Showing papers on "Antenna (radio) published in 1993"

Double-slot antennas on extended hemispherical and elliptical silicon dielectric lenses

Abstract: Far-field patterns and Gaussian-beam coupling efficiencies are investigated for a double-slot antenna placed on hemispherical lenses with varying extension lengths. The radiation patterns of a double-slot antenna on a silicon dielectric lens are computed using ray-tracing inside the dielectric lens and electric and magnetic field integration on the spherical dielectric surface. The measured radiation patterns at 246 GHz and Gaussian-beam coupling efficiencies show good agreement with theory. The theoretical results are presented in terms of extension-length/radius and radius/ lambda , and therefore result in universal design curves for silicon lenses of different diameters and at different frequencies. The theoretical and experimental results indicate that for single units, there exists a wide range of extension lengths which result in high Gaussian-coupling efficiencies (50-60%) to moderately high f 's. These Gaussian-coupling efficiencies can be increased to 80-90 degrees % with the use of a lambda /sub m//4 matching-cap layer. For imaging array applications with high packing densities, an extension-length/radius of 0.38 to 0.39 (depending on frequency) will result in peak directivity and a corresponding Gaussian-coupling efficiency 15-20% lower than for single units. >

Analysis of a reflectarray antenna using microstrip patches of variable size

Abstract: Microstrip reflectarrays typically use tuning stubs on each element to adjust the phase of the reflected field. The authors describe a new approach in which the need for tuning stubs is eliminated and phase control is achieved simply by adjusting the resonant length of the patch elements. The advantages of this approach are described, as are a full-wave analysis technique for computing the phase of the reflected field as a function of patch size and a design curve giving the change in patch size for a desired reflected field phase shift.< >

Impulse response modeling of indoor radio propagation channels

Abstract: If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming of the channel's transfer functions. It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations; a modified Poisson distribution shows a good fit to the arrival time of the multipath components; amplitudes are lognormally distributed over both local and global areas, with a log-mean value that decreases almost linearly with increasing excess delay; for small displacements of the receiving antenna, the amplitude of the multipath components are correlated; the amplitudes of adjacent multipath components of the same impulse response function show negligible correlations; and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antenna separation. >

Design of wideband circularly polarized aperture-coupled microstrip antennas

Abstract: Two variations of a novel feeding technique for a wideband circularly polarized aperture-coupled microstrip antenna are described. Prototype designs for wideband linearly polarized elements are first presented, and then used for circularly polarized designs. Techniques used for design of the feed network are detailed, for both series feed and parallel feed versions. Experimental results are shown for each antenna, and results for the two designs are compared. The impedance and axial ratio bandwidths for these antennas are among the best yet achieved for microstrip antenna elements. Several design variations are also discussed. >

Radiation properties of a planar antenna on a photonic-crystal substrate

Abstract: The photonic crystal is investigated as a substrate material for planar antennas in the microwave and millimeter-wave bands. Experimental results are presented for a bow-tie antenna on a (111)-oriented face-centered-cubic photonic-crystal substrate with a band gap between approximately 13 and 16 GHz. When driven at 13.2 GHz, the antenna radiates predominantly into the air rather than into the substrate. This suggests that highly efficient planar antennas can be made on photonic-crystal regions fabricated in semiconductor substrates such as GaAs.

Tunable microwave ablation catheter

Abstract: An ablation catheter is disclosed that include a mechanism for altering the impedance of the antenna during use in a controlled manner to tune the catheter. The impedance tuning may be accomplished in a variety of manners including altering the electromechanical configuration of the antenna and moving a material relative to the antenna or vice versa in order to vary the effective impedance during use. In a preferred embodiment, the ablation catheter transmits energy in the microwave frequencies and uses a coaxial transmission line as its waveguide. The antenna is preferably helical in nature and is carried by the distal end of the transmission line.

Radio propagation characteristics for line-of-sight microcellular and personal communications

Abstract: To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height. >

Microstrip patch designs that do not excite surface waves

Abstract: Two variations of a circular microstrip patch design are presented which excite very little surface wave power. Both of the designs are based on the principle that a ring of magnetic current in a substrate (which models the patches) will not excite the dominant TM/sub 0/ surface wave if the radius of the ring is a particular critical value. Numerical results for radiation efficiency and radiated field strength from a ring of magnetic current are shown to verify this basic design principle. The proposed patch designs are chosen to have a radius equal to this critical value, while maintaining resonance at the design frequency. The designs excite very little surface-wave power, and thus have smoother radiation patterns when mounted on finite-size ground planes, due to reduced surface-wave diffraction. They also have reduced mutual coupling, due to the reduced surface-wave excitation. Measured results for radiation patterns and field strength within the substrate are presented to verify the theoretical concepts. >

Automatic antenna tuning method and circuit

Abstract: A method of matching the resonant frequency of an antenna resonant circuit (18, 46) to the output frequency of a transmitter output stage (26), the method includes the step of providing a powering signal from the transmitter output stage (26) to the antenna resonant circuit (18, 46). The method further includes the step of receiving at the antenna resonant circuit (18, 46) the powering signal, the antenna resonant circuit (18, 46) comprising a tuning circuit (48). The tuning circuit (48) is operable to variably modify the resonant frequency of the resonant circuit (18, 46). At its output the antenna resonant circuit (18, 46) provides a phase correlation signal having a known relationship to the frequency difference between the resonant frequency and the powering signal. A phase comparator (60) then receives the powering signal and the phase correlation signal and correspondingly adjusts the resonant frequency of the resonant circuit (18, 46) based upon the known phase relationship. Other devices, systems and methods are also disclosed.

Effects on portable antennas of the presence of a person

Abstract: This work deals with the influence the presence of a person has on the performance of antennas for hand-held portable telephones. It is shown how input impedance, far-field radiation pattern, radiation efficiency, and the magnitude of the near field are affected by the presence of the human body. The investigations have been carried out by applying the finite-difference time-domain (FDTD) technique to a model of the telephone with a lambda /4 monopole antenna and a simple hand-head model of the operator. Results from this configuration are compared with results for the telephone box and antenna alone. Measurements have been performed to verify the results obtained by simulations. The results show that a shadow effect in the far-field pattern occurs in the direction of the person and that the radiation pattern, including polarization, changes considerably from the telephone with the antenna alone. The impedance results show a change in resonance frequency when the telephone is placed next to a person. Results for radiation efficiency show that close to half of the energy is absorbed by hand and head. On average a system loss of 3-4 dB should be included in a link budget, and there is considerable fading, even in a radio-anechoic chamber, when persons move around in a natural manner. >

Standard probes for electromagnetic field measurements

Abstract: Discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The standard probes described are an electrically short dipole, a resistively-loaded dipole, a half-wave dipole, an electrically small loop, and a resistively-loaded loop. A single-turn loop designed for simultaneous measurement of the electric and magnetic components of near-fields and other complex electromagnetic environments is also described. Each type of antenna demonstrates a different compromise between broadband frequency response and sensitivity. >

Radio frequency activated charge card

Abstract: A system for changing the activation status of a selected data card such as a charge card by broadcasting an appropriate RF signal. An antenna embedded in the card detects and decodes the signal, and operates a transducer which changes the card appearance, alters magnetic stripe information, or alters the information contained within the card.

System monitoring programmable implantable transponder

Abstract: A passive transponder includes a receive antenna for receiving an input signal. A frequency generator and modulator receives the input signal and outputs a data carrier signal having a frequency independent of the input signal frequency. A programmable memory and thermistor are provided to produce user ID data and temperature data which is combined with the output signal.

Portable point of sale terminal

Abstract: A point of sale terminal (11) is disclosed that provides all of the usual point of sale terminal functions, but that is entirely field portable. Data pertinent to each purchase can be input to the terminal via a keyboard assembly (17), a touch-screen display (19) or a signature-capture screen assembly (25), or via an antenna (39) and radio link from an associated bar code scanner. Data may be communicated at any time to a remote host computer, also via a separate antenna and radio link. The communication links with the host computer and the bar code scanner operate independently and simultaneously, using mutually compatible modulation schemes such as a spread spectrum scheme for the host computer link and a narrowband or spread spectrum scheme for the bar code scanner link. The terminal thereby functions as a portable repeater or node in a data communications network.

Novel ultrawide-bandwidth Vivaldi antenna with low crosspolarisation

Abstract: The conventional Vivaldi antenna typically has a bandwidth of less than 3:1, limited by the feed line to radiating slot transition. The antipodal Vivaldi antenna removes this limitation but gives very high crosspolarisation which is undesirable for phased array applications. The Letter describes a new balanced antipodal Vivaldi antenna that retains the wide bandwidth characteristics while reducing the crosspolarisation by 15dB across an 18:1 band. Measurements are presented that compare the performance of existing antenna structures with this novel antenna element.

Theory and experiment of a coaxial probe fed hemispherical dielectric resonator antenna

Abstract: A hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally. The Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations. The method of moments is used to obtain the probe current from which the input impedance of the DR antenna is calculated. Both delta gap and magnetic frill source models are considered. Moreover, the results using a reduced kernel as well as the exact kernel are presented. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used and the results are compared. The effects of the probe length, feed position, and dielectric constant on the input impedance are discussed. Finally, the theoretical radiation patterns for the first three resonant modes (TE/sub 111/, TM/sub 101/, and TE/sub 221/) of the DR antenna are presented. >

Method and apparatus for enhancing an operating characteristic of a radio transmitter

Abstract: In a radio transmitter (100) that includes a power amplifier (104) and an antenna (106), a method for enhancing an operating characteristic of the radio transmitter (100) can be accomplished in the following manner. The power amplifier (104) provides a signal (113) to a variable matching network (111), wherein the signal (113) comprises energy to be radiated by the antenna (106). The variable matching network (111) couples the signal (113) to a sampler (112) that is operably coupled to an output of the variable matching network (111 ) and the antenna (106). The sampler (112) samples a forward component (114) and a reflected component (115) of the signal (113). The radio transmitter (100) processes the sampled forward and reflected components (116, 118) to produce a feedback control signal (120). The feedback control signal (120) is used to adjust the variable matching network (111 ), such that an operating characteristic of the radio transmitter (100) is enhanced.

Dual polarized dual band antenna

Abstract: An antenna system is described including a reflector antenna, responsive to radio frequency signals at a first frequency, having a first reflector surface, a second reflector surface and a Cassegrain feed. The antenna system further includes an array antenna having a plurality of antenna elements responsive to radio frequency signals having a second different frequency, wherein a center element is in a common location with the feed of the reflector antenna. With such an arrangement, an improved dual band antenna system is provided. By providing the center element of the array antenna in a common location with the feed of the reflector antenna, a dual band radio frequency antenna system is provided which is more compact with improved radiation characteristics than known similar configured antennas.

Matching the input impedance of a broadband disc monopole

Abstract: The Letter deals with the analysis of a disc monopole with the method of moments (MOM) procedure using triangular cells. An accurate annular ring of magnetic currents models the feeding connector. This technique avoids the introduction of an attachment mode at the antenna-to-SMA connector junction. This method gives the theoretical input impedance of a disc monopole within a wide frequency band. Measurements and theory are in good agreement.

High-gain, waveguide-fed antenna having controllable higher order mode phasing

Abstract: A diverging shell antenna fed by waveguide supplying TE₁₁ mode is described. A dielectric rod (46) partially contained within the waveguide (36) converts the TE₁₁ mode to a dominant or HE₁₁ mode. The HE₁₁ mode is controllably converted to second and third order modes in the diverging shell (30) by discontinuities (54) placed in predetermined locations in the diverging shell. The discontinuities (50,52) generating the second mode are incorporated into the dielectric rod structure (46). Turning of the relative amplitude and phase of the second and third order modes relative to the HE₁₁ mode is achieved by slideably positioning the dielectric rod (46). An alternative embodiment of the inventive device includes a reactive surface of the diverging shell.

New Phenomena of Charge Damage in Plasma Etching: Heavy Damage Only through Dense-Line Antenna

Abstract: The effect of antenna shape on charge damage has been examined using electron cyclotron resonance (ECR) plasma metal etching and test devices with an 8-nm-thick gate oxide. A dense-line antenna causes capacitor breakdown and the positive shift of the transistor's threshold voltage (Vt), while a sparse-line antenna does not. This positive Vt shift corresponds to a positive charge-up of the dense line, and is not dependent on overetching. Such damage is hardly observed when the antenna's top surface is exposed to the plasma, indicating that the plasma is uniform in terms of conventional charge damage. These new phenomena can be explained by a new mechanism consisting of electron shading with photoresist patterns. This shading leads to less neutralization of the ion charge impinging onto the transitory metal which remains between the antenna lines because of the microloading effect, and thus the excess positive charge causes the damage.

Location monitoring system

Abstract: A location monitoring system is provided having a radio frequency transmitter for a person or object and radio frequency receiver for someone to monitor movement of said person or object, said receiver sounding an alarm at a predetermined time after failure to receive a signal The transmitter is made having an intermittent transmitted signal and the receiver is made having an off-timer to coordinate with said intermittent signal, said off times saving battery power The radio frequency receiver has an electronic switching means controlled by said radio frequency transmitter for sounding an alarm An antenna is located in part of the carrying strap of said transmitter The radio frequency transmitter can have various devices for sounding the alarm

Broadside radiation from periodic leaky-wave antennas

Abstract: A double-strip grating leaky-wave antenna consisting of two strips per unit cell is analyzed. The stopband behavior exhibited at broadside scan in the single-strip grating antenna is characteristic of all periodic leaky-wave antennas having a single strip per unit cell, and results in a drastic increase in the attenuation rate of the leaky wave as the beam is scanned to broadside. By nearly eliminating this stopband behavior, the double-strip leaky-wave antenna can scan from backward end fire to forward end fire without any large frequency regions of high attenuation. An approximate design rule for the double-strip antenna is discussed, and results are presented to show how the antenna may be further optimized to achieve the minimum possible variation in attenuation as the beam is scanned through broadside. Although the stopband behavior is never completely eliminated with the addition of the extra strip, the optimum design shows an almost negligible region of rapidly varying attenuation near broadside. >

Gap raidated antenna

Abstract: An antenna for broadcast and reception of electromagnetic waves in which all or a portion of the radiating structure is formed from coaxial cable or a functional equivalent thereof in which an annular opening exists, allowing alternating electrical current to propagate onto the outer surface of said radiative structure, thereby generating electromagnetic radiation.

Calibration of a synthetic aperture radiometer

Abstract: Calibration algorithms for a synthetic aperture microwave radiometer are presented. The calibration is geared to Earth remote sensing applications and is demonstrated on an airborne prototype thinned array imager. Two approaches to the system calibration are presented. The first utilizes commonly available reference brightness temperature scenes, such as open water, and the second utilizes data collected on the antenna range. Both algorithms yield spatial response information which is cast in matrix form and inverted to obtain the image reconstruction formula. Experimental results are examined, and errors in some reconstructed images are linked to the present prototype antenna design. Algorithms for improving the synthesized antenna pattern sidelobe performance are also presented. In one solution, the pattern efficiency is optimized by minimizing the pattern outside a defined beam. In another solution, the patterns are matched to a desired model pattern by the method of least squared errors. Both techniques offer an attractive alternative to aperture weighting. >

Automatic horizontal and vertical scanning radar

Abstract: An automatic horizontal and vertical scanning radar for aircraft for displaying weather conditions includes an antenna system mounted in the aircraft for sweeping horizontally and vertically in response to horizontal and vertical drive signals and for transmitting radar signals forwardly of the aircraft and receiving back reflected radar signals, a receiver for digitizing received reflected radar signals, a storage unit for storing the digitized signals, a display unit responsive to display control signals for displaying a plan view image of weather conditions ahead of the aircraft represented by reflected radar signals received by the antenna system sweeping back and forth horizontally and a vertical view image of weather conditions represented by reflected radar signals received by the antenna system moving up and down vertically, and a control unit for supplying horizontal and vertical drive signals to the antenna system, and for producing control signals from the stored digitized signals

High throughput slotted ALOHA packet radio networks with adaptive arrays

Abstract: The authors consider the use of a multiple-beam adaptive array (MBAA) in a packet radio system. In an MBAA, a given set of antenna elements is used to form several antenna patterns simultaneously. When it is used in a packet radio system, an MBAA can successfully receive two or more overlapping packets at the same time. Each beam captures a different packet by automatically pointing its pattern toward one packet while nulling other, contending packets. It is shown how an MBAA can be integrated into a single-hop slotted ALOHA packet radio system, and the resulting throughput is analyzed for both finite- and infinite-user populations. >

Personal identification system

Abstract: A personal identification system includes a number of antenna preamplifier nodes coupled to collection nodes which are in turn coupled to a central computer. A personal detector unit attached to a user is inserted into an enclosure of the antenna preamplifier node. The antenna preamplifier node is electrically isolated by RF attenuation material. An antenna of the antenna preamplifier node is a low gain antenna. The antenna preamplifier node reads a coded radio frequency signal of a personal detector unit inserted into an enclosure and rejects signals of other various personal detector units in the vicinity.

Cordless SPS smart antenna device

Abstract: Cordless antenna apparatus for determination of the location of an observer and/or of the time of observation by use of a Satellite Positioning System (SPS), such as the Global Positioning System or the Global Orbiting Navigational Satellite System. In each embodiment, the apparatus includes a Smart Antenna device and a display unit, connected by a wireless link. In a first embodiment, the Smart Antenna device includes: an SPS antenna to receive the SPS signals; an SPS signal frequency downconverter; an SPS signal processor to receive antenna output signals and to determine at least one of the present location of the SPS antenna or the time of observation; a transmitter to receive processor output signals and transmit these signals to the display unit; and a power supply. The display unit in the first embodiment includes: a receiver to receive the signals transmitted by the SPS Smart Antenna device transmitter; a display processor to receive output signals from the receiver and to process these signals for display of location or time information; display means to visibly or audibly display the location or time information; and a second power supply. In a second embodiment, the SPS signal processor is moved to the display unit. The transmitter and receiver may be replaced by two transceivers to allow the display unit to transmit messages, such as requests for information, to the SPS Smart Antenna device.

Automatic antenna pointing system based on global positioning system (GPS) attitude information

Abstract: An embodiment of the present invention is a system for automatically pointing a directional antenna. The system comprises two GPS antennas mounted at horizontally opposed extremities of the directional antenna, the placement is such that the GPS antennas lie on a line having a normal vector approximately parallel to a boresight of the directional antenna. The outputs from the GPS antennas are downconverted to a measurement frequency and differentially phase compared for each of a plurality of radio visible GPS satellites. A measurement controller that receives the phase comparisons. A navigation computer receives measurements from the measurement controller and uses a microprocessor to calculate the GPS latitude and longitude and the attitude angles of the pair of GPS antennas. A servo points the directional antenna at a particular target communications satellite, based on the computed azimuth, elevation, latitude, and longitude, as provided by the navigation computer. One of these servos is used to move the GPS antennas in roughly a circle to average out multipath effects to improve accuracy and to reduce integer ambiguities.