. A large-area plasmonic nanoantenna array is used to enhance and confine optical generation inside the photoconductive region with the highest built-in electric field, leading to the generation of a strong ultrafast photocurrent and broadband terahertz radiation. Thanks to a higher terahertz transmission through the silicon substrate and a shorter carrier lifetime in the InAs layers grown on silicon, higher signal-to-noise ratios are achieved at high terahertz frequencies compared with previously demonstrated bias-free terahertz emitters realized on GaAs. In addition to compatibility with silicon integrated optoelectronic platforms, the presented bias-free photoconductive emitter provides more than a 6 THz radiation bandwidth with more than 100 dB dynamic range when used in a terahertz time-domain spectroscopy system.

Design of coherent wideband radiation process in a Nd3+-doped high entropy glass system

We discover that the spatially coherent radiation within a certain frequency range can be obtained without a common nonlinear optical process. Conventionally, the emission spectra were obtained by de-exciting excited centers from real excited energy levels to the ground state. Our findings are achieved by deploying a high-entropy glass system (HEGS) doped with neodymium ions. The HEGS exhibits a much broader infrared absorption than common glass systems, which can be attributed to be high-frequency optical branch phonons or allowable multi-phonon processes caused by phonon broadening in the system. A broadened phonon-assisted wideband radiation (BPAWR) is induced if the pump laser is absorbed by the system. The subsequent low-threshold self-absorption coherence modulation (SACM) can be controlled by changing excitation wavelengths, sample size, and doping concentrations. The SACM can be red-shifted through the emission of phonons of the excited species and be blue-shifted by absorbing phonons before they are de-excited. There is a time delay up to 1.66 ns between the pump pulse and the BPAWR when measured after traveling through a 35 mm long sample, which is much longer than the Raman process. The BPAWR-SACM can amplify the centered non-absorption band with a gain up to 26.02 dB. These results reveal that the shift of the novel radiation is determined by the frequency of the non-absorption band near the absorption region, and therefore the emission shifts can be modulated by changing the absorption spectrum. When used in fiber lasers, the BPAWR-SACM process may help to achieve tunability.

Beam loss study for the implementation of corrugated structure at the European XFEL

The European XFEL is a free-electron laser facility based on superconducting linac with high repetition rate of up to 4.5 MHz. A corrugated structure is planned to be installed in front of the SASE beam line at the European XFEL, which can be used as a kicker for fresh-slice schemes or a dechirper to control the bandwidth of SASE radiation. When the beam passes through the corrugated structure module, strong longitudinal and transverse wakefields can be excited to introduce a correlated energy chirp and/or a kick along the bunch. However, due to the relatively small gap of the corrugated structure, beam halo particles experience large betatron oscillations after hitting the corrugated structure, which can lead to energy deposition in the undulator beam line. This may cause demagnetization of the undulators especially at high repetition rate. For this reason, we have performed beam loss simulations using BDSIM for two different configurations: double-plate corrugated structure with nominal FODO optics and single-plate corrugated structure with small beta optics. Our simulation results showed that the latter configuration can help us not only to relax the tolerance on beam halo extension, but also to reduce the peak radiation doses by more than factor 2. Besides, the possibility of adding a collimator downstream of the corrugated structure has also been studied, which can further help us to reduce the loss in the downstream cells by factor 100.

Metasurface-loaded printed monopole antenna: tailoring impedance for wideband radiation

In this paper, we propose a method of designing a wideband printed monopole antenna (PMA) by loading metasurface on its back. The metasurface-loaded PMA prototype is a double-sided structure, with the printed monopole on the front side and the metasurface etched on the back side, respectively. Driven by the printed monopole structure in the near-field zone, the metasurface can behave inductively or capacitively. By adjusting the geometrical parameters, the impedance of the metasurface can be tailored so as to compensate the mismatched impedance of the original printed monopole in a wide band, leading to a wideband omnidirectional radiation. To verify this method, a light-weight PMA is designed, fabricated and measured. Analyses of the impedance and the surface current distributions are employed in the design process. The height of the proposed PMA is 20.0 mm, about 16% of the wavelength corresponding to the lowest operating frequency. Both the simulated and measured results show that the antenna can achieve highly efficient omnidirectional radiation in 2.50–4.75 GHz and the relative bandwidth achieves up to 62%. This work provides an effective alternative of designing wideband PMA, and may find wide applications in modern wireless communications.

A Triple-Band Microstrip Antenna with a Monopole Impedance Converter for WLAN and 5G Applications

In this study, a triple-band microstrip antenna with compact size and simple structure is proposed for WLAN and 5G applications. The radiating element consists of a circular patch, a Y-shaped patch, and a monopole impedance converter. In order to obtain the desired operating bands, the monopole impedance converter is inserted between the circular patch and Y-shaped patch. The proposed antenna can work in the frequency range of 2.38∼2.53 GHz, 3.29∼4.11 GHz, and 4.72∼5.01 GHz, with the corresponding peak gains of 4.09 dBi (2.4 GHz), 2.95 dBi (3.5 GHz), and 4.01 dBi (4.9 GHz), respectively. The measures’ results are in approximate agreement with the simulated values, which shows that the proposed compact antenna can offer omnidirectional radiation, appropriate gains, and sufficient bandwidths.

Effect of H atoms and UV wideband radiation on cured low-k OSG films

Effects of hydrogen atoms and UV radiation (λ > 210 nm) on nanoporous organosilicate glass (OSG) low-k films are studied in the temperature range from 20 °C to 300 °C. The purpose of the study is to understand the mechanisms of low-k films modification that can happen during the cleaning from carbon containing residues formed from sacrificial porogen and accumulated during the air storage. It is shown that exposure of low-k films to hydrogen atoms at low temperature leads to slight modification of hydrocarbon bonds in hydrocarbon residues not bonded to Si. At high temperature (T ⩾ 300 °C), the relative concentration of –CH x bonds changes in a complex way and depends on the amount and structure of the carbon-containing compounds. The general trend is relatively rapid decrease of –CH2 bonds concentration, while the terminal –CH3 groups are more stable. Temperature also initiates the reaction of hydrogen atoms with low-k with partial modification of low-k matrix breaking Si–O bonds. The destruction of Si–O and Si–CH2 groups leads to the formation of oxygen-deficient centers, followed by the formation of Si–(CH3)2 groups due to their interaction with methyl groups. At 300 °C, the total number of Si–CH3 + Si–(CH3)2 groups starts to decrease indicating on partial removal of the methyl groups bonded to silicon. Besides with increasing temperature a slight modification of the structure of matrix under exposure to H atoms is also observed. UV radiation has almost no effect on these processes in the studied conditions. Thus, there exist the ‘optimal’ conditions for H atom impact on OSG low-k films which allows improving film performance by removing porogen residue without damage.

Wideband Dual-Polarized Endfire Antenna Based on Compact Open-Ended Cavity for 5G Mm-Wave Mobile Phones

This article describes a compact dual-polarized endfire antenna array for fifth-generation (5G) millimeter-Wave (mm-Wave) mobile application. The dual-polarized endfire antenna element is constructed by a compact open-ended cavity with cavity mode for vertical polarization (VP) radiation and open-slot mode for horizontal polarization (HP) radiation. With the integrated design of VP and HP elements, the proposed antenna shows a much more compact size compared to existing schemes. To enhance the bandwidth of low-profile VP radiation, a slot is etched on the cavity to create a new mode for dual-resonance response, realizing a wide bandwidth of 24.5&#x2013;29.5 GHz for both polarizations. In addition, radiation pattern modification techniques are employed to achieve good endfire beams with a high front-to-back ratio for both polarizations, thus enabling a high peak gain of 10.3 and 11.3 dBi for VP and HP, respectively. A wide beam scanning range of &#x00B1;50&#x00B0; with realized gain above 7 dBi is realized at 27 GHz for both polarizations. In virtue of compact size, wide bandwidth, high gain, and good spatial coverage, the proposed design strategy is promising for future 5G mm-Wave mobile phones.