Showing papers on "Coaxial antenna published in 1981"

The elliptical microstrip antenna with circular polarization

Abstract: A theoretical analysis of an elliptical microstrip antenna is presented. It is shown that radiation from this antenna is left-hand or right-hand circularly polarized in a narrow frequency band when the eccentricity of the ellipse is small. The theoretical result agrees with the experimental data.

Low profile circular array antenna and microstrip elements therefor

Abstract: An antenna element is comprised of two rectangular microstrip patch dipoles spaced by dielectric a predetermined distance above a ground plane conductor. One edge of each dipole is electrically shunted to the ground plane conductor. The dipole feedpoints are separated by a quarter wavelength of the antenna resonant frequency. An isolated power splitter and phase shifter connects an antenna element port with the dipole feedpoints so that the signal at one feedpoint lags the signal at the other feedpoint by 90°. The antenna element will end fire through the dipoles in the direction of the lagging signal feedpoint. A low profile circular array antenna is comprised of eight such antenna elements arranged on the ground plane conductor equally spaced with their phase centers on a common phase center circle.

Stripline fed hybrid slot antenna

Abstract: A planar antenna is described which employs a pair of closely spaced parallel ground planes and a radiating element which is a composite aperture (hybrid slot) formed into the upper ground plane. One portion of the radiating element is a long narrow slot which may have the shape of a rectangle of high aspect ratio. The other portion is an annular slot which may be circular in shape. Electromagnetic energy is conveyed to and from the slots in the upper ground plane by means of a feed conductor parallel to and sandwiched between the two ground planes. The maximum of the resulting field pattern is in the plane of the antenna and the pattern may be either directional or omnidirectional in that plane. When used as a receiving antenna, this antenna responds to both the electric and magnetic fields.

Frequency selective antenna

Abstract: There is disclosed herein an antenna, particularly for use at high frequencies such as approximately one gigahertz and above, which is frequency selective. The antenna design allows signals at a given frequency to be preferentially received, as distinguished from broadband reception. The antenna design can be modified for reception of signals of different given frequencies. The antenna comprises a plurality of parabolic sections in the form of concentric rings or segments with each segment being offset axially from the next adjoining segment to thereby provide an antenna which is relatively flat, or having a low profile, as compared to a standard parabolic antenna. The surface of each segment is a segment of a different focal length parabola, but with each parabolic surface being a function of the signal wavelength (or frequency) to be received by the antenna. The antenna may be round, rectangular or have other shapes. Also disclosed are feed and pick-up arrangements for the antenna. In addition to the frequency selective characteristic of the antenna it can be made from various materials and is relatively simple to manufacture, and its low profile minimizes wind loading and mounting problems, and the like.

An Analysis of Log Periodic Antenna with Printed Dipoles

Abstract: An analysis of Log Periodic Antenna with Printed Dioples is presented here. In this analysis, the wave equation for Hertz potential is solved in Cartesian coordinates applying the boundary conditions of a flat strip diople. Using this model, the input currents to the antenna elements, the current distribution of the antenna elements, and the radiation pattern are computed. The computed results are compared with experimental results.

Energy Absorption from Small Radiating Coaxial Probes in Lossy Media

Abstract: This paper describes the calculation of energy deposition around small open-ended coaxial antenna probes in lossy media. Two theoretical methods, a small monopole approximation (I) and an equivalent magnetic current source (II), are evaluated and compared. Method I is shown to be inappropriate for determining near field energy deposition. Power contour plots determined by method II in the vicinity of the open-ended coaxial antenna are presented as well as calculations of total power absorbed as a function of distance from the antenna center for various antenna dimensions and media dielectric properties. Our calculations of absorbed power distributions near the antenna are consistent with the limited experimental data which is available for comparison. A frequency of 2.45 GHz was selected for these calculations so that the results will be of value to workers interested in the application of own-ended coaxial antennas for invasive treatment of cancer by microwave hyperthermia.

Dual band collinear dipole antenna

Abstract: A collinear dual dipole antenna is split into two sections which are connected by a central conductor extending in spaced parallel relation within hollow support mast sections, and forming an effective transmission line providing RF continuity at a high band frequency f, and discontinuity at a low band frequency 1/2 f. The configuration provides a dual band antenna operating in either band from a single source without filtering and without modification of the antenna. In the high frequency band, the antenna operates as a dual dipole array. In the low frequency band, the antenna operates as a single dipole array with each mast section and its respective dipole acting as half of the single dipole array.

Combined dipole and ferrite antenna

Abstract: A small sized reception antenna for VHF and/or UHF band for the use in a room has been found. The antenna has a horizontal dipole type first antenna portion having a folded elongated conductor, and a vertical second antenna portion having a ferrite pole electromagnetically coupled with said horizontal first antenna portion. Said horizontal first antenna portion is rotatable in a horizontal plane, while the second antenna portion is fixed vertically. A tank circuit with a tank coil wound on the ferrite pole and a variable capacitor is provided to resonate the antenna with the reception frequency. An output coil is wound on the ferrite pole, and said output coil provides the output signal of the present antenna. Means for sliding the output coil along the ferrite pole is provided to adjust the output impedance of the present antenna for each of the reception frequencies.

Rod antenna, particularly for mobile FM signal transducing applications

Abstract: To provide a short FM antenna, of about for example 40 cm length for mobile radio, for example automobile radio application, without degradation of signal strength with respect to an about 1 m long FM antenna, a conically tapering insulating rod, for example of fiberglass, has two windings applied thereover, the two windings, each, having a straight wire length of about 1/4 the median wavelength of the FM band, and the overall length (l) of the rod having said two windings applied thereover being about 1/8 of the median wavelength. The oppositely wound windings (11, 12) are connected at their center, and may be formed as one bifilar winding, with the lower end of the lower winding being connected to an electrical terminal for standard connection to, for example, a coaxial antenna connector for an automobile radio. A spiral spring can be interposed if extreme deflectability of the antenna is desired, for example to prevent damage if the antenna, applied to an automotive vehicle, is passed through a power washing and scrubbing station.

Horn Image Guide Leaky-Wave Antenna

Abstract: A novel approach for designing a frequency-scanning millimeter-wave antenna is described. The antenna is constructed by using an image wide leaky-wave antenna embedded in a long trough with metal flares along both sides. The optimum flare angle for achieving maximum gain is theoretically predicted. The design of the leaky-wave antenna, which is comprised of metallic-strip perturbations on top of a dielectric guide, is also discussed.

A dielectric rod antenna as a high efficiency feed for reflector antennas

Abstract: Radiation characteristics of a short dielectric rod antenna excited by a circular waveguide is investigated experimentally. It is found that, by a proper selection of the waveguide radius and the exposed length of dielectric rod, the E and H plane radiation patterns, the side and back radiations and the bandwidth of the antenna can be controlled. Some experimental data are presented and the usefulness of this antenna as a feed for paraboloidal reflectors is also discussed.

Circularly Polarized Linear Array Antenna Using a Dielectric Image Line

Abstract: A new circularly polarized antenna using a dielectric image line is proposed. This antenna is composed of a slotted conductive plane and a rectangular dielectric rod. This paper describes the design of and experimental results achieved with the circularly polarized array antenna fed by a dielectric image line. The fundemental characteristics of the image line are also presented. Since this line's losses are far lower than the microstrip line losses in the millimeter wavebands, antenna feed line losses expect to be also very low. Bandwidth within the 2-dB axial ratio was more than 7 percent, and the angle range within the same ratio was more than +-7.8 degrees at 29.5 GHz. This antenna is far superior to the microstrip line feed array antenna in the millimeter wavebands.

Tunable citizen band antenna

Abstract: An improved tunable citizen band antenna includes an adjustable tuning assembly located at the tip of a wire wound fiberglass core antenna to lengthen or shorten the effective electrical length of the antenna, so that the antenna can be tuned to a specific, desired resonant frequency, resulting in enhanced antenna radiation, reception, and power transmission.

Inductor type half wave antenna

Abstract: A half wave antenna that is physically shortened by incorporating one or more inductors which are formed by convoluting a portion of the antenna wire and wrapping the convoluted section in a spiral.

Properties of 2-arm conical equiangular spiral antenna over extended bandwidth

Abstract: A frequency-independent type of antenna, the 2-arm conical equiangular spiral, has been studied for applications which require hemispherical coverage over a wide bandwidth. At low frequencies the antenna properties are modified by both truncation of the active region and end-reflected currents. These currents have been reduced by the addition of resistive loading and the performance of the antenna then falls of more gradually as the frequency is reduced. Theoretical and experimental results are presented for current distribution, input impedance and radiation patterns, for both the loaded and unloaded cases.

A design of back-feed type circularly polarized microstrip disk antennas having symmetrical perturbation element by one-point feed

Abstract: A one-point back-feed type circularly polarized microstrip disk antenna is investigated. To establish a design procedure, (1) the operating condition for circular polarization is studied and design formulas and data are presented and (2) the fabrication and radiation characteristics of arrays consisting of the present circularly polarized disk antenna element are discussed. It is demonstrated that this class of antennas can serve as a useful form of circularly polarized array element. Further, in order to analyze the mutual coupling of such antenna elements, the resonance and inter-element mutual admittance of an array consisting of two disk antennas located on the same plane are determined. The fundamental information on the mutual coupling thus obtained is presented for a design aid. Using these results, a circularly polarized array is realized with good axial ratio and boresight ratio less than 0.5 dB.

Subsurface antenna system

Abstract: A subsurface antenna system including at least one pair of radiating elements and feed system is buried within a subsurface medium The radiating elements comprising the system are spaced apart at least one quarter free space wavelength at an operating frequency The radiating elements are spaced from each other and the feed system provides appropriate relative phase to signals at the elements to produce from the antenna system a directional antenna pattern in free space

Electrically screened broadband antenna for the in-phase detection of the magnetic components of an alternating electromagnetic field

Abstract: The invention relates to a loop or frame antenna having screening against electrical fields. In conventional antennas of this type, the unavoidable switching capacitances in conjunction with the inductance of the loop winding lead to resonances at specific frequencies. The loop antenna described here consists of coaxial line sections in a specific interconnection, in which the inner conductors of the coaxial lines are connected in series but the outer conductors are connected in parallel. In conjunction with a matching receiver input impedance, this construction results in a compensation effect so that, when the alternating magnetic field amplitude is constant, the output signal of the antenna is free of resonances over a wide range, virtually independently of the frequency. Furthermore, the phase difference between the output signal and magnetic field in this frequency range remains low and virtually constant. The antenna can be constructed to be balanced or unbalanced with respect to earth. Areas of use of this broadband antenna - individually or as an antenna array - are, for example, field strength measuring apparatuses, communications apparatuses and direction-finding apparatuses.

Spiral array antenna

Abstract: A compact and light weight array antenna with a gain of approximately 13 dB comprises a plurality of axial-mode helical antennas with an antenna height of 0.4˜0.6λ (λ: Wavelength) as element antennas, having cylindrical metallic rims with a rim height of approximately 0.25λ surrounding each corresponding element antenna in order to suppress the characteristic degradation of the device caused by the mutual coupling of element antennas.

The near field of dipole antennas, part II: Experimental results

Abstract: The results of an experimental program to evaluate the electric field near dipole antennas are presented. The measured field intensities are compared with the numerical values computed using the theory developed in Part I of this paper. The theoretical and measured field intensities are in excellent correlation even for observation points spaced from the axis of the dipole less than one hundredth of a wavelength. For thin dipoles (radius ≃ .002λ) the experimental measure of the E-field at the antenna surface or at one antenna radius distance has not been possible because of the practical limitation of available instruments. The experimental and theoretical results show that the field intensities near some parts of a dipole antenna are higher than predicted by commonly used formulas.

Current distribution on a receiving dipole antenna

Abstract: The current distribution on a receiving dipole antenna is dependent on its feed-point load impedance. Calculations based on the modified King-Middleton approximation have been made of the distribution for antenna half lengths of 0.1, 0.2, 0.25, and 0.3 \lambda . Representative values of the antenna load impedance, resistive, capacitive, and inductive, are used to show their effects on the antenna current distribution.

Single membrane lens for space radar using microstrip antenna radiating elements

Abstract: A lightweight single layer microstrip membrane antenna for space radar applications which, in an exemplary application, is adapted to be furled on a spool and carried into space by a space shuttle orbiter where it is easily unfurled to form an antenna. The membrane antenna includes gore sections which are connected by metal mesh members that are folded in the furling process to avoid folding of the gore sections. The metal mesh members may also act as primary power busses for suitable transmit/receive antenna modules that are connected to series strings. Current regulators and zener diodes are connected in the strings of antenna modules to provide for continued operation of the antenna in the event of failure of antenna modules.

Coaxial antenna configuration with high inter-element isolation

Abstract: A two-antenna array includes first and second coaxial antenna members spaced such that the fore member is in the distant (far) front lobe field of the aft element. Each antenna member includes a like-oriented circularly polarized antenna element with microwave absorbing material disposed in a cavity about its aft, back lobe direction. A high degree of electrical isolation exists between antennas by reason of the aggregate inter-element transmission losses resulting from (i) space propagation loss, (ii) antenna front-to-back discrimination, and (iii) polarization isolation.

Hoop/column antenna technology development summary

Abstract: The Langley Research program for development of hoop/column antenna technology was redirected and includes the fabrication and test of models such as the 4 gore segment of a 50 meter antenna and the 15 meter diameter fully deployable antenna. Significant results were obtained in the point design that includes a quad aperture reflector system for multiple beam applications.

Modified difference mode coaxial antenna with flared aperture

Abstract: A coaxial radiating waveguide antenna is disclosed, comprising two conductive concentric right circular cylinders forming a cavity. Equally spaced within the cavity is a set of probes phased in such a manner as to produce TE 21 or a higher order difference mode of radiation. One side of the toroidal antenna is sealed by a flat conductive ring; the other side is generally open and terminates in two flared regions which serve to shape the beam in the desired fashion. A broad null surrounds the boresight axis with major lobes disposed approximately 45° therefrom in the case of TE 31 propagation. The resulting radiation can be circularly or linearly polarized.

Monopole inductively loaded antenna tuning system

Abstract: A monopole inductively loaded antenna system is disclosed in which the antenna system is tuned to resonance and impedance matched without making changes to the loading inductance or other antenna elements. The monopole inductively loaded antenna is supported by a base insulator having an antenna side and ground plane side. A variable capacitor is positioned on the ground plane side of the base feed insulator for tuning the antenna system to resonance. One of a plurality of impedance matching transformers is selectively switched into the antenna system to match the antenna load to the transmitter.

Travelling object with antenna

Abstract: PURPOSE:To enable a travelling object like a car, etc. to receive the superhigh frequency electric wave while it is travelling, by setting horizontally a plane antenna like a waveguide type slot array planar antenna, etc. on the roof of the car to decrease the air resistance. CONSTITUTION:A plane antenna 5 like a waveguide type slot array planar antenna, a microstrip antenna, etc. consists of plural waveguide radiators 1b formed by distributing a number of slots 1a in chevron shapes, an electric power distributor 1c and an antenna feeding part 1d. Such antenna 5 is set on the roof of a travelling object 4 like a car, etc. in nearly a horizontal position. An antenna elevation angle control mechanism 6 that controls the angle of elevation of the antenna 5 is added to increase the receiving accuracy of the antenna 5 while the object 4 is at pause.

Low profile antenna for data transponders

Abstract: A top-loaded low profile antenna for data transponders includes an antenna pin mounted vertically, affording vertical polarization for the antenna, an aluminum plate mounted in a horizontal plane and connected to an upper end of the pin, providing top-loading of the antenna, the plate being supported by a lucite frame mounted on an upper surface of the data transponder and which also dielectrically loads the antenna feed region. The load plate and lucite frame enclose the antenna pin so that the antenna is less susceptible to vandalism, and the top-loading results in a reduction in the height of the antenna structure improving the aesthetics of the antenna and data transponder installation.