Radiation Beamwidth Research Articles

An UWB spirally ridged antenna for high directive CP radiations

AbstractA broadband antenna designed to radiate high directive circularly polarized radiations is presented. This design utilizes spiral arms to achieve a broad frequency bandwidth and radiates circularly polarized fields. To enhance the directivity, the spiral arms are axially elevated to have a radiation beamwidth narrower than that radiated from an analogous spiral antenna in the upward direction. This antenna is suitable for many microwave applications. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 303–305, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24040

Fourier Transform Optical Beamformer Employing Spatial Light Modulator

Optically controlled beam forming techniques are effective for phased-array antenna control. We have developed the Fourier transform optical beamformer (FT-OBF). The antenna radiation pattern inputted into an amplitude spatial light modulator (A-SLM) is optically Fourier transformed to a specific phase-front light beam equivalent to an antenna excitation in the FT-OBF. Optical signal processing, used the Fourier transform optics, is effective to large-scale, two-dimensional, and high-speed signal processing. To implement a flexible and finer antenna beam pattern control, we use an A-SLM as input image formation of the FT optics. And, to realize a small-size FT-OBF, we use symmetric triplet lenses with convex, concave and convex lens. The total optical system becomes below 1/5 length compared with the length using single lens. Finally, we evaluated the developed FT-OBF with the generated amplitude and phase distributions, which excitation signal of an array antenna. We measured an antenna radiation beam pattern, beam steering and beam width control, in the C-band. Measurement results agreed with theoretical calculated results. These results show the feasibility of the spatial light modulator based FT-OBF.

Multi-Channel Microwave Reflectometer with Fermi Antenna Receivers

We have evaluated a Fermi antenna newly designed in X band for use in a multichannel reflectometer. The advantages of the Fermi antenna are that it can be adopted as an array antenna owing to its planer shape and fabricated with a low cost due to its compactness and a light-weighted structure. The radiation-beam widths in the E- and H-plane are almost equal to each other and the side-lobe levels are low. Plasma behaviors in the HITOP device are measured by reflectometry using two Fermi antenna receivers. Time evolution of the cutoff layer and plasma rotation velocity measured by the reflectometer are in good agreement with an electrostatic probe measurement.

Superlight source of radiation with a waveguide used for bunching an electron beam

A scheme of a generator of electromagnetic-wave radiation is proposed in which a radiating region moves along a radiator with a velocity greater than the velocity of light in vacuum. The superlight motion of the generating region leads to the situation in which the resulting radiation has the properties of Vavilov-Cherenkov radiation. The electron beam of a superlight source is formed while the particles travel across a waveguide along which an electromagnetic wave propagates. The construction of the generator makes it possible to vary the velocity of the radiating region, the radiation pattern, and the radiation beamwidth. Calculations are performed that allow one to evaluate the parameters of the generator and the characteristics of radiation.

Theoretical study of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium

The radiation properties of 2 X 2 element planar array of equilateral triangular patch microstrip antenna in plasma medium are studied. The array factor and far-zone EM-mode and P-mode radiation fields of the array geometry are derived using vector wave function techniques and pattern multiplication approaches. The total field patterns and various characteristics of pattern such as half power beam width (HPBW), first null beam width (FNBW) and direction of maximum radiation are computed for two different values of progressive phase excitation difference between the elements. The results of this array geometry are obtained both in plasma medium and in free space and compared with those of single element equilateral triangular patch microstrip antenna.

FM wide band panel dipole antenna

It is very common that when a broadcaster needs to install an FM transmitting antenna within a large metropolitan area he places it on the tallest structure or building available. When the rooftop is already occupied by a large number of other types of transmitting and receiving antennas, the panel dipole antenna should be chosen. This antenna is secured to the side walls of the upper floors with the panel oriented to obtain full coverage of the most desirable areas of the city. For the Buenos Aires area this orientation avoids radiating toward Uruguay and specifically toward Montevideo, some 140 miles away. A wide band antenna operation permits placing the station on the air and at the same time allows future stations to share it without the installation of new antennas. Details of model and full model impedance and radiation pattern measurements during the antenna development are presented in order to show its technical characteristics. The radiation patterns were measured on a scale model in an anechoic chamber. The full scaled model was measured in an outdoor antenna range. Both E and H plane radiation patterns were measured along the FM band in order to observe pattern variations on both planes. Practically no difference in a panel radiation beamwidth from 88 to 108 MHz was observed and at the same time good input impedance was maintained. A really wide band antenna in pattern and VSWR is obtained. Power division for the antenna system is obtained designing an eight port power divider using the microstrip line technique. In this case, however due to high power operation the ground plane and strip are contained in a sealed metallic box and are separated by high pressure dry air like into the 3" feeding coaxial line.

Beamwidth enhancement of a circularly polarized microstrip antenna mounted on a three‐dimensional ground structure

AbstractBy mounting a regular circularly polarized microstrip antenna on a three‐dimensional (3‐D) square ground structure, beamwidth enhancement of the circular polarization (CP) radiation can be obtained. Experimental results show that, owing to the 3‐D square ground structure, the 3 dB beamwidth of the CP radiation can reach more than 110°, which is about 30° greater than that of a corresponding regular microstrip antenna. Details of the proposed 3‐D square ground structure are described, and the effects of various dimensions of the proposed square ground structure on the beamwidth enhancement of CP radiation are experimentally studied. © 2002 John Wiley & Sons, Inc. Microwave Opt Technol Lett 32: 149–153, 2002.

Study of rotationally symmetric antenna with wider beamwidth

Numerical analysis is carried out for the antenna consisting of a rotationally symmetric oblate spheroidal conductor connected below and above a circular patch antenna with its dielectric substrate truncated at the edges of the patch. By means of the equivalence principle, the exterior and interior of the antenna are separated as problems equivalent to the original one. The cavity model is used for the electromagnetic field model inside the dielectric material while the equivalent electromagnetic current flows at the dielectric aperture are expressed in terms of sums of the mode functions. The current at the conductor surface is assumed from the continuity condition of the current at the junction plane of the dielectric and the conductor. The magnetic field integral equation at the dielectric aperture and the electric field integral equation at the conductor surface are solved by Galerkin's method in order to derive the unknown coefficients contained in the equivalent electromagnetic currents at the dielectric aperture and the current at the conductor surface. For the case of a conductor height of 0, a circular patch microstrip antenna with its dielectric substrate truncated at the edges of the patch is fabricated and its input impedance is measured. As the conductor height is increased, the radiation beamwidth in the E plane is expanded. Since this antenna has a wider radiation beam than that of the circular patch microstrip antenna, it is useful as an antenna for mobile satellite communication terminals. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(11): 1–10, 2000

CPW-fed slot antenna with CPW tuning stub loading

Adjusting the slot width in a slot antenna can determine the operating frequency bandwidth. In order to obtain a wider radiation beamwidth, a narrower slot width is needed. This paper uses a CPW tuning stub in the CPW-fed slot antenna to achieve this goal. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 257–258, 1998.

Beam characteristics of short-pulse radiation with electromagnetic missile effect

Beam characteristics such as beamwidth and beam intensity of short-pulse radiation with electromagnetic missile effect, not restricted to the electromagnetic missile, are generally range dependent in pulse propagation. An effective measure to study such beam characteristics is to investigate the local drop rate of the energy pattern in the beam profile and the local decay rate of energy in the pulse beam. It is shown that both the energy decay rate and the energy drop rate are definitely determined by the time–space source parameters so that the beam characteristics can be readily evaluated and properly controlled. Moreover, the underlying relation between the slow decay rate and the energy drop rate are constructed, which shows perfect harmony in achieving slower-energy decay and higher-energy concentration in the beam.

Analysis and design of beam-shaped rectangular polyrod antennas

Theoretical and experimental investigations on the near field and radiation characteristics show a fairly good agreement which justifies the TE11 x mode of excitation. Eight polyrod antennas of different configurations were built and tested as functions of taper angles, straight and curved axial lengths, and frequency of excitation. It is found that the radiation patterns, cross-polarization level, beamwidth and gain could be controlled not only by the axial length and taper angles but also by shaping the axis of the polyrods in order to realize an optimum design.

Second Harmonic Generation in an AlGaAs Double-Heterostructure Laser

Second-harmonic radiation emanating from an AlGaAs transverse-mode-stabilized laser diode has been observed under continuous-wave operation at room temperature. The far-field beam width of the second-harmonic radiation has been found to be apprecialy narrower than that of the fundamental laser radiation.

Technique for evaluating radiation beam and image slice parameters of CT scanners

A technique is described for determining in a single scan three important CT scan parameters: beam localizer accuracy, image slice width, and radiation beam width.

Superconducting superdirectional antenna arrays

Electrically and physically small antenna arrays in a superconducting state can be used to obtain a radiation pattern of moderate directivity with high radiation efficiency. The loss resistance is reduced by several orders of magnitude, and superdirectivity is achieved with a loop antenna array. Radiation beamwidth depends upon only the number and relative phase of the loops and is independent of array size. Experimental results show efficiency of an electrically small two loop antenna array increases 250 times when placed in a liquid helium environment. Its directive properties compare well with theoretical predictions.

A theoretical analysis of etched grating couplers for integrated optics

Grating couplers provide an attractive method for the excitation of optical thin-film waveguides. We present here a perturbation analysis of etched or deposited grating couplers based upon both the transmission line and the Green's Function approaches, which predict the coupling efficiency, the output radiation beamwidth, the angular dependence of excitation, and the intensities of the other orders of the diffracted beams as functions of the grating periodicity, grating groove depth, and excitation direction. It is found that the maximum excitation efficiency is 81 percent, that high efficiency can be achieved by excitation from the substrate, and that higher efficiency is obtained when the radiation leakage to the side orders is minimized.

Comparative spectra of microseisms and swell

Abstract Spectra of seismic and ocean wave recordings near San Diego, California, show closely related features. The wave spectra consist of a sharp peak whose frequency, f(t), increases linearly with time and consistent with the expected dispersive behaviour from a source at 6150 nautical miles (presumably a storm in the Ross Sea). The seismic spectra show peaks at f(t) and at 2 f(t); the double frequency peak contains 100 times the energy of the peak at the primary frequency. A comparison between the peak frequencies and band widths of the seismic and ocean wave spectra, and an estimate of the direction and beam width of the seismic radiation, leads to the following conclusions: that the microseismic generation area is predominantly local, being confined to a distance of 100 miles up or down the coast. For the primary frequencies the generative strip is presumably confined to shallow water; for the double frequencies it extends 200 miles seaward.

The Wavelength Distribution of the Scattered Radiation in a Medium Traversed by a Beam of X or Gamma Rays

A theoretical investigation, based on the Klein-Nishina formula, has been made of the amount and distribution of radiation in a scattering medium. It is shown that the experimentally observed maximum in the ratio between the amounts absorbed of scattered and primary energy as the primary wavelength varies is to be expected on theoretical grounds, and that the position of the maximum depends on the atomic number of the scattering medium. For water, the theoretically predicted maximum occurs at about 100 X.U., agreeing very well with the experimental value, while for heavier substances the maximum should move towards shorter wavelengths, occurring at about 10 X.U. for lead. It has been found possible to make an exact calculation of the quantity and quality of the once-scattered radiation absorbed at any point on the axis of a parallel homogeneous beam, taking into account the effect of the wavelength and beam-width of the primary radiation, the composition and thickness of the scattering medium, and the depth of the point considered below the surface; in particular, the following quantities have been evaluated:— The intensity spectrum of the once-scattered radiation received at any point in the medium, the corresponding spectrum of the absorbed energy, and the total amount of electronic energy set free per unit volume at any point in the medium by the primary and the once-scattered radiation. Taking water as the scattering medium, owing to its close approximation in scattering properties to a tissue, these quantities have been numerically evaluated for four particular primary wavelengths, namely, 17·1, 50, 200, and 400 X.U. The results obtained are discussed and compared with experimental observations. Certain conclusions are reached regarding the effect of the beam-width on the amount of scattered radiation, the part played by scatterings of higher orders than the first, the effect of scattering on the depth-dose, and the quality of the scattered radiation. These investigations were commenced while the author was attached as physicist to the Cancer Research Committee of the University of Sydney.