Showing papers on "Dipole antenna published in 1980"

Empirical formula for propagation loss in land mobile radio services

Abstract: An empirical formula for propagation loss is derived from Okumura's report in order to put his propagation prediction method to computational use. The propagation loss in an urban area is presented in a simple form: A + B log 10 R, where A and B are frequency and antenna height functions and R is the distance. The introduced formula is applicable to system designs for UHF and VHF land mobile radio services, with a small formulation error, under the following conditions: frequency range 100-1500 MHz, distance 1-20 km, base station antenna height 30-200 m, and vehicular antenna height 1-10 m.

Electronic tuning antenna system

Abstract: At the feed side of each antenna element having transmitting conductor paths formed in continuous meandering shapes and having distributed constant impedances are electrically connected a variable tuning unit including a voltage variable reactance circuit and an impedance adjusting reactance element, thereby constituting an antenna circuit. A voltage variable capacitor is connected within the voltage variable reactance circuit. Antenna feed terminals are connected through a coaxial cable to input terminals of a remote-set radio receiver. A tuning control signal generated within the radio receiver is fed to a voltage variable capacitor within the voltage variable reactance circuit of the antenna circuit through the coaxial cable. The tuning control signal allows the antenna circuit to resonate with a particular frequency within a frequency band, the freqency being variable. The antenna element having the distributed constant inductance functions so as to have the best possible antenna radiation efficiency at resonant frequency signal by being in combination with the variable tuning unit and the antenna element is considerably reduced in size. At the resonant frequency signal, the characteristic impedance at the feed terminals of the antenna circuit becomes equal to that impedance at the receiving input terminals at the radio receiver connected to the antenna circuit, whereby an RF signal at the resonant frequency is selected and fed most efficiency to the radio receiver through the coaxial cable.

A hybrid technique for combining the moment method treatment of wire antennas with the GTD for curved surfaces

Abstract: This hybrid technique is a method for solving electromagnetic problems in which an antenna is located near a conducting body. The technique accomplishes this by casting the antenna structure in a moment method (MM) format, then modifying that format to account for the effects of the conducting body via the geometrical theory of diffraction (GTD). The technique extends the moment method to handle problems that cannot be solved by GTD or the moment method alone. Wire antennas are analyzed to find their input impedance when they are located near perfectly conducting circular cylinders, although the methods used are not restricted to circular cylinders. Three orthogonal orientations are identified, and antennas to match them are analyzed. For each case, the hybrid solution is checked with one of three independent solutions: an MM-eigenfunction solution, image theory, or experimental measurement. In almost all cases, excellent agreement is obtained due in large part to the fact that the moment method near fields are, for the first time, cast into a ray optical form.

Dipole array lens antenna

Abstract: As electromagnetic energy passes through a planar array of linear dipoles, it undergoes a phase shift which is a function of the operating frequency and the array parameters. This property has been used to design and construct a lightweight zoned microwave lens antenna which has possible spacecraft applications. A description of the lens antenna, its principle of operation, and measured data are presented in this paper. Good agreement between the measured results and the predicted performance has been obtained.

Transients in a resistively loaded linear antenna compared with those in a conical antenna and a TEM horn

Abstract: The receiving and transmitting transient responses of the resistively loaded linear antenna, the TEM horn, and the conical antenna are investigated theoretically and experimentally using the fast Fourier transform (FFT) technique. The receiving transient response of the resistively loaded linear antenna indicates that the shape of a 70-ps impulse is well preserved.

Cavity-backed, micro-strip dipole antenna array

Abstract: A flush-mounted antenna assembly (10) including a generally rectangular, conductive, box structure (11) open along one face to form a cavity. Within the cavity a pair of mutually orthogonal dielectric plane surfaces (13) (14) in an "egg crate" arrangement are mounted normal to the plane of the open face, each diagonally within the cavity. Each dielectric plane supports a pair of printed circuit dipoles typically (16) each fed from the opposite side of the dielectric plane by a printed "cone-shaped" feed line trace (15) which also serves as an impedance matching device (19) and functions as a balun connected from an unbalanced strip line external feed (24 and 26). The open face of the conductive cavity can be flush mounted with a randome thereover, the assembly thereby being flush with the skin of a aircraft or space vehicle.

Wire antennas over a lossy half-space

Abstract: A recently developed technique for approximate but accurate evaluation of the various vector potential components associated with a current element radiating over a lossy ground is used to study the problem of antennas radiating over a lossy ground. A general integral equation for an arbitrarily shaped thin-wire antenna over a lossy half-space is derived, and the method of moments is employed to process this equation numerically. Illustrative numerical results are presented to demonstrate the effect of the lossy half-space on a number of antenna configurations.

The Pioneer Venus Orbiter Plasma Wave Investigation

Abstract: The Pioneer Venus plasma wave instrument has a selfcontained balanced electric dipole (effective length = 0.75 m) and a 4-channel spectrum analyzer (30-percent bandwidth filters with center frequencies at 100 Hz, 730 Hz, 5.4 kHz, and 30 kHz). The channels are continuously active and the highest Orbiter telemetry rate (2048 bps) yields 4 spectral scans/s. The total mass of 0.55 kg includes the electronics, the antenna, and the antenna deployment mechanism. This report contains a brief description of the instrument design and a discussion of the in-flight performance.

Loop antenna for security systems

Abstract: Disclosed is a loop antenna for the propagation of electromagnetic radiation with minimal electrostatic radiation for use in security systems. At least a single loop of conductor forms the radiating surface of the antenna. However, the loop is disposed in a tubular electrostatic shield which serves to minimize electrostatic radiation while not significantly interfering with the desired electromagnetic radiation. In preferred embodiments the electrostatic shield may be electrically grounded or a resistor may be placed in the conduction loop of the antenna to broaden the frequency response thereof. Additional preferred embodiments include twisting the single loop antenna one or more times such that two or more lobes are provided forming a twisted loop antenna. Far-field cancellation of transmitted signals is achieved and there is self cancellation in this antenna of received common mode signals. Additionally, the twisted loop antenna in a preferred embodiment has an electrostatic shield comprising a single unbroken loop of metal tubing around the periphery of the loop with at least one gap occurring in the electrostatic shielding where the shielding covers the conductor along the common side of adjacent lobes.

The low‐frequency continuum as observed in the solar wind from ISEE 3: Thermal electrostatic noise

Abstract: The low frequency continuum (LFC) noise between 30 and 200 kHz has been investigated from the ISEE 3 spacecraft in the solar wind by means of a radio astronomy experiment more sensitive than previously available. It is demonstrated that the LFC radiation observed in the solar wind is in the form of longitudinal plasma waves rather than transverse electromagnetic waves. The observed spectral characteristics are found to be a function of antenna length. In addition, both the absence of antenna spin modulation and the fact that these plasma waves do not propagate to large distances imply a local origin for the LFC.

Electromagnetic coupling between a thin-wire antenna and a neighboring biological body: theory and experiment

Abstract: Interaction between the near-zone EM field of a radiating antenna and a neighboring biological body is analyzed by considering the antenna current and the induced electric field in the body as unknown functions. A simultaneous pair of coupled, tensor integral equations is developed for these unknown functions. These equations are solved numerically by the method of moments using pulse function expansions for the unknowns and delta functions for testing. A monopole antenna coupled with a rectangular-cylindrical body model is used for the experimental verification of theoretical results. Accuracy of the numerical solution is substantiated by good agreement between the numerical and experimental results obtained for the antenna impedance and current distribution, as well as the induced electric field in the body. Electromagnetic (EM) radiation effects in various computer models of the human body are investigated to make a realistic assessment of potential radiation hazards associated with the coupled antenna-body system. It is found that an operator in the immediate vicinity of high-power transmitters may be exposed to harmful levels of radiation.

Analysis of a wire antenna in the presence of a body of revolution

Abstract: The problem of an arbitrarily oriented thin-wire antenna located near a body of revolution is analyzed. The usual integrodifferential equation for a thin wire in unbounded space is generalized to account for scattering from the nearby body. The presence of the body is accounted for by a numerical dyadic Green's function. The modified wire equation is solved by standard numerical techniques to obtain the current distribution on the wire. The effects of various bodies on input admittance are compared with results for an isolated antenna. Measured and theoretical input admittance data for a monopole near several different bodies of revolution are found to be in good agreement.

Antenna system for a jamming transmitter

Abstract: This invention relates to an antenna system for a jamming transmitter which is intended to protect a remote object which is remote from the jamming transmitter as well as itself or an object in the immediate vicinity of the jamming transmitter. Known jammer antennas for this purpose radiate either a pencil beam which presents considerable problems in the alignment and orientation and tracking in two planes or alternatively such known antennas are designed as omni directional antenna which however have low antenna gain and are easily detected. In the present invention the difficulties of the prior art are eliminated in that a separate antenna is provided for external or foreign protection and a separate antenna for self protection which antennas produced in the first plane a sharply focused pattern and in a plane perpendicular thereto a radiation pattern (7, 8) which is optimized for external or foreign protection or self protection, respectively. The two antennas can be switched and are structurally combined and designed to be jointly rotatable in the first plane. A single antenna can also be provided which can be tilted between two positions one for external or foreign protection and the other position for self protection so as to transmit and radiate instead of two separately optimized patterns a single pattern which is a mean of the two desired patterns.

Spiral slotted phased antenna array

Abstract: A flush mounting, cavity-backed, dual orthogonal slot antenna in which improved radiation pattern characteristics are obtained by making the spiral slot pattern elliptical in the aperture plane. A cavity (11) and a flanged aperture plate (11a) are shown in which one slot pair (12 and 13) is orthogonal with respect to another slot pair (14 and 15) within the aperture plate (11a). Coaxial split-tube baluns (12a and 14a) are used to drive the junctions between corresponding slot pairs. Optional cavity dielectric (18) is provided and a drive coupling arrangement includes a four port comparator hybrid (30) having ≦ and Δ ports (17 and 16) respectively, for alternate excitation to produce a single lobe or a double lobe pattern with null. Switching apparatus is provided to connect a common terminal (26) to either of the ports (17 or 16).

Integrated spiral antenna-detector device

Abstract: An integrated antenna-detector device sensitive over a broadband of frequencies with an extended high frequency limit comprising a pair of antenna elements each having first and second ends, the first ends of the elements being positioned proximate to each other while the second ends are displaced from the first ends, a detector unit positioned and connected between the first ends of the antenna elements, and signal output means connected with the antenna elements at a location displaced from their first ends The signal output means delivers detected output signals from the antenna elements, and also delivers a biasing signal to the detecting unit The device may take a number of forms including that of a dipole antenna having a linear or conical configuration, and in which a plurality of such dipole elements are arranged to form a log-periodic antenna, and where the pair of antenna elements are arranged to provide a pair of interwound spiral conductive windings to form a spiral antenna

Digitally tuned electrically small antenna

Abstract: An antenna system suitable for airborne use is disclosed. The system is of the type having a blade forming a folded monopole antenna with one terminal serving as a radio frequency input and a second terminal connectable to tuning apparatus. Tuning components switchable to various values are connected at the second terminal. A processor receives the value of a new frequency to be used, computes from stored reference values the values of tuning components calculated to render the antenna in tune at the selected frequency, and commands the switching of the tuning components to the calculated values. A phase discriminator at the first terminal provides the processor with an indication of the extent to which the antenna is in tune at the selected frequency. If it is not in tune, the processor iteratively commands the switching of the tuning components until new values are reached for which the antenna is in tune. Then, in response to the new tuning component values, the processor can compute and store new reference values. After some period of use, the adaptive nature of the system results in an antenna which can switch from frequency to frequency at speeds compatible with contemporary radio designs.

Microwave leakage detector

Abstract: A portable microwave leakage detector comprises a dipole antenna and a hot carrier diode connected in parallel with a light emitting diode, the circuit incorporating minimum solder joints and affording maximum sensitivity without moving parts such that the detector circuit does not decay with time. The dipole antenna is oriented diagonally in a detector case so that the user of the detector automatically presents the antenna to the radiating microwave field (or leakage field) at a maximum receiving attitude with respect to the field. The detector can be utilized to determine whether a microwave oven or any other device is leaking radiation beyond limits imposed by the Food and Drug Administration.

Non-dissipative load termination for travelling wave array antenna

Abstract: This specification discloses a nondissipative load termination for a traveling wave antenna array whereby energy incident at the end of the antenna array is applied directly to the main beam of the array with the same polarization as the main beam so that the gain of the antenna is improved.

End supportable dipole antenna

Abstract: An end supported antenna having inner and outer elements extending outwardly from a supported end and of which the inner and outer elements each form one element of the dipole. Such antennas are driven centrally of the inner and outer ends or intermediate the ends between the dipoles. There is a decoupling sleeve on the inner element that functions as a coaxial transmission line of variable characteristic impedance on its inside and functions as a radiating element of the antenna on its outside. Generally, one or two sleeves are employed, the sleeves being of non-uniform cross section so as to be either conical or generally conical in shape, flaring from the supported end. A dielectric member separates the inner and outer elements and has an impedance matching network formed therewith. A support pipe extends outwardly from its supporting end to adjacent the impedance matching network. Coaxial conductors extend into the support pipe and the center coaxial conductor is connected to the outer element and the outer coaxial conductor is connected to the support pipe and to the decoupling sleeve or sleeves. Each sleeve may be secured to the support pipe by a single band clamp. The sleeves have resonant length greater than 1/4 wavelength such as in the range of between 0.33 and 0.433 wavelength.

Compact television antenna system

Abstract: A highly compact and lightweight 82 channel all banded VHF-UHF television antenna having three antenna elements wherein each element is the identical physical length and each element includes two half sections. Each antenna element is separated a predetermined distance from each other element wherein the predetermined distance is substantially less than one-tenth of the shortest wave length in the VHF band. A first set of coils are utilized to electrically lengthen the halves of the two elements for reception in the VHF band and a second set of coils are utilized to provide proper delays between the signals received by each antenna element so that when the signals are combined the signals are substantially additive and in phase. The antenna system includes a weatherproof housing containing a rotor, a preamplifier, and electronic circuitry. A deloading mechanism is arranged around the housing to engage the circumference of each antenna element to provide stability under the driving forces that may occur in the atmosphere.

Circularly polarized feed for cylindrical parabolic reflector antennas

Abstract: The feed design described is a linear array of crossed dipoles above a ground plane. The radiation patterns of the longitudinal and the transverse dipoles are made equal by parallel longitudinal rods, referred to as beam forming rods or beam matching rods. When used as a circularly polarized feed for an offset parabolic cylinder antenna, aperture efficiencies (spillover included) as high as 0.89 are potentially available if the field distribution along the array is uniform. The beam patterns of the feed were computed both by the method of moments and the geometrical theory of diffraction and are compared with patterns measured on a model at 1.5 GHz. A method of matching the impedance for both linear polarizations is proposed using parallel impedance matching rods.

Transponder Antennas in and Near a Three-Layered Body

Abstract: The electric field in a three-layered half-space iluminated by an incident plane wave is reviewed and numerical data provided when the layers are skin, fat and muscle. The impedance and voltage across the load of a dipole antenna is discussed when this is located in each of the three Iayer and in the air near the surface. Bare and insulated antennas are considered over a frequency range up to 3 GHz with layer thicknesses of skin from 0.2 to 1.0 cm, and of fat from 0 to 1.5 cm. The transmitting problem is discussed as well as application of the results to finite bodies.

Method and antenna for improved sidelobe performance in dipole arrays

Abstract: The existence and method of suppression of spurious post mode to improve sidelobe performance of an array of dipole antenna elements together with examples of geometric configuration for suppression of such post mode is described.

Small broadband antennas using lossy matching networks

Abstract: A low-profile survivable antenna suitable for military use is described. pite its small size, which might be one tenth of a wavelength, the antenna has reasonable transmission range for these applications. Very little operator attention is needed in use, since a special matching circuit within the antenna network enables effective impedance matching, over a 3:1 frequency range, without necessity of switching to different matching circuits over different frequency bands. By including resistive components along with other passive inductive or capacitive elements, the reactance of the single matching circuit is made to effectively compensate the antenna's impedance over the entire frequency range. The impedance of the circuit has a decreasing positive reactance which compensates for the decreasing negative reactance, with frequency, of the antenna. Although the transmission efficiency of the matched antenna network is somewhat diminished by resistive losses, it is still satisfactory, and band switching with this matching circuit is completely eliminated. By including a slender whip screwed into the top, the range can be doubled with no further changes. The matching techniques to be described are most easily realized in the HF through VHF range (1-200 MHz).

Coupling unit for coaxial cable including means for radiating wave energy

Abstract: An optimum coupling unit for joining adjacent sections of coaxial cable and a coupled radiating antenna includes different diameters of the dielectric material, different diameters of central conductor and different values of the dielectric constant material in order to provide impedance matching at any section of the coupler including the coupled antenna to the impedance of the coaxial cable. The coupling unit is combined with the antenna as an integral unit. The antenna may be a dipole whose elements are coupled to the coupling unit through a parallel plate transmission line. Impedance matches are maintained at each coupling point.

Resolution of coherent sources incident on a circular antenna array

Abstract: A method of processing voltages received on a circular antenna array which calculates the number, azimuths, and relative strengths of coherent sources is described. The method can be extended to any array geometry where inverse filtering (or deconvolution by the inverse beamspreading function) can be applied. In particular, it can be applied directly to a linear array geometry. In the analysis, the effects of mutual coupling between elements hasn ot been considered.

Broadband radiation detector for microwave and lower frequencies

Abstract: A radiation detector for free space microwave radiation uses thin film resistive strips, having an equivalent surface resistivity that is large compared to the characteristic impedance of free space, and diode circuits in series with the strips for deriving d-c signals monitoring the radiation intensity over a broad frequency range. In part of that range, the strips operate like a short dipole antenna. The diode circuits are constructed to operate with a uniform response over the entire frequency range.

Antenna low-noise q spoiling circuit

Abstract: Input coupling circuit for detuning the Q of a high-Q ferrite rod antenna. A high impedence low-noise amplifier (4) is used to amplify the output signal from the LC resonant tank (L1, 1) of the rod antenna (M). A portion of the amplified signal is fed back directly into the magnetic circuit of the antenna tank. This negative feedback reduces the losses produced in the magnetic circuit due to the presence of nearby conductors. As a result of this reduction, an increase in the antenna sensitivity and a decrease in the cross-feed from other nearby antenna is produced.

Directivity-controllable antenna system

Abstract: An antenna circuit comprises an antenna element made up of a conductor bent into zigzag form and having a distributed inductance connected to a variable tuning unit including a variable reactance circuit and a reactance element. A plurality of dipole antennas comprising such an antenna circuit are grouped to form a phased array or Yagi antenna and voltage variable capacitors within the variable reactance circuits are interconnected. The grouped antennas are connected by a coaxial cable to a receiver which includes a generator circuit for generating a tuning control d.c. voltage for altering the capacitance of the variable capacitors. Control of the directivity of the grouped antennas is relieved by feeding slightly different tuning control d.c. voltages to each dipole antenna of the group so that the resonance of each dipole antenna is delayed to generate phase differences between the dipole antennas. The control is closed loop because a voltage difference signal is produced using the incoming radio wave and this voltage difference signal is used as a fine tuning signal.