Showing papers on "Conformal antenna published in 2002"

Broadband dual-polarized aperture-coupled patch antennas with modified H-shaped coupling slots

Abstract: This paper presents a new design of aperture-coupled patch antennas with modified H-shaped coupling slots for achieving dual-polarization radiation with high isolation over a wide bandwidth. By using the proposed coupling slots, whose two upper side arms are bent inward with a proper angle, the isolation between the two feeding ports of the patch antenna can. greatly be improved, compared to the case with conventional H-shaped coupling slots. Also, when using a pair of modified H-shaped coupling slots for each feeding port, the isolation can further be improved; a high degree of isolation ( 20 dB) for the two polarizations can be achieved. Details of the proposed design and experimental results are presented and discussed.

High-strength microwave antenna assemblies and methods of use

Abstract: High-strength microwave antenna assemblies (10) and methods of use are described herein. The microwave antenna has a radiating portion (12) connected by a feedline (14) to a power generating source (28), e.g., a generator. The antenna is a dipole antenna with the distal end of the radiating portion being tapered and terminating at a tip to allow for direct insertion into tissue. The antenna can be used individually or in combination with multiple antennas to create a combined ablation field. When multiple antennas are used, microwave energy can be applied simultaneously to all the antennas or sequentially between the antennas. Furthermore, to facilitate positioning the antennas in or near the tissue to be treated, RF energy may be applied at the tip of the antenna to assist in cutting through the tissue.

Coupling effects of two electric dipoles on an interface

Abstract: [1] Numerical modeling of thin-wire antennas is interesting to people working on antenna design and to people working on the processing and interpretation of radar data. They have different demands regarding the output of the model code. Our primary interest lies with improving image resolution through processing of ground-penetrating radar data. For this goal the effects of two antennas placed close together on the Earth's surface are studied. To study the antenna to antenna coupling and antenna to ground coupling, a model for linear dipoles is used. The model uses a thin-wire approximation for the transmit and receive antennas. The antennas are placed just above the air-Earth interface. The Earth is modeled as a horizontal layer stack. Using this model, we study the coupling effects between two parallel antennas, either in each other's E-plane or H-plane. For ordinary antenna distances, the coupling between two parallel antennas when they are resistively loaded is on the order of −70 dB, which is not negligible for GPR applications. The influence of the lower half-space on antenna behavior is strong but limited to a fraction of the wavelength in depth.

Multiple antenna diversity for wireless LAN applications

Abstract: An antenna system comprising a plurality of antennas designed and oriented to provide one or more of radiation pattern, signal polarization and spatial diversity. The various diversity operational characteristics are achieved by using similar antennas physically oriented to provide the diversity attributes or by using dissimilar antennas, that is, antennas having different radiation pattern and/or signal polarization characteristics.

Field pattern characteristics of GPR antennas

Abstract: Sub-surface radar has become increasingly popular for carrying out completely non-invasive integrity tests on concrete structures. Commercial systems are available with a range of antenna frequencies that may be selected for an investigation. The choice of a particular antenna frequency is often a compromise between the physical size of the antenna and the penetration and resolution capabilities provided by the antenna. However, there is an interaction between a surface contact antenna and the substrate under investigation that will alter the field pattern being transmitted that may have significant implications for interpretation of results. An experimental programme is described in which the characteristics of commercially available 900 MHz and 1 GHz antennas are compared in air and when in contact with concrete and water surfaces, together with an emulsion used in previous studies to simulate the radar properties of concrete. Results are presented showing the influence of the material being measured upon the signal divergence. These effects are considered in terms of the practical implications for field-testing using radar.

Radiation patterns and correlation of closely spaced linear antennas

Abstract: A simple point source analysis is used to prove that, in theory, completely decorrelated reception can be achieved from two linear antennas with an arbitrarily small spacing. The conditions necessary to achieve this are consistent with two high gain (superdirective) beams in opposite directions. It is shown that the horizontal radiation patterns and correlation coefficient of arrays of vertically orientated linear antennas can be found via an exact relation to simple, point-source theory that includes the effects of mutual coupling. This theory leads to practically achievable optimum diversity designs at closer spacings than previously thought possible. The theory is illustrated for a dual antenna configuration and can be extended to multiple antennas.

Filter technique for increasing antenna isolation in portable communication devices

Abstract: Provided is a system and method for reducing the effects of antenna coupling by increasing the isolation between closely mounted antennas on a portable wireless communications device. Increased isolation is achieved by providing a ceramic resonator in the path of each of the antennas. The ceramic resonator placed in the path of a particular antenna reduces the effects of coupling caused by a particular one of the other antennas by rejecting signals associated with the particular antenna.

Array antennas for JPL/NASA Deep Space Network

Abstract: Recently, JPL has begun an assessment of the long-term capability of the antennas for the Deep Space Network (DSN). Various alternative plans for upgrading or replacing the present 70-meter antennas have been considered. Several options have been studied which include modifying the present antennas for extended life and reliability, new 70-meter single aperture antennas with offset or symmetric feeds, 100-meter spherical antennas, an array of a few smaller 34-meter antennas, a much larger array (hundreds) of much smaller (5-10 meter) reflector antennas, and finally active planar phased arrays with millions of elements. In this paper we briefly discuss various options but focus on the feasibility of the phased arrays as a viable option for this application. Of particular concern and consideration will be the cost, reliability, and performance compared to the present 70-meter antenna system. Many alternative phased arrays including planar horizontal arrays, hybrid mechanically/electronically steered arrays, phased array of mechanically steered reflectors, multi-faceted planar arrays, phased array-fed lens antennas, and planar reflect-arrays are compared and their viability is assessed.

Compact WLAN disc antennas

Abstract: A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes.

Low-loss tuning circuits for frequency-tunable small resonant antennas

Abstract: Minimization of power loss in the tuning circuits of frequency-tunable small resonant antennas, such as microstrip patches, is studied. First, the frequency shift and the associated power loss in certain tuning circuits are theoretically calculated based on approximate circuit models of fairly narrowband resonant antennas. By investigating the ratio of frequency shift and loss, an optimal configuration for the tuning circuit can be determined. The theoretical results can be used to provide optimal starting values and design curves that facilitate the final design with a full-wave electromagnetic simulator. To support the theory, a design procedure is demonstrated with two example antenna structures, for which both simulated and measured results are presented.

Shorted spiral-like printed antennas

Abstract: We present two electrically small printed antennas suitable for mobile communication handset terminals. The conductor shapes of the proposed shorted patch antennas maximize the length of the current path for a given area thereby significantly reducing the resonant frequency of the antenna. Reductions in operating frequencies of the order of seven to ten have been achieved.

Low profile dual-band conformal antenna

Abstract: An antenna assembly including a resonator element having a complex shaped surface topography and discrete edge features disposed at various elevations above a ground plane and which is operatively connected to the ground plane of a wireless communication device (WCD). The resonator assembly may comprise a flexible or deformable resonator support substrate of dielectric material supporting a conductive resonator element or portion. Alternatively, the resonator element may comprise a electrically conducting resonator element formed to retain its complex shape and surface topography. In the latter form, the resonator element may be formed by traditional metal stamping techniques. The complex topography of the resonator element, the discrete resonator segments together provide WCD design flexibility by permitting the antenna assembly to be located at a variety of locations relative to a WCD, including the interior, the exterior, or within a portion of the housing of the WCD itself as long as the resonator element is coupled to the ground plane of a printed wiring board of a WCD. The antenna assembly preferably includes a resonator element comprising a complex substantially hemispherical, or a curving, topography and having a complex set of linear peripheral edge features. In addition, the ground terminal location and the signal feed terminal location are not located along an end region of the complex-shaped resonator element as in traditional planar inverted-F antenna (PIFA) types, but are preferably disposed closely spaced apart in a central region of the resonator element.

Efficient models for base station antennas for human exposure assessment

Abstract: Two simple and accurate models for base-station (BS) panel antennas are proposed for human-exposure assessment. Panel antennas comprise an antenna array with low coupling between its unit cells. The proposed model is based on the superposition of shifted radiating field contributions in amplitude and phase of a unit cell of the panel antenna. In the first model, the electric field is obtained via a full wave analysis of the antenna unit cell. In the second model, a far-field approximation of the unit cell is utilized, and is valid at about two wavelengths away from the antenna. It is shown that the second model can be used as an interactive tool for the verification of compliance to exposure limits of BS panel antennas as required by standards.

Conformal array antenna for observation platforms in low Earth orbit

Abstract: A conformal array antenna can provide the flexibility that platforms in low Earth orbit need to download their data to ground stations. It does this by producing multiple beams for various ground stations. Even if only one ground station is used at a time, the higher gain of this antenna, compared to a fixed-beam antenna, allows the ground-station antennas to be down-sized, or, equivalently, the data rate to be increased. Moreover, missions on which disturbances in the platform attitude are critical can take advantage of a phased array with no moving parts. Although the demonstration model was targeted at a low-Earth-orbit mission, the concept is equally applicable to future interplanetary science missions.

Fractal antenna with RF MEMS switches for multiple frequency applications

Abstract: A new concept of combining RF MEMS switches with fractal antennas is presented. The idea is to connect several antenna configurations together using RF MEMS switches to cover several frequency bands. By using a 'smart combination' of fractal shaped antennas, wideband coverage can be achieved for satellite and wireless communications. Moreover, the same antennas can be used for phased array applications as well. The analysis and design principles are discussed and presented. Several examples are shown to demonstrate the proposed concept.

Antenna array apparatus with conformal mounting structure

Abstract: A carrier structure apparatus (300) for mounting conformal antenna elements (300) to a non-planar mounting surface (207) as part of an antenna array (103) of an airborne vehicle (101) or ground-based system also comprising a seeker section (102), fairing and guidance processing system. The carrier structure (300) is a rigid and conductive apparatus that is made to conform to the geometric configuration of both the antenna element (300) as well as the mounting surface (207). The conformal antenna (330) is rigidly mounted to the carrier structure (300), which is in turn removably affixed to the non-planar mounting surface (207). With the carrier structure (300), each antenna element (330) of the array may be individually tested and replaced prior to and after installation in the array (103).

Patch antenna with switchable slots (PASS): reconfigurable design for wireless communications

Abstract: Reconfigurable antennas are becoming popular in antenna engineering because of their capability in frequency agility, bandwidth enhancement, and polarization diversity. Reconfigurable designs have been applied to dipole antennas, slot antennas, and microstrip antennas. Compared to normal designs, they exhibit attractive features of compact structure, similar radiation performance and little co-site interference. This paper presents a novel reconfigurable design: patch antenna with switchable slots (PASS). The PASS concept, various PASS designs, and its applications are discussed.

Four element array of cassegrain reflect or antennas

Abstract: A multi-reflector antenna array capable of simultaneously transmitting and receiving communication signals at Ku-band frequencies is mounted on an exterior surface of an aircraft. The antenna array provides four cassegrain reflector antennas mechanically connected together in a group capable of being simultaneously mechanically scanned. A common support structure fixes the antennas with respect to each other. A drive mechanism and directional azimuth and elevation motors control the position of the array. The aerodynamic drag of the array is minimized using four antennas rather than a single large diameter antenna. Each antenna is positioned on a common horizontal centerline. Two centrally located antennas are positioned between two smaller diameter antennas. The antennas and positioning equipment are both mounted for rotation within a radome. A corporate power combiner/divider is provided to adjust both an amplitude and a phase of each antenna signal.

Optimizing signal strength in-situ using an evolvable antenna system

Abstract: With the rise in wireless data communications, it is increasingly important that antennas be able to deliver the strongest and most consistent signal possible to a receiver. The evolvable antenna system in this paper shows that an evolutionary algorithm and a reconfigurable antenna can be used to optimize received signal strength in "real" surroundings and outperform a conventional antenna.

Electronic device and method of mounting radio antenna

Abstract: An electronic device comprises first and second antennas for a first radio communication scheme that uses a diversity scheme, and a third antenna for a second radio communication scheme arranged between the first and second antennas.

Design and measurement of conformal antennas

Abstract: An increasing number of complex and dedicated antennas in automotive systems, mobile communication and spaceborne and airborne applications require conformal integration. The term conformal antennas stands for antennas which are confined to the surface of the mechanical carrier. In addition to aerodynamical, aesthetic or integration features, conformal antennas can provide special antenna pattern requirement by an appropriate geometrical form. This contribution discusses the advantages and drawbacks of cylindrical and spherical microstrip array antennas in terms of electrical performance and mechanical setup. It further outlines the design of these antennas and shows measured results for aperture coupled microstrip patch arrays on cylindrical and spherical surfaces.

Wireless health monitoring of cracks in structures with MEMS-IDT sensors

Abstract: The integration of MEMS, IDTs (interdigital transducers) and required microelectronics and conformal antennas to realize programmable, robust and low cost passive microsensors suitable for many military structures and systems including aircraft, missiles and munitions is presented in this paper. The technology is currently being applied to the structural health monitoring of critical aircraft components. The approach integrates acoustic emission, strain gauges, MEMS accelerometers, gyroscopes and vibration monitoring devices with signal processing electronics to provide real-time indicators of incipient failure of aircraft components with a known history of catastrophic failure due to fracture. Recently a combination of the need for safety in the air and the desire to control costs is encouraging the use of in-flight monitoring of aircraft components and systems using light-weight, wireless and cost effective microsensors and MEMS. An in-situ Aircraft structural health monitoring (ASHM) system, with sensors embedded in the composite structure or surface-mounted on the structure, would permit the timely detection of damage in aircraft. Micromachining offers the potential for fabricating a range of microsensors and MEMS for structural applications including load, vibration and acoustics characterization and monitoring. Such microsensors are extremely small; they can be embedded into structural materials, can be mass-produced and are therefore potentially cheap. Additionally a range of sensor types can be integrated onto a single chip with built-in electronics and ASIC (Application Specific Integrated Circuit), providing a low power Microsystems. The smart sensors are being developed using the standard microelectronics and micromachining in conjunction with novel Penn State smart electronics or wireless communication systems suitable for condition monitoring of aircraft structures in-flight. A hybrid accelerometer and gyroscope in a single chip suitable for inertial navigation system and other microsensors for health monitoring and condition-based maintenance of structures, drag sensing and control of aircraft, strain and deflection of structures and systems, ice sensing on aircraft, remote temperature and humidity measurement of propellant in munitions, chemical sensing, etc. are discussed.

Archimedean-spiral and log-spiral antenna comparison

Abstract: For several years, ground-penetrating radar (GPR) has been used to search for buried landmines. Most of the evaluation effort on complete detection systems has focused on end-to-end performance metrics (e.g., Pd and Pfa). Here, we focus on the specific performance of one critical component of GPR systems-the antennas. This is the first in a series of papers that will compare the following parameters of many different antennas: (1) the most useful bandwidths, (2) the role of polarization and polarization diversity, (3) spurious coupling effects, and (4) phase-correction considerations. This paper compares four types of Planning Systems, Inc., antennas that were developed for current and past GPR systems. These are a 5.5-in. log-spiral antenna without balun or spiral-arm terminations; 5.75-in. log-spiral antenna with tapered balun and arm termination; 5.5-in. Archimedean-spiral antenna with tapered balun, but without arm terminations; and 5.75-in. Archimedean-spiral antenna with tapered balun and arm terminations. Three main tests were performed to compare the antennas: (1) S11, to show overall matching bandwidth and to reveal discontinuities in the balun-antenna-termination structure; (2) S21, to measure undesired direct-path coupling relative to intended target scattering; and (3) S21, to show direct coupling vs. antenna spacing.

Signal correlations in coupled cell and MIMO antennas

Abstract: Introduction Keeping signal correlation low across antennas is critical for good receive diversity in cell communications, and for creating independent transmission channels in high data rate MIMO (multiple-input multiple-output) techniques. Tools to achieve this are particularly important when trying to pack multiple antennas into small mobile terminals. Analyses of signal correlations for these applications usually neglect mutual antenna coupling. This paper presents precise formulas for the correlation between signals in mutually coupled antennas, for both 2D and 3D diffusive propagation environments. New values of optimal antenna spacing are given, and closely spaced antennas are predicted to work much better than previously expected.

Investigation of properties of electrical-small spherical ceramic antennas

Abstract: The fundamental properties of electrically small material loaded antennas are investigated by analysis of a spherical model. Data for antenna Q, resonance and efficiency demonstrate the new concept of compatible boundary conditions and its implication for practical design, particularly for mobile phones.

Assessment of vehicle-mounted antennas for NVIS applications

Abstract: The special requirements to be met by vehicle-mounted antennas for use in NVIS applications are examined and the performance of both whip and loop antennas assessed. From these results it is apparent that the loop is the preferable configuration and an optimised, loaded loop antenna is presented. The loading is necessary to control the current distribution around the loop and a procedure for determining the value of that capactive loading, using an equivalent transmission line, is presented and evaluated.

Anti-jam performance of small GPS polarimetric arrays

Abstract: Aircraft in an ECM environment require high-performance antenna arrays that are compact in size and easy to manufacture. Modern microstrip antennas are suitable candidates as elements for GPS arrays. It is shown that the small GPS polarimetric array has superior anti-jam capability compared with the conventional array. An N-element SGPA has 2N-2 degrees of freedom. It doubles the degrees of freedom as compared with the conventional array.

Reflectarray with slots of varying length on ground plane

Abstract: This paper presents a reflectanay based on a planar aperture coupled antenna configuration. The required phase shift at each position of the reflectarray surface is obtained by the variation of slot length on the ground plane.

Intruder/escapee detection system

Abstract: A detection system for detecting intruders moving in the vicinity of a defined path comprises a distributed antenna, for example an open transmission line, extending along the path, and an array of discrete antennas extending alongside the distributed antenna and within a predetermined distance therefrom. The discrete antennas and the distributed antenna define a plurality of detection zones. A radio frequency transmitter is connected to each of the discrete antennas, and a complementary receiver in a control unit at a remote location is connected to the distributed antenna. The control unit also controls the transmitters, and the array of antennas to exchange radio frequency energy between the distributed antenna and the discrete antennas and analyzes the energy received from the discrete antennas so as to detect perturbations caused by an intruder moving adjacent said path and adjacent a particular antenna. A plurality of cameras are associated with the plurality of discrete antennas, and coupled to the control means for transmission of video signals thereto. The control means selects for display a signal from a particular camera in dependence upon the detection of a perturbation from an adjacent discrete antenna.

Analysis and Design of Conformal Array Antennas

Abstract: Today there is a great need for communication between people and even between things, using systems onboard e.g. aircraft, cars, ships and satellites. As a consequence, these communications needs r ...