Showing papers on "Coaxial antenna published in 1983"

School of Electrical Engineering.

Abstract: The possibility of making the antenna of an MST radar too large is pointed out. It is not that the signal ceases to become stronger beyond some critical antenna size; the received scattered signal actually becomes weaker as the antenna size is increased whenever the target is in the near field, Fresnel region of the antenna. The Arecibo antenna is a case in point. It is supposed that MST work would benefit to use a feed which illuminated only a portion of the dish.

Single-element rectangular microstrip antenna for dual-frequency operation

Abstract: The letter describes a single-element rectangular microstrip antenna which can operate simultaneously for two different frequency bands.

Circular polarization antenna

Abstract: A circular polarization antenna having wide-band circular polarization characteristics and impedance characteristics is accomplished by feedng N-antenna elements which are shifted at an interval of π/N rad. with respect to the boresight direction with differential phase shift of an interval of π/N rad. corresponding to the angular orientation of the antenna elements so as to obtain perfect circular polarization with respect to the boresight direction. This antenna construction can be applied to circular polarization antennas of various types, thereby allowing a wide-band circular polarization array antenna or an array antenna for dual orthogonal circular polarizations having high polarization discrimination to be achieved.

Quadrifilar helix antenna tuning using pin diodes

Abstract: An antenna is tuned in separate discrete frequency bands by changing the ctrical length of the antenna. PIN diodes are placed at predetermined locations on the antenna coaxial cable radiating elements. When it is desired to shorten the antenna for a higher frequency band use, the diodes are biased short circuiting segments of the antenna. When the lower frequency band use is desired, diodes are unbiased so that the diodes act like a very small capacitance shunted by a large resistance which is essentially an open circuit permitting the entire length of the antenna to operate.

Frequency independent shielded loop antenna

Abstract: An antenna is disclosed that is especially useful for radiating and receiving non-sinusoidal electromagnetic waves. The antenna is an efficient and distortion-free radiator of electromagnetic pulses that do not use a sinusoidal carrier. The antenna's size is independent of frequency and the antenna, therefore, can be of small size relative to the wavelength of the radiated electromagnetic waves. When used for reception of electromagnetic wave energy, the antenna performs with low distortion. The basic concept underlying the invention is the modification of the Hertzian electric dipole into an antenna structure that can carry large currents without requiring a large driving voltage. Antennas for the transmission or reception of sinusoidal waves achieve that goal by employing resonant structures. The invention achieves the same result by changing the Hertzian electric dipole into a loop that forms a Hertzian magnetic dipole and preventing the undesirable magnetic dipole radiation by shields of conducting and absorbing materials.

Printed circuit balun with a dipole antenna

Abstract: A coplanar printed circuit balun for connecting an unbalanced feedline to a balanced dipole antenna.

Coaxial dipole antenna with extended effective aperture

Abstract: A coaxial dipole antenna includes a first radiator which is approximately one quarter wavelength long. A second radiator exhibits length less than one quarter wave length and is coupled to the feed port by a reactive element which has an electrical reactance which is insufficient to increase the electrical length of the second radiator to one quarter of the wavelength. The length of a dipole antenna is substantially shortened while an effective aperture of one half wavelength is maintained by causing a portion of the transceiver housing to radiate in phase with the antenna.

Microstrip antenna with circular ring

Abstract: A radar antenna is shown in a first embodiment to have a ground plane and a feed line on opposite sides of a dielectric sheet and a ring-shaped antenna element on another dielectric sheet to form a microstrip assembly wherein such antenna element is capacitively coupled to the feed line. In a second embodiment the radar antenna has a parasitic antenna element on still another dielectric sheet, such parasitic antenna element being in register with the ring-shaped antenna element.

A Holographic Surface Measurement of the Texas 4.9-m Antenna at 86 GHz

Abstract: An instrument has been built which allows the electromagnetic measurement of the surface accuracy of a large millimeter-wavelength antenna. The University of Texas 4.9-m radio telescope has been measured with this technique at 86.1 GHz to an accuracy of 4 ?m at the surface. Our technique is an interferometric one which is fast, accurate, and able to measure the whole antenna surface at once. While the technique is illustrated by its use on a large antenna, it could be used in a near-field measurement of a smaller antenna. Several antenna surface maps are presented. A comparison of run-to-run repeatability was made. The technique itself was tested by deforming the antenna surface in a known way and subsequently detecting the deformation.

Characteristics of a new class of diode-switched integrated antenna phase shifter

Abstract: The effectiveness and bandwidth of a new class of diode-switched integrated antenna phase shifter are examined. A well-known example of this type of antenna is the "spiraphase." The operation of this type of antenna is found to be for circular polarization only. When used as a reflecting element, the effectiveness of the antenna is not broadband. A much wider bandwidth is expected by using this antenna as a direct radiating device.

Bicollimated offset Gregorian dual reflector antenna system

Abstract: A dual reflector antenna having two reflectors concave to each other and specially shaped so that beams incident on the antenna from two directions are reflected therefrom in collimated beams in two other directions.

Omnidirectional, circularly polarized, cylindrical microstrip antenna

Abstract: A microstrip cylindrical antenna comprised of two concentric subelements on a ground cylinder, a vertically polarized (E-field parallel to the axis of the antenna cylinder) subelement on the inside and a horizontally polarized (E-field perpendicular to the axis) subelement on the outside. The vertical subelement is a "wraparound" microstrip radiator. A Y-shaped microstrip patch configuration is used for the horizontally polarized radiator that is wrapped 1.5 times to provide radiating edges on opposite sides of the cylindrical antenna for improved azimuthal pattern uniformity. When these subelements are so fed that their far fields are equal in amplitude and phased 90° from each other, a circularly polarized EM wave results. By stacking a plurality of like antenna elements on the ground cylinder, a linear phased array antenna is provided that can be beam steered to the desired elevation angle.

A Multi-Element Microstrip Antenna for Local Hyperthermia

Abstract: A multi-element microstrip antenna applicator designed for microwave local hyperthermia is described Design criteria for such a microstrip antenna array are presented Various antennas were built and compared Experimental measurements of heating patterns show the multiple microstrip spiral antenna provides controlled heating over a large area

Spiral antenna with selectable impedance

Abstract: A monopulse spiral antenna system of the type having a minimum of three, interwound spiral arms for multimode, direction of arrival sensing, is disclosed in which the antenna arms are shaped and arranged in an overlapping configuration that allows the interarm impedance of the antenna to be adjusted, substantially independently of other electrical properties of the antenna, for matching of the antenna impedance of a mode forming network while preserving the broadband, directional capabilities of the antenna. Several different embodiments of the impedance adaptive antenna are disclosed including a preferred, eight-arm exponential spiral in which the arms are conductive strips transversely inclined relative to a plane formed by the spiral so that opposed and parallel surfaces of adjacent arm strips create a dominant interarm capacitance that in turn determines the overall input impedance of the antenna. Furthermore, the opposed, proximate surfaces of the strip-shaped arms are dimensioned, spaced and inclined at an angle that adapts the input impedance of the antenna to a value matching that of the mode forming network.

Numerical analysis of 4-arm Archimedean spiral antenna

Abstract: The radiation fields of a 4-arm Archimedean spiral antenna excited with three types of balanced mode, M1(1, j, ?1, ?j), M2(1, ?1, 1, ?1) and M3(1, ?j, ?1, j), are evaluated on the basis of the current distributions which are determined numerically. An axial beam and conical beams are presented with experimental results. It is demonstrated that an axial ratio of less than 3 dB can be obtained over a wide angle range of about ± 60°, when the spiral is excited with modes 1 and 2. It is also found that the axial ratio for mode 3 is liable to be deteriorated by the reflected current, particularly around the spiral axis.

Spiral antenna deformed to receive another antenna

Abstract: A spiral antenna has a plurality of interleaved radiating elements winding outwardly in a spiral pattern about a common axis. The spiral pattern is deformed at outer regions of the antenna to define one or more circumferentially disposed concavities in the body of the antenna. Each concavity is adapted to receive another antenna such as a spiral antenna or horn antenna.

Fiber optic data distribution for phased array antenna

Abstract: A fiber optic data distribution system is disclosed for distribution of the phase shift commands to an electronically steered antenna array. Novelties include the fan-out of a single bundle to multiple receptors, equalization of optical path for precise synchronization, the use of the RF active side of the antenna for data distribution, the use of the antenna radome as support structure for the fiber optics, and an optical reflector to divert light from the plane of the radome to the transmit/receive element.

Miniature tactical HF antenna

Abstract: An improved miniature antenna is disclosed which provides an electrically short radiation pattern by providing shielding of selected portions of a current carrying conductor forming a loop antenna. The shielding is provided so that the shielded portion of the loop antenna does not cancel the radiation from an unshielded radiating portion of the antenna, thereby producing a uniform radiation pattern. A plurality of the current carrying elements formed by the shielded and unshielded portions may be coupled in a series and parallel relationship to provide optimum impedance matching at the frequency of operation of a transmitter or receiver.

Rotary scan antenna

Abstract: An antenna having a rotatable phase center is disclosed. The antenna includes a horn antenna having a phase center and at least one rod-like impedance element located adjacent a wall of the horn antenna near the phase center. The length of the impedance element is selected such that it shifts the phase center from its normal, undisturbed location without substantially affecting the amplitude pattern of the antenna. Means is provided for mechanically rotating the rod-like impedance element around the phase center so as to thereby cause the phase center to also rotate.

Vertical antenna with improved artificial ground system

Abstract: The present invention relates to vertical antenna systems employing an improved artificial ground system. In a low frequency design, the artificial ground system provided is in the form of a counterpoise or ground screen that is provided with an efficient, economical and practical electrical radial wire design. A high frequency design is also provided in the form of an integral antenna structure. This high frequency integral design entails a vertical antenna, a counterpoise in the form of a metal plate, a ground plate, and wherein said metal plate forming the counterpoise is insulated from the ground plate. In either type of antenna system, the counterpoise functions to collect antenna return currents and direct them back to the feed point of the antenna in an efficient and effective manner.

Formulation for wire radiators on bodies of translation with and without end caps

Abstract: A formulation, based on the method of moments (MM), is presented for active and passive wire radiators attached to, or near, a broad class of bodies and surfaces, including open or closed cylinders of arbitrary cross section as well as finite flat or curved panels. The development expands the utility of the MM theory for various antenna problems. The analysis incorporates a special junction basis set for the antenna attachment points. Total domain and piecewise continuous expansion functions are used on the surfaces. The formulation is primarily intended for prediction of radiation patterns of wire antennas (such as monopoles and loops) on asymmetric bodies of translation, open or closed (capped). The present method has shown satisfactory agreement with published data in the prediction of antenna input impedances as well.

Non-resonant coaxial monopole antenna

Abstract: A relatively short broad band monopole coaxial antenna is provided with a center conductor and an outer radiator. The antenna is mounted above a ground plane and comprises a bare outer radiator portion adjacent the ground plane and a portion remote from the ground plane which is covered with a variable thickness microwave absorbent material. The signal to be transmitted is applied to the base of the monopole antenna adjacent the ground plane. Non-radiated signals propagate up the antenna. The high frequency components are absorbed by the microwave absorbing material. A tip matching network and a base matching network are coupled between the outer conductor and the ground plane for attenuating and matching the low frequency components of the non-radiated signals. The resulting monopole coaxial antenna has no undesirable reflections and has the appearance of infinite effective length antenna.

The wave antenna for transmission and reception

Abstract: The traveling-wave horizontal-wire antenna over the earth is analyzed in its original form with vertical ground connections (the Beverage antenna) and with these replaced by horizontal terminations. For transmission, the electromagnetic field of an antenna with optimum length is determined, both along the surface of the earth in air and in the earth, in an accurate but simple form that takes full account of the proximity of the earth (lake, sea) on the distribution of current. For reception, the induced currents in the antenna and in the load are determined for a field incident along the surface of the earth. The two types of termination are compared and their contributions shown to be small when the horizontal wire has a length near the optimum.

Log-periodic antenna

Abstract: A log-periodic antenna comprises two arrays of dimensionally tapered radiating elements disposed in the E-plane and each fed by a balanced line consisting of the inner conductors of two coaxial cables. In one embodiment the elements of each array are dipoles and in another embodiment are formed of continuous conductive strips in zig-zag patterns on non-conductive support members. Each array preferably has two sets of elements disposed in planes, respectively, which converge toward the smaller end of the array with vertically aligned radiating elements of each set projecting in opposite directions from the array axis. Periodic gain dropout anomalies across the antenna operating band are eliminated by use of a shielded feed line. In another embodiment having advantage in direction finding, the sets of elements of each array are located on associated opposite sides of a right rectangular pyramid. These pyramidal arrays are used in pairs for direction finding.

Antenna with coaxial connector

Abstract: An antenna defines a coaxial connector receptacle when the antenna is in a fully retracted position

Theory and design considerations for a new millimetre-wave leaky groove-guide antenna

Abstract: A transverse equivalent network is presented for a new type of leaky-wave antenna based on the groove guide and suitable for millimetre waves. Employing this network, the antenna's performance characteristics are explained and systematic design considerations are deduced.

Automatic direction finder antenna array

Abstract: An automatic direction finder antenna array having a plurality of pairs of oppositely positioned antenna elements arranged radially from a common center with each pair forming a cardioid radiation pattern when energized. Switching apparatus energizes successive antenna pairs to produce a rotating cardioid pattern but with the cardioid being switched back and forth 180° at a higher switching frequency when each pair of antennas is energized during the rotating function. The antenna AX whose output bears the lowest ratio R to the output of its oppositely positioned antenna is determined as well as the antenna AZ having the largest output signal VZ. The precise angle of reception of a received signal is then determined from AX, AZ, and R.