Helical Antenna Array Research Articles

HIGH GAIN AXIAL-MODE HELICAL ANTENNA WITH CIRCULAR METAL DISK

A method to improve the gain of axial-mode helical antenna is proposed. This method involves a parasitical circular metal disk, which is installed on the front of general axial-mode helical antenna and is apart from the helical line. A circular current whose phase lags behind that of helical line current appears, which brings a more concentrated radiation fleld. Consequently, the antenna gain is improved. Based on the simulation results, an antenna array model fed independently is proposed. This model gives an excellent explanation of the radiation characteristic of helical antenna. Both the simulation and experiment results show that for obtaining the same gain, the antenna length in this new method is only 71% of that in traditional helical antenna. The reduction of antenna length favors the miniaturization of antenna. In addition, this method has little efiect on the bandwidth of antenna, so it can be widely used in the design of helical antenna element and array.

Experimental Investigation of the Performance of Two-Element Helical Antenna Array for Television and Mobile Phone Networks Operating at 400-900 MHz Band

Experimental Investigation of the Performance of Two-Element Helical Antenna Array for Television and Mobile Phone Networks Operating at 400-900 MHz Band

16-Element Single-Layer Rectangular Radial Line Helical Array Antenna for High-Power Applications

A 16-element single-layer rectangular radial line helical array antenna is proposed and investigated. In the single-layer radial line feed system, two new probes are used to satisfy the coupling requirement. The sequential rotation technique is introduced to improve the axial ratio of the antenna. An antenna prototype is designed, simulated, and measured. The results indicate its advantages of high aperture efficiency, low input VSWR, and favorable axial ratio. The field distributions of this antenna are analyzed through simulation, which prove its advantage of high power-handling capacity. This array is also used to form an 8 × 8 array antenna, which demonstrates its ability to be used as a subarray.

A GW Level High-Power Radial Line Helical Array Antenna

High-power radial line helical array antenna is a novel antenna developed to realize directional radiation of high-power microwaves. This antenna directly accepts an azimuthally symmetric output of a high-power microwave source and radiates circularly polarized microwave with a boresight peak. It has a high efficiency, a compact structure, and a notable power-handling capacity. Starting from its fundamental design theory, an antenna prototype consisting of 48 elements is proposed. Numerical simulation and experimental measurement are accomplished for the prototype. In the range of 3.7-4.1 GHz, the experimental result shows an antenna VSWR of below 1.2, an antenna gain of over 23.2 dB, an aperture efficiency of more than 65%, and an antenna axial ratio of below 1.6 dB. In addition, the high-power experiment proves that this antenna has a power-handling capacity of more than 1 GW.

A New Direction in Computational Electromagnetics: Solving Large Problems Using the Parallel FDTD on the BlueGene/L Supercomputer Providing Teraflop-Level Performance

Rapid developments in high-performance supercomputers, with upward of 65,536 processors and 32 terabytes of memory, have dramatically changed the landscape in computational electromagnetics. The IBM BlueGene/L supercomputer are examples. They have recently made it possible to solve extremely large problems efficiently. For instance, they have reduced 52 days of simulation on a single Pentium 4 processor to only about 10 minutes on 4000 processors in a BlueGene/L supercomputer. In this article, we investigate the performance of a parallel Finite-Difference Time-Domain (FDTD) code on a large BlueGene/L system. We show that the efficiency of the code is excellent, and can reach up to 90%. The code has been used to simulate a number of electrically large problems, including a 100 * 100 patch antenna array, a 144-element dual- polarized Vivaldi array, a 40-element helical antenna array, and an electronic packaging problem. The results presented serve to demonstrate the efficiency of the parallelization of the code on the BlueGene/L system. In addition, we also introduce the development of the high-performance Beowulf clusters for simulation of electrically large problems.

A small hemispherical helical antenna array for two‐dimensional GPS beam‐forming

A small hemispherical helical antenna array with multibeam output for GPS beam‐forming is designed and characterized. A Butler matrix beam‐forming network is designed to provide four spatial beams in a two‐dimensional directional space. The original design of the hemispherical helical antenna elements is modified in order to match it to the system impedance. Our study shows that even after an ∼30° scan from the normal direction, the maximum change in beam width is only 6°, the maximum change in axial ratio is 1.4 dB, and the maximum change in power gain is 1.1 dB. These characteristics indicate that the array can be potentially used for GPS beam‐forming.

Design of a Small and Low-Profile 2<tex>$,times,$</tex>2 Hemispherical Helical Antenna Array for Mobile Satellite Communications

A small and low-profile 2/spl times/2 hemispherical helical antenna array was designed for INMARSAT satellite reception. With only four elements fed by a simple network, the array can produce a gain of 15 dB, a 3-dB axial ratio bandwidth of nearly 14%, a cross-polarization level of smaller than -20 dB over the half-power beamwidth, and a radiation pattern with a sidelobe level of -20 dB. These characteristics are better than those obtained by previously proposed INMARSAT-M antennas.

Compensating for the mutual coupling effect in a normal-mode helical antenna array for adaptive nulling

A practical normal-mode helical antenna array together with a new method for the compensation of the mutual coupling effect is proposed for the efficient adaptive nulling of interferences in a mobile communication environment. The helical antenna array is shown to be able to generate deeper nulls than an equivalent monopole antenna array in the presence of the mutual coupling effect. The helical antenna elements are smaller in size and less susceptible to the mutual coupling effect than monopole antenna elements. The new method for compensation of the mutual coupling effect is shown to have a greater ability and flexibility than previous methods. A new definition of mutual impedance is introduced and used to find the coupling-free signal voltages across the antenna terminal loads. Numerical examples demonstrate the superior performance of the proposed adaptive array and the new compensation method.

The Mauritius Radiotelescope

The Mauritius Radiotelescope (MRT) is a T-shaped array of helical antennas with a 2048 m EW arm and a 890 m South arm. The primary objective of the telescope is to produce a sky survey in the declination zone -15° to -65° with a point source sensitivity of ≈200 mJy and an angular resolution of 4'×4.6'cosec(z) at 151.6 MHz, z being the zenith angle . This paper describes the telescope and the present status

Multiple multipole program computation of periodic structures

The three-dimensional multiple multipole program (MMP) code based on the generalized multipole technique is outlined for readers who are not familiar with its concepts. This code was originally designed for computational electromagnetics. Rayleigh expansions and periodic boundary conditions are two new features that make MMP computations of arbitrary periodic structures efficient and that at the same time allow us to take advantage of the benefits of other MMP features, including surface impedance boundary conditions and a variety of available basis functions for modeling the electromagnetic field. The application of three-dimensional MMP to a simple grating of highly conducting wires with rectangular cross sections illustrates the high accuracy and the fast convergence of the method as well as the use of surface impedance boundary conditions. A more complicated biperiodic array of helical antennas demonstrates the application of thin-wire expansions in conjunction with regular MMP expansions. This model can be considered a simulation of a thin, anisotropic chiral slab with interesting characteristics.

Computer aided design of an overmoded cavity-backed helical antenna array

The design of an overmoded cavity backed helical array by using the FD-TD (finite difference-time domain) method is described. A resonant cavity designed to operate in the TE770 mode is used to couple power to a 16 element helical array. To reduce the computational requirements several approximations are used to characterise the helix in the 3-D modelling domain.

Comparison of six microwave antennas for hyperthermia treatment of cancer: SAR results for single antennas and arrays

Interstitial techniques of inserting catheters into tumors for the purpose of applying therapeutic irradiation and hyperthermia are in widespread use. Several miniature microwave antenna designs are currently used for these treatments. These include multisection, hot-tip, 2- and 3-node, dipole and helical antennas, all of which are commercially available. The antenna designs are diverse enough to have a dramatic effect on the power deposition patterns either as single antennas or when used in arrays. Aside from the dipole antenna, most of the antennas have never been evaluated experimentally or theoretically in arrays, although the array configuration is used in the vast majority of all clinical treatments. Power deposition or SAR (specific absorption rate) tests were run in muscle equivalent phantom. Single antennas were evaluated at 400 points in a plane and isoSAR contours drawn, normalized to maximum SAR. Single antennas were also compared in large and small diameter catheters to evaluate catheter dependent antenna performance. The dipole, multisection, hot-tip and helical antennas were evaluated in arrays of four antennas located at the corners of a square, spaced 2.0 cm apart. Arrays of antennas were evaluated at 441 points in three planes orthogonal to the antenna axes. Results in the single antenna studies showed that the dipole was less affected by snugness of catheter fit than the multisection, hot-tip or helical antennas. In large catheters, the latter three antennas showed more extreme tip heating performance. The 2- and 3-node antennas deposited only 20% SAR in the distal 30 mm of antenna length. In arrays, the multisection, hot-tip, and dipole antennas all yielded 80–90% SAR centrally in the central measurement plane. Comparing the three antennas, the dipole array deposited 20% more power centrally in a plane near the insertion point, and the multisection and hot-tip antenna designs deposited 10% more central power in a plane near the antenna tips. The helical antenna array deposited only 30% SAR centrally in the plane near the antenna tips and in the central plane. Only 10% SAR was measured centrally near the insertion point, as expected for tip-heating antennas. Finally, the clinical significance of the results is discussed as applied to human tumors undergoing hyperthermia treatments.