Vertical Antenna Array Research Articles

Diffraction focusing of the sound field of a vertical antenna array in a range-dependent shallow sea

Using the adiabatic approximation for the mode representation of the sound field, it is shown that the efficiency of the diffraction focusing grows when the thickness of the isovelocity water layer increases with distance.

The nocturnal service area of MF AM broadcast stations using vertical arrays

The nocturnal service area, or distortionless area, of MF AM broadcast stations depends on the radiation properties of the transmitting antenna and the physical constants of the ground surrounding the transmitting site. These ground constants limit the maximum antenna height and establish how large the nocturnal service area will be. In some instances the nocturnal service area can be increased by the use of vertical antenna array. In this case it is very important to know the increase of the theoretical nocturnal service area of the station and if the use of more sophisticated radiating systems is justified. Calculations were made to determine the theoretical nocturnal service area of a station using vertical arrays, and curves with maximum distortionless distance are given as a function of frequency and ground physical constants. Measurements on reduced-scale models in HF and VHF bands are described, and improvements in antenna antifading properties and in nocturnal service area are shown. >

Phase and amplitude measurements of transhorizon microwaves: Angular response patterns in elevation

Results from two 48-hour beam-swinging experiments in transhorizon microwave propagation are presented. A 3.2-GHz signal was transmitted over a 164-km path and received with a 12-element vertical antenna array (beamwidth <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.29\deg</tex> elevation by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5\deg</tex> azimuth). The beam was rapidly scanned in elevation. Experimental angular response patterns (antenna scans) averaged over about 3 min are compared with theoretical patterns computed from turbulent scattering theory. There is considerable variability in the experimental patterns for different time periods. The experimental patterns for different time periods are separated into three groups. Signal group 1 patterns resemble the response of the array to a point source. A propagation model based on partial reflection or refraction from a stratified atmospheric layer best describes these signal characteristics. Signal group 2 patterns can be described by a model predicting a smooth decrease in scattered power with scattering angle at a rate inversely proportional to the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> th power of the angle with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> between 4 and 10. A propagation model based on atmospheric turbulence can describe these signal characteristics only if it includes modifying factors to account for the difference in the exponent <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> observed at different time periods. Signal group 3 patterns are characterized by broadened maxima, by two or more maxima, or by a maximum which is significantly displaced above the horizon. These signals can be explained only by a model which contains a nonuniform scattering mechanism. A variation in signal characteristics as a function of time of day was evident in both experiments.

A data-gathering antenna array for transhorizon propagation research

A versatile vertical antenna array and receiving system have been developed for measuring relative phase and amplitude along the wavefront of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</tex> -band transhorizon signal. The array, which operates at 3.200 GHz, consists of 12 parabolic antennas 1.22 meters (4 feet) in diameter which are spaced 1.39 meters apart on a tower for a total effective vertical aperture of 15.24 meters ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">162 \lambda</tex> ). The raw data outputs from the array are amplitude and differential phase successively sampled from the 12 elements. Data can be taken at variable rates of up to 100 passes per second over the 12 elements. The data are processed in a computer to form conventional uniformly illuminated array beams 0.3 degree wide with a grating lobe spacing of 3.9 degrees or to produce many combinations of correlation functions. A reference signal is used to cancel the effects of relative motion of the array support structure from the phase data. The array and receiving system and actual performance characteristics are described.