No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Antennas for nonsinusoidal waves. III - Arrays
Abstract
The variation in time of the electric and magnetic field strengths of a nonsinusoidal wave radiated by an array of radiators is a function of the azimuth and the elevation angle. For simple time variations, such as that of a rectangular pulse in the direction of the array axis, this time variation can be determined analytically as a function of the angle. Peak-amplitude, peak-power, and energy patterns, which are the equivalent of amplitude and power patterns of sinusoidal waves, can then be determined. In addition, a rise time or slope pattern can be obtained that yields a much better angular resolution for large signal-to-noise ratios. No equivalent exists for sinusoidal waves owing to their lack of bandwidth. It is noted that the principle of the monopulse antenna array can also be carried over from sinusoidal to nonsinusoidal waves. A monopulse amplitude pattern is obtained which changes rapidly from positive to negative values in the vicinity of the angle of incidence beta = 0. The resulting improvement in the accuracy of angle measurement is fully analogous to sinusoidal waves. In addition to the monopulse-antenna pattern, a monopulse antenna slope pattern can be obtained that promises a much better accuracy of angle measurement.
... The transmitted signal is generated by applying current steps through a Large-Current Radiator (LCR) [21,22] antenna. This launches an impulse when the current is turned on or off. ...
Analytical expressions have been obtained for calculating an optimal waveform of the pulse exciting elements of an ultra-wideband antenna array. The criterion of optimality is the minimum of integral side-lobe level. The proposed approach enables us to take into account the signal duration and spectrum limitations and also the impulse response of antenna elements.
The radiation patterns of an array of hertzian electric dipoles fed by a pulsed signal have been obtained in the time domain and the conditions under which the field slope pattern is highly directive are shown.
In this paper, the fields created by a hertzian electric quadrupole fed by a non-sinusoidal signal are analysed in the time domain. The results are compared with those obtained for an electric dipole and are applied to the study of the field created by the practical antenna, the large-current radiator.
The work is devoted to investigations aiming at developing special type of radiating antennas which are known as Harmuth's large current radiator. Physical and technical problems encountered when radiators designed and ways for their overcoming are discussed
In the ultra-wideband monopulse receiver, the incident signal is received with two receiving antennas in sum and difference mode. The received signals' phase and energy are then compared to find the incident signal. The received signals, however, are susceptible to antenna noise. In this paper, we establish the relationship between the angle accuracy of the proposed receiver and the signal-to-noise ratio. The receiver modeled in this paper consists of two co-located ridged-horns, with their sum/difference signals received by cross-correlation receivers and processed by an ideal amplitude-comparison monopulse processor. The derived angle accuracy is compared with monopulse measurements at angles -5deg to +5deg at 1deg intervals. Measurements verify the derivations, showing a root-mean-square error of 0.43deg (measured) vs. 0.46deg (theoretical) at boresight; 0.13deg (measured) vs. 0.09deg (theoretical) at -5deg; and 0.17deg (measured) vs. 0.09deg (theoretical) at +5deg.
The present paper first resumes the general architecture of an ultra wide-band transceiver system. Two different system architectures are then studied and compared : the first of these terms an approbated Gaussian pulse; the second utilises a quasisinusoidal pulse. A comparison between the two, in terms of the power spectral density, the ease of signal generation, leads to the conclusion that the latter form offers a more advantageous solution.
In this paper, we propose a novel amplitude-comparison monopulse receiver architecture for ultra-wideband radars. This monopulse receiver consists of four ridged-horn antennas placed in a square-feed configuration, a comparator circuit that generates the monopulse sum and difference signals, cross-correlation receivers that detect the monopulse signals, and an amplitude-comparison monopulse processor that determines the target's angular position. The derived monopulse sum and difference signals are verified through measurements. The derived sum and difference patterns are compared with measured patterns, and they show good agreements-measured 3-dB beamwidth=6.4deg(derived=6deg), measured unambiguous tracking range=plusmn5deg(derived=plusmn5deg), and measured sum pattern sidelobe level=-6 dB (derived=-8 dB)
The principle of a one-dimensional self-steering array system for beam forming with nonsinusoidal waves has been developed previously. In this paper, an adaptive antenna system consisting of a two-dimensional planar array of sensor elements and a real-time adaptive receiver processor is described. The sensor elements of the planar array are arranged into rows and columns so that the steering commands for the azimuth ald elevation directions can be generated separately. The array system electronically steers a beam in the direction of the source from which the waves are arriving without prior knowledge of the source location.
A self-steering array system is described for beam forming with nonsinusoidal waves. The array system electronically steers a main beam in the direction of the source from which the wavefront is arriving without prior knowledge of the source locatiora. The principle of monopulse tracking radar is applied to the array system so that the angular coordinate of tihe source can be determiined with respect to the array axis. If the source is in rmotion, it can be tracked on pulse-to-pulse bases. Finally, the self-steering array system is advanced further to suppress the additive thermal noise presenit with the incoming signals, and to achieve good angular resolution and accuracy.
The radiation and reception characteristics of a planar array of straight-wire coupled antennas are analyzed by a numerical method in the time domain. The numerical method allows us to calculate some significant magnitudes in an array of coupled wire antennas, such as the frequency dependence of the self- and mutual impedances between antennas. The antennas are fed by a time-varying Gaussian pulse, and they are loaded with various nonlinear elements to exert some control over the radiation field. The results are used to show how the monopulse technique with the slope pattern promises a much higher accuracy of angle measurement for a target.
Nonsinusoidal waveforms with the time variation of a rectangular pulse, received (or radiated) by a line array of sensors (or emitters), yield various antenna patterns which are very attractive for achieving good angular resolution. These antenna patterns, such as peakamplitude, peak-power, energy, and slope patterns, have been derived for various array lengths under a noiseless assumption. The slope patterns are the most attractive for angular resolution. In this paper, line-array beamforming techniques are developed to provide slope patterns for nonsinusoidal signals. The techniques employ sliding correlators (SC's) for suppressing the additive Gaussian noise present with the received signal, and pulse-shaping processors for determining the slope pattern. Computer simulation is done for deriving peak-amplitude and slope patterns for various array lengths. Also, a method for obtaining monopulse peakamplitude and slope patterns is presented.
The calculation of the electric and magnetic field strength produced by a radiator is usually done only for distances large compared with the geometric dimensions of the radiator. This approach makes it Impossible to obtain exact relations between the power fed to the radiator by the driver, the voltage between the radiator terminals, the power radiated to or received from the near zone, and the power radiated to the far zone. This paper develops a solution for the large-current radiator that can be evaluated numerically by computer for any distance, and thus permits the calculation of the power flowing at any time through the surface of the radiator. The knowledge of this power is the basis for the design of efficient radiators.
The development of antenna theory for nonsinusoidal
electromagnetic waves has been based on the idealized rectangular pulse.
In practice, an antenna that is designed to operate in the mode of an
electric hertzian dipole would radiate a pulse that best approximates a
Gaussian one when the driving current consists of a linear transient.
The principle of radiation of nonsinusoidal electromagnetic waves with
the time variation of Gaussian pulses is discussed. The properties of
the Gaussian pulse are presented, i.e., the autocorrelation function,
energy spectral density, and spectrum. Antenna patterns, such as
peak-amplitude pattern, peak-power pattern, energy pattern, and slope
pattern are derived for a Gaussian pulse received (or radiated) by a
linear array antenna. Computer plots of the derived antenna patterns are
presented that show a considerable improvement in the angular resolution
capability over that of the antenna patterns that have been derived for
a rectangular pulse
The principle of a self-steering array system which has been
developed in theory for beam forming with nonsinusoidal waves is
analyzed and computer-simulated. A tradeoff between the maximum-scan
angle of the array system, the array length, the operating frequency
bandwidth, and the signal power for a small-resolution angle is
established. Such a tradeoff is desirable in practice, but is not
applicable to the conventional method of beam forming with
zero-bandwidth sinusoidal waves. A design criterion for the optimal
reception of nonsinusoidal waves by a linear array of sensors is
established. The simulation results of the signal processor of the
self-steering array system show that the beam-steering mechanism based
on slope processing is efficient in the absence of thermal noise. The
principle of the signal processor is slightly modified to enhance its
performance in practice. The design of a variable-delay circuit that
uses a charge-transfer device is presented. A novel mechanism of
delay-time adjustment is developed for the self-steering array system to
improve its response time
This paper investigates a certain class of three-dimensional (3-D)
(volume) sources to the scalar wave equation that are capable of
radiating high-amplitude short-duration pulses in a selected (main)
direction and low-amplitude long-duration pulses in other directions.
Parameterization and characterization of such sources and the fields
that they radiate is carried out in both the frequency and time domains
and various measures of ultrawideband radiation (transmit mode)
performance are evaluated and discussed within both domains. Frequency
and time-domain results corresponding to uniformly distributed
parallelepiped sources are presented to elucidate the role of the
source's space distribution on the radiation performance. These results
provide insight about the possibility of optimizing the radiation
performance of scalar, ultrawideband volume sources by a proper
selection of the space distribution of the source
For sinusoidal waves with bandwidth zero, one obtains the classical formula ϵ = κNL = kc//spl conint/L for the resolution angle of a sensor array, where L is the length of the array, λ the wavelength, /spl conint/the frequency, and c the phase velocity of the wave, while κis a constant whose value is usually chosen to be 1. Waves with the time variation of a rectangular pulse of duration ▵T yield the resolution angle ϵ = 2Kc/▵/spl conint/ P/P /sub N/, where P/P/sub N/ is the signal-to-noise ratio and ▵/spl conint/ = 1/2▵T the nominal bandwidth of the pulse; the same result holds for coded pulse sequences, such as Barker codes or complementary codes, if the main lobe of their auto-correlation function has the shape of a triangle with rise time ▵T. Hence, the resolution angle e can be reduced by increasing the signal power, as well as by increasing the array length L or the bandwidth ▵f. For sinusoidal waves, an increase of the signal power brings no reduction of the resolution angle. The trade between signal power and frequency bandwidth is of interest whenever the attenuation increases rapidly with frequency, e.g., in high-resolution all-weather radar or in underwater acoustic beam forming.