Showing papers on "Radiation pattern published in 1994"

Antenna pattern synthesis: a new general approach

Abstract: The antenna pattern synthesis problem is of the utmost importance in almost every kind of antenna applications. Therefore, a very large number of contributions have appeared on this subject. But virtually all of them deal with simplified versions of the complete synthesis problem, wherein the degrees of freedom available in principle are strongly reduced, and/or idealized design criteria or requirements are considered. In this paper we present a formulation which allows us to overcome this fragmentation of the synthesis problem. A clear and direct description of the performance actually required by the antenna and a representation of the radiating properties of the antenna as a system allows us to formulate the synthesis problem as an intersections finding problem, i.e., to find a common element between a number of sets, each one containing elements fulfilling part of the requirements. This allows a completely general and flexible formulation of the problem, independent of the actual structure of the antenna. Then the practical implementation of this formulation is widely discussed, showing how an efficient solution procedure can be devised. The implications of the well-known ill-conditioning of the synthesis problem are also discussed. In order to show how the approach works and to assess its flexibility and power, a couple of significant examples are included, namely, a phase-only reconfigurable array and a shaped reflector synthesis. These examples are unconventional since no a priori choice of the intensity distribution (for the array case) or of the feed cluster (for the reflector case) is required. The method presented is able to exploit all the available degrees of freedom in order to fulfill the design requirements. >

Integrated antenna system

Abstract: Disclosed herein is a low profile quadrifilar helix antenna system having the non-fed ends of the helix conductor arms shorted to a first ground plane, the ground plane mounted below the helix. The first ground plane is mounted perpendicularly to the central axis of the helix and extends radially outward therefrom to form an effective electromagnetic shield between the helix and adjacent ground planes. The extension of the first ground plane combined with the shorted non-fed ends of the helix arms minimize the influence of placement of the antenna system near adjacent ground conductors on the VSWR performance of the antenna. The conical frustum geometry of the helix conductors is configured to provide a low profile, resonant antenna. An integrated signal conditioning network is mounted within a cavity defined between the first ground plane and a second ground plane below the first ground plane. The conductive elements of the network are thus shielded from influencing the radiation pattern of the antenna system. The perpendicular orientation of the electronics also provides an integrated antenna system having lower overall height. A refractive dielectric dome is provided enclosing the helix and electronics. The dome thickness and dielectric constant are selected to provide increased gain for the antenna system at low elevation angles, i.e. near the horizon.

Antenna array having two dimensional beam steering

Abstract: An array antenna includes a ferrite substrate having a two-dimensional planar array of antenna elements disposed over a first surface thereof and means for applying an external magnetic field having a magnitude and direction which can be varied at least in a plane in which the antenna elements lie. The amplitude and direction of the external magnetic biasing field is varied to control the relative phases between each of the plurality of antenna elements and to steer the direction of a main antenna beam in two dimensions.

Optimization of bow-tie antennas for pulse radiation

Abstract: Resistively loaded bow-tie antennas are considered as radiators for temporally short, broad-bandwidth pulses. Analysis is by the finite-difference time-domain (FDTD) method. The geometrical details of the antenna and the resistive loading along the antenna are chosen to optimize this antenna for pulse radiation. Theoretical results for the reflected voltage in the coaxial feed line and the time-varying radiated electric field are compared throughout with experimental measurements. The optimized, resistive bow-tie antenna is shown to radiate a pulse that more closely resembles that of the excitation than is radiated by a metallic bow tie of comparable size. Issues involving the use of the FDTD method for modeling fully three-dimensional antennas are also discussed. These issues include the use of a simple feed model and the staircasing of the edges of the antenna. >

Human operator coupling effects on radiation characteristics of a portable communication dipole antenna

Abstract: EM coupling effects of a human operator on antenna radiation characteristics, such as the antenna input impedance, radiation patterns, the radiation power (into free space), the power absorbed by the body, the radiation efficiency, etc., of a portable communication dipole antenna were investigated in detail. A realistically shaped 3D man model and an approximate linear dipole antenna were used to model this problem. Coupled integral equations (CIE) and the method of moments (MoM) were employed to numerically solve this antenna-body coupling problem. Numerical examples are presented for the antenna located in front of the head (distance ranging from 5 to 1 cm) or adjacent to the abdomen (0.6 cm distance) at 830 MHz. It is found that, when coupled with the operator body, the antenna input impedance will have significant deviation from those in free space and different positions. Due to the operator body absorption effect, the maximum attenuation of the H-plane antenna gain may reach about 15 dB for the antenna at the head position and 25 dB for the abdomen position, toward the direction of the body side. Also, the antenna radiation efficiency is reduced to the range from 0.72 to 0.29 for the head position and 0.15 for the abdomen position, respectively. Moreover, the cross-polarization field is significant, especially in the E plane of /spl phi/=90/spl deg/. This is important for the antenna RF design and communication link budget consideration of portable radio systems. >

Characterization of fast fading vector channels for multi-antenna communication systems

Abstract: In a wireless communication environment, multipath propagation and mobile user motion result in a dispersive time-varying communication channel. In order to analyze the performance of wireless communication systems, it is necessary to define models which reasonably approximate the time varying impulse response of the radio channel. Many widely accepted scalar channel (single antenna) statistical models have been reported. In order to analyze performance for real time adaptive antenna array techniques, it is necessary to extend existing scalar channel statistical models to the vector channel (multiple antenna) case. The paper develops a statistical, time varying, dispersive, wireless vector channel model which is based on the physical propagation environment. The model is shown to be consistent with the known characteristics of the wireless communication channel. Antenna pattern interference rejection as a function of update rate is presented as an application example for the vector channel model. >

Construction of a slot-coupled planar antenna for dual polarisation

Abstract: A new type of feeding technique for a dual polarisation antenna is presented. The proposed feeding system was experimentally investigated for both a single element antenna and basic planar array antenna. This antenna system demonstrated high performance in both isolation characteristics and radiation patterns.

New stacked microstrip antenna with large bandwidth and high gain

Abstract: A new radiating element is presented, which can provide simultaneously a large bandwidth and high gain. It consists of four identical patches uniformly displayed within a rectangular aperture (2*2) and fed electromagnetically by a driven patch etched on a lower substrate. It is shown that a good coupling with the parasitic patches is obtained, causing a large bandwidth, and the resonance modes of each patch are excited in phase, giving a high gain.

Circularly polarised dielectric resonator antenna

Abstract: A circularly polarised dielectric resonator antenna is reported. The circular polarisation is obtained by exciting the two orthogonal HE/sub 11 delta / modes of a cylindrical ring dielectric resonator in phase-quadrature. Measured results show that the antenna has an axial ratio of less than 3 dB over a beam width of 100 degrees with a minimum value of approximately 0.5 dB in this range. >

Wideband interference suppressor in a phased array radar

Abstract: A phased array radar antenna uses time-steering subarray notch weightings to produce a wideband notch in the direction of interference for Electronic-Counter-Measure (ECM) interference suppression. A predetermined set of subarray notch weightings, each set being identical for each subarray, is stored in controllers each of which is coupled to a plurality of phase shifters and attenuators for feeding radiating elements of the antenna. Interference suppressors operate from a plurality of controllers to produce a subarray pattern having a notch in the direction of interference. Beamformers then combine outputs of all time-steering subarrays in the antenna so as to produce an antenna pattern having a wideband notch in the direction of interference.

Improvement of microstrip patch antenna radiation patterns

Abstract: Microstrip patch antennas typically have radiation patterns containing unwanted sidelobes or local minima caused by surface waves, especially when fabricated on high dielectric-constant substrates. The paper shows that removal of the substrate beneath the patch can greatly improve the pattern. A variation of this technique, compatible with monolithic fabrication, is applied to fabrication of a patch on GaAs and shows similar pattern improvement. >

Antenna Effects on Indoor Obstructed Wireless Channels and a Deterministic Image-Based Wide-Band Propagation Model for In-Building Personal Communication Systems

Abstract: In this paper, the effects of antenna pattern and antenna polarization on indoor obstructed (OBS) wireless channels are investigated experimentally. Our results show that linearly polarized (LP) directional antennas are more effective in combating multipath components than other types of antennas in OBS channels. The measurement results are verified with a deterministic wide-band propagation model based on image theory that takes into account the effects of building geometry, antenna pattern, and antenna polarization. Preliminary prediction results show that the propagation model holds promise for accurate and efficient in-building wireless channel prediction.

An annular slot antenna on a dielectric half-space

Abstract: The radiation properties of both singly and multiply fed annular slot antennas on a dielectric/air interface have been analyzed using Galerkin's method applied in the Hankel transform domain. The validity of our method has been confirmed through comparison with both theoretical and experimental results. The magic slot configuration has also been studied. The polarization diversity of this radiator makes it suitable for implementing a quasioptical balanced mixer. >

Spiral-mode microstrip (SMM) antennas and associated methods for exciting, extracting and multiplexing the various spiral modes

Abstract: A first spiral-mode microstrip (SMM) antenna has an antenna element situated over and spaced from a parallel ground plane. The antenna element is a frequency-independent planar structure having a plurality of spiraling arms extending outwardly in a plane from a central portion, the arms having respective feed points to excite the spiral modes. Of particular significance, a shorting mechanism connects one or more arms to the ground plane element for influencing the shape of the electromagnetic radiation pattern. A second embodiment of the SMM antenna is constructed as the first, but has a center feed and an off-center feed, and further comprises shorting mechanisms situated well within the periphery of the antenna element. A third embodiment of the SMM antenna is constructed similar to the first, but has a concentric gap situated within the arms so that there is, in effect, a first antenna element having a first plurality of arms and a second concentric antenna element having a second plurality of arms. Capacitors, inductors, and electrical/mechanical switches can be included in the shorting mechanism to facilitate multi-mode, multi-function, and/or broadband operations. By recognizing that the SMM antenna is equivalent to a slot antenna or a magnetic current antenna, a super-thin fourth SMM antenna can be constructed and is a fourth embodiment of the present invention. In this super-thin antenna, the distance between the antenna element and the ground plane is less than or equal to 0.03 of the geometric mean wavelength of the operating band.

Coplanar waveguide fed coplanar strip dipole antenna

Abstract: A novel coplanar waveguide fed coplanar strip dipole antenna is presented. Return loss data as well as antenna patterns are shown. The antenna is matched with the use of a novel, wideband balun.

Integrated nanostrip dipole antennas for coherent 30 THz infrared radiation

Abstract: We report on the experimental study of infrared nanostrip dipole antennas which are connected to thin-film nanometer Ni-NiO-Ni diodes. The integrated Ni-NiO-Ni diodes are used to detect 30 THz (≈10 µm) CO2-laser radiation. The diodes are deposited on 385 µm silicon substrates which are covered with a layer of 1.6 µm SiO2 on both sides. We have found that in low-power applications 1.6 µm of SiO2 yields excellent quarter-wave matching layers for wavelengths centered at ⋋0 = 10.8 µm. By this method 79% of the incident CO2-laser radiation is transmitted into the Si substrate compared to 48% without SiO2 layer. The use of SiO2 quarter-wave matching layers considerably improves the efficiency of infrared nanostrip dipole antennas. This has been confirmed by the study of the laser-induced response of the Ni-NiO-Ni diode detectors as a function of the lengthL of the dipole antenna. Thus, we have observed that the laser-induced response strongly increases for shorter antennas and exhibits a distinct maximum atL=2.8 ± 0.3 µm. For the first time, we have investigated the 30 THz radiation patterns of nanostrip dipole antennas of different lengths. On this occasion, we have observed that the radiation pattern changes when the lengthL of the dipole antenna is varied. This observation indicates that antenna currents propagate on the nanostrip dipole antenna.

Multilayer radiating structure of variable directivity

Abstract: The invention relates to antennas, and more particularly to plane or shaped array antennas. The antenna of the invention comprises radiating sources having a multilayer dielectric/conductor structure and a multiplicity of coupled elements distributed over the interfaces between successive dielectric layers, all being fed by a single radiating patch situated at the bottom level of the antenna. The geometrical parameters of the conductive patches and their distribution within the successive layers giving rise to a high degree of flexibility in antenna design, in particular with respect to simultaneously optimizing antenna parameters such as: directivity, bandwidth, efficiency, polarization purity, and symmetry of the radiation pattern. These advantages of the invention stem mainly from the possibility of increasing the radiating aperture of a source without increasing the complexity of passive distributors for distributing the radiated signals. This is obtained by coupling elements together between levels, and by devising shapes that enable the equivalent radiating area to be increased at each successive level.

Planar near-field to far-field transformation using an array of dipole probes

Abstract: A method is presented for computing far-field antenna patterns from measured near-field data measured by an array of planar dipole probes. The method utilizes the near-field data to determine some equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna. These currents are then used to find the far fields. The near-field measurement is carried out by terminating each dipole with 50 /spl Omega/ load impedances and measuring the complex voltages across the loads. An electric field integral equation (EFIE) is developed to relate the measured complex voltages to the equivalent magnetic currents. The mutual coupling between the array of probes and the test antenna modeled by magnetic dipoles is taken into account. The method of moments with Galerkin's type solution procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient-fast Fourier transformation (CG-FFT) method exploiting the block Toeplitz structure of the matrix. Numerical results are presented for several antenna configurations to show the validity of the method. >

A design procedure for classical offset dual reflector antennas with circular apertures

Abstract: A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors. >

The bi-polar planar near-field measurement technique, part I: implementation and measurement comparisons

Abstract: A novel customized bi-polar planar near-field antenna measurement technique is presented as an alternative to the plane-rectangular and plane-polar measurement techniques. The bi-polar near-field scanner incorporates an axially rotating test antenna and a rotating probe-carrying arm to sample the near-field on a data grid consisting of concentric circles and radial arcs. This technique offers a large scan plane size with reduced "real estate" requirements and a simple mechanical implementation resulting in a highly accurate and cost-effective antenna measurement and diagnostic system. Part I of this two-part paper gives an introduction to the bi-polar near-field technique and a description of the unique hardware implementation at the University of California, Los Angeles (UCLA). Measured results are compared with those produced by a far-field range and a plane-rectangular planar near-field range to verify the implementation and validate the method. Excellent agreement was obtained for both the co-polarized and cross-polarized fields. >

Certain considerations in aperture synthesis of ultrawideband/short-pulse radiation

Abstract: The authors consider certain characteristics of the radiation from collimated, ultrawideband short-pulse aperture distributions. It is shown that an efficient radiation must account for the multifrequency nature of the field. Two alternative schemes for wideband aperture synthesis of an impulse-like radiation pattern are examined. The first, entitled the "iso-width aperture", utilizes only temporal shaping of the excitation pulse. In the other, the "iso-diffracting aperture", they suggest source shaping in space-time so that all the frequency components in the field have the same collimation distance. The "iso-diffracting" scheme yields higher directivity and more efficient pulsed radiation. Explicit examples for the pulsed source distribution and for the pulsed radiation patterns are presented, parametrized, and contrasted. >

Non-invasive hyperthermia apparatus including coaxial applicator having a non-invasive radiometric receiving antenna incorporated therein and method of use thereof

Abstract: A coaxial hyperthermia applicator for applying non-invasively electromagnetic energy to a body against which it is placed. The coaxial applicator antenna has formed integrally within it a non-invasive radiometric antenna for receiving thermoelectromagnetic emissions. The coaxial-configured applicator produces a bell-shaped radiation pattern symmetric about the axis of symmetry of the coaxial applicator. Integrating the radiometric antenna within the coaxial applicator produces a single device that performs dual functions. The first function is to transmit non-invasively energy for heating a subcutaneous tumor. The second function is to receive non-invasively thermal electromagnetic radiation from the tumor by which temperature is sensed and fed back to control the output of the coaxial applicator.

FD-TD analysis of Vivaldi flared horn antennas and arrays

Abstract: This paper summarizes a detailed computational study of Vivaldi flared horn antenna designs including single element, double element crossed-pair subarray elements, and linear arrays using the finite-difference time-domain (FD-TD) method. FD-TD, which numerically solves Maxwell's time dependent curl equations, accounts for the complex geometrical and electrical characteristics associated with this antenna design and array implementation. Validations have been made relative to a moment method (MM) model of an electrically large linearly tapered slot antenna. Also, good correlation is shown to exist in the primary features of the antenna patterns between computed and measured data for all cases. This work has achieved a number firsts for the FD-TD methodology. It represents the first "exact" computational model of a single quad Vivaldi slot antenna; the first "exact" computational model of a phased array of Vivaldi quad elements; and the first FD-TD model to demonstrate grating lobes for a phased array antenna of any sort. Lastly, this research represents an extensive study of the largest grid-based antenna models conducted to date. >

Dielectric cover effect on rectangular microstrip antenna array

Abstract: A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Green's function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4/spl times/4 microstrip array is presented to validate the theory. >

Design of planar arrays to obtain efficient footprint patterns with an arbitrary footprint boundary

Abstract: An antenna pattern synthesis technique is presented that permits the design of planar antenna arrays with footprint patterns of a specified boundary. This technique is applicable to planar arrays of a wide variety of grid structures and can produce patterns with controlled ripple and sidelobe levels. The approach involves two steps: the first consists in stretching the pure real-continuous aperture (an extension of circular Taylor distributions, developed by Elliott and Stern [1990]) into a distribution with a boundary that is inversely proportional to the flat-top beamwidth; the second is the minimization of a cost function (the square of the difference between the resulting power pattern and the desired one) using the Fletcher-Powell method. A square footprint, produced by a rectangular grid (obtained by sampling this distribution) with the corner elements appropriately removed, is presented as an illustration of the method. >

Method and apparatus for producing diversity gain of a received signal

Abstract: A receiver (100) that includes an antenna (101) employs a method and apparatus for producing diversity gain of a signal (106) received by the antenna (101), wherein the signal (106) is subject to a time-variant fading condition Upon receiving the signal (106), the receiver (100) determines a signal quality metric of the signal (106) and compares the signal quality metric to a quality threshold When the signal quality metric is below the quality threshold, the receiver (100) orients a predetermined antenna pattern (304) of the antenna (101) to improve the signal quality metric, thereby producing the diversity gain

Magnetically tunable ferrite resonator antenna

Abstract: An experimental investigation of a novel ferrite resonator antenna has been carried out. The ferrite antenna was subjected to a static magnetic bias field, applied in directions parallel and perpendicular to the antenna length. The effects on the resonance frequency of the antenna when subjected to this bias were investigated. A maximum frequency shift of 8% above (parallel bias) or 8% below (perpendicular bias) the unbiased resonance frequency was achieved. >

Method of performing beam compression process on antenna pattern of radar

Abstract: An antenna system comprising two similar radiation antenna elements with a single monopulse feed system is scanned while transmitting in-phase radio waves from the two elements. Reflected radio waves are received by the two elements and fed to a hybrid circuit which in turn produces a sum signal Σ and a difference signal Δ. After detection is performed by a detector, a signal processing unit subtracts the difference signal Δ from the sum signal Σ. In this processing step, the output signal produced by the above subtraction process is actually output only if the receiving pattern waveform associated with the sum signal Σ has an upwardly convex form, that is, its double differential coefficient is negative and further if the receiving pattern waveform associated with the difference signal Δ has a downwardly convex form, that is, its double differential coefficient is positive, whereby an antenna pattern with beam compression is provided.

Comment: New kind of microstrip antenna: the monopolar wire patch antenna

Abstract: The monopole wire patch antenna is described as a new invention. It is, in fact, a member of a well known family of monopole variants, well known and much used in the aircraft antenna industry. Some of the early development work was done by Seeley in the late 1950s. The antenna had also been developed by Willoughby and was the subject of UK patents.

Varactor-diode loaded passive polarisation-agile patch antenna

Abstract: A passive polarisation-agile microstrip patch antenna has been developed. Using independently biased varactor diodes on the patch axes to tune or detune orthogonal modes, it can produce linear polarisation, or left or right hand circular polarisation according to the bias voltages. Crosspolar levels when operated in the linear state, and axial ratios in the circular state can be optimised by fine adjustment of the diode bias.