John D. Kraus

A backward angle-fire array antenna

A new type of array is described which consists of a grid or mesh structure situated parallel and close to a flat conducting sheet. It operates as a linearly polarized traveling-wave antenna with the main lobe of radiation in a backward angle-fire direction. The direction of the beam is a function of the frequency. Operation of the antenna is analyzed by simple array theory and comparisons are made between calculated and measured performance. An application of the array as a radio telescope antenna is mentioned.

The Helical Antenna

The helix is a fundamental form of antenna of which loops and straight wires are limiting cases. When the helix is small compared to the wavelength, radiation is maximum normal to the helix axis. Depending on the helix geometry, the radiation may, in theory, be elliptically, plane, or circularly polarized. When the helix circumference is about 1 wavelength, radiation may be maximum in the direction of the helix axis and circularly polarized or nearly so. This mode of radiation, called the axial or beam mode, is generated in practice with great ease, and may be dominant over a wide frequency range with desirable pattern, impedance, and polarization characteristics. The radiation pattern is maintained in the axial mode over wide frequency ranges because of a natural adjustment of the phase velocity of wave propagation on the helix. The terminal impedance is relatively constant over the same frequency range because of the large initial attenuation of waves on the helix. The conditions for circular polarization are analyzed, and the importance of the array factor in determining the radiation pattern of a long helix is discussed.

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.

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

Characteristics of Helical Antennas Radiating in the Axial Mode

A helix is a fundamental form of antenna with many radiation modes. A recently reported mode, called an axial or beam mode, occurs for a relatively wide range of helix dimensions, in the region of 0.2 to 0.5 wave‐lengths diameter and as high as 0.5 wave‐lengths spacing between turns. The radiation is maximum in the direction of the helix axis and is nearly circularly polarized. This mode may persist with a given helix over a considerable frequency range. In this range the phase velocity of wave propagation along the helical conductor is reduced. An approximate expression for the field pattern of a single turn helix is developed. The pattern of a helix of a number of turns is then calculated as an array of such turns. Measured and calculated patterns show good agreement.

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.

Planetary and Solar Radio Emission at 11 Meters Wavelength

Observations are described of radio emissions from the Sun, Jupiter, and Venus during 1956 and early 1957 at a wavelength of 11 meters. Records are presented of solar 11-meter radiation at the time of a large (importance 3) flare on August 31, 1956, and during other periods of solar activity. The effect of scintillation on records of radio stars also is illustrated. A number of records of impulsive radiation from Jupiter at both slow and fast recorder speeds is shown. The radiation is of a bursty or intermittent nature which can be classified into two main types: one which may persist for several seconds and produces a rumbling sound in the loudspeaker and another which is of very short duration (10 milliseconds or less) and produces a cracking or clicking sound. Many of the short pulses consist of distinct pairs or triplets which fall into two main groups, one having pulse separations of about one-quarter second and the other, pulse separations of about one tenth this value. An echo mechanism to explain the multiple pulses is postulated and observed trends in pulse separation compared to those expected with such a mechanism. The stronger Jupiter pulses indicate a peak radiated radio power at the source of the order of 10 kilowatts per cps bandwidth.

The Satellite Ionization Phenomenon

A number of observations are presented which show a close correlation between CW-reflected HF signals and passes of artificial earth satellites. The periodic (nonrandom) occurrence of the signal bursts and the symmetry of some burst sequences are indicative of satellite-related phenomena. The occurrence of a variety of satellite-related Doppler effects are described and several satellite ionization mechanisms are also discussed. The possible relation of the satellite phenomenon to prior solar activity is mentioned.

Sputnik I's Last Days in Orbit

Observations during the last days of Sputnik Is orbiting are presented. These observations were made at The Ohio State University Radio Observatory using a simple CW reflection technique. The data suggest that the breakup of an artificial satellite upon its reentry into the denser atmosphere is a complex phenomenon in which a sequential series of events may occur over a period of days. Graphs of the average height of the satellite and its associated fragments as a function of time are presented, and some conclusions are drawn as to the details of the actual breakup phenomenon.

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>>