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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]

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]

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]

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]

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]

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]

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]

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]

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]

ABSTRACT The planar spiral antenna being connected with the waveguide and operating in the long-wave region of the millimeter range is proposed. The antenna has the bandwidth of 6 GHz and the axial ration which does not exceed −3dB in the frequency band 32-36.5 GHz. The radiation pattern shape is slightly changed within the operational frequency band. The results of simulations and experimental data are in good agreement. The nature of radiation pattern and axial ration changing within the operational frequency band is explained from the analysis of near-field distributions measured at two orthogonal polarizations. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:293-297, 2014 [ABSTRACT FROM AUTHOR]

A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide.The proposed structure has a return loss of <−10 dB over a broad bandwidth of 0.5-5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are investigated through various simulations. A case of the proposed antenna is fabricated, and measurement results are presented including return loss, gain, and radiation patterns. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1338-1341, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27535 [ABSTRACT FROM AUTHOR]

The ultrawide-band antenna with original transformer providing the required electromagnetic matching of the coaxial cable with the small-size single-arm equiangular spiral antenna is proposed. The measured input reflection coefficient of the small-size spiral antenna is less than −10 dB within the frequency band from 7.5 to 40 GHz. The near-fields, radiation patterns and axial ration within the impedance antenna bandwidth are presented and discussed. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:2190-2194, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27018 [ABSTRACT FROM AUTHOR]

A spiral antenna matched to a SAW sensor for blood pressure and body temperature monitoring is proposed. As the antenna/SAW device is dedicated to be implanted in a human body, a small antenna with omnidirectional pattern is required. The proposed structure has a total area of 4 × 2.5 mm2 and a 1.1 mm height. To take into account the human body effect, we use a homogenous phantom with a dielectric permittivity of 52 and a conductivity of 1.74 S/m. The -10 dB impedance bandwidth of the proposed antenna is 66% from 2.22 to 3.83 GHz; moreover, a quasi-isotropic radiation pattern is achieved. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2286–2293, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24622 [ABSTRACT FROM AUTHOR]

ABSTRACT This article presents a novel antenna with an improved impedance bandwidth and axial ratio bandwidth. This new design is comprised of an equiangular spiral and two annular rings on the same plane. These are printed on a Taconic substrate with a dielectric constant of 2.2 and a thickness of 1.52 mm. The proposed antenna has good performance compared with the conventional equiangular spiral antenna. The simulation results are validated through experimental measurements, and the overall size of the spiral antenna is visibly reduced. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2865-2867, 2015 [ABSTRACT FROM AUTHOR]

Analysis of spiral antenna with open circuits on its arm is presented for beam adaptive applications. It is shown theoretically and experimentally that when the open circuits are appropriately positioned in the arm, the current distribution varies, causing the beam to steer. This effect can be exploited to design various novel beam switchable antennas. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2567–2570, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22738 [ABSTRACT FROM AUTHOR]

A spiral antenna with a helix loaded is investigated in this paper. Through combining the spiral with a helix together, circular polarization can be achieved in dual bands. Since the helix is loaded in the lower part of the spiral, this technique doesn't increase the antenna's volume but at the same time introduces another CP band. The experimental result shows that the lower band and upper band are 4.0% and 62.07% respectively. The characteristics of impedance, current distribution and radiation pattern will also be presented. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1939–1942, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22596 [ABSTRACT FROM AUTHOR]

Based on a planar inverted-F antenna (PIFA) configuration, two different shaped (meandered and spiral) antennas are designed using finite-difference time-domain (FDTD) simulations and measurement results. The antennas are installed on an implantable medical device in a biological-tissue simulating model. The impedance-matching and radiation characteristics of two PIFAs are compared in order to observe which shape is more appropriate for wireless communication links of implantable medical devices. Additionally, the effects of the human skin's thickness on the antennas are studied in order to consider medical devices which are implanted in various subcutaneous tissues. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 567–572, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21409 [ABSTRACT FROM AUTHOR]

A low-cost, small-size, broadband antenna array of Archimedean spiral elements is designed with beam-steering and interference-nulling capabilities for mobile platforms (for example, laptop computers). Its adaptive beam-forming and beam-steering capabilities are investigated using two well-known techniques; the finite-difference time-domain (FDTD) method and the method of moments (MoM)-based numerical electromagnetic code (NEC2). Although the structure is optimized for 3rd-generation GSM and Bluetooth applications (that is, around 2.5 GHz), it is illustrated that this structure may also be used to cover all radio/TV broadcast (from FM radio to UHF TV stations) and up to several GHz frequencies that are reserved for future applications. © Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 195–200, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21304 [ABSTRACT FROM AUTHOR]

A dual spiral-loop strip antenna fed by coplanar stripline (CPS) is proposed and developed for circularly polarized printed antennas with miniaturized size and broad bandwidth. The overall size is reduced in circumference by about 33%. A printed feeding circuit is designed and implemented using uniplanar CPS technology in order to realize good impedance matching. The predicted results are validated by the experiment. The measured bandwidths under a 3-dB axial ratio and voltage standing-wave ratio are found to about 10% and 6%, respectively. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 46: 506–508, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21030 [ABSTRACT FROM AUTHOR]