Beam Scanning Angle Research Articles

An aperture-coupled linear leaky-wave antenna array with 2-D dual-beam scanning capability

An X-band four-element linear microstrip leaky-wae () antenna LWA array with a dual-beam radiation pattern and two- dimensional scanning capability is deeloped. The measured half- power beamwidths of the H-plane and quasi-E-plane radiation patterns are less than 308. By tuning the dc bias of thearactor phase shifter between the antenna elements, the main beam can be scanned in the azimuth plane from y138 to q138 off broadside. In the eleation plane, the beam-scanning angle is close to 208 as the operating frequency is tuned from 11.58 to 12.5 GHz. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 52)53, 2000.

Active Frequency-Tune Beam-Scanning Leaky-Wave Antenna Arrays

X-band active beam-scanning leaky-wave antenna arrays, including 1 × 1,1 × 2 and 1 × 4 prototypes, have been demonstrated. These antennas integrated one or several microstrip leaky-wave antenna elements with a single varactor-tuned HEMT VCO as an active source. Measured results on experimental antennas indicate that the beam scanning angle of the 1 × 1 antenna close to 40° can be achieved and the scanning range of 1 × 2 and 1 × 4 antenna arrays are both close to 32°. Furthermore, reflected wave due to the open end of each leaky-wave antenna element has been suppressed by the symmetric configuration of this antenna array and the antenna efficiency increases. When comparing with the measured radiation pattern of the single element antenna, we found that the 1 × 2 and 1 × 4 antenna arrays can effectively suppress the reflected power by more than 5.5 dB and 10.5 dB, respectively, at 10.2GHz. The power gain are more than 2 dB and 3.16 dB higher than the single element antenna with a measured EIRP of 18.67 dBm.

Dose distributions in tubing irradiated by electron beam: Monte Carlo simulation and measurement

A set of nine tube sleeves was prepared by wrapping polyethylene film around a mandrel. Wall thicknesses ranged from a nominal 0.3 to 0.6 cm and diameters ranged from 2 to 5 cm. The sleeves were irradiated with a scanning 3 MeV electron beam and were dose-mapped by indexing and unwrapping the tube sleeves and measuring the dose by an FTIR spectroscopic technique. A Monte Carlo simulation model is also described which includes all important elements of 3-D geometry necessary to describe this experiment including window foil and beam scan angle. The simulation results were compared with the highly detailed dose distribution measurements in the tubing and the differences were found to be generally within 3 to 6 percent.

Mode competition in fourth-harmonic magnicon amplifiers

In the magnicon RF amplifier, the drive and gain cavities are cylindrical deflection cavities which operate in a rotating TM/sub 110/-mode and spin up an electron beam to high transverse momentum. As a result of the rotating-mode interaction, the electron beam entry point into the output cavity rotates about the axis at the drive frequency. The gyrotron-like output cavity can be operated at m times the drive frequency by using a mode with an azimuthal index of m, as this mode rotates at m/sup -1/ times its RF frequency, thus maintaining synchronism with the electron beam. Previous frequency-multiplying magnicons have used m=2; in this paper it is shown that magnicons with m=4 may be practical, provided one also operates the output cavity at the m/2 harmonic of the cyclotron frequency. Operation at higher harmonics lowers the frequency of the deflection cavities allowing lower RF fields, reducing cavity breakdown problems; lower magnetic fields, reducing magnet cast and complexity; and a larger electron beam, relaxing beam quality constraints. On the other hand, higher order azimuthal-index magnicon modes interacting at higher order cyclotron interactions are subject to competition with nonsynchronous (gyrotron) modes and are more sensitive to electron beam scanning angle spread. A time-dependent multimode gyrotron code has been modified to examine competition in the output cavity between the phase-synchronous operating mode and other nonsynchronous modes which interact via the conventional gyrotron interaction. Calculations have been carried out for fourth-harmonic magnicons with TM/sub 410/ and TE/sub 411/ mode output cavities and include the effects of mode competition with nonsynchronous modes as well as a spread in entry-point angles of the scanning electron beam.

Beam scanning characteristics of an optically controlled array antenna fed by a fiber optic array

AbstractFor an optically controlled array antenna in which the microwave excitation distribution is generated and controlled in the optical domain by means of the optical Fourier transform and the optical/electrical (O/E) conversion, element antenna excitation, and the radiation characteristics are theoretically and experimentally studied in the case in which the image mask is shifted from the optical axis of the Fourier transforming lens for an intended beam scanning. A planar fiber optic array was constructed and the excitation profile and the radiation pattern were experimentally investigated by means of a fiber optic array. First, the excitation profile and the beam scan angle were theoretically expressed in the case in which the circular aperture image mask shift and beam scan angle is derived. From the excitation profile experiment using a type of two‐laser optically controlled array system, it is shown that the excitation profile necessary for the beam scanning can be obtained. From the calculation of the radiation pattern, the beam scanning corresponding to the computed value is possible. A 61‐element fiber optic array was then designed for trial. By using the excitation profile experiment with this array, it is shown that the excitation profile and the beam scanning characteristics can be obtained with the fiber optic array if the transmission loss of the fiber optic array is compensated for.

Theoretical analysis of a leaky millimeter-wave antenna consisting of a layered magnetic slab image line with periodic corrugation

In this paper, a millimeter-wave antenna is constructed with layered magnetic thin films with different saturation magnetizations placed on a grounded conductor and with a periodic structure on the upper layer interfacing with air. Under the condition in which a dc magnetic field is applied externally, the scanning characteristics and the radiation efficiency of the antenna are analyzed with a perturbation method. In the analysis, the multiple scale method also is applied. From the primary field, the coupling characteristics of the radiation field with the guided field and the incident field are derived while the amplitude transport equation is derived from the secondary field. By means of these results, the expressions for the radiation efficiency and the radiation angle of the antenna are obtained. Numerical calculations are carried out in the millimeter-wave frequency range so that the magnetic field dependence of the beam scanning angle and the radiation efficiency are investigated. From the numerical results obtained, it is found possible to construct a magnetically tuned millimeter-wave antenna with a large radiation efficiency and a large beam scanning angle by adjusting the structural parameters of the antenna consisting of two layers of magnetic slabs with different saturation magnetizations.

Tracking error of phased array antenna

The tracking error of a phased array antenna between transmitting and receiving frequencies was measured by in-flight experiments using a geostationary satellite. The tracking error was found to depend on beam-scanning angle and the ratio of transmitting and receiving frequencies. Measured results agreed well with a theoretical prediction. An effective method to eliminate the tracking error is proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Planar channeling effects in Si(100)

Effects of axial and planar channeling in Si(100) crystals on junction depth and sheet resistance control are studied for the case of shallow junction implants. Whole-wafer sheet resistance mapping, SIMS and spreading resistance profiling are used to characterize the effects of tilt and azimuthal angle variations for electrostatic and mechanical-scan implanters. Additional effects studied include critical angle variations with atomic mass and ion energy, beam scan angles for electrostatic-scan systems, implants through thin dielectric layers, wafer flexing over heat-sink pads and errors in crystal orientation. Planar and axial channel critical angles are modeled for B, P and As implants into Si(100) for energies between 20 and 200 keV. System requirements for avoidance of direct channeling effects are reviewed for IC production conditions.

IMPROVING GATED CARDIAC SCANNING USING LIMITED-ANGLE RECONSTRUCTION TECHNIQUE

Selected phases of the cardiac cycle can be imaged by the method of gated cardiac scanning using whole body scanners. However, since there is no synchronization between the random heart beats and the CT machine, the output will have gaps in the angular coverage of each scan. The missing projections in these gaps result in artifacts in the reconstructed images. In this paper the technique of limited-angle reconstruction is employed to fill in the missing projections to remove the artifacts. The object is transformed back and forth between the object space and the projection space, being corrected in each step by the constraints of the finite spatial extent and of the upper and lower bounds of the object in the object space, and the known projections in the projection space. It is found that by using the proposed algorithm the rms errors of the limited-angle images are reduced to a level comparable to those of the complete-angle images. The same iteration algorithm can also be used to reduce the fan beam scanning angle from 360 degree to 180 degree without sacrificing much image quality.

Improving Gated Cardiac Scanning Using Limited-Angle Reconstruction Technique

Selected phases of the cardiac cycle can be imaged by the method of gated cardiac scanning using whole body scanners. However, since there is no synchronization between the random heart beats and the CT machine, the output will have gaps in the angular coverage of each scan. The missing projections in these gaps result in artifacts in the reconstructed images. In this paper the technique of limited-angle reconstruction is employed to fill in the missing projections to remove the artifacts. The object is transformed back and forth between the object space and the projection space, being corrected in each step by the constraints of the finite spatial extent and of the upper and lower bounds of the object in the object space, and the known projections in the projection space. It is found that by using the proposed algorithm the rms errors of the limited-angle images are reduced to a level comparable to those of the complete-angle images. The same iteration algorithm can also be used to reduce the fan beam scanning angle from 360 degree to 180 degree without sacrificing much image quality.

Design considerations for ruze and rotman lenses

Ruze and Rotman lenses are types of parallel-plate lens which can be used to form multiple beams for antenna arrays. An algebraic analysis is used to relate the different orders of phase aberration to the lens contours, and shows that lenses with zero second- and third-order aberrations can be designed. For a given array length and beam scan angle requirement, the analysis determines the minimum lens size and simplest design which can be used.

Antenna temperature for a scanning microwave radiometer

Expressions for the antenna temperature are derived for a scanning Earth-viewing satellite-borne microwave radiometer. The result is in the form of an integral that includes the antenna gain function and brightness temperature. A composite emissivity term appears in the brightness temperature equation that contains the horizontal and vertical components of surface emissivity weighted by their respective antenna gains. Analysis is performed to obtain the antenna temperature components corresponding to the emission of horizontally and vertically polarized radiation. Calculations are performed showing the effects of beam width and scan angle on the two components of antenna temperature for a linearly polarized antenna. Effects resulting from antenna cross polarization are also analyzed.