Helix Antenna Research Articles

Minimum $Q$ Electrically Small Antennas

Theoretically, the minimum radiation quality factor <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of an isolated resonance can be achieved in a spherical electrically small antenna by combining TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1m</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1m</sub> spherical modes, provided that the stored energy in the antenna spherical volume is totally suppressed. Using closed-form expressions for the stored energies obtained through the vector spherical wave theory, it is shown that a magnetic-coated metal core reduces the internal stored energy of both TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1m</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1m</sub> modes simultaneously, so that a self-resonant antenna with the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> approaching the fundamental minimum is created. Numerical results for a multiarm spherical helix antenna confirm the theoretical predictions. For example, a 4-arm spherical helix antenna with a magnetic-coated perfectly electrically conducting core ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> =0.254) exhibits the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of 0.66 times the Chu lower bound, or 1.25 times the minimum <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> .

A novel frequency-selective metamaterial to improve helix antenna

A novel frequency-selective metamaterial with negative permittivity and permeability for improving directivity and gain of a helix antenna is presented in this paper. The proposed metamaterial is composed of two Z-shape resonators printed on opposite sides of a dielectric substrate. Two forms of multilayered cells are found to be suitable for antennas and waveguides applications. In addition, a new method of designing a metamaterial-based helix antenna is presented with high directivity and gain. A comparison on radiation properties is given between the conventional and the new metamaterial-based helix antennas. Two comparisons on radiation properties are performed: (1) the effect of proposed Z-structure on monopole, dipole, and helix antennas; (2) the effect of OE3, split-ring resonator (SRR), and proposed Z-structure unit cells on the performance of helix antennas. The results show improvement of parameters such as directivity, gain, and radiation power of the new metamaterial-based helix antenna. Therefore, the combination of Z-structure with the helix antenna shows the best performance.

Design of a wideband rasorber with a polarisation-sensitive transparent window

The present thesis considers two different subjects in the research area of electromagnetics. The first part is concerned with antenna design and the second with radar absorbers and rasorber.In the first part, a novel excitation technique for cylindrical dielectric resonator antennas is introduced to produce circular polarization. The exciter is a tape helix that is wound around the dielectric resonator and is fed by a coaxial probe. The helix excites the HE11σ modes in phase quadrature in the cylindrical dielectric resonator antenna. The height of the helix is determined using the Hansen-Woodyard condition for an end-fire array based on the phase velocity of the surface wave traveling along the dielectric resonator side wall. This phase velocity is estimated from the phase velocity in an infinitely long dielectric rod with the same permittivity and radius as the dielectric resonator antenna. The helical exciter is required to operate in the helix axial mode. The height of the helix is usually taller than the height of the dielectric resonator core. Using this type of excitation, a 3 dB axial-ratio bandwidth of 6.4% was achieved for a sample design with dielectric constant er ~ 11. The achieved 3 dB axial-ratio bandwidth is greater than that typical of other reported single feed cylindrical dielectric resonator antennas. A prototype of the sample design is fabricated and measured and a good agreement between simulation and measurement is observed. Furthermore, two approaches for the enhancement of the 3 dB axial ratio bandwidth are proposed: removing the central portion of the cylindrical dielectric resonator and using stacked cylinders. The advantages and limitations of each approach are discussed. Another perspective on the proposed design is to consider the antenna as a helix with a dielectric resonator core. In this perspective, the effects of the dielectric core on the helix antenna are discussed.The second part of the thesis is concerned with the design of thin wideband electromagnetic planar absorber for X- and KKu-band which also has a polarization sensitive transparent window at frequencies lower than L-band. The design is based on a two layer capacitive circuit absorber with the backmetal layer replaced with a polarization sensitive frequency selective surface. The structure is studied for normally incident waves with two orthogonal linear polarizations. The structure is optimized to have high transparency at low frequencies for one of the polarizations and at the same time good absorption efficiency for both polarizations at the high-frequency band. For one of the polarizations a -1.9 dB transmission with a transmission loss of less than 10% at 1 GHz as well as a 2.25:1 (75%) bandwidth of -20 dB reflection reduction are achieved. For the other polarization we obtained more than 3:1 (100%) bandwidth of -19 dB absorption. Compared with our earlier design based on a Jaumann absorber, we succeed in significantly reducing the transmission loss at the transparent window. Furthermore, the module of absorption quality is extensively improved. The improvements are based on using periodic arrangements of resistive patches in the structure design. The investigation of the structure for oblique angles of incidence and non-ideal materials is also accomplished.

DESIGN OF A WIDEBAND MONOPULSE ANTENNA USING FOUR CONICAL HELIX ANTENNAS

A novel S-band monopulse antenna with four conical helix antennas on a microstrip substrate comparator is designed, fabricated and measured. Conical helix antenna height is 3‚, and comparator size is 130mm £ 150mm. The bandwidth (SWR < 2dB) of the antenna is 21.3% with an operating frequency range of 2.7GHz{3.35GHz. The maximum gain of the sum pattern is 17.4dB, and the null depths of the difierence pattern are less than i30dB.

FAST ANTENNA CHARACTERIZATION USING THE SOURCES RECONSTRUCTION METHOD ON GRAPHICS PROCESSORS

The Sources Reconstruction Method (SRM) is a noninvasive technique for, among other applications, antenna characterization. The SRM is based on obtaining a distribution of equivalent currents that radiate the same field as the antenna under test. The computation of these currents requires solving a linear system, usually ill-posed, that may be very computationally demanding for commercial antennas. Graphics Processing Units (GPUs) are an interesting hardware choice for solving compute-bound problems that are prone to parallelism. In this paper, we present an implementation on GPUs of the SRM applied to antenna characterization that is based on a compute-bound algorithm with a high degree of parallelism. The GPU implementation introduced in this work provides a dramatic reduction on the time cost compared to our CPU implementation and, in addition, keeps the low-memory footprint of the latter. For the sake of illustration, the equivalent currents are obtained on a base station antenna array and a helix antenna working at practical frequencies. Quasi real-time results are obtained on a desktop workstation.

Properties and Applications of Electrically Small Folded Ellipsoidal Helix Antenna

A comprehensive analysis of the radiation properties of an electrically small folded ellipsoidal helix antenna (EHA) is presented, showing its ability to self-resonate and impedance match without external components. Three antennas with different sizes and geometries have been designed to work at the 2.4-GHz ISM band and are realized using a selective laser sintering (SLS)-based fabrication process. The benefits of using this antenna for various size-restricted applications such as medical implants are also described.

Experiments on Broadband EMP Radiation with an Axial Mode Helix Antenna

To produce broadband electromagnetic pulse (EMP) radiation, we design and test a sub-ns pulse system which is utilized to drive an axial mode helix antenna. This sub-ns pulse system consists of a 10-stage Marx generator, an intermediate storage capacitor, an impedance transforming line, and can generate a high voltage of 570 kV with a rise time of 1–1.5 ns on a 300-Ω-resistance load. The diameter, pitch and turns of the helix antenna are 29 cm, 19.5 cm and 5, respectively, with a design frequency of 300 MHz. When the charging voltage of the Marx generator is 30 kV, the electric field of radiated EMP measured 3m from the source is 35 kV/m with a central frequency of 250 MHz. The relatively spectral bandwidth is 25%. The radiated EMP results are reproducible and the system will work in repetition mode if the available dc power is utilized.

Size Reduced Multi-Band Printed Quadrifilar Helical Antenna

A simple and innovative method for designing a spiral folded printed quadrifilar helix antenna (S-FPQHA) for dual-band operations is presented. The axial length of a conventional PQHA is miniaturized of about 43% by meandering and turning the helix arms into the form of square spirals. Parametric studies are performed to explore the performance improvements. Based on the studies a dual band antenna working in L1/L5 GPS application is realized with a good gain and a good circular polarization. Measured results are presented to validate the concept.

Simulations of Multipactor Breakdown Between Two Cylinders

Simulations have been performed to determine the multipactor breakdown threshold in a microwave structure composed of two parallel cylinders, chosen to be an approximate model of an open helix microwave antenna system. The electromagnetic field between the cylinders is available in closed analytical form, and a Monte Carlo software has been developed to calculate the 2-D electron trajectories and to simulate the multipactor avalanche in this inhomogeneous electric field for different ratios of cylinder radius and distance of separation between the cylinders. The results are compared with those of a recently published analytical theory and show a qualitatively good agreement. In particular, it is confirmed that, for a given distance between cylinders, there exists a smallest cylinder radius below which no two-sided multipactor breakdown can occur. The basic physical explanation is a loss mechanism for secondary emitted electrons that is caused by the curvature of the cylinder surfaces together with the strong electric field at the surfaces. The results imply that the breakdown threshold in realistic open helix antennas is significantly higher than those predicted using extrapolations based on resonance theory and the classical two parallel plate model.

The effect on wireless sensor communication when deployed in biomass.

Wireless sensor networks (WSN) have been studied in a variety of scenarios over recent years, but work has almost exclusively been done using air as the transmission media. In this article some of the challenges of deploying a WSN in a heterogeneous biomass, in this case silage, is handled. The dielectric constant of silage is measured using an open-ended coaxial probe. Results were successfully obtained in the frequency range from 400 MHz to 4 GHz, but large variations suggested that a larger probe should be used for more stable results. Furthermore, the detuning of helix and loop antennas and the transmission loss of the two types of antennas embedded in silage was measured. It was found that the loop antenna suffered less from detuning but was worse when transmitting. Lastly, it is suggested that taking the dielectric properties of silage into account during hardware development could result in much better achievable communication range.

Reconfigurable Axial-Mode Helix Antennas Using Shape Memory Alloys

Reconfigurable structures based on smart materials offer a potential solution to realize adaptive antennas for emerging communication devices. In this paper, a reconfigurable axial mode helix antenna is studied. A shape memory alloy spring actuator is used to adjust the height of a helix antenna. With the total length of the helix wire fixed, the pitch spacing and pitch angle are varied as the height is varied. This in turn can alter the antenna pattern in order to adjust to altered operating conditions. In order to undertake the design, the Kraus equations for the axial mode helix are compared with simulation results, and their range of applicability is clarified. It is shown that based on these equations, antenna gain variation is possible by varying the height of the antenna, while keeping its conductor length fixed. We then show that a pattern can be reconfigured using a two-helix structure. Finally, a proof-of-concept helix antenna is implemented using a shape memory alloy actuator. Measurement results confirm that the pattern can reconfigure while maintaining a reasonable impedance match.

Compact dual‐band printed square quadrifilar helix antenna for global navigation satellite system receivers

AbstractA miniaturized dual‐band printed square quadrifilar helix antenna (QHA) is proposed for global navigation satellite systems (GNSS) receivers applications.The antenna consists of four printed helices forming a cube with a very small size of 1 cm3 only. It can cover both L1 and L2 bands, centered at 1.575 and 1.227 GHz, respectively. It can achieve good impedance matching and circularly polarized radiation patterns within both L1 and L2 bands. The antenna is very light weight and easy for fabrication. The feed network for the antenna is also designed. To prove the concept, a prototype is developed, fabricated and measured. Both measured and simulated results are presented and discussed. Because of its advantages of compact size, low mass and low cost, the antenna is useful for GNSS receiver onboard small satellites, and mobile terminals on the ground. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:993–997, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25949

Compact square quadrifilar helix antenna for SDARS application in portable terminals

Presented is a new method for designing a compact square quadrifilar helix antenna with circular polarisation, operated at satellite digital audio radio service (SDARS) band (2320–2345 MHz) and intended for applications in portable terminals. This new antenna comprises four helix antennas, which are wound around a square pillar orthogonally and excited with a phase difference of 90°

Super Numerical Electromagnetic Code (S-NEC) Softwareand Antenna Simulation

In this paper, we can learn what is the S-NEC and how do we do simulation by it. S-NEC software is one of a specific for antenna design and simulation. Then a wire meander helix antenna with a new structure had been designed and simulated. The length of this antenna in relation to wave length is very small, in addition to this antenna have a high radiation resistance and low imaginary resistance. Also the antenna dimension gets better for having a high efficiency and the most bandwidth in 20 MHz to 24 MHz frequencies.

ANALYSIS AND SYNTHESIS OF RADAR CROSS SECTION OF ARRAY ANTENNAS

Our previous work has proved that the Monostatic Radar Cross Section (MRCS) of array antennas can be decomposed into the multiplication of array MRCS factor and element MRCS factor. The principle was derived in a special case that the array only had dipole antenna elements. However, many array antennas have more general antenna elements whose current is aperture distributed along the antenna structure. Obviously it encounters limited application problem when the principle is used to analyze more general array antennas other than dipole arrays. Therefore, the principle is extended into the more general array with arbitrary aperture antenna elements in this paper. In deriving the principle, the devices in the feed are assumed to have identical transmission and re∞ection coe-cients. In order to validate the principle the scattering pattern of a waveguide slot array and an array with helix antenna elements are synthesized utilizing the array RCS factor. The simulation and calculation results prove that the principle is correct for the RCS pattern synthesis of general arrays with aperture antenna elements.

Low profile meander line Printed Quadrifilar Helix Antenna

In this paper, a new approach of meander line technique for Printed Quadrifilar Helix Antenna (PQHA) is studied. Compared with other meander line techniques, this approach has lowered the axial height of antenna greatly and improved the efficiency of model-building in simulation processing. We have focused on the analysis of radiation pattern, axial ratio, and design graph for the Meander line Printed Quadrifilar Helix Antenna (MPQHA). Finally, we have reduced successfully 67% size in geometry compared with traditional PQHA method, and obtained rather reasonable results.

GPS-only gravity field recovery with GOCE, CHAMP, and GRACE

Gravity missions such as the Gravity field and steady-state Ocean Circulation Explorer (GOCE) are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD), instrument time-tagging, and the extraction of the long wavelength part of the Earth’s gravity field. The very low orbital altitude of the GOCE satellite and the availability of dense 1 s GPS tracking data are ideal characteristics to exploit the contribution of GPS high-low Satellite-to-Satellite Tracking (hl-SST) to gravity field determination. We present gravity field solutions based on about 8 months of GOCE GPS hl-SST data from 2009 and compare the results with those obtained from the CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) missions. The very low orbital altitude of GOCE significantly improves gravity field recovery from GPS hl-SST data above degree 20, but not for the degrees below 20, where the quality of the spherical harmonic coefficients remains essentially unchanged. Despite the limited time span of GOCE data used, the gravity field of the Earth can be resolved up to about degree 115 using GPS data only. Empirically determined phase center variations (PCVs) of the GOCE onboard GPS helix antenna are, however, mandatory to achieve this performance.

Microwave Multipactor Breakdown Between Two Cylinders

An analysis has been made of the microwave breakdown threshold for multipactor in an open structure comprising two parallel cylinders, approximating, e.g., parts of a helix antenna. The electron motion in the corresponding electromagnetic field is analyzed by separating the motion into a slowly varying drift velocity (driven by the ponderomotive force due to the electric field inhomogeneity) and a rapidly oscillating part (driven by the oscillating electric field). Furthermore, the curvature of the cylindrical surfaces of emission is shown to give rise to a new effect that implies a loss of electrons. This leads to a more stringent multipactor breakdown condition for the two-wire structure than for the classical situation corresponding to the case of two plane parallel infinite plates. The importance of this effect is determined by the ratio of the cylinder radii and the distance between the cylinders, and it is shown that when this ratio is small, multipactor can only occur for surfaces having very large secondary emission coefficients. A detailed analysis is also made to determine the lowest voltage between the cylinders at which multipactor becomes possible.

Low-Q Electrically Small Spherical Magnetic Dipole Antennas

Three novel electrically small antenna configurations radiating a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> spherical mode corresponding to a magnetic dipole are presented and investigated: multiarm spherical helix (MSH) antenna, spherical split ring resonator (S-SRR) antenna, and spherical split ring (SSR) antenna. All three antennas are self-resonant, with the input resistance tuned to 50 ohms by an excitation curved dipole/monopole. A prototype of the SSR antenna has been fabricated and measured, yielding results that are consistent with the numerical simulations. Radiation quality factors (Q) of these electrically small antennas (in all cases ka <; 0.26) approach the limit of 3.0 times the Chu lower bound for a given antenna size, which is in line with a theoretical prediction made by Wheeler in 1958.

A Low-Profile Linearly Polarized 3D PIFA for Handheld GPS Terminals

A 3D planar inverted F-antenna (PIFA) is proposed for a Global Positioning System (GPS) receiver. The antenna is designed to be integrated in a portable device and must meet compact size requirements. The 3D PIFA consists of a single metal sheet properly cut and bent in order to minimize costs for realization, materials and series production. The linearly polarized antenna exhibits good impedance matching performance, wide beam radiation patterns and a relatively high gain, which allow the reception from a wide angle toward the satellite constellation. An antenna prototype has been embedded in a commercial GPS receiver and an experimental measurement campaign has been carried out to evaluate the most important performance parameters. Measurements have been performed out by collecting time sweeps signal samples along urban and suburban routes. Time to first fix, carrier to noise ratio distribution and horizontal dilution of precision have been calculated; these parameters are shown and discussed. Comparisons with respect to some reference circularly polarized antennas (a nearly square patch and a quadrifilar helix antenna) and to a simpler inverted-F antenna printed on the receiver PCB have been performed and are shown in the paper.