Jimmy L. Wong

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.

Broadband quasi-taper helical antennas

A unique approach is described for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics. The antenna may be described as a nonuniform or quasi-taper helix, which consists of a combination of uniform and tapered helix sections. Measured patterns, gain, axial ratio, and VSWR for various helical antenna configurations are presented and compared. It is shown that a nonuniform quasi-taper helix can provide an operating bandwidth twice that of a conventional uniform-diameter helix.

A cavity-backed dipole antenna with wide-bandwidth characteristics

This communication describes a cavity-backed dipole antenna that has a broad-band VSWR response, unidirectional radiation patterns, and almost constant gain ( 10.5 \pm 1 dB) over an operating bandwidth of 1.8: 1. Measured pertinent electrical characteristics are presented.

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.

Height-reduced meander zigzag monopoles with broad-band characteristics

The characteristics of a meander dual zigzag wire monopole antenna are described. The antenna provides low height and broad-band performance. Measured voltage standing-wave ratio (VSWR) and pattern characteristics are compared with a conventional, straight-wire monopole over a 3:1 bandwidth.

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.

Experimental evaluation of a circularly polarized metallic lens antenna

The performance of a 3-foot-diameter circularly polarized metallic lens antenna at X -band frequencies is described. The measured antenna gain, efficiency, half-power beamwidth, sidelobe level, and optimum focal length were determined for both on-axis and scan conditions. The effect of different lens illuminations for the on-axis case was ascertained.

240-400 MHz antenna system for the FleetSatCom satellites

The measured performance characteristics of the FleetSatCom UHF antenna system are described. The transmit antenna consists of a parabolic reflector with a backfire, bifilar helix feed and the receive antenna is a non-uniform diameter helix mounted to the side. The gain, axial ratio, VSWR and interaction effects are presented.