Double Loop Antenna Research Articles

A new internal matching impedance concept for ICRF antennas

As an alternative to commercial capacitors which have experienced reliability problems and are irrelevant to the next step, a new all-metal impedance concept has been elaborated for Tore Supra ICRF Resonant Double Loop (RDL) antenna. Two detailed design versions are presented, both based on the principle of a parallel LC transformer inserted in a coaxial structure. First low power measurement results on a full-scale mock-up are discussed.

VHF helicopter antennas that incorporate the airframe and reduce rotor modulation

Antennas at VHF frequencies mounted to small (with respect to wavelength) helicopter platforms are usually limited to whip and loop antennas. Antenna placement and rotor position can drastically change antenna performance due to induced currents on the platform. This work illustrates deliberate antenna-platform interactions that cause induced currents to reinforce and improve the radiating system performance. Additionally, rotor modulation effects can be simultaneously limited. This is accomplished by using oppositely placed loop antennas at a location on the airframe that is nominally one wavelength in circumference. The resulting broadcast pattern admits low cross-polarization radiation and low copolarized rotor modulation, but is not uniform. The dipole moment of the loops dictates this nonuniformity. Double-loop antennas are used to create a more uniform broadcast pattern without sacrificing the desired low cross-polarized radiation and low copolarized rotor modulation.

Helicon wave propagation in the SHEILA heliac

The behaviour and structure of waves launched from a novel double-loop antenna in the SHEILA heliac are presented. Radial wave field and azimuthal phase measurements are compared with cylindrical helicon wave theory after an appropriate magnetic coordinate transformation. This comparison provides strong evidence for the involvement of helicon waves. Damping of the waves is investigated by comparing measured spatial damping rates with theoretical estimates. Comparison of measured density with predictions from the helicon dispersion relation reveals how geometry influences propagation of the waves in SHEILA.

Helicon wave plasma reactor employing single-loop antenna

Helicon wave plasma excited by a single-loop antenna and etching characteristic of Si and SiO2 is studied on a basis of plasma parameters and wave patterns measurements. A wide variety of wavelength with space is observed in the single-loop antenna, and because of no external boundary for the wavelength, the best match of the rf source with plasma is possible. This fact is ascribable to the density enhancement rather than in the conventional double-loop antenna. A condition that the magnetic field is lowered in the antenna portion is also effective on the density enhancement. This is explained by a longer time in resonance of the electron. The etching uniformity is also improved by using a larger diameter one-loop antenna, with a great usefulness.

Resonant Double Loop Antenna Development at ORNL

As part of the development of ion cyclotron resonant heating (ICRH) systems for fusion research, Oak Ridge National Laboratory (ORNL) has built resonant double loop (RDL) antennas for the Tokamak Fusion Test Reactor (TFTR) (Princeton Plasma Physics Laboratory, Princeton, NJ, US) and Tore Supra (Centre d'Etudes Nucleaire, Cadarache, France). Each antenna has been designed to deliver 4 MW of power. The electrical circuit and the mechanical philosophy employed are the same for both antennas, but different operating environments lead to substantial differences in the designs of specific components. A description and a comparison of the technologies developed in the two designs are presented. 5 refs., 4 figs., 1 tab.

The calculation of radiation characteristics of antennas near a rectangular cylinder reflector by GTD

The horizontal radiation patterns of dipoles and double-loop antennas near a rectangular cylinder reflector are calculated and analyzed by the geometrical theory of diffraction (GTD). The magnitudes of the direct field, the reflected field and the diffracted field at a field point are studied. The effects on the resultant field pattern of the size of the reflecting cylinder, of the relative position between the antennas and the reflecting cylinder, and of the methods of feeding of antennas are analyzed. The results obtained show that in order to obtain the optimum omni-directional characteristics of rediation, the optimum design for the parameters of antenna system is needed. The method and results in this paper provide means and bases for the optimum design of this kind of antenna system.