Helical Beam Antenna Research Articles

Characterization of an Eight-Element Circular Patch Array for Helical Beam Modes

This paper reports on a new method for characterizing intermodal isolation, power penalty, and reception zone area of helical beam (HB) antennas. As an example, an eight-element circular patch array is fully characterized and its performance is critically assessed. Validation through beam measurements is accompanied with precise electromagnetic modeling using conformal finite-difference time domain computation on a graphics processing unit.

A Circularly Polarized Single-Frequency Multimode Helical Beam Antenna

An antenna based on a TM coaxial resonant cavity with radiating annular slots on one face and excited by multiple open-ended TE mode coaxial resonators on the opposite face is shown to simultaneously radiate the corresponding circularly polarized helical beams modes over a single-frequency band with good isolation between modes. S-parameters are calculated for a transmit–receive configuration with the antennas separated by 10 wavelengths. The initial antenna concept was developed interactively using the conformal finite difference time domain method with a Titan-XP GPU.

A helical-beam antenna without a ground plane

The helical-beam antenna (a.k.a. axial-mode helix), which the author devised in 1946, was fed via a ground plane. This arrangement has proven very satisfactory for many applications. Now, almost 50 years later, he presents a version in which the ground plane is replaced by one or more loops. This design is well suited for pole mounting. It has less wind resistance, and presents a much-cleaner appearance, while providing equivalent performance to a helix with ground plane. The new version retains the broadband and non-critical nature of the ground-plane helix to a marked degree.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Study of an internally matched helical beam antenna

An internally matched helical beam antenna has been designed and constructed. The helix winding of a helical antenna was designed to be a slow wave section by placing a ground copper sheet on the inner side of the winding and inserting a dielectric sheet between the winding and the ground copper sheet to form a distributed capacitance along the antenna. By carefully adjusting the internal inductance of the helix winding and the distributed capacitance, the antenna can radiate in the axial mode and be internally matched to the 50- Omega transmission line feeding it. With this arrangement, the dimension of such an antenna can be much smaller than that for an ordinary helical beam antenna at the same operating condition. Details of the antenna design and experimental results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 50-ohm input impedance for helical beam antennas

A helical beam antenna with uniform conductor size has a nominal impedance of 140 ohms. This may not be convenient for some applications. The purpose of this note is to call attention to the fact that the impedance can be adjusted to 50 ohms by increasing the conductor size close to the feed point at the ground plane. This lowers the characteristic impedance of the conductor-ground plane combination (acting as a transmission line) and transforms the helix impedance to a lower value over a substantial bandwidth

Polarization stability of the helical beam antenna

An analysis of the axial ratio variation over the main beam of the helical beam antenna shows that the polarization stability improves with increasing number of turns, with smaller pitch angle, and with decreased To mode amplitude.

The two-helix method for polarization measurement of meteoric radio echoes

A method employing two helical-beam antennas is described for measuring polarization effect of radio echoes from non-shower meteors of unknown trail orientation. Results obtained by the method are in good agreement with theoretical values and with measurements made on shower meteors by another method by Clegg and Closs.

Radiation Field of a Square, Helical Beam Antenna

Rigorous formulas have been derived for the field from a square, helical antenna with a uniformly progressing current wave of constant amplitude. These formulas that have the advantage of great simplicity are of direct use for helical antennas in the meter band, where for practical reasons only square helices are used. Further, in connection with corresponding rigorous formulas for the field from a circular, helical antenna with a uniformly progressing current wave of constant amplitude the present formulas may be used for an investigation of the magnitude of the error introduced in Kraus' approximate calculation of the field from a circular, helical antenna by replacing this antenna with an ``equivalent'' square helix. This investigation is carried out by means of a numerical example. The investigation shows that Kraus' approximate method of calculation yields results in fair agreement with the results obtained from the rigorous formulas. A statement to the contrary made recently in the literature is shown to rest on a trivial error.

Helical Beam Antennas for Wide-Band Applications

The helical beam antenna has inherent broad-band properties. Over a wide frequency band the pattern shape, circularity of polarization, and terminal impedance are relatively stable. Measured performance data are presented for a medium-gain helical beam antenna of optimum dimensions with a bandwidth of about 1.7 to 1. A high-gain broadside array of four such helices is described. Other wide-band applications of helical beam antennas, including omnidirectional types, are also discussed.

Measured Impedances of Helical Beam Antennas

Experimentally determined impedance characteristics are presented for helical antennas. At frequencies too low for the axial or beam mode, the terminal impedance changes greatly with small variations in frequency. However, in the frequency range of the fundamental axial mode, the impedance is relatively constant, especially if the number of turns and the pitch angle of the helix are not too small. This characteristic is an advantage in wide frequency-band applications. For example, the resistance variation of a 5-turn, 18-degree helix over a frequency band of about 1.7 to 1 is only 105 to 145 ohms, and the reactance variation only 0±15 ohms. The effect of the pitch angle and number of turns is discussed.