Showing papers on "Slot antenna published in 1972"

Microstrip antennas

Abstract: Microstrip antennas consist of a planar resonant radiating element parallel to, but separated, from a ground plane by a thin dielectric substrate ( t \ll \lambda ). These antennas are very thin and consequently rugged and easy to mount. They may be fed from the back through the ground plane or from the edge by depositing microstrip lines on the dielectric substrate. Several varieties of microstrip antennas are discussed in this paper. Design procedures are given for both linearly and circularly polarized antennas. Measured patterns are presented for antennas from UHF through C band.

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.

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.

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.

A Novel Slots-and-Monopole Antenna with a Steerable Cardioid Pattern

Abstract: The outputs of a vertical monopole and two mutually perpendicular slots in a horizontal plane can be properly combined to yield a steerable cardioid-shaped pattern for vertically polarized waves. The required weighting factors for placing the pattern null in any desired direction are presented in graphical form. The shape and the half-power beamwidth of the steerable pattern are examined. This combination antenna unit offers important advantages in direction finding and other applications, especially at microwave frequencies.

Engineering approach to the design of tapered dielectric-rod and horn antennas

Abstract: The taper profile of optimized dielectric-rod and horn antennas is synthesized as a series of non-interacting planar radiating apertures. The method is semi-empirical, straightforward to apply, enables the dielectric-rod antenna to be satisfactorily optimized and provides a means of evaluating and optimizing a dielectric-horn antenna with variable wall thickness. The optimum profiles are taken as those which smoothly transform the surface-wave power from the launcher to the radiating aperture. The optimization of the dielectric-rod antenna considerably improves the radiation pattern while computations supported by measurements confirm earlier reports that a dielectric-horn can have a higher gain than a metal horn of similar dimension but side-lobe level is seen to be an important issue. Wide flare-angle horns give ideal E-plane patterns at the expense of a high side-lobe level in the H-plane; for small flare angles the dielectric horn gives similar patterns to the tapered rod antenna and thus preserves rotational symmetry. Calculations throughout are restricted to cylindrical geometry but other geometries and variations on the dielectric-horn principles are described. Useful engineering design data have been compiled for both the dielectric-horn and rod antennas and curves are given which determine near-optimum parameters for gains up to about 20 dB which is seen to be a practical operating limit for these surface wave devices. A unified impression of dielectric antennas emerges with the important conclusion that, when optimized, dielectric-rod and horn antennas are in fact competitive with small metal horns for some applications; furthermore the dielectric-horn antenna, used singly or in arrays, is an ideal device for producing a low side-lobe level in the E-plane.

The monopole slot: A small broad-band unidirectional antenna

Abstract: A small radiating structure has been developed which, operating on a large ground plane, maintains stable input impedance and a unidirectional-beam pattern over bandwidths of 10 to 1 or more. Impedance stability and directivity are obtained from this small antenna at the cost of frequency-dependent efficiency. Useable bandwidth, being determined by factors other than impedance match, may therefore exceed that for other small antennas with fixed matching networks.

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.

The effect of the thin-wire approximation and the source gap model on the high-frequency integral equation solution of radiating antennas

Abstract: The effect of using the thin-wire approximation in the integral equation solution of radiating antennas is discussed in this communication. In addition, the effect of having a source region which varies with the number of matching points used for solving the integral equation is considered. It is found that these effects can cause large errors in the solution at high frequencies and may cause appreciable error in the time domain response of the antenna if it is calculated by Fourier inversion.

A dielectric-loaded circular waveguide antenna

Abstract: A highly directive antenna of simple and lightweight structure is designed and tested experimentally. It consists of a dielectric rod with conical hole loading an open-ended circular waveguide. The test has shown that three different radiation patterns can be obtained depending on the depth of penetration of the rod inside the waveguide. Also an improvement on the axial gain can be obtained when the flare angles are smaller than 30\deg . The optimum design consists of a rod of conical flare angle of 7.5\deg which results in an improvement of 5 dB over the unloaded waveguide accompanied with a beamwidth which is half that of the unloaded structure. One practical application of the proposed design is its use as a feeder for parabolic reflectors, the advantage being the sharp nulls on both sides of the main lobe which will result in minimizing edge diffraction.

Acoustic antennas for atmospheric echo sounding

Abstract: The successful utilization of acoustic waves for atmospheric echo sounding requires an efficient antenna, with high on‐axis gain and suppressed sidelobes. Existing microwave antennas and optical searchlights have been adapted for acoustic use, and their performance measured. A conical horn reflector antenna made of fiberglass has given excellent performance at 1–5 kHz after being coated with a viscous damping tar to keep reverberation time short for the reception of weak echoes with minimum delay following the transmission of 20 acoustic watts from the antenna. Septum dampers have been used successfully on parabolic dish antennas. Antenna beam patterns have been measured on an outdoor range, across a canyon, and the results agree closely with predictions from diffraction theory. Absorbing, cylindrical antenna enclosures have been found effective in reducing sidelobe reception by 10 to 20 dB, also in agreement with predictions. Attention to antenna design should provide unimpaired echo sounder operation in...

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.

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.

High-frequency waveguide feed in combination with a short-backfire antenna

Abstract: A high-frequency waveguide feed in combination with a short-backfire antenna having a cavity and multiple reflectors to permit high power handling capabilities and high frequency applications. An open end of a waveguide is used as the primary radiator in the antenna cavity. The waveguide intrudes into the cavity from behind the larger reflector plate. The polarization response of the antenna is determined by the type of waveguide chosen.

Frequency-scanned X-band waveguide array

Abstract: This paper presents the design of an X -band frequency scanned array in RG 52/U waveguide. The radiating elements consist of edge slots machined in the narrow wall of the guide. Experimental results of the measured slot conductances for the feed system and the antenna elements are given for slot spacings of 0.8 in and various slot orientations and depths. Finally, theoretical and experimental radiation patterns are compared for a 400-element planar array.

Radio frequency transmitting apparatus having slotted metallic radio frequency windows

Abstract: A slot antenna or radome having increased bandwidth capability may be made of a metallic sheet which is curved in the case of a radome, or flat in the case of the side of a waveguide, the sheet has a plurality of slots with edges which are beveled toward each other from the outer surface of the sheet, such that the metallic walls of the window are thin and approach the skin depth for the highest frequency of radio frequency waves which are to be transmitted. With longer wavelengths the electromagnetic field penetrates through the thin edge so that the window is effectively larger, thereby providing improved transmittance over a broad bandwidth.

Design and performance of four buried UHF antennas

Abstract: As a result of a 10-month study by the Institute for Telecommunication Sciences, four UHF antennas were designed and fabricated, and their absolute power gains for elevation angles from 1\deg to 45\deg and azimuthal patterns at 5\deg elevation angle were measured with each antenna buried beneath 1 m of refractory concrete. Relative response of the four antennas, placed in solid granite, to a signal transmitted from an aircraft at ranges up to 300 km were recorded. The performance of the best buried antenna was comparable to that of a \lambda/4 monopole fed against a 1\lambda diameter ground plane resting on the ground surface near the buried antenna.

A slot-unipole energy-density mobile antenna

Abstract: Radio signals received by moving vehicles in mountainous regions or in cities with high buildings may exhibit violent amplitude fluctuations because of the existence of standing-wave patterns. An energy-density antenna which samples the electromagnetic energy density has been suggested as a means for combatting this spatial fading phenomenon. A unipole and crossed slots combination with suitable circuitry serves as a novel and convenient energy-density antenna. Using a simple reflecting-plane model, the range of amplitude variation of the receiver output as a function of signal direction is examined.

Signal-to-noise performance of cryogenic electrically small receiving antennas

Abstract: The performance of electrically small antennas in the presence of noise is studied. Signal-to-noise ratios (S/N) are formulated and compared to the ideal case. It is found that cooling can result in a considerable increase of the product (bandwidth) \times (S/N) . Some practical examples are presented.

Radiation from slot antennas on cones

Abstract: Integral representations are given for the radiation field from slots on the surface of a semi-infinite conducting cone. The corresponding normal mode representations for delta function circumferential slots are evaluated numerically for various cone angles, slot positions, and azimuthal variations. Experimentally measured patterns for two finite models are reported and compared with the semi-infinite cone theory. In particular, effects due to finite cone length and finite tip radius are discussed.

Electromagnetic wave receiver

Abstract: Video pulse radio frequency receivers are rendered sensitive to continuous waves by means of an amplitude modulation technique involving coupling between circularly polarized antennas. The circularly polarized antennas incorporate semiconductor diodes as an integral part of the antenna structure. Two circularly polarized antennas with diodes incorporated therein are mounted in tandem with counter rotating faces directed toward a source of linearly polarized electromagnetic wave. One circularly polarized component of the electromagnetic wave excites the first antenna, while the counter rotating component passes through the first antenna and excites the second antenna. The integral diode of the antennas acts respectively as a detector and modulator, with radio frequency coupling being provided by the tandem arrangement which locates the antenna faces of like polarization sense adjacent each other. By arranging a multiple of the pairs of tandem mounted antennas in a distributed pattern, direction finding capabilities are provided.

Wideband dual-slot waveguide array

Abstract: A slotted waveguide array having a unique dual-slot configuration which significantly increases the bandwidth and scanning angle capability of a linear waveguide slot array. The pattern of the array sub-group has a null in the direction at which a grating lobe would normally occur. With the grating lobe suppressed in this manner, slot conductances are stable with frequency. The result is good pattern integrity and high antenna efficiency.

Analysis of antennas on finite circular cylinders with conical or disk end caps

Abstract: The techniques of wedge diffraction and edge currents are applied to compute the radiation patterns of radial monopole and circumferential slot antennas on a finite circular cylinder having conical or disk end caps.

Conical-reflector antennas

Abstract: The mechanical advantages of a singly curved conical reflector are demonstrated by the experimental test of a furlable 1.83 m conical-Gregorian antenna at 16.33 GHz. The measured gain of 47.5 dB corresponds to a net efficiency of over 57 percent. A ray-optics analysis of conical-reflector antennas is presented, and data useful in the design of conical antennas is given. The conical-Gregorian antenna, in which a subreflector is used in conjunction with a conventional horn feed, is considered in detail. A physical-optics analysis of the conical-Gregorian antenna is used to investigate diffraction and other effects, and to analytically confirm the high performance of the antenna. It is concluded that conical antennas are a valuable addition to available antenna-design concepts.

On the relationship between classical and matrix design methods for arrays of wire antennas

Abstract: The H -plane radiation pattern of an array of parallel wires is identical to that of an array of point sources with transformed excitations. It is shown how this result applies with matrix methods for wire antenna analysis and design. Examples are given for pattern synthesis with linear and circular arrays of parallel wires.

Radiation by a dielectric-loaded cylindrical antenna with a wall airgap

Abstract: Previous solutions for the radiation by a cylindrical antenna loaded with a single dielectric layer are extended to the multilayered case. For the sake of convenience, and without any loss of generality, only the 2-layered method of loading is considered by a boundary-value approach. Graphical results are presented to show the effect of the dielectric on the radiation pattern and conductance when the first layer is a thin air gap. It is shown that significant improvement in the pattern may be achieved with critical dimensions of the air gap.With a single or double layer, the dimensions may be selected to produce a broadside pattern similar to that of the unloaded dipole of less than half a wavelength. It is expected that this behaviour will be employed to improve the radiation characteristics when the antenna length is finite, provided that optimisation techniques are employed in designing the critical dimensions.

Radiation resistance of small electric and magnetic antennas in a cold uniaxial plasma

Abstract: A study is made to evaluate the radiation resistance of dipole and loop antennas embedded in a cold, uniaxial plasma. Analytical closed-form expressions for the radiation resistance are derived.

Diffraction coefficients for a slot-excited conical antenna

Abstract: First-order diffraction coefficients for a slot-excited conical antenna are calculated, beginning with integral expressions for the radiation field. Simple formulas based on these coefficients are presented for the radiation patterns that correctly reproduce the interference structure as well as predict the magnitude of the field down to quite low frequencies. Plots of the diffraction coefficients are given for both symmetric and asymmetric excitation of a circumferential slot. Radiation fields are compared with those obtained by summing the exact normal mode series.

An experimental and theoretical study on the circuit properties of a cylindrical antenna in a hot lossy plasma

Abstract: Experimental results on the input impedances and the current distributions of cylindrical antennas of various lengths in a large volume of hot lossy plasma are presented. A relatively simple theory based on an integral equation and a grid antenna model is developed. The theoretical results are in good qualitative agreement with the experiments. The theory is also compared to theories of some other researchers. Because of its simplicity, the present theory may prove useful in practical applications.

Frequency independent non-resonant series fed slot antenna

Abstract: An interferometer antenna comprises upper and lower arrays, each having a non-resonant, terminated, center fed series feed with slot or hole coupling into individual horn radiators non-resonantly spaced somewhat off a half wavelength apart, each half of each array being at an angle other than 180 DEG with the other half. Each half of the upper and lower array is fed with a power divider located near the apex of the array which equally divides the energy between the left and right hand halves of the array. Non-resonant horn spacing and the angular disposition of the array halves provides a beam in the far field along the bisector of the angle between the right and left halves, independent of variations in frequency over useful frequency ranges.