H. King

Characteristics of 1 to 8 wavelength uniform helical antennas

The measured voltage standing wave ratio (VSWR), gain, pattern, and axial ratio characteristics of a uniformly wound helical antenna are presented. Experimental parametric studies were made of 1) fixed length helices with variable diameter and pitch angle (8.6 to 10 turns), and 2) variable length helices with constant diameter and pitch angle (5 to 35 turns). Parametric curves are presented to show the gain and half-power beamwidth (HPBW) of a constant pitch helix as a function of axial length L/\lambda and circumference C/\lambda . Empirical expressions are derived for the antenna peak gain and bandwidth as a function of the helix parameters. In addition, the antenna gain-beamwidth products are examined.

An experimental study of a balun-fed open-sleeve dipole in front of a metallic reflector

The characteristics of a balun-fed open-sleeve dipole mounted in front of a metallic reflector for operation in the 225 to 409 MHz band are investigated. A parametric study is made of the VSWR response as a function of dipole and sleeve diameter, sleeve length, and sleeve-to-dipole spacing. It is shown that an open-sleeve dipole can be operated over a bandwidth of 1.8:1 as compared with an operating bandwidth of approximately 1.25:1 for a conventional cylindrical dipole with the same diameter. Pattern and gain data are presented for an open-sleeve dipole mounted in front of a flat metallic reflector. Preliminary results on mutual coupling effects are also discussed.

A shallow ridged-cavity crossed-slot antenna for the 240- to 400-MHz frequency range

An experimental study has been made of a shallow ridged-cavity crossed-slot antenna to determine its feasibility for operation in the 240- to 400-MHz band. The various trends are summarized for the VSWR response characteristics as the cavity and slot parameters are varied. The wideband antenna characteristics using a ridged cavity configuration are demonstrated. Based on the limited amount of data obtained from the experimental model, the VSWR is < 2.7:1 from 240 to 270 MHz and < 2.1:1 from 290 to 400 MHz for a cavity with a maximum dimension of 33 by 33 by 4 in. Measured radiation patterns with the cavity mounted on a finite-size fiat ground plane are shown.

Effects of a human body on a dipole antenna at 450 and 900 MHz

The VSWR and pattern characteristics of a dipole held close to or touching a human body have been experimentally determined and the results are reported. Two choke-sleeve dipoles, tuned for the two test frequencies of 450 and 900 MHz, were used for this study. The measurements were made with the antenna held at a persons waist, chest, and shoulder levels and also held above the head. The radiation characteristics of the combined body and antenna were compared with the dipole characteristics in free space. Propagation shadowing by the body and the effects of the body on the VSWR characteristics are illustrated.

Characteristics of body-mounted antennas for personal radio sets

The development of a multiturn loop antenna for a police officers personal radio set is described. The antenna is small, low profile, lightweight, with dimensions of 2.7 \times 2.7 \times 0.7 in high ( 1.06 \times 1.06 \times 0.28 cm), and is tunable over the 150- to 170-MHz band. VSWR and radiation patterns are presented with the antenna mounted on a mans shoulder. The shoulder-mounted antenna characteristics are described with conditions where the man is in standing, stooping, and prone positions, with various head and arm movements, and with light and heavy clothing. Radiation patterns are referenced to a 6-in helical whip commonly used by police officers. Radiation patterns also indicate body absorption loss for loop and whip antennas mounted at waist level as compared with shoulder levels. The instantaneous bandwidth is 1.4 MHz for a VSWR \leq 3:1 . A dual-frequency model for use in a two-frequency push-to-talk mode, is also shown to be practical.

A 2.8 arc-min beamwidth antenna: Lunar eclipse observations at 3.2 mm

This paper describes the principal electrical and mechanical features of a millimeter-wave antenna facility. The basic instrumentation consists of a 15-foot (4.57 meter) diameter parabolic antenna, a servo control system, an on-line general purpose computer, and radiometric receiving equipment. In the zenith attitude position of the antenna reflector, the measured contour accuracy, with respect to a true parabola, is 0.0018-inch rms. At horizon attitudes, the rms value degrades to 0.0036 inch. These contour accuracy measurements include the effects of partial solar heating and wind velocities up to 20 mph. Although the reflector is not unusually large physically, it is extremely large in terms of electrical aperture; i.e., D/\lambda = 1436 at 94 Gc/s and 3660 at 240 Gc/s. The measured pointing accuracy is 20 arc-sec (0. 1 mrad) for the overall system. The tracking rate ranges from 0.001\deg /s to 3\deg /s. The facility features automatic program control. Ephemeris data existing on magnetic tape or in computer memory provide real-time attitude control of the antenna. High-resolution measurement of the lunar surface during the total eclipse of December 30, 1963, at a wavelength of 3.2 mm (94 Gc/s) is described. Specific areas of the lunar surface were monitored before, during, and after the eclipse. A summary of the relative brightness temperatures and the cooling rates of the observed areas is included. A typical high-resolution radiometric contour map of the moon is also shown.

Characteristics of a tapered anechoic chamber

The characteristic features of a tapered anechoic chamber are described. The smooth illumination amplitude in the chamber makes it usable as an indoor range for antenna pattern measurements, even at low frequencies. Variations in the transmission attenuation in the chamber as compared to free space require careful interpretation of absolute gain and cross section data.

Empirical helix antenna design

Empirical design relations are presented for a uniform diameter helical antenna operating in the axial mode. The antenna peak gain, HPBW, and bandwidth are expressed as a function of the helix design parameters (diameter, pitch angle, and number of turns). Computed values are compared with experimental data for various helix configurations.

Directivity of a uniformly excited N X N array of directive elements

The directivity characteristics of a uniformly excited N \times N array of high- or low-gain elements are described. The voltage patterns of the individual elements were assumed to be of the form cos^{m} \theta and J_{1}(K\theta)/K\theta , where m and K are parameters used to vary the element pattern beamwidths. Directivity curves are presented as a function of the element spacing in wavelengths with N as a parameter ( N = 2, 3, 4, 5, 6, 8, 10 , and 12) for the Bessel element pattern. The array directivity characteristics using the cosine element pattern are not greatly different from those computed using the Bessel element pattern. Comparisons between the computed and measured directivities of two array configurations show good agreement.

Broadband characteristics of an open-sleeve dipole

An antenna radiating element capable of providing a broadband VSWR response and unidirectional radiation patterns over nearly an octave bandwidth is described. The basic radiating element consists of a balun-fed dipole with one or more parasitic elements (sleeves) added. Addition of these parasitic elements results in an antenna bandwidth many times greater than that of a conventional cylindrical dipole, VSWR, pattern, and gain measurements were made in the UHF band for a variety of dipole/sleeve configurations.