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We propose a new dual-band passive RFID tag antenna design by combining a rectangular spiral coil and patch-meander-line dipole with an interconnected structure. This design enables operation in high-frequency (HF) and ultra-high-frequency (UHF) RFID systems, suitable for energy harvesting and tracking applications. The simulations by the CST full-wave software demonstrate conjugate impedance matching between the tag antenna and two RFID tag chips. At 13.56 MHz (HF), the tag antenna exhibits an inductive reactance of 422.79 Ω, while at 922.5 MHz (UHF), it presents an impedance of 9.41 + j 174.96 Ω. The antenna generates a maximum magnetic field intensity of 0.5 A/m and omnidirectional electromagnetic fields with an antenna realized gain of -4.26 dBi at 922.5 MHz. We also analyze the impact of the tag antenna combination using numerical software. Furthermore, we fabricate a prototype tag antenna and validate its performance with RFID readers. The proposed tag antenna achieves the maximum read ranges of 11 cm and 6.9 m for the HF (13.56 MHz) and UHF (920-925 MHz) bands, respectively, accompanied by the energy harvesting of 1.48 volts at the HF band by the coupling magnetic field received by the HF antenna to the chip ST25DV04K at the output voltage pin. [ABSTRACT FROM AUTHOR]

A highly frequency reduction technique for three‐dimensional dipole antennas has been presented using linear spiral, modified linear spiral wire‐based structure and wheel on either end of dipole arm. The dipole with wheel on either end of dipole arm reduced the resonant frequency by 65.53% compared with the reference frequency at 3.83 GHz. The electrical properties of ka esteem is 0.59, which are less than the electrically small antenna limit 1. The bandwidth (‑10 dB) enhanced from 11.48 for reference dipole to 17.88% without alleviating the antenna efficiency. The radiation pattern is also seen to be unaffected by the presence of those structures. To verify the simulated theory, prototypes were fabricated and complied with measured results and attained excellent agreement between them. [ABSTRACT FROM AUTHOR]

A double spiral antenna with an artificial magnetic conductor (AMC) is designed, fabricated, and experimentally tested for hyperthermia treatment as a microwave power radiator. The proposed double spiral antenna has a compact structure, designed on an FR4 substrate with a thickness of 1.6 mm, and the dimensions of the proposed antenna is 32 × 32 × 3.27 mm3. The width and space between the spiral arms is 1.54 and inner and outer radius of the spiral is arm 1 and 12.82 mm. The antenna is fed by aperture feeding having dimensions of 16 × 14 mm2 that enhances the antenna's bandwidth. Further, an AMC unit cell (as a reflector) is designed to enhance the proposed antenna's performance, which is designed on an FR4 substrate with a size of 16 × 16 × 1.6 mm3. The size of an AMC structure is optimized to 64 × 64 mm2, consisting of 4 × 4 unit cells and placed at a 5 mm distance at the backside of a double spiral antenna, which enhances the directivity, and gain of the proposed antenna and also converges backfield in the forward direction. At a 5 mm distance, the AMC structure behaves as a reflector and converges all back field radiation in the required direction to make a directional radiation pattern which enhances the antenna's bandwidth and gain. The proposed applicator (antenna + AMC structure) is simulated with a heterogeneous phantom (112 × 112 × 86 mm3), and the performance of the applicator is evaluated by using a specific absorption rate (SAR) in terms of penetration depth (PD) and effective field size (EFS) inside the phantom. The PD and EFS are improved when an AMC structure is placed at the backside of the antenna. Further, the proposed applicator is analyzed for the regular shape of the tumor inserted in the phantom, with the tumor size as 20 × 20 × 10 mm3, located at 10 mm distance from the skin surface. The study of temperature distribution inside the phantom is also done when 2.5 W of power is applied to the applicator in a simulation environment, a temperature rise of the tumor that between the range of 41–45°C is observed, allowing the proposed antenna with an AMC structure to be a good choice for the hyperthermia treatment. [ABSTRACT FROM AUTHOR]

A hybrid frequency‐selective rasorber (HFSR) with low‐frequency absorption and high‐frequency polarization conversion based on rectangular spiral resonator (RSR) is designed, which implements a broad transmission band in the middle band, simultaneously. The HFSR is made up of three components, which are separated by two air gaps. A bandpass frequency‐selective surface (FSS) is employed to realize a broad transmission window at the bottom layer, serving as a metal background of the top layer. The middle lossy layer is composed of the RSR and T‐type metallic strips with four resistors, which is used to absorb the electromagnetic waves (EMWs) in the low‐frequency band and provide a broadband transmission band. The top layer is formed by a pair of arrows to achieve the linear polarization conversion at the high‐frequency band. A four‐port equivalent circuit model (FP‐ECM) with absorbing function is established to explain the physical principle of the proposed HFSR. The simulation results reveal that the 1 dB transmission band is obtained in 7.67–12.06 GHz with a 44.5% fractional bandwidth (FBW). Besides, the co‐polarized reflection coefficients (S11 < −10 dB) are achieved in 4.51–15.81 GHz with a 111.2% FBW. Moreover, the HFSR has a stable oblique incident angle of 30° under TE‐ and TM‐polarized waves. In addition, the radar cross‐section (RCS) of the HFSR can be reduced from 3.0 to 16.0 GHz, which has a 136.8% FBW. Finally, the archetype of the designed HFSR is fabricated and tested to validate the reliability of the simulation results. [ABSTRACT FROM AUTHOR]

An axial‐mode helical antenna with a spiral strip arm excites circularly polarized plane waves propagating along the axis of a drill string bore. This antenna extends the transmission distance of downhole signals in drill strings, thereby increasing the depth of possible measurements. The half‐power lobe width and directivity of the axial‐mode helical antenna matched the microwave channel of the drill string bore. The helical radiator in the antenna was optimized to ensure that center frequency was within the optimal operating frequency band of microwaves in the drill string bore. The reflector in the antenna was optimized through the creation of gas vents, which reduced its cross‐sectional area. The axial‐mode helical antenna reduced the effects of drill string twisting on the microwave channel, reduced reflection in the walls of the drill pipe, and reduced the loss of microwave signals. Compared to linear antennas, the axial‐mode helical antenna had superior performance because S21 increased to about 45 dB in the 2.4 GHz frequency band. The use of axial‐mode helical antennas in drill string bores during microwave measurement while drilling (MMWD) helped in monitoring downhole safety risks and expanding the scope of gas drilling. Therefore, axial‐mode helical antennas have practical applications and require further research. [ABSTRACT FROM AUTHOR]

A circularly polarized Yagi array with a compact structure, small size, and symmetric pattern is reported in this paper. It consists of four 3‐segment counter‐wound helices, one driven element, one director, and two reflectors, for a moderate gain and front‐to‐back ratio. Similar to conventional Yagi with linear polarization, all helical elements have different but close resonant frequencies. The driven element has a resonant frequency higher than that of the reflectors but lower than that of the director. Owing to the uniform pattern of the counter‐wound helical element, a very symmetric pattern with circular polarization at the endfire direction is achieved. A prototype of the 4‐element array is fabricated and tested. Measured results show that an impedance bandwidth with |S11| < −10 dB from 1.345 to 1.42 GHz (5.42%) and a 3‐dB AR band from 1.34 to 1.43 GHz (6.5%) are obtained, showing an overlapped bandwidth of 5.42%. A realized gain up to 7.03 dBi and an offset angle within 3° are also realized. The overall size of the array is as small as 0.66λ0 × 0.107λ0 × 0.40λ0, showing possibility of further being formed to large scanning or multi‐beam arrays. [ABSTRACT FROM AUTHOR]

An omnidirectional circularly polarized (OCP) collinear helical antenna employing a form of self‐canceling sections is proposed in this paper. It consists of three separateλ/2 (where λis the free space wavelength at the center frequency) helical sections, which serve as the radiating elements, and two λ/2 self‐canceling sections to connect them. The self‐canceling section is simply a wire folded in half to form two parallel sections with surface current directions opposing each other, thereby canceling out the far‐field components. The current direction is reversed every half wavelength at the operating frequency. Thus, the surface current vector along the three helical wires would point in the same direction, achieving enhanced radiation. A prototype of the proposed antenna with a diameter of 0.12λand a height of 0.51λhas been fabricated and tested. Measured results demonstrate a maximum gain of 2.23 dBic, an axial ratio and impedance bandwidth of 15.8% and 2%, respectively. [ABSTRACT FROM AUTHOR]

In this article, Dual port excitation spiral shaped dielectric resonator multiple input multiple output (MIMO) antenna is explored for wideband application. Dual coaxial feeding in inner and outer edge of spiral geometry generates orthogonal hybrid modes. Merging of various hybrid modes lead to a wide bandwidth of operation. HE11δx, HE11δy and HE12δx, HE12δy orthogonal radiating modes are investigated at 8.7 GHz and 11 GHz resonant frequencies, respectively. Proposed antenna covers wide operating frequency range from 8–15.1 GHz to 7.8–14.6 GHz corresponding to excitation of Port‐1 and Port‐2, respectively, is achieved between ports. Isolation below −25 dB. Envelope correlation coefficient, diversity gain, Total active reflection coefficient, radiation pattern, channel capacity loss, gain, efficiency and various other characteristics of MIMO antenna are explored. This antenna can be used for various C and X band wireless applications. [ABSTRACT FROM AUTHOR]

In this paper, a wideband circularly polarized two‐layer concentric cylindrical dielectric resonator antenna (CDRA) is proposed for C‐band applications. To generate the circular polarization in the CDRA, the proposed antenna is excited with four turn helical wire. The helix excites the two orthogonal modes (HE11δ) in quadrature phase, which result in the circular polarization. The four different design cases are investigated and the best one is fabricated and measured. The impedance bandwidth is improved when two‐layer concentric CDRA is used. The simulated and measured bandwidth of the proposed antenna varies from 3.60 to 6.03 GHz with impedance bandwidth of 50.46% and 3.65 to 6 GHz (48.70% impedance bandwidth) respectively, while axial ratio impedance bandwidth are 43.13% (4.20–6.51 GHz) and 38.82% (4.40–6.52 GHz) respectively. The proposed antenna attains 10.9 dBi measured peak gain at 4.5 GHz. The fabricated prototype is experimentally measured and its results are found to be in good agreement with the simulation results. [ABSTRACT FROM AUTHOR]

Cancer is the leading cause of death in recent centuries and microwave ablation (MWA) has been evolving to thermally treat cancerous tissue through cell necrosis and is also a promising substitute to radio frequency ablation. In this article, a novel normal‐mode helical antenna based MWA probe is investigated for the effect on ablation diameter in the presence of five critical parameters. The antenna consists of an intertwining helix structure mounted on a very small ground plane. An external tapping is used to match the antenna impedance. In the proposed design at the center frequency, a reflection coefficient of more than 23 dB without insertion into the tissue model and a reflection coefficient of more than 14 dB with insertion into the tissue model have been observed at 5 GHz frequency. The gain and percentage bandwidth of the antenna is 0.6 dB and 10%, respectively. At 20 W power, a maximum ablation diameter of 32 mm (transversal‐T) and 44 mm (axial‐A) is reached within 5 min of application time at a distance of 30 mm from the probe. Further, the L27 Taguchi's orthogonal array has been employed to study the effect on ablation diameter by varying five thermo‐electrical parameters. The outcome of Taguchi's analysis has been ranked according to the contribution of each parameter. Further, F‐ and p‐value test has been employed using analysis of variance to study the significance of each parameter on ablation diameter. [ABSTRACT FROM AUTHOR]

A circularly symmetric high impedance surface (HIS)‐based low‐profile circularly polarized antenna with stable phase center is investigated. The antenna consists of a series‐fed eight‐arm spiral slot antenna and a circularly symmetric HIS (CSHIS) used as the ground plane. As the use of CSHIS, the profile of antenna is decease to as low as 0.09λ (λ is the free space wavelength), while the phase center of the antenna maintains stable. Also, the gain of the presented antenna is enhanced compared with that utilizing HIS with rectangular unit cell. For verifying, a prototype of the antenna was fabricated and measured. The measured results show that the overlap bandwidth of 3‐dB axial ratio and impedance matching covers 1.14–1.45 GHz (23.9%), and the gain can reach as high as 7.79 dBic. Over the operation band, stable phase center also can be observed. [ABSTRACT FROM AUTHOR]

In this paper, a full‐wave analytical theory has been proposed based on the field theory approach and numerically solved for computing radiation properties of the dielectric‐loaded helical antenna (DLHA). First, the dispersion equation is analytically derived from the source‐free Maxwell equation subject to necessary boundary conditions. Then radiation characteristics of DLHA are derived using the field theory approach. The effect of polarization current arising due to dielectric on radiation properties is addressed for the first time in the case of DLHA. All the numerical analysis is carried out in MATLAB. To further validate the results, computation analysis is carried out using CST Microwave Studio Software. From the result, it was observed that when the circumference of the antenna (C) is comparable to the wavelength (λ) corresponding to operating frequency then the wave propagates axially through the helical wire in the axial direction and is radiated in the end‐fire direction whereas when the circumference is not equal to the wavelength then the wave gets radiated in the normal direction and attenuated in the axial direction. Also, the impedance bandwidth of the antenna is increased from 2.5% to 52.9% and the gain is increased from 8.35 dB to 11.5 dB due to teflon loading. Finally, the antenna prototype is fabricated, measured, and compared with the numerical and computational results. A close agreement between the analytical, computational, and measurement results are found. [ABSTRACT FROM AUTHOR]

Microwave field near‐field radiation imaging technology is widely used in the failure analysis of chips, but due to the low resolution, it is hard to obtain the field distributions of miniaturized and precision devices. In this article, we built two testing systems based on the method of electromagnetic induction and diamond color‐center, respectively. The traditional system uses a multilayer PCB microstrip, while the novel system uses nanoscale high‐sensitivity sensing of color centers in the design of resonant microwave field probes with near‐field measurement sensitivity to enable nanoscale high‐sensitivity measurements of different physical quantities. We tested two devices in this article, and the results show that compared with traditional measurement method, the novel method promotes higher resolution (submicron level), higher sensitivity, and nondestructive imaging. This method can accurately characterize the near‐field distribution of microwave integrated circuit chips, such as spiral antennas, and amplifiers. Especially in the amplifier chip, the signal change trend of the amplifier circuit can be clearly characterized. It is expected to provide a new measurement concept in real word applications, such as chip electromagnetic compatibility, microwave chip failure analysis, and antenna near‐field scanning radiation emission testing. [ABSTRACT FROM AUTHOR]

This article presents a 2 to 18 GHz absorber‐loaded cavity‐backed (AL‐CB) two‐arm Archimedean spiral antenna fed by a 186 Ω Phelan balun for direction finding (DF) and radar warning receiver (RWR) applications. The balun's cross‐sectional area diameter at the antenna feeding region is less than the diameter of the active region ring at 18 GHz. This feature provides a lower axial‐ratio (AR) and wobble‐on‐wave (WoW) at higher operating frequencies and far theta angles and distinguishes the proposed AL‐CB spiral antenna from its counterparts and commercial off‐the‐shelf (COTS) products. The proposed antenna is 60 mm in diameter and 50 mm in height. The voltage standing wave ratio is typically less than 2 (max. 2.6), which is within 2 to 18 GHz frequency range, and the AR is less than 1 dB with a peak of 3.1 dB in off‐axis Ɵ < 60°. The WoW is less than 2 dB in off‐axis Ɵ < 60°. This study's simulation and measurements both demonstrate the ultrawideband (UWB) with 1:9 bandwidth, unidirectional, symmetric, and circularly polarized radiation characteristics of the proposed antenna for DF and RWR applications. [ABSTRACT FROM AUTHOR]

A new quasi‐analytical synthesis method is presented for designing spiral defected microstrip structures (DMS). A comprehensive analysis based on circuit models, mathematical relations, and extensive simulations is used to achieve an exact, straightforward, and tunable wide‐range frequency design process. The design process benefits of some novel formulas derived based on the overall form of resonance frequency functions and the study of extensive simulations. We used the Levenberg Marquardt Iteration (LMI) algorithm for the derivation of closed‐form formulas. The resonance frequency of a spiral DMS called notch frequency can be independently tuned in a large frequency span by employing the proposed method. The designed spiral DMSs and the new synthesis method can be applied to applications such as filters, antennas, amplifiers, and multipliers. The proposed spiral DMS design/synthesis method and the derived closed‐form formulas are verified and validated by simulations and fabrication of six filters with different geometries and specifications. A comparison of the simulation and measurement results of the fabricated filters proves the accuracy and validity of the proposed design method and formulas where the relative effort is less than 0.38%. The return loss and group delay of the filters are less than 0.48 dB and 0.5 ns, respectively. [ABSTRACT FROM AUTHOR]

This article proposes an ultra-wideband coplanar strips (CPS) rectangular spiral antenna that is fed by coplanar waveguide (CPW). The CPS is formed by gradually reducing the width of the CPW ground planes without the need of a balun. The antenna operates in the frequency band (3.5-10.6 GHz) and has miniaturized size of 50 × 40 × 0.508 mm on a Rogers RO4003C substrate. The CPS spiral is terminated with a 100 Ω chip resistor for matching. A parametric study was performed to choose the CPS spiral dimensions. A good agreement is found between simulations and measurements in the radiation pattern and the return loss which was found to be better than 10 dB over the band. The measured peak gain ranges between 1 and 4.7 dBi. [ABSTRACT FROM AUTHOR]

Single-layer and bilayer four-arm spiral antennas and their feeding methods for Mode 1 operation are discussed in this article. Important design parameters such as metal-to-slot ratio and growth rate for better impedance matching and reduced far-field contamination are studied. Three feeding methods for Mode 1 operation are compared: a bundle of four coaxial cables for a single-layer spiral and vertical and horizontal feeds by two coaxial cables for bilayer spirals. It is shown that the single-layer spiral maintains beam symmetry with Wobble on Wave better than 1 dB at θ = 30° over 10:1 bandwidth. However, the required beamformer is complex and expensive. Proposed, horizontally and vertically fed bilayer spirals need simpler beamformer while maintaining similar far-field performance over narrower 6:1 and 2:1 bandwidths, respectively, thus making them useful for many wideband applications. Modeling is conducted by a method of moments and validated with a finite element method and measurements. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE 22: 652-662, 2012. [ABSTRACT FROM AUTHOR]

This article presents a broadband circularly polarized two‐arm Archimedean spiral antenna with a novel simple feeding method. Contrary to the conventional spiral antenna excited by a vertically or horizontally balun, the presented design is directly fed by a coxial cable with a planar feeding section optimized to provide a broadband input impedance matching. An antenna prototype has been fabricated and measured to validate the concept. Measured results of reflection coefficient and axial ratio show a good performance over a frequency range from 1.0 to 3.5 GHz, equivalent to ~111.1%. Within this band, the antenna prototype exhibits bidirectional radiation with broadside gain values of better than 3.6 dBic. [ABSTRACT FROM AUTHOR]