Boresight Axis Research Articles

Multiple scattering of EM waves by dielectric spheres located in the near field of a source of radiation

An analysis of multiple scattering of electromagnetic (EM) waves by two loss-free dielectric spheres with radii greater than a wavelength and located in the bear field of a source of radiation is presented. The incident field is expressed in terms of spherical vector wave functions (SVWF). Translational and rotational addition theorems are employed to express the SVWF of the incident field in the coordinate system associated with the dielectric scatterer. Numerical computations are performed for obtaining the amplitude and phase patterns of fields multiply scattered by two loss-free dielectric spheres, whose centers are located on the boresight axis and in the nearfield of an open-ended circular cylindrical waveguide excited in its dominant mode. Numerically computed results show good agreement with measured results obtained from a systematic experimental study on forward scatter performed in the X -band.

Design and Study of the Elevation Difference Channel Feed of the Single Aperture Monopulse Feed System

The technique to generate the higher order modes TE11 and TM11 in the square waveguide, required for the E plane error single channel feed in the single perture monopulse feed system, has been presented and the appropriate assembly for this purpose has been designed in the 8.5-9.0 GHz frequency band. The assembly can be incorporated as an E plane error signal channel feed in the design of a single aperture monopulse feed system. The features of the design are a suppressed cross-polarised component of the radiation field and a deep null in the E plane pattern at the boresight axis of the feed. A qualitative explanation for the behaviour of the feed has been presented.

Radiation of conical horns excited in higher-order modes

Theoretical investigations carried out for the far-field-radiation-pattern prediction of conical horns excited in the spherical TMmn and TEmn modes are applied on the radiation-pattern analysis of TM01 and TE01 modes. The results, valid even for conical horns with large flare angles, provide an optimum horn design for a maximum gain slope near the boresight axis.

Automatic Checkout and Monitoring in the AN TPQ-27 Radar System

This paper describes automatic monitoring equipment built in to a precision tracking radar system to detect and isolate faults. The purpose of the monitoring equipment is to minimize the mean time to repair faults and to exercise the overall system for pre-mission alignment and calibration. In addition, it is used to periodically check for performance degradation in key areas of the system. The paper describes the design approach used to meet the above requirements. Three types of signals are monitored: analog, digital, and switch closure. A list of each type is given and the technique used to monitor each is described. The design approach for pre-mission alignment and calibration is outlined. Tests performed are: RF alignment of the boresight axis, range tracking accuracy, angle servo calibration and accuracy, and receiver figure of merit measurements.

Simulation of the Feed Patterns due to Four Horns Used in Sum and Difference Comparison Monopulse Radar from Single Horn Radiation Pattern

The simulation of the radiation patterns due to four pyramidal horns, from the radiation pattern of a single pyramidal horn for the sum and difference comparison type monopulse radar system is the prime concern of this paper. The simulation is done to facilitate the optimization of slope and linearity of the difference mode patterns in the two principal planes and automatic optimization of the boresight axis characteristics is observed. The specific value of the squint angle of the individual horn axis from the boresight axis for the optimum slope and linearity is determined through simulation at various squint angles. The practical results obtained with the excitation of the system from trimode four-channel monopulse bridge and the simulated results are compared.

Analysis of a Multiplicative Feed System for Monopulse Tracking Applications

In angle tracking antenna applications, the angle sensing boresight accuracy capabilities are important. The ability of an antenna to precisely determine the bearing angle to a point source is determined by the slope of the control function pattern at boresight. In the presence of extraneous interference, the magnitudes of the sidelobe and backlobe responses are important. Control pattern slope (angular sensitivity) is primarily a function of aperture illumination. It can be described by a current distribution in intensity and phase at every point. Once distribution is defined, lobe structure is defined by the associated transform. When more than one feed is used, the distribution will be a vector sum of the individual feed distributions. The resulting secondary pattern can be defined in terms of the amplitude distribution and the phase center locations of the contributing feeds. With a four-horn monopulse configuration, the feed phase centers are displaced from the boresight axis. Placing the phase centers on the boresight axis by rotating the feeds through 45 degrees results in a different set of intensity and phase values. A quite different secondary pattern results. The control function obtained by the subtraction of the powers from a paired set of on-axis feeds results in a lower sidelobe level than that obtained with a conventional monopulse combiner for a given feed taper.

A Ku-band mixer steering electronic scanning phased array system

An eight-element K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</inf> -band linear phased array system with frequency of operation between 16 and 17 GHz is described. Beam scanning is performed by steering mixers located in the element channels, with element phasing information generated at L-band frequencies. The system employs a hybrid mode of beam scanning. That is, the beam steering programmer can digitally deploy the beam in target space with continuous straddle scan about each discrete beam position. The beam can be scanned 45 degrees off the boresight axis in nominal steps of 11 degrees. However, the beam steering programmer design is flexible enough to permit finer steppings within the scan sector using up to 15 discrete beam positions. This paper gives information on the array design and performance data.

Technique of Observing the 5‐mm Self‐Emission From the Oxygen of the Earth's Atmosphere to Obtain a Vertical Sense

The results of previous calculations have shown that, due to the heavy absorption of the atmospheric oxygen, the resultant radiation both in the wells and in the cores of the 60‐Gc/s spectral complex provides a radiometrically bright mantle surrounding the earth. It becomes evident when viewed from space that this oxygen mantle could supply a uniform, nonftuctuating signal for radiqmetric sensing.This paper presents a quantitative expression of a technique of observing the 5‐mm self‐emission from the oxygen of the earth's atmosphere in order to obtain a vertical sense. The choice of operating frequency is a selection process in which a frequency is determined for which the atmospheric opacity is great enough to reject the radiation from the lower atmosphere, and at the same time have sufficient transmissivity in the upper atmosphere to allow predominance of radiation from the 15‐ to 32‐km region. Under these conditions a uniform and well‐defined radiating disk should be seen. To the degree that the observed disk exhibits circularly uniform emission and the mantle possesses spherically homogene US density, the line through its center of brightness may be defined as the direction corresponding to the local vertical at the spacecraft. This may be determined as the boresight axis of a lobe comparison antenna system.

Monopulse Radar Air-ti-Ground Ranging

The use of a two-lobe monopulse radar for measuring slant range to the surface of the earth in the absence of discrete targets is analyzed. It is shown that tracking dispersion can be considered as the resultant of two components. One component is independent of range and results from the finite pulse length and gate length and the random nature of the return signals. The other component is due to receiver noise and increases as the signal-to-noise ratio decreases. The dispersion component independent of range is shown to be proportional to the pulse length and tracking gate length. The variable dispersion is shown to be proportional to the five halves power of the range and the three halves power of the cotangent of the depression angle of the antenna boresight axis. Performance calculations for a specific radar are carried out and compared with experimental data.

Wind Measurement by Conventional Radar with a Dual Beam pattern

Abstract A method of measuring wind velocities by a dual beam modification to conventional (non-Doppler) radars is described. The two beams are disposed slightly to either side of the antenna bore-sight axis. This results in a double-peaked Doppler velocity (frequency) spectrum which is centered on the radial velocity component and whose peaks are spaced proportionally to the transverse velocity component. Such a dual beam Doppler radar is therefore able to measure the complete vector velocity. But the conventional radar can measure only the echo fluctuation spectrum. For any Doppler spectrum, there is a unique fluctuation spectrum, and in the case of the double peaked Doppler spectrum, the fluctuation spectrum has a secondary peak at a frequency corresponding to the peak spacing. Thus, the conventional radar can also measure the transverse velocity component. While spectrum contamination by turbulence and wind shear may cause the peaks to blend with one another, it is shown that the variance of the fluct...