Showing papers on "Antenna (radio) published in 1989"

An impedance-matching technique for increasing the bandwidth of microstrip antennas

Abstract: The nature of the inherent narrow bandwidth of conventional microstrip patch antennas is considered. It is observed that, except for single-feed circularly polarized elements, their bandwidth is limited only by the resonant behavior of the input impedance and not by radiation pattern or gain variations, which usually are negligible over a moderate 10 to 20% bandwidth. Therefore, broadband impedance matching is proposed as a natural to increase the bandwidth. The maximum obtainable bandwidth is calculated using Fano's broadband matching theory. It is found that by using an optimally designed impedance-matching network, the bandwidth can be increased by a factor of at least 3.9, the exact value depending on the degree of matching required. A transmission-line prototype for a proper matching network is developed. The translation of this prototype network into a practical structure (e.g. a microstrip or stripline circuit) is considered. Practical design examples and experimental results which clearly show the validity of the technique are given. >

The tapered slot antenna-a new integrated element for millimeter-wave applications

Abstract: Tapered slot antennas (TSAs) with a number of potential applications as single elements and focal plane arrays are discussed. TSAs are fabricated with photolithographic techniques and integrated in either hybrid or MMIC circuits with receiver or transmitter components. They offer considerably narrower beams than other integrated antenna elements and have high aperture efficiency and packing density as array elements. Both the circuit and radiation properties of TSAs are reviewed. Topics covered include: antenna beamwidth, directivity, and gain of single-element TSAs; their beam shape and the effect of different taper shapes; and the input impedance and the effects of using thick dielectrics. These characteristics are also given for TSA arrays as are the circuit properties of the array elements. Different array structures and their applications are also described. >

A study of microstrip array antennas with the feed network

Abstract: The radiation and losses in microstrip antennas with a corporate feed network are studied. A surface current approach is applied in which the electrical currents in the feed lines are modeled as in ideal transmission lines. The free-space radiation and the surface-wave excitation of typical segments in printed feed networks are studied. A four-element array antenna with its printed feed network is analyzed and predicted radiation patterns, directivity, and gain are presented and compared with experimental results. The gain and directivity of large arrays of 16, 64, 256 and 1024 elements are calculated and measurements in the frequency range of 10 to 35 GHz are reported. >

High‐brightness terahertz beams characterized with an ultrafast detector

Abstract: We have significantly improved the emission and detection of electromagnetic beams of single‐cycle 0.5 THz pulses, through the use of new dipolar antenna structures. The frequency response was extended to well beyond 1 THz, and the beam power was increased by more than 15 times. The antennas were located at the foci of sapphire lenses and were photoconductively driven by ultrafast laser pulses. An additional collimation by a paraboloidal mirror produced a beam with a 25 mrad divergence, and subsequent focusing by a second identical mirror improved the coupling between the transmitting and receiving antenna by orders of magnitude.

Effect of microstrip antenna substrate thickness and permittivity: comparison of theories with experiment

Abstract: A set of measurements of patch antennas on substrates of varying thickness and permittivity, using three types of feeds, is presented. Resonant frequency and resonant resistance are compared with calculated values from the representative theories. The measurements show that erratic results may be obtained for substrates thicker than about 0.02 lambda /sub 0/, where lambda /sub 0/ is the free-space wavelength at the resonant frequency. These problems may be related to coax-to-microstripline transitions, but their cause is not yet definitely known. The theoretical models that are compared give reasonably good results for resonant frequency, but none give impedance results that are consistently reliable. It thus appears that further work is needed to develop analytical models that can adequately predict the impedance performance of microstrip antennas on thick and/or high dielectric constant substrates. >

Design optimization of interstitial antennas

Abstract: The radiation characteristics of multisection insulated antennas in conductive tissue are discussed. The effects of varying the diameters and lengths of the center conductors in the various sections of the antenna and the diameter and type of the insulation on the electromagnetic power deposition pattern and input impedance characteristics were examined. An approximate numerical model which calculates the current distribution and the radiation characteristics of multisection insulated antennas was developed. The numerical predictions were verified in a qualitative way experimentally by mapping the various near- and far-field components of the antennas. On the basis of these results, design tradeoffs are identified and quantified and guidelines for optimum designs are specified. In particular, it is shown that an insulation-to-center-conductor diameter ratio between 1.5 to 2.0 is optimum for uniform Teflon insulation, and that a multisection arrangement with the thinnest insulation near the antenna tip has superior performance compared with the uniform-insulation or other multisection designs. >

Passive keyless entry system.

Abstract: A passive keyless entry system is disclosed that is specifically adapted for use with automotive vehicles. The system is designed to automatically unlock the vehicle as the operator approaches the vehicle. The system is further designed to automatically lock the vehicle as the operator, carrying the beacon, moves away from the vehicle. The system includes a portable beacon that is carried by the operator, a receiver/controller located in the vehicle, and an antenna connected to the receiver/controller for receiving the encoded transmission from the beacon. The beacon includes a motion sensor to conserve battery life when the beacon is stationary. Transmission between the beacon and the receiver/controller is characterized by a magnetically coupled radio frequency signal embodying differential phase encoded data with error correction coding of the data to enhance noise immunity and signal discrimination.

Tool kit for antennae and thermal noise near the plasma frequency

Abstract: This paper provides the essential tools for deriving quickly the quasi-thermal noise spectrum or the impedance of a given electric antenna near the plasma frequency, for calibration or diagnosis in space plasmas. The authors give simple analytical expressions and numerical results for either wire or sphere dipoles in an isotropic plasma with one or two Maxwellian electron populations. They include the contribution of the particles collected and/or emitted by the antenna surface. They also indicate some modifications brought about by using more complicated antenna geometries, and a drifting or a magnetized plasma. Finally, they give some conclusions for antenna design or data interpretation in plasma wave experiments.

Short distance attenuation measurements at 900 MHz and 1.8 GHz using low antenna heights for microcells

Abstract: Short-distance, low-antenna-height signal attenuation measurements are presented in connection with their use in the design of future microcell cellular radio networks. Measurements presented are based on the propagation along busy city streets in a direction radial to a fixed antenna site. Antenna heights between 5 m and 20 m were chosen for the fixed site, while 1.5 m was chosen for the mobile vehicle. The signal strength was then measured out to a distance of 1 km in a line-of-sight path from the fixed site at both 870.15 MHz and 1.8 GHz. The measurements show that extrapolation of the M. Hata (1980) and Y. Okumura et al. (1968) formulas into the low-antenna-height, short-distance area is not valid and can lead to inaccuracies. The results show that at short distances from the antenna the signal attenuation slope is very much less than that predicted by extrapolating the results of Hata and Okumura et al. >

Relationships between antennas as scatterers and as radiators

Abstract: The field scattered by an antenna contains a component that is the short circuit scattered field normalized by the short circuit current and a second component that is the radiation field normalized by the transmitting current and multiplied by a factor (1- Gamma ). The RCS is the magnitude squared of the difference between two terms, one being the square root of a complex 'structural' cross section, and the other (1- Gamma ) times the square root of a complex 'antenna' cross section. These relationships, and the role of the load impedance are clarified. The connection between antenna directivity and load effective receiving area is also derived. >

Phased array antenna calibration and pattern prediction using mutual coupling measurements

Abstract: A technique which utilized the inherent mutual coupling in an array to both calibrate and predict the radiation patterns of a phased-array antenna is investigated. The only restriction of the technique is that the ability to transmit and receive with pairs of the array elements is required. The theory associated with array mutual coupling and its relationship to both array calibration and array patterns is discussed. The design of a test bed phased-array antenna is covered. The mutual coupling technique (MCT) is used experimentally to calibrate the test array as well as to predict the array radiation patterns. It is shown that the results obtained by MCT are in good agreement with conventional far-field measurements. >

Multi-antenna gas receiver for seismic survey vessels

Abstract: Method and apparatus are disclosed for accurately determining position from GPS satellites and received on a ship using observations of C/A code group delay, L1 band center frequency carrier phase, L1 band 5115 MHz implicit carrier phase, and L2 band 5115 MHz implicit carrier phase A precise measurement of the range to each satellite is made based upon the L1 center frequency carrier phase A correction for ionospheric effects is determined by simultaneous observation of the group delays of the wide bandwidth P code modulations in both the L1 and L2 bands These group delays are determined by measuring the phases of carrier waves implicit in the spread-spectrum signals received in both bands These carriers are reconstructed from both the L1 and L2 band signals from each satellite without using knowledge of the P code The unknown biases in the L1 center frequency carrier phase range measurements are determined from simultaneous, pseudorange measurements, with time averaging The instantaneous position of the antenna receiving these signals, and therefore the ship, may then be determined from the ranges so determined, with both the bias and the ionospheric effects having been eliminated Additional antennas are positioned on the ship and a seismic streamer towed by the ship to reject false signals, compensate for blockage of signals by the ship's structure, and determine the position of sensors in the streamer

Antenna system with adjustable beam width and beam orientation

Abstract: The antenna system is provided with at least one active radiation source (1) and a reflective surface (2), which is located in at least one part of the radiation (3) generated by the active radiation source (1). The reflective surface (2) is provided with a number of independently adjustable plates (2.j) for generating at least one radiation beam. The antenna system may be provided with means (4) to independently adjust the plates (2.j) for the purpose of (dynamically) orientating the antenna beam.

Impact of random pointing and tracking errors on the design of coherent and incoherent optical intersatellite communication links

Abstract: Given the RMS transmitter pointing error and the desired probability of bit error (PBE), it can be shown that an optimal transmitter antenna gain exists which minimizes the required transmitter power. Given the RMS local oscillator tracking error, an optimum receiver antenna gain can be found which optimizes the receiver performance. The impact of pointing and tracking errors on the design of direct-detection pulse-position modulation (PPM) and heterodyne noncoherent frequency-shift keying (NCFSK) systems is then analyzed in terms of constraints on the antenna size and the power penalty incurred. It is shown that in the limit of large spatial tracking errors, the advantage in receiver sensitivity for the heterodyne system is quickly offset by the smaller antenna gain and the higher power penalty due to tracking errors. In contrast, for systems with small spatial tracking errors, the heterodyne system is superior because of the higher receiver sensitivity. >

Personal locator transmitter

Abstract: A personal locator transmitter adapted to be worn on the wrist and having the size and appearance of a conventional wrist-watch. This transmitter is provided with a programmable memory, a transmitter controlled by the memory, an antenna for reliably radiating signals from the transmitter regardless of orientation of the wrist of a user and including both a manually operable alarm activated by pressing a button, and an automatic alarm actuated by an attempt to remove the unit from the wrist of the wearer. The unit is controlled by a control memory comprised of an EEPROM encoded with unique identification codes and other information as required in the specific application.

Diversity transmission and reception method and equipment

Abstract: In an antenna-selection diversity transmission and reception equipment (10) which is in digital communication with a transmission and reception equipment (16) having a single antenna (17), and performs transmission and reception with time division by using the same radio frequencies, the antenna-selection diversity transmission and reception equipment (10) comprises a plurality of antennae (11, 12), a receiving part (15) having receiving means (61, 62), comparing means (63) and selecting means (64, 65) which are adapted for a receiving-antenna selection diversity, and a transmitting part (14) having memory means (52) for storing antenna information that was selected by the receiving part (15). An antenna for transmission is selected from the plurality of antennae (11, 12) at the time of transmission in accordance with the information of the memory means (52).

Analysis of the cylindrical-rectangular patch antenna

Abstract: An analysis is presented of a thin cylindrical-rectangular microstrip patch antenna. After obtaining the electric field under the curved patch and the resonant frequencies using the cavity model, the far-field is found by considering the equivalent magnetic current radiating in the presence of a cylindrical surface. The input impedance and the total Q-factor are then calculated. Numerical and graphical results are presented to illustrate the effect of curvature on the characteristics of the TM/sub 10/ and TM/sub 01/ modes. >

Analysis of microstrip patch antennas using finite difference time domain method

Abstract: The study of microstrip patch antennas is directly treated in the time domain, using a modified finite-difference time-domain (FDTD) method. Assuming an appropriate choice of excitation, the frequency dependence of the relevant parameters can readily be found using the Fourier transform of the transient current. The FDTD method allows a rigorous treatment of one or several dielectric interfaces. Different types of excitation can be taken into consideration (coaxial, microstrip lines, etc.). Plotting the spatial distribution of the current density gives information about the resonance modes. The usual frequency-dependent parameters (input impedance, radiation pattern) are given for several examples. >

Methods for calculating the electromagnetic fields from a known source distribution: application to lightning

Abstract: Two different techniques (monopole and dipole) for calculating the electric and magnetic fields from a distribution of currents and charges are discussed. Both techniques have been used for calculating the fields from lightning. A simple lightning return stroke current model, consisting of a square current pulse traveling up a vertical antenna above a ground plane, is used to compare the two techniques. Analytical expressions are obtained for the fields using each technique. These expressions are shown to be numerically equivalent, but the authors are unable to prove their equivalence analytically. It is concluded that the monopole and the dipole techniques can both be derived from Maxwell's equations and hence that both are correct. In attempting to dispel the apparent confusion that has existed regarding the validity of the monopole technique, the authors show that the monopole approach, as discussed in the literature, is applicable only to upward-traveling current waves and hence is not particularly useful in the realistic modeling of lightning return strokes. >

Microwave radiometry: its importance to the detection of cancer

Abstract: The author discusses developments in the medical uses of microwave radiometry, particularly in relation to the early detection of cancer, as well as the significance of and progress in related antenna technology. In the treatment of cancer, microwave hyperthermia is accepted as an adjunct to radiation therapy in the treatment of superficial lesions. Although not as widely reported, the use of microwave radiometry as a noninvasive, passive technique for the early detection of cancer appears promising. Wider acceptance of these methods, however, awaits fundamental improvements in the ability to focus energy at depth in human tissue, an important and nontrivial antenna problem. Antenna development is described, and the improvements required if microwave technology is to provide a practical solution to the detection and treatment of cancer are indicated. >

Nonphotochemical hole burning of the native antenna complex of photosystem I (PSI-200)

Abstract: Nonphotochemical hole burning is used to determine the frequencies and Franck-Condon factors for 41 chlorophyll a (Chla) and 15 Chlb intramolecular modes for PSI-200. The linear electron-vibration coupling for all modes is very weak with the maximum Franck-Condon factor observed being {approx} 0.04. No activity by modes with a frequency lower than {approx} 260 cm{sup {minus}1} is observed. The linear electron-phonon coupling for protein modes of mean frequency 22 cm{sup {minus}1} is stronger but can still be categorized as weak since the Huang-Rhys factor is 0.8. The experimental mode and phonon frequencies and Franck-Condon factors are used with multiphonon excitation transport theories to analyze the available temperature-dependent data on the kinetics of transport within the core antenna complex. The calculations indicate that it is the phonons (and not the intermolecular modes) that mediate excitation transport within the antenna and from the antenna to the reaction center. They indicate also that a subunit or cluster model for the antenna provides a more accurate picture than the regular array model for excitation transport.

Conformal aperture feed array for a multiple beam antenna

Abstract: A multiple beam array antenna that is designed with an aperture shape which conforms to the particular coverage area to which the antenna is directed. The antenna consists of individual horn antennas (20) that are nested together to form the array (14). The outer walls (50) of the peripherally disposed horn antennas (40) are individually shaped such that the combined shape of the outer walls (50) of the peripherally disposed horn antennas (40) determine the perimeter shape of the aperture (12) of the horn array (14). Where the desired coverage area is circular, elliptical or irregularly shaped, the shape of the perimeter of the aperture (12) of the horn array (14) is similarly circular, elliptical or irregularly shaped, respectively.

Using model-based parameter estimation to increase the efficiency of computing electromagnetic transfer functions

Abstract: Two main ideas are introduced: (1) the use of model-based parameter estimation based on rational function approximations, which reduces the number of frequencies at which solutions or samples are required; (2) a sampling approach that uses frequency derivatives of the response and a novel analytical technique based on differentiating the moment method impedance equation, which provides derivative information in a time proportional to N/sup 2/ in contrast with the N/sup 3/ dependence in solving the original problem. Antenna input admittances are modeled using frequency samples and derivatives. The rational function model is shown to offer a large advantage over polynomial interpolation of a frequency response. Application of the frequency-derivative approach is demonstrated for problems having well-defined resonances such as a dipole antenna, and for more challenging problems having narrow resonances. >

Controlled microwave sample irradiation system

Abstract: A microwave antenna structure couples electromagnetic microwave energy from a microwave transmission line into a sample contained in a sample container without invasion of the sample. The microwave antenna structure is formed by a bifilar helix of conducting first and second helical elements. The first and second helical elements are arranged in a parallel relationship defining a double helix with alternating spaced apart helical turns from the respective first and second helical elements. The double helix forms a holder for receiving and holding a sample container within the turns of the double helix. The first and second helical elements are formed with coupling extension for coupling to opposite polarity conductors of a microwave transmission line. Electromagnetic microwave energy propagating along the transmission line is coupled into sample material within the sample container. A multiple sample microwave irradiation system provides an oil bath in the form of a reservoir containing relatively low dielectric constant fluid oil. A temperature regulator and circulator is immersed in the oil bath for uniform temperature control throughout the reservoir. Multiple microwave antenna structures and sample containers are suspended and immersed in the oil bath. Multiple microwave branch transmission lines couple microwave energy into the respective antenna structures.

A circular polarization antenna system

Abstract: A circular polarization antenna system has a thin cylindrical antenna body bounded by a pair of parallel conductive disks (10, 11) short-circuited by a conductive ring (12) at their periphery so that the disks are spaced by less than a wavelength. A plurality of antenna elements (20) are located on one of the disks (11) and feed means (16) are coupled to the centre of the other disk (10). The antenna system has high gain because of the use of many antenna elements, and wide operational frequency band as the antenna elements are energized by travelling wave (TEM mode), whilst being small in size. The antenna elements may be helical, spiral or be formed by flat disks.

Self-cohering large antenna arrays using the spatial correlation properties of radar clutter

Abstract: A technique for self-calibrating a large antenna array system in the absence of a beamforming point source is presented that uses the spatial correlation properties of radar clutter. The array could be real or synthetic. It is shown that if R(X), the spatial autocorrelation function of the field (as measured by adjacent element pairs), is ensured to be real and positive in the neighborhood of the origin, both periodic and aperiodic arrays can be synchronized, forming retrodirective beams pointing at the axis of symmetry of the radar transmitter, provided that the interelement spacing does not exceed some limit (the order of the size of the transmitting aperture). If the spatial autocorrelation function is complex but has a linear phase, it is shown that one can still synchronize both periodic and aperiodic arrays, while if the phase of R(X) is nonlinear, only periodic arrays can be synchronized. In both cases of complex R(X), a residual beam-pointing error occurs. Computer simulations and airborne sea clutter data are reported that verify the theory and practicality of the algorithm. >

Wide band antenna for mobile communications

Abstract: An antenna to be mounted on a vehicle. The antenna includes a ground plate with an L-shaped radiator plate and an L-shaped sub-radiator plate. One leg of the radiator plate and sub-radiator plate are parallel to the ground plate. The parallel legs are spaced from the ground plate. The other leg is perpendicular to the ground plate. The perpendicular leg is separated from the ground plate by a small gap. The two legs are opposed to each other with a gap between the legs parallel to the ground plate. In some embodiments, filler is placed between the plates.

Aspect sensitivity measurements of VHF backscatter made with the Chung‐Li radar: Plausible mechanisms

Abstract: A new technique, using beam broadening effects, has been developed to measure the aspect sensitivity of atmospheric clear air VHF radar echoes. It uses the relatively broad antenna beam of the vertical-pointing antenna of the new Chung-Li stratospheric-tropospheric radar (25°N, 120°E). The aspect sensitivity measurement using this method is straightforward and free from convolution effects introduced by the finite width of the antenna beam pattern. The observed results agree very well with other measurements. The authors propose a turbulent layer model to explain the aspect sensitivity of the echoes. In this model, anisotropic turbulence is confined to a very thin (few meters) region at the boundary of a turbulent layer. This region is responsible for the aspect sensitivity of the echoes obtained from the vertical direction. The isotropic echoes obtained from the oblique beam arise from the isotropic turbulence embedded in the center of the layer, with 30–300 m in vertical extent. We show in an appendix that the magnitude of the partial reflection coefficient is much more sensitive to the shape, length scale, and smoothness, than to the slope of the refractive index profile. Therefore the functional shape of the refractive index profile is very important for estimating the reflection coefficient. Large errors can be made when assuming, for simplicity, nonphysical profiles. For partial reflecting mechanisms to be important, steplike discontinuities, confined within length scales of the order of a meter, would be required.

Cordless headset telephone

Abstract: Cordless headset telephone system including at least one headset having at least one earpiece, a swingout microphone and a headset transmitter and receiver connected to a common antenna, at least one base having a base transmitter and receiver having a common antenna, respectively tuned to the headset transmitter and receiver, and apparatus included in the base circuit for seizing at least one telephone line.