Showing papers on "Dipole antenna published in 1972"

A Microstripline Slot Antenna (Short Papers)

Abstract: A microstripline slot antenna is treated experimentally at X-band frequency. First, the input impedances of the slots for various geometries and the radiation patterns for the matched slots are measured. Second, the dependence of input impedances and radiation patterns on the slot-to-reflector spacing is tested. Finally, a two-dimensional X-band Dolph-Chebyshev slot-array antenna is designed and fabricated as an application of this type of slot.

A numerical solution for the near and far fields of an annular ring of magnetic current

Abstract: A simple method for calculating the near and far zone fields from an annular ring of circumferentially directed magnetic current which may be used to represent coaxial apertures is presented. Near-field contours are given for two ring sizes. The utility of the method has been illustrated by its application in several practical antenna problems where the magnetic ring current serves as the primary source. Among these are the analysis of dipole antennas mounted on a conducting sphere or cylinder, the impedance of a coaxially fed Yagi-Uda antenna, a coaxially driven wire loop, and the radiation from a coaxial aperture at the base of a cone.

Automatic antenna impedance tuner including digital control circuits

Abstract: An automatic antenna tuner includes digital control circuits for selecting reactive tuning elements of an antenna impedance matching network. The tuner arrangement provides for rapid transforming of multiple antenna impedances to the load resistance required for efficient transfer of power from a power amplifier of a portable radio transmitter to any selected antenna over a broad frequency range of 2 to 80 MHz, for example. The impedance matching network includes series inductive elements and shunt capacitive elements in an L configuration. Both inductive and capacitive elements are incrementally adjustable in binary value and are adjusted automatically by digital control of latching relays in response to sensed antenna impedance to switch component values in a binary sequence. The tuning of the antenna for matching to the power amplifier is detected by individual phase and impedance broad band sensors for sequencing of capacitive and inductive reactances to approach 0* phase and the desired load resistance for efficient power transfer. The tuning is continuously monitored by a voltage standing wave ratio (VSWR) sensor which initiates and controls the duration of the tuning cycles according to the detected antenna impedance matching condition.

Analysis of Wire Antennas in the Presence of a Conducting Half-Space. Part II. The Horizontal Antenna in Free Space

Abstract: An integral equation approach for the analysis of a horizontal wire antenna(s) located in free space near a lossy half-space is described. Two methods, a rigorous one based upon the Sommerfeld form...

An improved element for use in array antennas

Abstract: An antenna element consisting of a slot plus two parasitically excited wires has been found to exhibit many properties useful in array applications. The introduction of the wires provides a means of controlling both the E - and H -plane element radiation patterns. Specifically, the principal plane radiation patterns can be equalized and the directivity increased. If desired, the element pattern can closely approximate a cos \theta pattern in both planes. A 14-dB reduction in interelement mutual coupling is also achievable with this source as compared to a slot alone. A comparison of the characteristics of a four-quadrant 60-slot monopulse array with and without the wire elements indicates a 0.6-dB increase in gain and a significant reduction in back radiation for the former.

Optimum element spacings for Yagi-Uda arrays

Abstract: A method is developed for the maximization of the forward gain of a Yagi-Uda array by adjusting the interelement spacings. The effects of a finite dipole radius and the mutual coupling between the elements are taken into consideration. Currents in the array elements are approximated by three-term expansions with complex coefficients which convert the governing integral equations into simultaneous algebraic equations. The array gain is maximized by the repeated application of a perturbation procedure which converges rapidly to yield a set of optimum, generally unequal, element spacings. This method eliminates the need for a haphazard trial-and-error approach or for interpreting a vast data collection. Illustrative examples are given.

A portable coaxial collinear antenna

Abstract: A novel collinear antenna constructed of coaxial cable with inner- and outer-conductors interchanged at half-wavelength intervals is described. A 26-element antenna of this type has been constructed and evaluated. Design criteria presented allow extension to the use of coaxial cable of different types in a variety of radio/radar arrays.

An experimental study of a balun-fed open-sleeve dipole in front of a metallic reflector

Abstract: The characteristics of a balun-fed open-sleeve dipole mounted in front of a metallic reflector for operation in the 225 to 409 MHz band are investigated. A parametric study is made of the VSWR response as a function of dipole and sleeve diameter, sleeve length, and sleeve-to-dipole spacing. It is shown that an open-sleeve dipole can be operated over a bandwidth of 1.8:1 as compared with an operating bandwidth of approximately 1.25:1 for a conventional cylindrical dipole with the same diameter. Pattern and gain data are presented for an open-sleeve dipole mounted in front of a flat metallic reflector. Preliminary results on mutual coupling effects are also discussed.

Telescope-Performance Reciprocity for Propagation in a Turbulent Medium

Abstract: : The authors demonstrate that, with the effects of atmospheric turbulence included, reciprocity exists between the performance of a telescope (i.e., an antenna) when it functions as part of an optical heterodyne receiver and its performance when it functions as part of a laser transmitter. For a given optical antenna operating through atmospheric turbulence to some distant point, the effect of atmospheric turbulence upon antenna gain is the same whether the antenna is used as part of a laser transmitter, of an optical heterodyne receiver, or of an image-forming device. It follows that, if the same antenna is used in two or more ways simultaneously, e.g., as a transmitter and as an imaging device, measurements of the performance in one role may be used to gauge the concurrent performance in the other role. (Author)

Formulation of echelon dipole mutual impedance for computer

Abstract: A concise formula suitable for computer calculations is given for mutual impedance of two dipoles with sinusoidal current in echelon. It is a rearrangement of that of King [2].

The Toeplitz matrix: Its occurrence in antenna problems and a rapid inversion algorithm

Abstract: A special form of the Toeplitz matrix which frequently occurs in the numerical solution of antenna analysis and synthesis problems is discussed. Specific examples are presented illustrating its occurrence in the solution of the integral equation for a thin cylindrical antenna and in the theory of arrays. A matrix inversion algorithm is presented which, by exploiting the unique symmetry properties of the Toeplitz matrix, specifies the inverse matrix elements in terms of recurrence relationships. In this way computational time is proportional to the square of the matrix order rather than the cube as is the case with a general algorithm.

Surveillance system and method utilizing both electrostatic and electromagnetic fields

Abstract: A microwave signal generator projects an electromagnetic wave into a space under surveillance to establish a first field. A pulse or frequency modulated low frequency generator is used to apply a voltage to a discontinuous conductor for establishing a second field, electrostatic in nature, throughout the space. Presence in the space of a miniature passive electromagnetic wave receptor-reradiator in the form of a semiconductive diode connected to a dipole antenna causes the reradiation of the low frequency component modulated on the microwave component as a carrier. The front end of a receiver system is tuned to the microwave frequency and feeds a suitable detector circuit responsive to the low frequency signal. A coincidence circuit energizes an alarm circuit whenever the detected signal coincides with the original modulation envelope being applied to the low frequency generator.

The extended boundary condition solution of the dipole antenna of revolution

Abstract: By applying Waterman's extended boundary condition a general formulation is developed for the dipole antenna of revolution. Both transmission and scattering from the antenna are considered with no formal restrictions on the antenna dimensions. As examples, the prolate-spheroidal and solid-cylindrical geometries are considered.

Radiation from an Axial Slot Antenna Coated with a Homogeneous Material

Abstract: Radiation from a slotted-cylinder antenna coated with a homogeneous material is investigated. It is found that for some values of the coating thickness certain modes may resonate, which greatly enhance the radiated power and affect the shape of the radiation patterns.

Mutual coupling effects in semi-infinite arrays

Abstract: An analysis of mutual coupling effects in linear and planar uniformly spaced semi-infinite arrays is presented. The currents under arbitrary excitations at the array ports are obtained by solving an infinite order difference equation with the aid of an extension of the Wiener-Hopf factorization procedure to finite Fourier transforms. The solution for mutual coupling coefficients as well as for the active reflection coefficients in a phased semi-infinite array is expressed explicitly in terms of the active impedance in a phased infinite array. The analytical results are directly applicable to the evaluation of "edge effects" in large phased arrays. Numerical results for active reflection coefficients and element patterns are presented for a semi-infinite array of slots in a perfectly conducting ground plane and for a linear dipole array.

Nonlinear Sheath Admittance, Currents, and Charges Associated With High Peak Voltage Drive on a VLF/ELF Dipole Antenna Moving in the Ionosphere

Abstract: We consider a bare antenna consisting of two line elements driven by a VLF source and immersed in the ionosphere. Nonlinear effects associated with high voltages up to 1000 volts and with an additional induced v×B·1 voltage are included. The applied voltage is visualized as a dc effect. For various instantaneous voltage values, we obtain the distribution along the antenna of voltage and resis'ive current, sheath size, and charge per unit length. At the feed points, waveforms for the charge and both resistive and displacement currents are illustrated, assuming an applied cosine voltage form. Averaging over a cycle yields, as a function of peak bias voltage, the average power dissipated in collection of particles from the medium, the average work done in moving charge between the two half-antennas, and the average sheath conductance and capacitance. Numerical results are given for three altitudes and two antenna lengths.

Dielectric-loaded horn antenna

Abstract: A wide-band dual-mode horn, which has a rotationally symmetric beam and extremely low sidelobe levels, can be obtained by loading a dielectric band inside the horn antenna. Measured radiation characteristics of such antennas, including the so-called shaped-beam antenna, are shown.

Dipole antenna array

Abstract: An antenna array is disclosed for generating and directing a narrow beam or beacon of wave energy along a predetermined path. Illustratively, the antenna array includes a plurality of dipole elements disposed upon a substantially flat support member and connected by a distribution circuit through a single transition to an axial input cable. Significantly, the distribution circuit takes the form of an insulating member upon either side of which are disposed electrically conductive elements for establishing across the dielectric member a balanced conduit for the passage of high frequency signals (or waves) to each of the dipole elements. Further, the distribution circuit serves to divide and to appropriately distribute the input signal to each of the dipole elements of the array. A shell housing is disposed about the distribution circuit to provide in combination with the plurality of dipole elements an effective shielding therefore and also to provide a reflective surface to appropriately direct the discrete wave generated by each of the dipole elements.

On designing a supersynthesis antenna array

Abstract: An analytical approach to the design of a super-synthesis antenna array is applied in this paper. It involves isolation and separate optimization of the influence of different parameters on the sampling of the spatial frequency components. The approach requires a detailed understanding of the geometry of tracking by an ensemble of baselines, but it gives a nearly optimum array design without much help from a computer. A feature of this design is that by simply doubling the array elements, the synthesized main beam area of the array is reduced 16 fold. Extensive computations have been used to demonstrate this extraordinary result.

Phase optimization of antenna array gain with constrained amplitude excitation

Abstract: The formulation of antenna array optimization with variable phase and constant amplitude excitation is presented. The method shown using steepest ascents is general in that a nonlinear performance index expressible as a ratio of Hermitian quadratic forms can be optimized. Directive gain optimization of a linear array of isotropic elements is illustrated and compared with gain optimization using variable excitation. Endfire gain is emphasized and compared to the Hansen-Woodyard condition showing that the Hansen-Woodyard condition is not optimum in the directive gain sense for a discrete endfire array. In addition a 0.4\lambda spaced linear array is optimized using phase only for scanning from endfire to broadside.

Direction finder antenna and system

Abstract: Unambiguous 360° high frequency direction finding is achieved by the use of an energy receiving antenna having two orthogonally mounted vertically oriented, loop antennas, a monopole antenna and a horizontally oriented loop antenna. Signals from the two orthogonally mounted loop antennas contain bearing information for processing in a phase comparison system. The monopole antenna signal provides for elimination of any ambiguity in the bearing information signal as received from the two orthogonally mounted loop antennas. Sensing the polarization of the energy waves at the receiving antennas is provided by comparison of the horizontal loop antenna signal with the resultant signal obtained by the quadrature summation of the signal from the two vertical loop antennas. A bearing indication from the two orthogonally mounted loop antennas is generated by phase shifting one of the antenna signals. This phase shifted signal is combined with the second loop antenna signal in both a summing network and a difference network. A phase detector coupled to the summing network and the difference network provides a signal representing a multiple of the bearing angle between the emitting source and the receiving antenna. The ambiguity in this multiple of the bearing angle is removed by coupling a phase detector to the summing network and the monopole antenna. The output of this second phase detector is combined with the output of the first phase detector in an ambiguity resolver to produce a true bearing angle.

Airborne multi-mode radiating and receiving system

Abstract: An improved directional antenna for use in an airborne vehicle is shown. The contemplated antenna includes a planar phased array of antenna elements mechanically rotatable about an axis of rotation, the plane of such array making an acute angle with such axis. The beam from such array may be electronically scanned, within wide limits, regardless of the orientation of the phased array. Also shown is an improved constrained centerfeed for the antenna elements in each row thereof in such array, the disclosed feed incorporating a double ladder arrangement, including wideband couplers, to permit the extensive use of stripline and at the same time to allow practically independent adjustment of azimuth and elevation difference patterns when the phased array is used as an element in a monopulse system.

The radiation efficiency of a dipole antenna located above an imperfectly conducting ground

Abstract: The dyadic Green's function technique is used to develop integral expressions for the radiation efficiency of three types of dipole antennas located above an imperfectly conducting, infinite ground plane. The three antennas treated are: 1) vertical Hertzian dipole, 2) horizontal Hertzian dipole, and 3) a vertical half-wave dipole with sinusoidal current distribution. The results of numerical evaluation of the integral expressions for several values of ground constants are presented in graphical form. The radiation efficiency of a vertical Hertzian dipole is found to exhibit a distinct peak when located at a height of one-eighth wavelength.

Excitation of a Coaxial Line Through a Transverse Slot

Abstract: A rocket with removed access plate is simulated by a section of coaxial transmission line with a transverse elliptical slot cut in its sheath. The internal circuit consists of two arbitrary impedances in series with the inner conductor at its ends. The object is to find the currents in these impedances when the cylinder is illuminated from the outside by an electromagneticfield that enters the aperture and excites the internal circuit. The problem is solved by application of the reciprocal theorem. The current in a dipole antenna is determined when this is inthe far field maintained by the slotted coaxial line when driven by a generator in series with one of the load impedances. The field in the aperture is replaced by equivalent electric and magnetic dipoles. The reciprocal theorem gives the current in the load impedance when the distantdipole is driven. A numerical example is given.

Broadband plane antenna with log-periodic reflectors

Abstract: A broadband unidirectional linear or circularly polarized plane antenna with or without reflecting cavity is constructed with a plurality of log-periodically related reflecting rings or bands stacked behind the antenna elements symmetrically of the antenna axis. The conductive rings reflect backwardly directed radiation and comprise the exposed peripheral portions of a series of stacked plates, the dimensions and spacings of which increase progressively in increments of a predetermined ratio from a minimum adjacent the antenna elements to a maximum remote from the elements. In order to prevent the formation of an electromagnetic field in the spaces between axially aligned portions of the plates, field arresting material is located in these spaces.

Turnstile slot antenna

Abstract: A novel turnstile slot antenna is disclosed, the antenna being for and integral with a spacecraft having a substantially cylindrical body portion. The antenna comprises a circumferential slot about the periphery of the spacecraft body portion with an annular wave guide cavity defining a radial transmission line disposed within the spacecraft body portion behind and in communication with the circumferential slot. Feed stubs and associated transmission apparatus are provided to excite the annular cavity in quadrature phase such that an omnidirectional, circularly polarized, rotating radiation pattern is generated. The antenna of the instant invention has utility both as a transmitting and receiving device, and ensures continuous telemetry and command coverage with the spacecraft.

Method and apparatus for sidelobe reduction in radar

Abstract: In a system for reducing sidelobes in adaptive receiving array antennas, an auxiliary signal is radiated through an omnidirectional antenna collocated with the phase center of an adaptive array antenna. The auxiliary signal is so transmited as to form a probe or pilot beam with a notch in the main-beam direction by transmitting through both the omnidirectional and the array antenna simultaneously. The relative phases of both antennas are controlled to obtain near-zero radiation in the main-beam direction. Adaptive control loops receive returns from the probe beam and adjust the weights of the receiving array antenna. The receiving array weights are used to form a low sidelobe antenna pattern for reception of the main radar signal, which is transmitted with a directional pattern. Either time or frequency separation may be used to distinguish the probe beam from the main beam.

Travelling wave chain antenna

Abstract: A travelling wave chain antenna including a ground plane, having a radiation beam, the direction of which can be varied by altering the frequency, wherein the antenna consists of four-sided links made of conducting material and of connection parts between the links, these being located one after another, either in a straight row, in such a manner that the connection parts are at right angles to the longer sides of the links, or in an oblique row, in such a manner that the connection parts are at an angle to the longer sides of the links, the center points of the longer sides of the links being electrically connected to the center point of the longer side of the following link by means of the connection parts which are parallel to the shorter sides of the links, and the antenna being fed from either end by means of a cable, in such a manner that one conductor is connected to one end of the chain structure of the antenna and the other conductor is connected to the ground plane, the end of the antenna opposite the feed point being either open or loaded with a load impedance connected between the end of the antenna and the ground plane.

Magnetic antenna with time variations of core permeability

Abstract: An antenna system using a magnetic core provided with coils wound thereon such as to cause time variations of the permeability of the core itself is disclosed. With the time variations of the core permeability the inductances of the antenna coil and output coil wound on the core is changed for parametric amplification of the reception signal to obtain amplified antenna output. Also, by using a plurality of such antenna systems an array antenna having desired and controllable directional characteristics are obtained.

Towards faithful radio transmission of very wide bandwidth signals

Abstract: The necessary characteristics are derived for an antenna system which is to transmit efficiently and faithfully a very wide bandwidth (of an octave or more) signal. It is demonstrated that a suitable antenna for such a system may radiate isotropically in azimuth but be focused in all vertical planes. It is shown that a phase-corrected conical monopole is a convenient approximate realization of the antenna. Results are presented of an experimental investigation (inferring frequency responses from nanosecond time-domain-reflectometer techniques) of the driving-point and far-field responses of conical monopoles phase-corrected with cylindrically symmetrical lenses. Included is an experimental verification of previous theoretical predictions of the frequency dependence of the radiation which occurs when a transient is radiated from the base and the tip of a thin cylindrical monopole.