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A detailed characterization of a high-power radio frequency (RF) broadband circularly polarized two-arm spiral antenna is designed to operate within the frequency range of 0.1–1.0 GHz. The impedance matching network technique is introduced to optimize its performance. The traditional spiral antenna is excited by a vertical or horizontal balun, whereas the proposed design is directly fed by a coaxial cable featuring a planar feeding section specially optimized to achieve broadband input impedance matching. The spiral antenna is designed as per the steady-state superconducting tokamak (SST-1) port space constraints. The simulated efficiency of the RF power coupling with the hydrogen plasma is ∼70 %. Through simulation, it was evident that the proposed antenna exhibited inherent resonance at 0.5 GHz with a reflection coefficient of −27.94 dB and an axial ratio is 3.39 dB respectively. The obtained outcomes unequivocally demonstrate the circular polarization of the designed antenna. Overall, the findings support the enhancement of plasma heating and current drive techniques in fusion research. [ABSTRACT FROM AUTHOR]

In this study, a plasma frequency selective surface (PFSS) was designed with an array of ordinary fluorescent lamps backed by a conducting plate. The proposed PFSS structure was used as a reflector with the spiral two arms Archimedean type Global Navigation Satellite System (GNSS) antenna to reduce the overall size of the antenna system. Characteristics and the performance of the proposed system were presented by using the results of simulations and experiments in the GNSS band. The optimum distance between antenna and PFSS was found to be around 35 mm to achieve a maximum gain in the simulation which is a lower profile than antenna with conventional conductive plate (66 mm at the GNSS center frequency). Experimental results show that the antenna system has mean values of around 6.7 dBiC gain, 1.27 dB axial ratio and less than -10 dB return loss in the range of 1.14 and 1.61 GHz. All these results show that the proposed novel antenna system is suitable for the reception of the GNSS signals with the advantage of its low profile design. [ABSTRACT FROM AUTHOR]

An integrated automatic optical inspection (iAOI) system with a procedure was proposed for a printed circuit board (PCB) production line, in which pattern distortions and performance deviations appear with process variations. The iAOI system was demonstrated in a module comprising a camera and lens, showing improved supportiveness for commercially available hardware. The iAOI procedure was realized in a serial workflow of image registration, threshold setting, image gradient, marker alignment, and geometric transformation; furthermore, five operations with numerous functions were prepared for image processing. In addition to the system and procedure, a graphical user interface (GUI) that displays sequential image operation results with analyzed characteristics was established for simplicity. To demonstrate its effectiveness, self-complementary Archimedean spiral antenna (SCASA) samples fabricated via standard PCB fabrication and intentional pattern distortions were demonstrated. The results indicated that, compared with other existing methods, the proposed iAOI system and procedure provide unified and standard operations with efficiency, which result in scientific and unambiguous judgments on pattern quality. Furthermore, we showed that when an appropriate artificial intelligence model is ready, the electromagnetic characteristic projection for SCASAs can be simply obtained through the GUI. [ABSTRACT FROM AUTHOR]

Numerous designs and methods have been examined to improve penetration depth (PD), but there is a need for research to explore the potential increase in PD through uniform heating, a compact applicator, and low input power. This paper presents metasurface based hyperthermia lens applicator with water bolus for uniform heating of cancerous tissues. The proposed applicator consists of a stacked spiral antenna and a spiral-shaped frequency selective surface as a superstrate. The spiral antenna and superstrate are optimized on a low cost FR4 substrate having a size of 32 × 32 × 3.27mm3 and 10 × 10 × 1.6mm3 (size of the unit cell), respectively. The proposed applicator is simulated with heterogeneous phantom (skin, fat, and muscle layers) and with the Gustav voxel model with and without a water bolus layer. The number of unit cells in the superstrate is optimized to direct the maximum energy toward the tumor location. The performance study of the applicator is carried out in terms of specific absorption rate, PD, and effective field size. Further, thermal analysis is carried out with 1.9 W of input power at the antenna port, and the highest 44.7 °C temperature rise is obtained. The cancerous tissue's (tumor) surrounding temperature is between 41 and 45 °C, which is adequate for efficient hyperthermia treatment. Finally, the proposed metasurface hyperthermia lens applicator is fabricated and experimentally validated in a mimicked phantom's presence. [ABSTRACT FROM AUTHOR]

The article is dedicated to the analysis of electrodynamic properties of the cylindrical spiral structure. Internal problem for the considered structure in the framework of the thin-wire approximation is reduced to a pair of independent integral Fredholm equations of the first kind, written with respect to even and odd components of the unknown current function. A study of spectral characteristics of the integral operator of the integral equation for various electrical lengths and ratios cylinder radius to its height for a fixed number of turns. Using corresponding systems of projection functions in the framework of the method of moments two independent systems of linear algebraic equations are formed with respect to the unknown expansion coefficients of the even and odd components current function. Certain features of the behavior of eigenfunctions in depending on the wave dimensions and geometrical parameters of the spiral. Features of the frequency dependence of the eigenvalues integral operator were revealed. The conclusion is made about the resonant nature of these dependencies, what makes a cylindrical spiral structure in many respects similar to the previously considered tubular vibrator, a spherical spiral particle and an elliptical frame structure. A hypothesis is put forward about the relationship between the quality factor of resonances of eigenvalues and the emergence of a traveling wave mode in the spiral. Presented results contribute to the formation of an in-depth understanding of emerging in the structure internal processes and serve as a guideline in the construction of approximation models for solving an internal problem. [ABSTRACT FROM AUTHOR]

This paper presents the design and fabrication of a wideband array antenna module for a two-dimensional (2-D) interferometer direction-finding system. The array antenna module comprises an installation panel, spiral antennas, absorbers, and a radome. The absorber was configured to minimize the phase difference between vertical and horizontal polarizations to reduce the degradation of the direction-finding performance. Rubber and foam absorbers were applied in a hybrid form to minimize diffuse reflection. The radome was applied using an A-sandwich structure and manufacturing a laminated structure with a small vertical- and horizontal-polarization phase difference. The average phase difference between the vertical and horizontal polarizations of the array antenna was measured as an azimuth of 8.09° and elevation of 7.89°. Therefore, the fabricated array antenna can be applied to the 2-D interferometer direction-finding system. [ABSTRACT FROM AUTHOR]

A compact focused metamaterial‐based applicator is investigated for hyperthermia cancer treatment in this letter. The metamaterial‐based applicator consists of a double spiral antenna (DSA), an artificial magnetic conductor (AMC) as a reflector, and a frequency selective surface (FSS) as a lens. An AMC structure (64 × 64 mm2) is placed in the back of the antenna at a 5 mm distance that converges the bidirectional field pattern of the antenna into the directional field pattern. Further, to increase penetration inside the tissue, an FSS structure (64 × 64 mm2) is placed at the top of DSA at a distance of 4 mm. The FSS directs the energy toward the tumor location and provides a uniform heating pattern. The field and temperature distribution are numerically obtained for the proposed applicator in the heterogeneous phantom (layers of skin, fat, and muscles), and the performance of the applicator is evaluated in terms of the specific absorption rate, penetration depth, and effective field size. The performance of the applicator is also analyzed for a deeply placed (at 16 mm from the skin surface) irregular‐shaped tumor. The temperature profile calculates 44°C at an input power of 2.5 W. The results show that the applicator is capable of heating sufficiently deep‐seated tumors. [ABSTRACT FROM AUTHOR]

This paper presents the conceptual stages of the simulation and development of a modified transceiver antenna for a high-power pulsed nuclear quadrupole resonance (NQR) detector of explosives containing the 14N isotope. At a frequency of 4.645 MHz, better characteristics are obtained using a nine-turn coil shaped as half of a Fermat spiral with an outer radius of 75 mm. Using a COMSOL Multiphysics numerical parametric simulation and a materials browser, it was possible to calculate a physical system with parameters as close to reality as possible. According to the results of the experimental studies of the radio frequency (RF) energy, the proposed antenna features an increase in the working area compared to a similar antenna, the topology of the conductive coil of which has the form of an Archimedean spiral. The resulting diagrams of the distribution of the magnetic induction also indicate that the topology of the electromagnetic (EM) field does not depend on the orientation of the sample under study relative to the axis of the radial symmetry observed in square–rectangular planar antennas. [ABSTRACT FROM AUTHOR]

A compact, omnidirectional, dual-polarized and electrically small spiral antenna with improved isolation, bandwidth and gain characteristics for 5G-WLAN applications is discussed in this article. The proposed MIMO spiral radiator is composed of two asymmetric CPW trapezoidal spiral-shaped (TSS) structures loaded with an aperiodic (2 × 1) array of SRRs for achieving better isolation characteristics. The TSS antenna operates at TM11 mode which resonates at 5.2 GHz, 5.8 GHz, and TM21 mode resonating at 5.5 GHz, for radiators 1 and 2, respectively. The experimentally validated gain of the TSS antenna is found to be 5.2 dB, 7.2 dB and 6.5 dB at the resonating bands, respectively. The proposed MIMO antenna radiating performances, such as TARC, ECC, DG and isolation characteristics, are evaluated using S-parameters. The modeled TSS–MIMO antenna has a compact size of 35 × 30 × 1.6 mm3, with triple-band resonances at 5.2 GHz, 5.5 GHz, and 5.8 GHz. With these attributes of the proposed TSS configuration, it can be considered a good candidate for WLAN, 5G-WiFi and future multi-band 5G applications. [ABSTRACT FROM AUTHOR]

This letter work develops a liquid metal-based spiral antenna for frequency reconfiguration over an ultrawide band and polarization reconfiguration at a partial operating band. Dual-layer polymethylmethacrylate microfluidic is glued on the dielectric substrate to provide channels for liquid metal flow. The syringe could smoothly control the liquid metal to change the lengths of the spiral antenna arms and result in effective frequency reconfiguration. Moreover, polarization reconfiguration between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) is achieved by redistributing the liquid metal from the upper layer microfluidic channels to the lower layer microfluidic channels. Experimental results demonstrate that the proposed antenna supports continuous frequency reconfiguration from 0.6 to 13.5 GHz and realizes polarization reconfiguration between RHCP and LHCP from 1 to 2.5 GHz. The presented design enabled robust communications over a broad frequency spectrum. [ABSTRACT FROM AUTHOR]

Low-profile wideband spiral antennas suffer from poor impedance matching and cross polarization at lower frequencies or high variation in gain at higher frequencies. These significant differences, primarily caused by electromagnetic coupling with a conventional conductive backing, and the resulting interference are addressed in this letter by suitably designing the profile of the conductor. The proposed geometry has a maximum height of 0.08 $\lambda _{m}$ at the minimum operating frequency and has wideband circular polarization performance with a good boresight gain response over 2–18 GHz range. After numerical investigations, a prototype antenna is fabricated and characterized. An excellent impedance matching and circular polarization behavior are measured close to 2 GHz while the variation in gain is limited between 5.8 and 8.6 dBic above 10 GHz. [ABSTRACT FROM AUTHOR]

We report here that spiral and curl antennas are essentially the same when using the moment method. This aids in the understanding and design of the two antennas, and serves as the groundwork for new ideas regarding antennas. First, the spiral antenna height above the ground plane was gradually reduced, and at each height, the spiral configuration parameters were optimized for an axial ratio of less than 0.1 dB. It was found that the spiral antenna had configuration parameters almost the same as those for a curl antenna at a height of 0.15 wavelengths. Next, the curl antenna was analyzed with a reduced height. The antenna, at a height of 0.10 wavelengths, showed a 3 dB axial ratio bandwidth of 3%, with a VSWR of less than two. The analysis results are verified with experimental results. [ABSTRACT FROM AUTHOR]

Spiral antennas are often used for communication applications. However, this antenna has a two-way radiation pattern. The back-lobe antenna can reduce the main lobe transmit power. This article discusses the design of a spiral antenna with a directional radiation pattern. The antenna substrate uses RO4350B with a thickness of 1.524mm and a dielectric constant of 3.66. On the antenna arms, there is a resistive load to extend the bandwidth and reduce the dimensions of the antenna. A balun is used to feed the Archimedean spiral antenna as a balanced antenna. The absorbed cavity is used to reflect the beam in an undesired direction. The simulation results show that the antenna's operating frequency is in the range of 2.5-12.5GHz for a return loss of less than-10 dB. The absorber helps suppress undesired radiation fields and reduces the back lobe of the antenna. In addition, the use of an absorber can reduce antenna gain. Therefore, the thickness of the absorber needs to be considered. The simulation results show the performance of this antenna. [ABSTRACT FROM AUTHOR]

A compact wideband four‐arm circularly polarized (CP) spiral antenna with both sum mode (1) and difference mode (2) is presented. The antenna is composed of a modified four‐arm equiangular spiral, a four‐arm z‐directional helix, a ring‐shaped absorber, and a ground plane. By using the modified equiangular spiral and the z‐directional helix, the impedance matching of mode 1 and mode 2 is improved, and the cross‐polarization discrimination of mode 2 is also improved in the low frequency band. The z‐directional helix is also applied to achieve a compact size of the antenna and an enhanced AR bandwidth of mode 2. A prototype of the four‐arm spiral antenna is fabricated and measured with a beamformer operating at 0.5 to 2 GHz. It is shown that both sum and difference radiation patterns are generated in the whole frequency band of 0.5 to 2 GHz. The overall size is 0.486λ0.5 GHz × 0.097λ0.5 GHz (diameter × height, λ0.5 GHz is the free‐space wavelength at 0.5 GHz). [ABSTRACT FROM AUTHOR]

A novel artificial magnetic conductor (AMC) ground plane with spherical curvature is proposed. The metallic patches used to form the high impedance surface (HIS) ground plane are of circular periodicity. A detailed description on the design procedure and reflection phase characterization of such ground planes is provided. The impact of the curvature on the reflection characteristics and the maximum curvature which can be applied to the flat HIS are also examined. Two curvilinear antenna elements (loop and spiral) are located above the designed ground plane, and their performances are compared when the two are placed on a flat HIS. Measurements are performed to validate the simulations. An excellent agreement is attained. [ABSTRACT FROM AUTHOR]

A low-profile spiral antenna backed by a circular high-impedance surface (HIS) reflector composed of homogeneous (CirHISRhomo) fan-shaped patch elements is investigated. The total antenna height from the bottom of the CirHISRhomo to the spiral antenna is very small: 0.09 wavelength at a lowest design frequency of 3 GHz. It is revealed that the CirHISRhomo contributes to a constant input impedance and a small axial ratio (AR) across the design frequency range of 3–10 GHz (the fractional bandwidth is approximately 108%). For comparison, the AR for the spiral antenna backed by a conventional perfect electric conducting reflector is also presented. The analysis results are verified by the measured results of the fabricated antenna. [ABSTRACT FROM AUTHOR]

This paper studies a unidirectional ultra‐wideband circularly polarized (CP) spiral antenna array. The ultra‐wideband high‐gain CP operation is realized by implementing four‐element sequentially rotated spiral array antennas fed with an ultra‐wideband feeding network. Tapered multisections power dividers and broadband microstrip‐slot phase shifters are utilized to provide accurately equal power division and constant phase shifts of 90°. In order to further improve the CP operating bandwidth, foam of absorber is adopted between the radiating aperture and the feeding network substrate. The proposed CP array is designed, fabricated, and measured. Test results show that the impendence bandwidth of the proposed array covers 2.2 to 11.6 GHz (5.3:1) and 3 dB axial‐ratio bandwidth covers 2.3 to 13 GHz (5.65:1), demonstrating a stable CP array performance within an ultra‐wide working bandwidth. [ABSTRACT FROM AUTHOR]

Stepped frequency continuous wave (SFCW) radar is a promising noncontact method to detection of human vital signs. Antenna as a key component of radar directly related to the performance of the radar. In this letter, we present a 0.5‐1.2 GHz compact multiple cut‐corners square spiral antenna for SFCW radar system. Compared with conventional planar spiral antennas, the improved antenna possesses the advantages of miniaturization and excellent axial ratio. The gradient‐change of the cut‐corners along the radiation determines its operation range: large cut‐corner corresponds to high frequency, while small cut‐corner affects low frequency. This design successfully leads to a small geometric size of 0.282 × 0.282 × 0.133 m. We measured this improved antenna in an anechoic chamber, and the results demonstrated that the circular polarization bandwidth for axial ratio ≤3 dB approached 100%, and a right‐hand circularly polarization (RHCP) gain of 4‐8.98 dBic in end‐fire direction is achieved in its operational range. Finally, we designed the experiment, experimental results show that the proposed antenna can work well with the SFCW radar in the detection of human vital sign (respiratory signals), indicating a great potential for detected life in practice. [ABSTRACT FROM AUTHOR]

This paper proposes a stepped-width spiral antenna for gain enhancement at a low operating frequency. The frequency-dependent characteristic of the stepped-width transmission line is applied to the spiral arm to enhance the gain at the low end of the operating frequency, and a cavity-backed ground is added to the bottom side of the antenna to further improve the gain at the bore-sight direction. To verify the gain enhancement at the low operating frequency and impedance matching characteristic, we observe the antenna performances such as bore-sight gains and reflection coefficients according to the shape of the spiral arm. The results confirm that the proposed stepped-width structure can enhance the gain at the low operating frequency by improving the impedance matching characteristic. [ABSTRACT FROM AUTHOR]

The paper presents design, simulation and experimental results for the reconfigurable square spiral antenna. This antenna is reconfigurable for two bands: band-I is 0.4–3 GHz which covers GSM, CDMA, Wi-Fi, multipoint communication system and band-II is 4.4–5.9 GHz which covers Wi-Max, 802.11Y, WLAN and 802.11a/h/j/n/ac standards. The antenna can be tuned to other aerospace and electronic warfare applications. This antenna structure offers a good radiation efficiency as the cavity is filled with low dielectric constant material and has high gain and directivity. PIN diodes have been used to achieve the reconfigurability. [ABSTRACT FROM AUTHOR]

A flexible low-impedance wideband antenna with a hybrid structure of Archimedean spiral and equiangular spiral is presented in this letter. The input impedance of the antenna is reduced to about 75 Ω by the attenuation effect of the equiangular spiral connected to the Archimedean spiral. The prototypes of the designed flexible antennas with and without polydimethylsiloxane encapsulation were fabricated with the copper-clad polyimide film and the transfer-printing technique. The simulation results of impedance and voltage standing-wave ratio show the fabricated antenna can be operated over the frequency range of 2.5–4.5 GHz. The S-parameters of the antennas were measured before and after applying uniaxially tensile strain and complex strain induced by balloon. The results show that S11 parameter of the antennas maintains less than –10 dB in the operating frequency band with deformation. The mechanical reliability of the antennas was also confirmed by the finite-element analysis of the strain in the copper layer. [ABSTRACT FROM AUTHOR]

This paper reports on the development and testing of a wideband spiral-shaped coupler for a partial discharge (PD) detection in the UHF spectrum. The coupler design, which is based on the log-periodic spiral slot antenna, has been optimized using finite element simulation. The following parameters have been optimized: feed location, arm termination shape, width of arm root, and termination. The unique feature of the coupler is the inclusion of tuning nodules on the spiral arms, which widen its bandwidth without the need for additional components. Tests in an anechoic chamber have shown a close agreement with the simulation results. The coupler exhibits a wide bandwidth (S11 < −9.55 dB) between 0.5–2.6 GHz and a peak gain of 4.8 dBi (at 1.35 GHz), while using an infinite balun coaxial feed, which allows for an input impedance of 50 Ω. The PD testing in the laboratory has shown that the phase resolved PD patterns acquired with the coupler are very similar to those captured with conventional PD sensors. An application of the coupler as an internal sensor in a gas-insulated busduct is detailed and a bandwidth comparison with other UHD PD sensors is provided. [ABSTRACT FROM AUTHOR]

A novel method of radiating circularly polarized (CP) impulse through a dispersive spiral antenna is presented. The proposed method utilizes time‐reversal‐based pulse compression to radiate a CP impulse without any modification to the existing antenna design, providing flexibility where the antenna can be used as a normal dispersive spiral antenna when TR is not applied. Using an Archimedean spiral antenna, the proposed method is validated with numerical simulation and measurement. [ABSTRACT FROM AUTHOR]

Objective: This numerical study was designed to evaluate the feasibility of using an inductive coil for monitoring the changes in the volume of a hematoma in the head in situ and to compare the inductive coil performance to that of a spiral antenna based on the radar principle. Methods: Numerical analysis was used to solve the complete set of Maxwell's equations in full three-dimensional anatomical model of a head and brain with data on clinical occurrence of hematomas from the clinical literature, for frequencies of 100 MHz, 500 MHz, and 1 GHz. Results: 1) The analysis shows that the spiral radar antenna provides a better resolution when the antenna can be placed exactly facing the center of the volume of blood. Under any other circumstance, the inductive coil has a better resolution at both 500 MHz and 1 GHz. 2) The induction coil is more sensitive to rotation artifacts than the spiral antenna. 3) Single frequency measurements do not provide conclusive results. Conclusion: The inductive coil has the ability to monitor small changes in the volume of a hematoma in the head. However, multifrequency measurements are required for correct diagnostic. Significance: This study provides a new, low-cost alternative to the conventional medical imaging for monitoring the hematoma increase. [ABSTRACT FROM AUTHOR]

This article presents a high‐efficiency dual‐band rectenna, for RF energy harvesting in GSM bands (900‐1800 MHz). The rectifier used is a dual‐diode rectifier topology based on a Delon voltage doubler. To ensure, the highest efficiency as possible, source‐pull simulations are used to determine the optimal diodes input impedance. The antenna is a spiral planar structure, where two slots ring resonators have been added to expand bandwidth at low frequencies without increasing its initial size. It is associated with a broadband balun to transform its impedance into the desired 50‐Ω rectifier input impedance. The antenna and balun are sized for broadband operation to cover the main wireless communication bands. Measurement results show high RF‐DC conversion efficiencies of 28% and 20% at 890 MHz and 1780 MHz, respectively, for a low RF input power of −20 dBm and with a 10 kΩ DC load. Efficiency reaches 43.5% with a dual‐tone signal at −20 dBm. [ABSTRACT FROM AUTHOR]

We use a genetic algorithm to minimize the relative sidelobe level (RSLL) of a dual polarized concentric ring array. The optimization variables are the placement of uniformly weight spiral antennas in an aperture with a small area. We optimized a cost function with isotropic sources instated of spiral elements to make the cost function reasonable to evaluate. We developed approaches to calculate a faster cost function and reduce the number of function calls in the optimization. We then calculated the array with an approximation of the element pattern to evaluate its performances. [ABSTRACT FROM AUTHOR]

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A new approach to generate beam steering for the circularly polarized (CP) antenna array without phase shift circuits is proposed. The proposed approach is a low cost one compared with those with phase shifters. It is found that in spherical coordinate system ( $r$ , \theta $ , and \varphi $ ), for any constant r$ and \theta $ , as \varphi $ varies from 0 to 2\pi $ , the phase of the CP antenna’s copolarized far field will progress linearly by 2\pi $ , and the magnitude is constant. If a CP antenna is rotated around its own phase center by certain degrees, there is a phase difference between the copolarized electric far fields generated by the antenna before and after rotation. An N \times N , 45°, and 90°, the mainlobe can be scanned from −25° to +24°, −36° to +35°, and −24° to +25°, respectively. [ABSTRACT FROM PUBLISHER]

A wideband, multimode, and monostatic simultaneous transmit and receive (STAR) antenna subsystem is proposed. The configuration is composed of a single four-arm spiral and two analog circuit layers designed to maximize isolation between the transmitting (TX) and receiving (RX) channels. The first layer consists of two Butler matrix beamformer networks (BFNs); one for each TX and RX. The second layer integrates four, ideally phase-matched, circulators between the spiral arms and the BFNs. Theoretically, this configuration achieves infinite isolation irrespective of circulator’s quality. However, the BFN imbalances and the dissimilarities between the four circulators degrade the overall isolation. The operational principles are discussed under the ideal conditions and in the presence of circuit imperfections. For a four-arm spiral, the utilized BFN provides orthogonal modes 1, −1, 2, and 3, allowing STAR capability with multimode and diverse radiation patterns. The subsystem isolation and far-field performances are characterized experimentally and computationally for different modes of operation. A simple approach to achieve a dual-polarized STAR operation over narrower bandwidth with the proposed subsystem is also discussed. The multimode subsystem is demonstrated over 4:1 bandwidth with high isolation, VSWR < 2, consistent patterns, axial ratio < 3 dB over a wide field of view for the broadside modes (1, −1) and < 4.2 dB for other conical modes (2, 3). [ABSTRACT FROM PUBLISHER]

This paper describes the design of a slit on ground plane to improve the axial ratio of the spiral antenna for the NLJD system application. A proposed slit shape located on the ground plane is changed to compare with the archimedean spiral slit shape of the antenna in reference [7]. In order to improve the axial ratio, the slit on the ground plane is divided by the uniform angle and the conductor of position where the current has the opposite direction each other is eliminated. Measured return loss, radiation pattern and gain show a good agreement with the computer simulation results. Even though the proposed slit structure on the ground plane was changed to compare with ones of reference [7], the characteristics such as return loss, radiation pattern and gain are not almost changed and only the axial ratio was remarkably improved at 4.88 GHz. [ABSTRACT FROM AUTHOR]

Bolometer sensor is a good candidate for THz imaging due to its compact system, low cost, and wideband operation. Based on infrared microbolometer structures, two kinds of antenna-coupled microbridge structures are proposed with different spiral antennas: spiral antenna on support layer and spiral antenna with extended legs. Aiming at applications in detection and imaging, simulations are carried out mainly for optimized absorption at 2.52 THz, which is the radiation frequency of far-infrared CO lasers. The effects of rotation angle, line width, and spacing of the spiral antenna on THz wave absorption of microbridge structures are discussed. Spiral antenna, with extended legs, is a good solution for high absorption rate at low absorption frequency and can be used as electrode lead simultaneously for simplified manufacturing process. A spiral antenna-coupled microbridge structure with an absorption rate of more than 75% at 2.52 THz is achieved by optimizing the structure parameters. This research demonstrates the use of different spiral antennas for enhanced and tunable THz absorption of microbridge structures and provides an effective way to fabricate THz microbolometer detectors with great potential in the application of real-time THz imaging. [ABSTRACT FROM AUTHOR]

In this paper, the performance of logarithmic spiral antennas as feeds of dense dielectric lens are investigated in detail. The performances are evaluated in terms of clean symmetric radiation patterns, high polarization purity, antenna efficiency, and radiation dispersivity. A logarithmic spiral antenna placed in the dielectric-air interface can provide high aperture efficiencies over large bandwidths if coupled to a synthesized elliptical lens. The use of an air gap increases the directivity of the spiral radiation inside the dielectric allowing for lens directive patterns without sidelobes and reducing the dispersivity of the radiated pulse. The directivity enhancement of the fields inside the dielectric is validated by the measurement of a prototype. The highest frequency at which these antennas can be fed by a planar microstrip line is limited by the thickness of the microstrip substrate. [ABSTRACT FROM PUBLISHER]

ABSTRACT This paper is intended to introduce a two-arm Archimedean spiral antenna fed by a novel feed structure based on DSPSL (Double Sided Parallel Strip Line). A DSPSL provides an ease perpendicular matching network and an impedance transition between input impedance of a spiral antenna and system's impedance of 50 Ω in broadband frequency range. Measured and simulated VSWR and radiation pattern results show a good performance over ultra-wide band from 2 to 20 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1879-1883, 2016 [ABSTRACT FROM AUTHOR]

ABSTRACT This paper reports the investigation on a new spiral antenna constructed using well-known Fibonacci sequence. Its performance has been compared first with a universal logarithmic spiral antenna (LSA) of nearly the same dimension. Next the discontinuous geometry of the proposed Fibonacci spiral antenna (FSA) has been exploited to fractalize it using Koch curve. The fractalized Koch-FSA has nearly two-third of physical size miniaturization while retaining antenna radiation characteristics.However like other spiral antennas, the multiband behavior of FSA is evident because of conducting ground plane just below it. The geometries of the antenna have been simulated using CST Microwave studio and fabricated over lossy FR-4 substrate with dielectric constant εr = 4.33, loss tangent tanδ = 0.0025 and thickness, ts = 1.5 mm. The measured results are in well agreement with simulations. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1315-1319, 2016 [ABSTRACT FROM AUTHOR]

In an earlier work, the design of a 2:1 bandwidth dual-polarized phased array of Archimedean spiral antennas with cavity was presented. The reflection coefficient, circular polarization, and grating lobes goals were obtained independently in the design process. The low end of the final bandwidth was constrained to the frequency cutoff of the spiral antenna, at the low end of its bandwidth. In this communication, an extension of the bandwidth of the array is achieved by connecting the spiral antennas of the array. Hence, with the same size, the bandwidth is enlarged almost three times (a total of 6:1). The measurements confirm the simulations. The array can scan up to $\theta=30^\circ$ keeping a low reflection coefficient, good right- and left-hand circular polarization, low-sidelobe levels, and using a low-profile cavity. [ABSTRACT FROM PUBLISHER]

ABSTRACT Log spiral antenna is famous model for ultrawideband (UWB) application with circular polarization (CP) and coplanar waveguide (CPW) feed techniques for this antenna are noticed for wipe out the external balun. Therefore, in this letter, CPW feed is used for feeding the log spiral slot parts. The prototype antenna shows good performance for UWB application in the range of 2-11 GHz. The final antenna is covered 2-11 GHz with VSWR less than two in experimental. The antenna radiates Omnidirectionally in the E-plane and bidirectionally in the H-plane, and has a gain that varies between 3 and 7 dBi between 2-11 GHz, with an average gain of 4.5 dBi. The total size of the antenna is 70 × 45 × 1.6 mm3. The antenna has CP at 2.5, 5.5, and 8-9 GHz with axial ratio less than three. The simulated results of prototype antenna are obtained with HFSS and CST and final model antenna is fabricated on FR-4 low cost substrate. The experimental results are confirmed the simulation results. The additional elliptical slots are used for improve the CP in antenna. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:17-21, 2016 [ABSTRACT FROM AUTHOR]

A circularly polarized wideband omnidirectional array of spiral antennas is presented. It covers the frequency band from 1.2 up to 3.6 GHz while keeping a good S11 and an omnidirectional coverage. This array achieved a dual polarization using left- and right-hand Archimedean spiral antennas. The gain of the array is enhanced using a unique cavity for the entire array, and the realized gain is above the maximum theoretical gain of a single spiral antenna. [ABSTRACT FROM PUBLISHER]

An analytical method to estimate the bandwidth of planar phased array of spiral antennas is presented. Three main parameters are considered: circular polarization, reflection coefficient, and sidelobe levels. An application of the method for a planar array of asymmetrical Archimedean spirals is presented for a scan angle of \theta = 30^ \circ . The estimated bandwidth and the bandwidth obtained with the simulation results differ in 3.5%. [ABSTRACT FROM PUBLISHER]

A circularly polarized (CP) spiral antenna array for wideband application is presented, which employs a simple single-arm spiral antenna (SASA), as the radiating element. By introducing a small round disc backed near the antenna center and loading a termination resistor, the SASA achieves a wide impedance bandwidth without a balun circuit and a good axial ratio (AR) performance, respectively. A total of four array elements are used in the 2 × 2 configuration to obtain a higher gain. Particularly, a method of sequentially rotating the elements is used to improve the axial ratio. The array performs an impedance bandwidth for VSWR ≤ 1.5 of 40% ranging from 1.25 to 1.88 GHz, an excellent AR of better than 0.74 dB, and a gain variation from 11.34 to 14.56 dB within the operating band. Measured and simulated results presented for the array confirm its wide impedance, axial ratio, and gain bandwidths. Acceptable agreement between the simulation and measured results validates the proposed design. [ABSTRACT FROM AUTHOR]

ABSTRACT Effects of lossless cavity-backing on time-domain performance of a two-arm combined equiangular/power spiral antenna are discussed. The impact of cavity depth is studied and guidelines for achieving low pulse distortion are established. The resistive arms' termination is found to be necessary to achieve a compromise between good time and frequency performances at the expense of efficiency at low frequencies. Developed antenna with diameter to depth ratio of 8:1 has wide-angle fidelity factor of 90% while maintaining VSWR <1.5, nominal gain >5 dBic, and axial ratio <2.2 dB. Presented results show that the proposed antenna is viable candidate for many applications including pulsed and continuous-wave through-wall imaging, electronic attack/support measures, and ground penetrating radar. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:677-681, 2015 [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, spiral type parasitic elements of the patch antenna are investigated. Composite name of this antenna is 'patch feed curls antenna' (PFCA). Four spirals or curls are symmetrically introduced around the corners of a rectangular patch in plane; they receive their excitation from the latter via a capacitive gap of 1 mm. Due to the effect of the spiral type parasitic elements the gain and bandwidth enhancement found in the patch characteristics. The composite antenna is working in the frequency range 4.24-4.92 GHz. Simulation results obtained from CST-microwave studio are in good agreement with measurements of the fabricated structures. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2773-2778, 2014 [ABSTRACT FROM AUTHOR]

The design of a wide bandwidth dual-polarized phased array of Archimedean spiral antennas with cavity is presented. The reflection coefficient, circular polarization and grating lobes are addressed independently in the design process. Uniform concentric rings array is used to control the grating lobes, thanks to its non uniform spatial distribution, and obtain a good circular polarization, thanks to its rotational symmetry. Simulations of one-ring array agree with the measurements. Adding more rings keeps the side lobes level to less than -10 dB, relative to the main lobe. The dual-polarized array can scan up to \theta=30^\circ keeping a low reflection coefficient and low side lobe levels. [ABSTRACT FROM PUBLISHER]

Conformal load-bearing antenna structures, which afford load-bearing structures with radar capability, are a promising technology to reduce weight and drag of air vehicles. This article presents an investigation of the mechanical and electromagnetic performance of slot log-spiral antenna in carbon-fibre composite structures. Compared with traditional rectangular slots, equiangular slot spiral antenna is found to offer broader bandwidth and better mechanical strength. Through experimental testing and finite element analyses, a new tip design is proposed that can significantly reduce the stress concentration of the non-load-bearing log-spiral antenna. Results of mechanical tests also show that the compressive strength of a carbon-fibre composite plate featuring a spiral slot is comparable with that pertinent to a plate with a circular hole of the same size. Filling the slots with epoxy resin can further enhance the compressive strength. [ABSTRACT FROM AUTHOR]

ABSTRACT A right-hand circularly polarized beam steering spiral antenna is presented in this article. It is designed using the standard p-i-n technology, enhanced with arm switches and biasing lines. The ensuing design is easily manufactured and is functionally competitive with the more complex ones, based on RF-MEMS. Three beams, tilted 40° with respect to the spiral central axis, are generated at 3.3 GHz, suitable for WiMax systems at this frequency. These beams are directed at approximately 90°, 180°, and 270° in the azimuth space. Beam directions depend on various configurations of the seven p-i-n diodes added to the spiral structure. The states of the diodes are subjected to the two DC bias voltages connected to the spiral arm. The radiation performance over the 200-MHz bandwidth (3.2-3.4 GHz) is relatively stable. Measurements in this band show the reflection coefficient below −10 dB and the axial ratio below or close to 3 dB at the peak beam directions. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1636-1640, 2014 [ABSTRACT FROM AUTHOR]

This paper deals with partial discharge (PD) measurement in gas insulated switchgear (GIS) using spiral antenna as UHF external sensor. PD detection in UHF band is effective because it detects electromagnetic (EM) wave induced by PD with high S/N ratio. External sensor was used to detect leaked EM wave signals from insulation spacer of GIS tank. The experiment was conducted in 66 kV GIS model with metal type spacer. There is insulation window in the spacer. PD was generated by some artificial defects in GIS and an external PD source. The leaked EM wave propagated through spacer aperture was measured using spiral type sensor without filter and amplifier. The peak to peak value (Vpp) and the transmission rate of electromagnetic wave signals were evaluated. The PD patterns were observed. The results showed that the PD was detected by the spiral antenna. PD pattern was unique for each defect. These results are considered to be useful for enhancement of database PD diagnosis. [ABSTRACT FROM AUTHOR]

This paper presents design and optimization methods for spiral coils utilized for wireless power transfer in wireless medical implant applications. A theoretical model was examined for near-field distributions of spiral-type transmitter antennas in both orthogonal components. Finite-element simulations were performed to verify the theoretical radiation patterns. Receiver antenna voltages were measured at planes of interest as a means to map field distributions. Theoretical, simulation, and experimental results were conducted in free space and they agreed well. Understanding the orthogonal field components and their distributions in various distances between the worn transmitter coil outside the body and the receiver coil of implant that has a much smaller size provides a means to find the optimal location and angle to harvest maximum energy. The analysis method for near-field wireless power transmission can be utilized to determine design strategies of the transmitter spiral coil with considerations also in the amplifier circuit and physical constraints in practical scenarios to obtain maximum power and link efficiency for the implant devices. The method can be extended to investigate field distributions affected by human tissues, which construct a much more complex environment, and will be conducted in future works. [ABSTRACT FROM AUTHOR]