Showing papers on "Coaxial antenna published in 1991"

Microstrip Yagi array antenna for mobile satellite vehicle application

Abstract: A novel antenna structure formed by combining the Yagi-Uda array concept and the microstrip radiator technique is discussed. This antenna, called the microstrip Yagi array, has been developed for the mobile satellite (MSAT) system as a low-profile, low-cost, and mechanically steered medium-gain land-vehicle antenna. With the antenna's active patches (driven elements) and parasitic patches (reflector and director elements) located on the same horizontal plane, the main beam of the array can be tilted, by the effect of mutual coupling, in the elevation direction providing optimal coverage for users in the continental United States. Because the parasitic patches are not connected to any of the lossy RF power distributing circuit the antenna is an efficient radiating system. With the complete monopulse beamforming and power distributing circuits etched on a single thin stripline board underneath the microstrip Yagi array, the overall L-band antenna system has achieved a very low profile for vehicle rooftop mounting, as well as a low manufacturing cost. Experimental results demonstrate the performance of this antenna. >

Photon-noise-limited laser transducer for gravitational antenna

Abstract: We have constructed and tested a laser interferometer transducer for a long, wideband, laser-linked gravitational radiation antenna. Photon-noise-limited performance was achieved using 80 microW from a single mode Spectra-Physics 119 laser in a modified Michelson interferometer on a vibration isolation table in a quiet room. A piezoelectric driver on one of the interferometer mirrors was used to generate subangstrom (3 x 10(-14)-m) vibrations of known amplitude. The measured displacement sensitivity of the system in the kilohertz region was 1.3 x 10(-14)m/Hz(1/2), which compares well with the calculated photon noise limit of 1.06 x 10(-14) m/Hz(1/2). This is the smallest vibrational displacement measured directly with a laser to date.

Conformal phased array antenna

Abstract: An array of antenna elements are configured in a lattice-like layer, each element being similarly oriented such that the elements form a two-dimensional antenna aperture that may form a planar or curved surface of a desired shape. The antenna elements are connected in a one-to-one correspondence in both number and form to a lattice of identical, multiport, isotropic, wave-coupling networks physically located under the antenna element array as a backplane of the antenna element layer. Each wave-coupling network or "unit cell" couples signals to and/or from its corresponding antenna element and further functions as a phase delay module in a two-dimensional signal distribution network. This invention can be embodied in a two-dimensional signal distribution network and in a wrap-around, conformal, millimeter-wave, phased array antenna, such as on the nose of a missile. A backplane of densely-packed resonant cavities feeds an outboard-facing layer of resonant slots configured in a rectangular or hexagonal lattice for maximum density. Instead of using a corporate feed network to feed each element, the array can be fed from circumferencial points on the edge of the array farthest from the nose of the missile, with each element being electromagnetically coupled to each of its four or six adjacent elements by either dielectrically-loaded irises with concentric probes or simple irises. By differently tuning the individual cavities, the beam may be directed off-axis azimuthally in any forward direction.

Planar microstrip Yagi antenna array

Abstract: A directional microstrip antenna includes a driven patch surrounded by an isolated reflector and one or more coplanar directors, all separated from a groundplane on the order of 0.1 wavelength or less to provide endfire beam directivity without requiring power dividers or phase shifters. The antenna may be driven at a feed point a distance from the center of the driven patch in accordance with conventional microstrip antenna design practices for H-plane coupled or horizontally polarized signals. The feed point for E-plane coupled or vertically polarized signals is at a greater distance from the center than the first distance. This feed point is also used for one of the feed signals for circularly polarized signals. The phase shift between signals applied to feed points for circularly polarized signals must be greater than the conventionally required 90° and depends upon the antenna configuration.

A dipole antenna for interstitial microwave hyperthermia

Abstract: An improved interstitial microwave antenna design was investigated in static phantom experiments at 915 MHz and different insertion depths. Compared with conventional interstitial antennas, the presented dipole microwave antenna shows heating patterns which are concentrated on the dipole irrespective of the insertion depth. By analogy to interstitial radiotherapy, the microwave antenna allows a high concentration of energy in the target volume with as little damage as possible to the healthy surrounding tissue. The undesired heating of healthy tissue along the feeding line observed with conventional interstitial antennas is avoided. A lambda /4 sleeve on the feeding line (which does not radiate microwave energy itself to the surrounding tissue) transforms an open end, i.e. a high impedance at the generator end of the dipole antenna. The current flowing back along the outside of the outer conductor of the feeding line in the direction of the generator is zero at this point. Both dipole sections have the same terminating impedance. Since the lambda /4 sleeve is mounted outside the antenna, its mechanical length is not restricted by the mechanical length of the antenna. It can be charged with dielectric materials of low dielectricity constants. >

Integral diversity antenna for a laptop computer

Abstract: An integral diversity antenna especially suited for use in a laptop computer device without the need for changing or otherwise altering such devices pre-established form factor. Two separately located printed circuit board antenna structures are orthogonally mounted in an associated counterpoise. One such antenna structure is vertically polarized and the other horizontally polarized. In this manner, both spatial and polarization diversity is achieved. The counterpoise serves the additional purpose of affecting both RFI and EMI shielding of the laptop computer's LCD display and driven circuitry.

Personal positioning satellite navigator with printed quadrifilar helical antenna

Abstract: A navigation unit (10) for receiving navigation signals from a source thereof such as global positioning satellites is configured to rack mount and connect with a remote fixed antenna and for detached, self-powered operation using a directly mounted helical antenna (14). The preferred antenna (14) includes antenna elements composed of a thin film of conductive material (50) printed on a flexible dielectric substrate (44) rolled into a tubular configuration.

Antenna circuit for a multi-band antenna

Abstract: A branching filter, which is operatively connected between an antenna and a communication device which utilizes different frequency bands, suppresses a mutual interference between signals transmitted to and from the communication device. An antenna circuit, which is operatively connected between the antenna, or a branching filter, and the communication device, converts an impedance with respect to a signal in a frequency band having a lower frequency, and reduces loss resulting from a capacitive antenna impedance.

Device for information transmission

Abstract: A device for information transmission, a so-called transponder, for receiving a first microwave signal, modulating and coding, and retransmitting a second microwave signal, comprising at least one antenna means made in microstrip technique is described. The device is characterized primarily in that the antenna means comprises an antenna layer (20), acting towards a ground plane (21), the antenna layer and the ground plane having essentially equal area, and in that the device further comprises a reflex means (23), arranged next to or at a distance of at most 1/6 of the air wave length of the first microwave signal from the edges of the antenna layer and the ground plane, so that an antenna lobe directional from the antenna means is obtained, comprised of directly transmitted microwave signal and reflected microwave signal. With this embodiment a device is obtained that is compact, effective, light and inexpensive and gives a well defined and directional antenna lobe for communication with a good range.

Sea surface antenna

Abstract: A sea surface antenna comprises a cylindrical tube of metallic material 13 on a dielectric former. The tube has a longitudinal slot shorted at each end and coupled at its midpoint to a coaxial feed. The slot is bridged by two groups of capacitances each group being distributed along a respective half of the slot. The length of the antenna is less than 0.25 λ and the diameter of the antenna is less than 0.02 λ, where λ is the free space wavelength at the operating frequency. The antenna is dimensioned so as to operate in an evanescent mode at a resonant frequency less than the cut-off frequency.

Complementary bowtie dipole-slot antenna

Abstract: The antenna system includes a complementary "bowtie" dipole-slot antenna, the antenna having symmetrical halves about a plane of symmetry. The two halves of the antenna are slanted at the plane of symmetry such that the total included angle between the halves is between 70 degrees and 120 degrees. A ground plane is positioned between the halves of the antenna extending through the plane of symmetry. A circuit is included for independently exciting the halves of the antenna. In a second embodiment the ground plane incorporates a pair of notch antennas. Thus, both vertical and horizontal polarization can be achieved independent of each other.

Pane antenna having at least one wire-like antenna conductor combined with a set of heating wires

Abstract: Disclosed is a pane antenna installed in a heated window pane of a motor vehicle to receive frequencies above the high frequency range. The antenna includes at least one wire-shaped first antenna conductor extending across parallel heating conductors of a heating field. The crossing points of the first antenna conductor with heating conductors are preferably in galvanic contact to create a capacitive antenna region along the first antenna conductor. The capacitive antenna region is coupled via a second antenna conductor extending also perpendicularly to the heating conductors, to an antenna terminal arranged on the window pane in proximity to a rim. The window pane is surrounded by a conductive frame and a grounding point is created on the frame opposite the antenna terminal.

Antenna structure used in portable radio device

Abstract: An antenna structure comprises a loop antenna electrically connected to a high-frequency circuit of a portable radio device. The antenna structure also comprises a supplemental antenna including a coil spring which is used for fixing a dry battery powering the portable radio device, and a negative cylindrical conductor of the dry battery which conductor is electrically connected with the coil spring. The coil spring is placed to be inductively coupled to the loop antenna. The longitudinal axis of the dry battery is substantially perpendicular to a plane including the loop antenna. Thus, deterioration in signal reception sensitivity due to the directivity of the loop antenna can be compensated by the supplemental antenna.

Dual-polarized microstrip array with high isolation and low cross-polarization

Abstract: A 2 x 2 dual-polarized microstrip array antenna with high isolation between the two input ports and low cross-polarization level has been developed. The technical background for this achievement and antenna performance results are presented.

High-isolation collocated antenna systems

Abstract: The need to widely separate antennas (e.g., transmit and receive antennas) for VHF radio and other applications is avoided by high-isolation antenna systems with collocated antennas and cancellation of intercoupled signals. A transmit antenna in the form of a vertical dipole can be mounted atop a mast with a receive antenna comprising a multi-element array of vertical dipoles supported on the same mast below the transmit antenna. Opposing pairs of the dipole receiving elements are located in 180° positions on opposite sides of the mast so as to be symmetrically located in the omnidirectional antenna pattern of the transmit antenna. Resulting intercoupling to the receive dipoles is equal and in-phase and is cancelled out by the antiphase combining of signals from the dipoles of each pair of the receive dipoles. Reciprocally, cancellation of coupled signals is achieved with reversal of the receive and transmit functions of the respective collocated antennas. Dipole and monopole high-isolation antenna systems can also be configured on yardarms and ground planes.

A slot antenna with electronically tunable length

Abstract: The authors describe a 1 lambda slot antenna with a layered structure loaded with two 1-port reactive FET components electromagnetically. By changing bias voltages, the reactance of the FETs varies and the length of the slot is tuned electronically. The resonant points of S/sub 11/ measurements were shifted over a range of 1 GHz around 10 GHz. The antenna patterns are essentially unchanged in spite of this electronic tuning. >

A planar dipole array antenna with an elliptical lens

Abstract: We describe a planar antenna structure consisting of two half-wave dipoles, which are backed by a metallic reflector to create an image of two more elements. The array produces rather a wide main beam, and is therefore used with a dielectric lens. The far-field pattern of the dipole liens antenna has cross-pol better than −20 dB, and side lobes below −13 dB over an octave band. The impedance at the feedpoint of the antenna is approximately 70 - j10 Ω at the center of the band.

Wideband dual-polarized multi-mode antenna

Abstract: A generally planar antenna structure having at least six radial antenna elements, each of which uses log-periodic principles to provide a broad bandwidth of operation. Each antenna element has a radial arm and integral, arcuate teeth extending in opposite directions from the radial arm, such that the spacing, width and length of the teeth increases with increasing radial distance from the center of the structure. The teeth are preferably interleaved with teeth in adjacent antenna elements. A feed region of the structure is provided near its center, to connect the antenna elements through a connection matrix to input/output terminals and provide operation in multiple modes and multiple polarization senses. The antenna structure is capable of operating in high order modes, to provide multifunctional operation and enhanced performance in angle-of-arrival systems, and is capable of transmitting and receiving both right-hand and left-hand circularly polarized signals, and all dual linearly polarized signals, all over a broad frequency band.

Integrated antenna/mixer for the microwave and millimetric wavebands

Abstract: A microwave/millimetric receiver of the kind in which a dielectric lens focusses incoming radiation on to an integrated antenna/mixer supported by a dielectric substrate. In one embodiment the antenna/mixer comprises a slot antenna and diode means coupled thereto for mixing the received signal with a local oscillator signal to form an IF signal. The local oscillator signal may be irradiated on to the antenna/mixer to be picked up by a crossed slot antenna or the local oscillator signal may be directly injected into the antenna/mixer circuit say via a microstrip line. In an alternative embodiment, the slot antenna is replaced by a dipole and a local oscillator signal is directly injected into the antenna/mixer via a coplanar line.

A millimeter-wave omnidirectional circular dielectric rod grating antenna

Abstract: A millimetre-wave omnidirectional circular dielectric rod grating antenna is investigated theoretically and experimentally. As an eigenvalue problem, the antenna is analyzed with the rigorous mode matching method. The radiation characteristics of the antenna are calculated and measured in the Ka-band frequency range. A comparison between the experimental results and the theoretical predictions is made and good agreement is found. The practicality of the omnidirectional antenna and the effectiveness of the theory are thus justified. >

See-through microstrip antennas constructed on a transparent substrate

Abstract: The main parameters affecting the optical transparency of the see-through microstrip antenna are the dimensions of the metallic mesh and the optical transmittance of a dielectric substrate. A thinner mesh will result in better transparency of the antenna, however, the performance of the antenna will clearly be degraded. It is significant to find the optimal dimensions of the mesh for practical use. The paper describes experimental and calculated results of a see-through microstrip antenna. Firstly, an antenna structure is shown. Then, some typical experimental results of five antennas with different mesh spacings including a patch antenna are demonstrated. Next, a simplified calculation model for the method of moments is shown. The model is reduced to a parallel wire structure. Finally, some calculated results are demonstrated.< >

Microstrip Yagi antenna for mobile satellite service

Abstract: A major aspect of the JPL MSAT (mobile satellite) program has been the introduction of new antenna concepts to satisfy the requirements of a mobile antenna to provide medium gain (10 dBic) and low profile and low cost, and to automatically remain pointed toward the proper satellite as the vehicle moves about. The microstrip Yagi antenna is discussed. This system consists of a microstrip Yagi array, a stripline RF beamformer circuit, a motorized turntable for azimuth pointing, and a pointing control computer. The diameter of the antenna is 56 cm and its height 3.8 cm. >

Vehicular slot antenna system

Abstract: To provide for ominidirectional reception/transmission of slot antennas installed on a vehicle, a plurality of slot antenna units (12, 13, 13a, 14) are installed on the vehicle, facing, for example, forwardly, rearwardly and laterally of the vehicle. Each of the slot antenna units is connected to a common feed point (28) which is coupled to a radio equipment, which may be a transmitter or receiver, by a connecting cable which has a length of n.λ/2, wherein n is a whole integer and λ is the average operating wave length for which the antenna is designed. For about 500 MHz, an antenna length of about 55 cm with a slot length of 35 cm and a width of about 7 mm is suitable. The antenna can be formed in U shape and function as a license plate holder for, for example, a license plate made of insulating material. The antenna units are insulated from the body of the vehicle.

Stabilized antenna system

Abstract: A stabilized antenna system is installed on a moving platform such as a ship to track a communication satellite. The antenna system examply employs either X1-Y-X2 or Y1-X-Y2 antenna mount. Rolling and pitching of the moving platform are offset by mechanically steering outside and intermediate axes, X1 and X, or Y1 and Y axes. The innermost axis is electronically steered to prevent instability which is caused by the mechanical steering, thereby improving reliability of the antenna system. The frame for rotatable supporting the array antenna is also supported by the radome rotatably. Further, the access hutch for maintainance is opened at the center of the radome and just below the array antenna.

Array antenna and stabilized antenna system

Abstract: An array antenna can control directions of beams by phase-shifting signals received and/or transmitted by a plurality of antenna elements. When the antenna elements are arranged two-dimensionally, sidelobes and beamwidth are determined according a distance between two adjacent antenna element columns. The distance between the adjacent columns can be reduced by arranging the antenna elements in a staggered manner, thereby suppressing the sidelobes, and enlarging the width of beams around an XEL axis. A stabilized antenna system controls the direction of the array antenna and beam directivity by compensating for inclination of a moving platform, so that the array antenna can always track a satellite reliably.

Lens-Type Compact Antenna Test Range at MM-Waves

Abstract: A lens-type compact antenna test range (CATR) has been studied both theoretically and experimentally. For a lens with low dielectric constant ?r, the surface accuracy requirement is much less stringent than for a reflector. An experimental CATR with a shaped polyethylene (?r, = 2.32) lens was made at 110 GHz. In order to make the amplitude ripple in the quiet zone small, the use of saw tooth serrations around the lens was studied. Theoretically the quiet zone field is exellent (peak to peak ripple 0.27 dB). Preliminary measured values are promising (peak to peak ripple 2.0 dB).

Vehicle rear window glass antenna for transmission and reception of ultrashort waves

Abstract: The invention provides a vehicle window glass antenna for transmission and reception of ultrashort waves used for mobile phones and/or personal radios. The antenna has a primary antenna which is a combination of at least two vertical (in the sense of perpendicular to a horizontal line) elements and at least two horizontal elements each of which directly connects with at least one of the vertical elements and a secondary antenna which is essentially a horizontally elongate element located in a space between the primary antenna and the lower or upper edge of the window glass. The primary antenna is arranged within a rectangular area having a limited horizontal width and a limited length, and the horizontal element of the secondary antenna has a limited length. The antenna feeder is a coaxial cable, and the primary antenna and the secondary antenna are connected with the inner conductor and the outer conductor of the coaxial cable, respectively. In a preferred embodiment the major part of the primary antenna is in the form of a rectangular grid.

A dual-frequency circularly polarizing whole-body MR antenna for 69/170 MHz.

Abstract: The design concept of a dual-frequency whole-body MR antenna for circular polarization is presented. First, the principle of the capacitively shortened transmission line antenna, which is the basis of the design, is discussed. Emphasis is given to the antenna design at high frequencies. Two variants of possible antenna constructions are described and the RF efficiency is calculated for both frequencies. The antenna performance is discussed for the example of 69 and 170 MHz, the nuclear magnetic resonance frequencies of the nuclei 31P and 1H at 4 T. For 31P experiments, a whole-body antenna is useful only for transmitting and, thus, the antenna performance can be optimized for 1H. The design principle is not limited to two frequencies; however, the RF efficiency decreases with an increasing number of resonance frequencies. Results of a laboratory version and 1H images at 4 T are presented.