Showing papers on "Slot antenna published in 1991"

Improved coupling for aperture coupled microstrip antennas

Abstract: An aperture shape that gives significantly improved coupling for an aperture coupled microstrip antenna is described. This ‘dogbone’ aperture consists of the usual rectangular slot, augmented with loading slots at each end. Measured data show an increase of more than three for the resonant input impedance of an antenna using the dogbone-shaped aperture, as compared with the input impedance of the same antenna with a rectangular slot of the same overall length. The field distributions of both slots are also measured, and compared.

A slot design for uniform aperture field distribution in single-layered radial line slot antennas

Abstract: A single-layered radial line slot antenna (RLSA) is proposed for a direct broadcast from a satellite (DBS) subscriber antenna. It utilizes a radially outward-traveling wave and the aperture field is intolerably tapered if the uniform slots are used. Two novel techniques are applied. First, the slot design for uniform aperture field distribution is introduced. Second, the radial line is terminated by a matching spiral, in place of a dummy load. It suppresses reflection and radiates all the residual power in circular polarization. For a model antenna of 600-mm diameter, the efficiency of 65% is observed. >

Serrated-roll edge for microwave antennas

Abstract: The invention presents an optimum method and mean for reducing the side robes of microwave antennas whether mounted or through the serrated-roll treatment of their edges. The reduction of side robes leads to the enhancement of the main robe, the suppression of the unwanted electromagnetic interference, the improvement of antenna performance, as well as lowering the size of antenna.

A dipole antenna for interstitial microwave hyperthermia

Abstract: An improved interstitial microwave antenna design was investigated in static phantom experiments at 915 MHz and different insertion depths. Compared with conventional interstitial antennas, the presented dipole microwave antenna shows heating patterns which are concentrated on the dipole irrespective of the insertion depth. By analogy to interstitial radiotherapy, the microwave antenna allows a high concentration of energy in the target volume with as little damage as possible to the healthy surrounding tissue. The undesired heating of healthy tissue along the feeding line observed with conventional interstitial antennas is avoided. A lambda /4 sleeve on the feeding line (which does not radiate microwave energy itself to the surrounding tissue) transforms an open end, i.e. a high impedance at the generator end of the dipole antenna. The current flowing back along the outside of the outer conductor of the feeding line in the direction of the generator is zero at this point. Both dipole sections have the same terminating impedance. Since the lambda /4 sleeve is mounted outside the antenna, its mechanical length is not restricted by the mechanical length of the antenna. It can be charged with dielectric materials of low dielectricity constants. >

Analysis of a cavity-backed annular slot antenna with one point shorted

Abstract: Analysis of a cavity-backed annular slot antenna with one point shorted is performed experimentally and theoretically. Resonance frequencies, bandwidths, and radiation patterns are studied with respect to slot width, cavity depth, and slot shorting position. In the theoretical analysis, the method of moments is applied to find the magnet current on the slot, and the Green's function for the field inside the cavity has been newly derived. By selecting a slot shorting position, circular polarization, and a bandwidth of more than 10%, the voltage standing-wave ratio (VSWR) >

System for determining direction or attitude using GPS satellite signals

Abstract: For determining spatial orientation based on the carrier phase of signals received from a set of GPS satellites, an antenna array (16) includes a number of antennas (20a, 20b, 20c) coupled to GPS radio receivers (22a, 22b, 22c), a mechanism (28, 30) for reconfiguring the positions of the antennas (20a, 20b, 20c) within the array (16) and a signal processing module (24) for processing the data collected by the antennas (20a, 20b, 20c) and the receivers (22a, 22b, 22c). The mechanism (28, 30) for reconfiguring the antenna array (16) is adapted for exchanging the positions of one pair of antennas (20b, 20c) and for rearranging the antennas (20a, 20b, 20c) from collinear (Fig. 8a, Fig. 8b) into non-collinear patterns (Fig. 8c). Phase measurements are taken by the antennas and their associated receivers, both before and after antenna exchange and after antenna rearrangement in order to provide the data necessary to determine direction or attitude.

Stacked slot-coupled printed antenna

Abstract: An aperture-coupled microstrip stacked patch antenna is studied with the goal of obtaining wide bandwidth, low cross-polarization, and weak parasitic radiation from the feeding aperture for applications in printed phased array antennas. Recently, it has shown that the poor bandwidth of this type of antenna can be increased by coupling the resonant patch to the slot near its resonance. In this case, although the bandwidth is increased drastically, this technique induces a quite high back radiation level, due to the proximity of the resonance of the slot that radiates on both sides of the ground plane. To alleviate this problem, stacked patches were used to achieve the bandwidth. In this case, the resonance of the slot is chosen to be as far as possible from the operating band of the antenna so that its radiation level will be small. The comparison of the calculated and measured impedance loci of C band antenna shows good agreement. >

Meandering long slot leaky-wave waveguide-antennas

Abstract: A theoretical study is made of the aperture field distributions, the far-field amplitude patterns, and the mutual coupling characteristics of several long leaky-wave slot antennas cut on the broadwall of a rectangular waveguide mounted in an infinite ground plane. Straight long slots have high inner sidelobes in the far-field amplitude patterns, which reduces their utility as high-performance antennas. To reduce these sidelobes, a long slot may be meandered from waveguide centerline to sidewall and back to centerline in such a way to produce the desired radiation patterns. Calculated results for antennas of several meander patterns are presented and discussed. >

Sea surface antenna

Abstract: A sea surface antenna comprises a cylindrical tube of metallic material 13 on a dielectric former. The tube has a longitudinal slot shorted at each end and coupled at its midpoint to a coaxial feed. The slot is bridged by two groups of capacitances each group being distributed along a respective half of the slot. The length of the antenna is less than 0.25 λ and the diameter of the antenna is less than 0.02 λ, where λ is the free space wavelength at the operating frequency. The antenna is dimensioned so as to operate in an evanescent mode at a resonant frequency less than the cut-off frequency.

Comparison of six microwave antennas for hyperthermia treatment of cancer: sar results for single antennas and arrays.

Abstract: Interstitial techniques of inserting catheters into tumors for the purpose of applying therapeutic irradiation and hyperthermia are in widespread use. Several miniature microwave antenna designs are currently used for these treatments. These include multisection, hot-tip, 2- and 3-node, dipole and helical antennas, all of which are commercially available. The antenna designs are diverse enough to have a dramatic effect on the power deposition patterns either as single antennas or when used in arrays. Aside from the dipole antenna, most of the antennas have never been evaluated experimentally or theoretically in arrays, although the array configuration is used in the vast majority of all clinical treatments. Power deposition or SAR (specific absorption rate) tests were run in muscle equivalent phantom. Single antennas were evaluated at 400 points in a plane and isoSAR contours drawn, normalized to maximum SAR. Single antennas were also compared in large and small diameter catheters to evaluate catheter dependent antenna performance. The dipole, multisection, hot-tip and helical antennas were evaluated in arrays of four antennas located at the corners of a square, spaced 2.0 cm apart. Arrays of antennas were evaluated at 441 points in three planes orthogonal to the antenna axes. Results in the single antenna studies showed that the dipole was less affected by snugness of catheter fit than the multisection, hot-tip or helical antennas. In large catheters, the latter three antennas showed more extreme tip heating performance. The 2- and 3-node antennas deposited only 20% SAR in the distal 30 mm of antenna length. In arrays, the multisection, hot-tip, and dipole antennas all yielded 80–90% SAR centrally in the central measurement plane. Comparing the three antennas, the dipole array deposited 20% more power centrally in a plane near the insertion point, and the multisection and hot-tip antenna designs deposited 10% more central power in a plane near the antenna tips. The helical antenna array deposited only 30% SAR centrally in the plane near the antenna tips and in the central plane. Only 10% SAR was measured centrally near the insertion point, as expected for tip-heating antennas. Finally, the clinical significance of the results is discussed as applied to human tumors undergoing hyperthermia treatments.

A slot antenna with electronically tunable length

Abstract: The authors describe a 1 lambda slot antenna with a layered structure loaded with two 1-port reactive FET components electromagnetically. By changing bias voltages, the reactance of the FETs varies and the length of the slot is tuned electronically. The resonant points of S/sub 11/ measurements were shifted over a range of 1 GHz around 10 GHz. The antenna patterns are essentially unchanged in spite of this electronic tuning. >

On the use of metallized cavities backing microstrip antennas

Abstract: A cavity-backed patch phased array is proposed. The antenna configuration has some extra degrees of freedom not found in conventional microstrip patch antennas. These include the cavity dimensions and the slot size. It may be possible to exploit these features in order to further increase the bandwidth (e.g. by double-tuning) or to decrease the antenna mode scattering. The integral equation approach is used to analyze the structure considered. Through the use of the equivalence principle, solution of the problem is facilitated by dividing the analysis into two distinct (but coupled) problems: one for the cavity region below the ground plane, and one for the half-space above the ground plane. The input impedance and radar cross section of cavity-backed patch antennas have been investigated in both single-element and infinite phased-array environments. >

Slot hyperfrequency antenna with a structure of small thickness

Abstract: An antenna having a "suspended stripline" structure with two metal plates encircling a dielectric film is disclosed. In this structure, a channel is made for a feeder of a slot with the end of a central conductor of the line penetrating a cavity whose thickness is approximately equal to that of the channel. The slot is made in the upper wall of the cavity.

Integrated antenna/mixer for the microwave and millimetric wavebands

Abstract: A microwave/millimetric receiver of the kind in which a dielectric lens focusses incoming radiation on to an integrated antenna/mixer supported by a dielectric substrate. In one embodiment the antenna/mixer comprises a slot antenna and diode means coupled thereto for mixing the received signal with a local oscillator signal to form an IF signal. The local oscillator signal may be irradiated on to the antenna/mixer to be picked up by a crossed slot antenna or the local oscillator signal may be directly injected into the antenna/mixer circuit say via a microstrip line. In an alternative embodiment, the slot antenna is replaced by a dipole and a local oscillator signal is directly injected into the antenna/mixer via a coplanar line.

Asymmetrically flared notch radiator

Abstract: An asymmetrical notch radiating element comprising a metal or metal-clad dielectric substrate into which a tapered slot or notch is disposed. The direction of the axis of the tapered slot lies along any preselected axis and is not constrained to be collinear with the normal to the aperture of the element. An asymmetrical antenna array comprises a plurality of asymmetrical notch radiating elements as described above. Each of the plurality of radiating elements is disposed such that the apertures of each of the elements are substantially coplanar and are at an angle relative to the notch axis. The present antenna uses asymmetric slot lines to control the antenna's electrical performance. The precise slot dimensions are chosen to optimize radiation and reduce scattering. The asymmetric flared notch allows optimization of the transmit gain in a direction that is not necessarily normal to the array surface. The asymmetrical notch radiator is designed for use in phased array antennas where reduced radar cross section and wide bandwidth are essential, or in conformal arrays, where the surface normal and array axis are not collinear. The normally high specular radar reflection from the antenna radiators, that lies along the array normal, no longer points in the same direction as the peak antenna gain. This allows the design of a low radar cross section array antenna that does not suffer poor gain due to its reduced cross section.

Vehicular slot antenna system

Abstract: To provide for ominidirectional reception/transmission of slot antennas installed on a vehicle, a plurality of slot antenna units (12, 13, 13a, 14) are installed on the vehicle, facing, for example, forwardly, rearwardly and laterally of the vehicle. Each of the slot antenna units is connected to a common feed point (28) which is coupled to a radio equipment, which may be a transmitter or receiver, by a connecting cable which has a length of n.λ/2, wherein n is a whole integer and λ is the average operating wave length for which the antenna is designed. For about 500 MHz, an antenna length of about 55 cm with a slot length of 35 cm and a width of about 7 mm is suitable. The antenna can be formed in U shape and function as a license plate holder for, for example, a license plate made of insulating material. The antenna units are insulated from the body of the vehicle.

Single-layered radial line slot antenna

Abstract: An inner-feed-type planar antenna of single-layered structure excited by an axially symmetric mode for propagating radio waves from the center toward the outer periphery within a propagation layer having an antenna surface. If the planar antenna is used for transmission, it is provided with a plurality of coupling slots formed and arrayed in one surface of an axially symmetric mode waveguide member in such a manner that the coupling factor of the external radiation is high at the outer periphery and becomes successively lower as the center is approached. A spiral or ring-shaped terminating slot is provided in the antenna surface at the outer portion of the axially symmetric mode waveguide member. A region not coupled with the outer portion is provided at the center of the antenna surface. Furthermore, the planar antenna is provided with a reflector member arranged along the terminating slot for reflecting a propagating radio wave between the inner and outer portions of the axially symmetric mode waveguide member. A comparatively flat aperture distribution in which the electromagnetic field is uniform can be obtained. In addition, by providing the central portion with a non-radiating region, long-line effect is suppressed and bandwidth enlarged.

Method of selecting the most suitable receiver antenna from two or more receiver antennas

Abstract: The invention relates to the selection of an antenna in a receiver of a mobile radio station which forms part of a time-multiplexed radio communication system. The signal strength of each antenna is measured in each time slot which immediately precedes the time slot intended for the station concerned, and the antenna selection is effected in dependence on the measured signal strengths. In order to eliminate the risk of unsuitable antenna selection as a result of momentary falls in signal strength, the signal strength for each antenna is measured on several occasions during the time slot in which the measurements take place. The signal-strength values for each antenna are thereafter combined linearly, so as to form a suitability measurement. The antenna having the highest suitability measurement is selected for the next arriving time slot.

End-loaded crossed-slot radiating elements

Abstract: Three cavity-backed crossed-slot antenna configurations are described that offer simple design, easy frequency tuning, light weight, low loss, and low cost. These antennas are designed for mobile satellite vehicle phased-array applications. The slots in these antennas are end-loaded. The end loading makes the slots effectively longer, and hence reduces their resonant frequency. Therefore, relatively small radiating elements can be achieved for large-angle-scanning phased-array antennas. These antennas have good RF characteristics and provide a relatively wide bandwidth without needing external tuning circuits for impedance matching. Measurements for the return loss and the far-field pattern of these antennas are presented. >

Dual-spiral slot antennas

Abstract: Two types of dual-spiral slot antennas characterised by their simple feed are studied; one is a bidirectional radiation type (Bi-DSS) and the other is a unidirectional type (Uni-DSS). The radiation characteristics of the Bi-DSS are evaluated using the numerically determined magnetic current distribution. It is found that a travelling wave magnetic current distribution becomes dominant for a particular range of slot-arm lengths, contributing to the radiation of a circularly polarised wave. On the basis of the investigation of the Bi-DSS radiation mechanism, the Uni-DSS antenna with a triplate configuration is designed. Formation of a circularly polarised, unidirectional beam is experimentally realised. A 4 × 8 Uni-DSS array antenna with a simple feeding system is constructed, achieving an aperture efficiency of 60% over a frequency range of 11.6 GHz to 12.0 GHz.

Electronically scanned antenna for collision avoidance radar

Abstract: A millimeter wave antenna capable of electronic scanning for automobile collision avoidance radar. The antenna includes a linear ferrite loaded slot array which illuminates a dielectric lens. The antenna system has no moving parts. Beam scanning is achieved by controlling the bias magnetic field along the ferrite rod of the slot array.

Low-profile steerable cardioid antenna

Abstract: A multimode low-profile avionics antenna is disclosed for use in Automatic Direction Finder (ADF) systems. The low profile antenna generates a steerable cardioid radiation pattern having a minimum bandwidth of 30% and an unusual degree of independence from mutual coupling and coupling to ground-plane currents. The antenna includes two resonant cavity-backed slot antennas. The upper cavity, which backs a directional crossed-slot antenna, is the larger of the two cavities. The shallow lower cavity is actually a short-circuited radial transmission line employing a stepped inner radius and band-switching to extend the operating bandwidth to the required 30%. The crossed-slot antenna elements are configured orthogonally and the slot ends are folded over the side of the cylindrical cavity to minimize the resonant cavity diameter for the requisite slot length. The slot width is stepped open at the crossover point to enhance antenna bandwidth and to provide for greater spacing between the symmetrically-located feedpoints. The shallow circumferential slot antenna is equipped with two band-switched inductances for wider bandwidth. The two stacked cavities have a combined height of less than 0.1λ at the operating frequency and are suitable for use as a flush-mounted aircraft or helicopter ADF antenna.

Reduced-confinement GaAlAs tapered waveguide antennas for enhanced far-field beam directionality

Abstract: Reduced-confinement tapered waveguide antennas are shown to produce reductions of >35% in the transverse far-field beam divergence for radiation emitted from GaAlAs slab waveguides, resulting in far-field beams as narrow as 82 degrees full width at half-maximum (FWHM) along the direction perpendicular to the wafer surface Reduced confinement of the guided mode near the output endface is achieved using a novel molecular-beam-epitaxy growth technique to produce a longitudinal reduction in the refractive index and thickness of the waveguide film The reduced-confinement geometry has the distinct advantage over horn antennas of being compatible with two-dimensional antenna development A numerical simulation is used to verify and predict the performance limitations of reduced-confinement antennas Requirements on both the amplitude and phase profiles of the electric field at the antenna output are shown to impose a stringent lower limit on the acceptable taper length for optimal antenna performance >

Theoretical and experimental study of the input impedance of the cylindrical cavity-backed rectangular slot antennas

Abstract: The authors study the input impedance of a cylindrical cavity-backed slot antenna based on mode matching and the complex Poynting theorem. Two cavity-backed slot antennas were fabricated to verify the theory. The numerical results agree very well with measurements. Two resonant frequencies were found from the input impedance. One resonant frequency is attributed to the rectangular slot and the other is due to the cavity. The slot length controls the first resonant frequency and has a much stronger effect on the input impedance at the antenna operating frequency as compared with the cavity length. >

Radiation and scattering analysis of infinite arrays of endfire slot antennas with a ground plane

Abstract: A Green's function moment-method analysis of infinite arrays of endfire slot antennas is described that includes the constant width slot antenna (CWSA) and the linearly tapered slot antenna (LTSA), with a ground plane. The method utilizes an application of equivalence at a plane in front of the array which facilitates the extension of this analysis to antennas printed on protruding dielectric sheets and/or the addition of a radome. Numerical calculations are compared with waveguide simulator experiments for CWSA and LTSA arrays as well as several less complex problem. Relevant numerical considerations and convergence issues are also discussed. >

A two-layer self-diplexing antenna using a circularly polarized ring patch antenna

Abstract: Isolation between the transmitting and receiving antennas due to orthogonal circular polarization has been investigated for a two-layer self-diplexing antenna. The total isolation due to the polarization and the frequency separation was shown to be more than 35 dB by the experiments. The isolation due to the orthogonal circular polarization was more than 22 dB. The isolation can be estimated according to the axial ratio of far-field radiation patterns. The antennas can be used as mobile terminal antennas for satellite communications. >

Array antenna with slot radiators offset by inclination to eliminate grating lobes

Abstract: An antenna (20) is formed of a two-dimensional array of radiating apertures disposed in rows (22) and columns (24), each of the radiating apertures being formed as slots (40) within a top broad wall (28) of a waveguide (26). The width of the broad wall is many times greater than the height of a sidewall (32, 34) of the waveguide, the waveguide having a rectangular cross section. A wave launcher (56) connected to a first end wall (36) of the waveguide launches a higher-order mode of electromagnetic wave wherein the order of the mode is equal to the number of columns of the radiating elements. The top broad wall (28) has an enlarged thickness of approximately one-eighth free-space wavelength. Each of the slots extends via a passage (46) from an input port (48) at an interior surface (52) of the top broad wall to an output port (50) at an exterior surface (54) of the top broad wall. All of the slot output ports are centered at the locations of maximum intensity of electric field. In order to provide for magnetic coupling from an electromagnetic wave within the waveguide to longitudinal sides of each slot, each slot passage is inclined so as to displace the slot input port to a location wherein there is sufficient magnetic field component parallel to the slot to couple power from the wave to be radiated from the antenna. Inclinations of successive ones of the slot passages are staggered for coupling from magnetic wave components of equal polarization and phase.

Design and characteristics of ring-slot type FSS

Abstract: The electrical design and measured characteristics of a newly developed ring-slot type FSS (frequency selective surface) are described. This FSS is a highpass type that transmits the 30 GHz band and reflects the C band. The measured results show low insertion loss and low crosspolarisation characteristics and it is confirmed that this FSS is sufficiently practical as onboard equipment.

Design of high efficiency Fresnel zone plate antennas

Abstract: With a family of ideal radiation patterns, the theory for designing high-efficiency phase-correcting FZP (Fresnel zone plate) antennas is presented. The optimum 3-dB beamwidth of the feed pattern as a function of F/D (focal length/diameter) of the plate, the relation between the phase efficiency of the antenna and the number of subzones used in each full-wave zone, and the total efficiency limits of various versions are given. It is found that the maximum efficiency of a practical FZP antenna is usually less than 70%. The theory has been employed in designing a four-layer experimental FZP reflector antenna, and good agreement between the theoretical expectation and the measured value is obtained. >