Showing papers on "Conformal antenna published in 1995"

Bandwidth study of microstrip reflectarray and a novel phased reflectarray concept

Abstract: A microstrip reflectarray is a flat reflector antenna that can be conformally mounted onto its supporting structure without consuming a significant amount of real estate and without adding significant mass. The article concentrates on the bandwidth study of a form of reflectarray that uses identical patches with different-length transmission delay lines attached to compensate for the spatial phase delays. This antenna suffers from one major shortcoming, its limited bandwidth. A new concept of mechanically phased reflectarray is also presented.

Photonic wideband array antennas

Abstract: Presents an introduction to the optical control of array antennas by using fiber optic links for remote control and a photonic time shift network for wide instantaneous bandwidth. An overview of the development of a wideband conformal array designed for airborne surveillance radars is given. The paper covers the system design and the performance of an L-band (850-1400 MHz) M-element array controlled by photonics. Packaging techniques of the photonic components and the array aperture are discussed. The wideband performance of the system is highlighted. A nano-second impulse response has been measured to demonstrate a 50% instantaneous bandwidth (550 MHz, 30 cm range resolution) for target ID and imaging. A built-in signal injection technique based on time-domain impulse measurement was used to calibrate the wideband components in the time-shift beamforming network. >

Double C-patch antennas having different aperture shapes

Abstract: Double C-patch antennas having different aperture shapes are experimentally investigated and reported. The effect of different design parameters on the performance of the antenna is studied and presented. The advantages of such antennas over the conventional rectangular microstrip antennas are explained.

Method and apparatus for beam steering and bessel shading of conformal array

Abstract: This invention describes a methodology to image features using an array of multiple piezo-electric elements which employs the selective use of mechanical and electronic beam focusing, electronic beam steering and amplitude shading to increase resolution and overcome side lobe effects. This invention introduces a novel signal reconstruction technique utilizing independent array element transmission and reception, creating focusing and beam steering. Application of the methodology can be used in wireline, measurement while drilling, pipe and pipeline and medical applications. Applications include, but are not limited to Bore hole Caliper, Bore hole Geometry, Bore hole Imaging, Casing Inspection, Cement Evaluation and Volumetric Scanning Applications (e.g. Fluid, Behind Casing and Open Hole). The configuration of the transducer array is preferably cylindrical, but may be conical, biconical, convex, concave or may take the form of a number of suitable geometric configurations. The transducer array may incorporate a transformer block having an array of multiple transformers therein for connection to individual transducer circuits. The transformers may be fixed or capable of being mechanically tuned as desired.

A dielectric-loaded miniature antenna for microcellular and personal communications

Abstract: The barium titratitanate is used as a substrate for two microstrip antennas designed on 900 MHz and 1800 MHz bands, respectively The objective is to study the feasibility of miniaturization of the antennas used for microcellular and personal communications The resonant frequencies, input impedances, and VSWR have been measured to assess the achieved performance of this type of antenna

Radiation by cavity-backed antennas on a circular cylinder

Abstract: Conformal antenna arrays are popular for deployment on curved aircraft, spacecraft and land-vehicle platforms because of their inherent low weight, cost and drag properties. The finite element-boundary integral method is extended to radiation by cavity-backed structures recessed in an infinite, metallic cylinder. The accuracy of the developed FE-BI code for a microstrip patch array is established by comparison with measurements. The formulation is then used to investigate the effect of the finite aperture on the radiation pattern. In addition, the effect of curvature on resonant frequency, gain, input impedance and pattern shape is examined.

Radio apparatus having a plurality of antennas

Abstract: A radio apparatus according to the present invention comprises a plurality of antennas to be selectively connected to a radio circuit, switches capable of grounding a maximum point in the current distribution of a standing wave of each antenna, and a circuit for operating a switch of a non-selected antenna of these antennas to be grounded. The present invention also includes an antenna switching circuit for synchronizing each switch to selectively perform switching operation. In such an arrangement, one of a plurality of antennas is selected to be connected to the radio circuit, and an intermediate terminal of the selected antenna is opened to obtain a predetermined current distribution of a standing wave, thereby assuring the normal communication operation. Meanwhile, a point having a maximum value of the current distribution of a standing wave of one or more non-selected antennas is grounded to collapse the impedance thereof, and these antennas are prevented from interfering with the selected antenna, avoiding the affection of these antennas to the selected antenna.

Phase-equivalent interferometer arrays

Abstract: A method is described modifying initially linear or planar interferometer arrays such that the arrays can be placed in conformal installations. The method commences with a conventional linear or planar array design and then using certain techniques and relationships allows for the possibility of antenna placement with materially reduced restrictions. A plurality of phase equivalent antenna locations obeying prescribed relationships are generated. These positions lie on the conformal surface on which the array is to be mounted. This permits an optimal set of antenna positions to be chosen based on operational requirements.

Handbook of Antennas for EMC

Abstract: Part 1 Introduction to antennas: requirements of an antenna for EMC main characteristics of an antenna. Part 2 Basic mathematics for EMC engineers: angles basic trigonometry powers, indices, and logarithms real and complex numbers scalars and vectors Fourier analysis and transforms parameters fundamental units and dimensions. Part 3 Antenna theory: unit vectors scalar and vector fields Maxwell's equations boundary conditions fields due to a radiating dipole power flux density for a plane wave wave impedance for a plane wave radiation resistance far field of antennas. Part 4 Antennas for frequencies below 1 MHz: mechanism of radiation near and far fields of antennas wave impedance difference between receive and transmit antennas small antennas baluns radiation power factor matching antennas effective length and effective height E field antennas H field antennas. Part 5 Antennas for frequencies between 1 MHz and 1 GHz: resonant monopoles discone cavitenna resonant and large dipoles folded dipoles triangular dipoles biconical Yagi-Uda frequency independent (FI) antennas log periodic antenna bilog helical antennas large and resonant loops double-ridged horns. Part 6 Antennas for frequencies above 1 GHz: band theory log spiral archimedes spiral microstrip planar spiral discone antenna double-ridged horns. Part 7 Calibration of antennas: gain calculation of gain antenna correction factor. Part 8 List of acronyms and abbreviations: useful tables and conversion factors.

A wideband dual meander sleeve antenna

Abstract: The rapid growth of the personal communications industry calls for low-profile antennas. These antennas would operate as PCN (personal communication network) handset antennas around 880 MHz and 1900 MHz. Subscribers who travel over service areas employing different frequencies, will therefore, need two separate antennas. If a single, low-profile antenna can be developed for use in both bands that would certainly be an advantage. An attempt was made to develop such an antenna. The meander dual zigzag monopole configuration described by Wong and King (1986) was considered for this purpose.

Near-far effects in adaptive SDMA systems

Abstract: In an adaptive SDMA system users can share the same channel which is made possible by using adaptive array antennas at the base station site and forming multiple independent beams to serve the users. Though the enormous capacity enhancements of this approach are obvious, there are two constraints which limit its performance: 1. Any two users sharing the same channel should be located in different directions and 2. the difference between the received power levels should not be too large. If one of these constraints is violated, the users cannot be separated, i.e. one of the connections is blocked or lost. While the capacity increase of SDMA taking into account the first constraint have been analysed in a previous paper [18], this paper is focused on the implications of the second constraint, which represents a near-far problem similar to those encountered in CDMA systems. To solve the near-far problem, grouping of the mobile users into power classes is suggested. The resulting channel allocation scheme is analysed, and it will be shown that the gain reduction caused by the second constraint will be only marginal in most realistic environments, i.e. still a large capacity gain can be achieved. Fig. 1: Typical scenario for A-SDMA application * This wok has been supported by EU within the RACE project TSUNAMI 0-7803-3002-1/95 $4.00 0 1 995 I E E E 1293

Reconfigurable array antennas with phase-only control of quantized phase shifters

Abstract: In this paper a new synthesis method for electronically controlled, reconfigurable array antennas for future wireless communication systems such as vehicle to roadside communications or cellular telephone systems is presented. Quantized phase shifters can already be taken into account during synthesis. The shape of the main beam as well as the sidelobe level can be reconfigurated with phase-only control of quantized phase shifters. The amplitude of the weighting factors in the antenna beamforming network remains constant resulting in only one antenna beamforming network for several antenna patterns. Results for linear as well as planar array antennas show the efficacy of the new synthesis method.

Conformal antenna for wireless local area network transceivers

Abstract: In a transceiver for a WLAN having a two-part folding housing of electrically insulating material, one part having a shielded compartment for the radio circuitry, there is provided a two-part strip-conductor antenna conforming with the outer surface of the one part of the housing, the radio compartment shielding forming a ground plane for this antenna.

Shaped coverage of elongated cells at millimetrewaves using a dielectric lens antennas

Abstract: A reasonably uniform coverage with significant ground reflection discrimination can be obtained at 60 GHz over an elongated cell like a section of a street a few hundred meters long, or like a long indoor corridor by using a conveniently designed dielectric lens antenna. The lens is fed directly by the waveguide open-end, and its 3D surface is shaped so that the antenna gain ideally compensates the free space attenuation at each direction wihin the cell limits, and falls-off outside this region. This lens antenna was developed in the framework of the European RACE II R2067-MBS project, to equip its Demonstrator. In this communication, the actual yielded coverage in a long indoor corridor and the fading of the received signal are compared with the performances of conventional rectangular horns when used in the same type of cells, showing a significant improvement.

The use of multiple-beam directional antennas in wireless messaging systems

Abstract: The use of narrow beam directional antennas in wireless messaging has the potential of improving the transmission quality, increasing base station capacity, and reducing the number of base stations needed to provide a service for portable radio users. Directional antenna beams increase the protection to cochannel interference. The performance of a three-sector, twelve beam antenna system is compared with an omnidirectional and a conventional three-sector antenna configuration via computer simulation.

Numerical pattern synthesis of difference beams in conformal arrays

Abstract: A numerical pattern synthesis technique for low and shaped sidelobe difference beams is described. The approach is based on adaptive array theory and is a modification of a technique developed for sum beam synthesis. The method has been applied to a conformal array and the results of synthesising low sidelobe (-40 and -50 dB) difference beams are presented.

Adaptive feedback frequency tuning for microstrip patch antennas

Abstract: Antennas for hand-held portable equipment must be lightweight and compact. Microstrip patch antennas meet these requirements and, in addition, their manufacture using printed circuit technology allows easy integration with the transceiver's RF-circuitry. However, the main disadvantage with the low-profile microstrip patch antennas is their inherently narrow input bandwidth. Although, the input bandwidth may not be wide enough to cover all channels for a particular application, the bandwidth is usually perfectly adequate for a single channel requirement. For these applications frequency tunable antennas can be employed. Such antennas, using varactor diodes have been reported with operating bandwidths exceeding 20%. However, the antenna is a part of a system that will be operating in a time-varying environment. This environment may de-tune the feed-antenna match due to temperature changes or coupling and reflections from local objects. An adaptive feedback is introduced that is intended to optimise the feed-antenna match, and therefore act against any change in input impedance of the patch antenna. It is shown that the adaptive feedback gives a good match at any desired frequency inside the operating frequency range of the microstrip patch antenna, when the antenna is subjected to a local disturbance.

Conformal low-profile multifunction antennas

Abstract: The spiral-mode microstrip (SMM) antenna of Wang and Tripp (see IEEE Trans. Ant. Prop., p.332-335, March 1991) has two characteristics which make it uniquely suitable as a multifunction antenna: (1) multioctave frequency bandwidth, (2) radiation pattern diversity. In addition, the SMM antenna is conformable, low-profile, and includes a conducting ground plane; therefore, it can be readily mounted on the surface of an aircraft, missile, or other vehicle. The development of a multifunction SMM antenna for aircraft communications in the 0.2 to 1.6 GHz range is discussed.

Smart skin spiral antenna with chiral absorber

Abstract: Recently there has been considerable interest toward designing 'smart skins' for aircraft. The smart skin is a composite layer which may contain conformal radars, conformal microstrip antennas or spiral antennas for electromagnetic applications. These embedded antennas will give rise to very low radar cross section (RCS) or can be completely 'hidden' to tracking radar. In addition, they can be used to detect, monitor or even jam other unwanted electromagnetic field signatures. This paper is designed to address some technical advances made to reduce the size of spiral antennas using tunable dielectric materials and chiral absorbers. The purpose is to design, develop and fabricate a thin, wideband, conformal spiral antenna architecture that is structurally integrable and which uses advanced Penn State dielectric and absorber materials to achieve wideband ground planes, and together with low RCS. Traditional practice has been to design radome and antenna as separate entities and then resolve any interface problems during an integration phase. A structurally integrable conformal antenna, however, demands that the functional components be highly integrated both conceptually and in practice. Our concept is to use the lower skin of the radome as a substrate on which the radiator can be made using standard photolithography, thick film or LTCC techniques.

Radiation efficiency of conformal microstrip antennas on cylindrical surfaces

Abstract: Conformal antennas play a more and more important role in mobile communication and automotive applications, where antennas have to be integrated on existing curved surfaces like fuselages, wings, bumpers, etc. The paper describes the basic theory used to analyze patch antennas on cylindrical bodies by means of a spectral domain approach. To the knowledge of the authors for the first time a detailed description of the specific behavior of the surface wave poles is given. Differences and relations to the planar case are worked out. A physical explanation is given, which makes it possible to interpret the differences of planar and cylindrical antenna configurations concerning the radiated power, surface waves, and radiation efficiency. It is shown that cylindrical structures in general have better radiation efficiency performance.

Linearity considerations in adaptive antenna array applications

Abstract: The use of adaptive antenna in mobile communications base stations is self-explanatory. It offers the potential of increased spectrum efficiency, extended range of coverage and reduced delay spread. However, one major concern for adaptive antenna system is the non-linearity effects of the RF/IF chain upon digital baseband beamforming network. This contribution investigates these effects on the performance of adaptive antennas and suggests the use of linearised transceiver system to tackle the nonlinearity problem.

Impact of the antenna set-up and arrays on mobile radio systems

Abstract: This paper outlines the impact of the antenna set-up and antenna array configurations on mobile radio system at millimetre-wave frequencies. Simulations in typical indoor environments using directive antennas have shown a significant reduction in the channel time dispersion and in power requirements. Also in a typical city street, specially when some objects (cars, buses, etc.) are present, it gives significant performance improvements when compared with an omnidirectional antenna. The significant reduction of channel time dispersion achieved with directional antennas, associated to the fact that a mobile terminal must be able to communicate in any direction, indicates that the best performance of a broadband system is obtained with either switchable beams or antenna arrays. The propagation channel is modelled with a ray tracing tool that takes into account the propagation environment and the antennas used.

Space Geodesy Techniques: An Experimental and Theoretical Study of Antenna Related Error Sources

Abstract: This thesis presents work associated with antenna related error sources, as well as antenna design, in space geodesy utilizing the techniques of Very-Long-Baseline Interferometry (VLBI) and the Global Positioning System (GPS). Geodetic VLBI uses large radio telescopes, often in global networks observing at least a few times per year. As the number of dedicated antennas for this purpose is limited, also antennas designed for radio astronomical research are used. However, new feed systems are needed to handle the simultaneous dual-frequency observations and the large bandwidth in geodetic VLBI. This thesis describes and numerically evaluates such a feed system. The design has the advantage of not interfering with existing front-end receivers of traditional Cassegrain antennas. In contrast to VLBI antenna systems, GPS antennas have low directivity in order to receive signals from the satellites in different directions simultaneously. The disadvantage with such antennas is the relatively high susceptibility to scattering from structures close to the antenna. Two studies presented in this thesis show that signal scattering from structures associated with the mounting of the antenna to the pillar and with the pillar itself, might be a significant source of error. As nearby structures are in general located below the antenna, scattering from these structures may be minimized using antennas with reduced side- and back-lobe levels. This thesis presents results from a preliminary study of two new designs of such antennas. The Swedish permanent GPS network, SWEPOS, consists of 20 stations distributed across Sweden. One of the scientific motivations for this network is to monitor crustal motions associated with postglacial rebound. This thesis describes SWEPOS, and results from almost 18 months of daily observations are presented and compared to models of postglacial rebound. The results from SWEPOS have also uncovered two major error sources. One of them is the scattering effect mentioned above. The other, which also is investigated in this thesis, is related to snow accumulated on the top of the pillars and on the radomes that covers the antennas. This accumulation appears to refract and delay the GPS signals, and thus degrade the positioning accuracy.

Design and analysis of slot array antennas on a radial feed line

Abstract: Antennas based on narrow slots directly coupled to a radial line have been used previously in direct broadcast satellite (DBS) receivers and reported by Ando (1985, 1990). One of the most important features for such antennas is their low cost and low loss feeding line, making it ideal for DBS (11.7 to 12.5 GHz operation). Most of the designs reported are based on experimental work or at least no systematic design procedure have been shown. This paper shows an easy design procedure based on the analysis of several narrow slots coupled to the line. A final, more accurate analysis can be done for the complete antenna including the coupling effect between slots.

Non-linearity effects on adaptive antennas

Abstract: The effects of nonlinearity on the performance of adaptive array antennas has been presented. The feed forward linearisation technique is identified as the most suitable for mobile communication base station applications. This is because that the large bandwidth requirement and multiple carrier operations at base stations. The effect of using linearised amplifiers in the communications system has also been briefly discussed.

Trends in antenna design over 100 years

Abstract: Antennas are an essential part of every radio system and they have been in use for more than 100 years. The continual growth of radio has steadily increased the types of antennas in use. Hertz used reflector antennas and loops in his classic experiments in the 1880s. Other pioneers, such as Lodge, developed early examples of microwave horns and lenses. The simple monopole wire antenna was crucial to the success of Marconi's first experiments. The indispensable nature of the antenna was recognised even in the early days. This paper surveys the general trends in antenna design over the 100 years of radio. It concentrates on describing early antennas, antennas for mobile communications, antennas for microwave communications and a short review of the methods of antenna design and validation.

Smart electronics and sensors for IVHS and automobile collision warning antenna systems

Abstract: In this paper, the feasibility of using electronically steerable antennas for health monitoring of civil structures and early warning of collapsing bridges to the approaching vehicles is presented. These antennas can also be used in automobile collision warning systems. These antennas are lightweight, low volume, low profile and conformal. They have low fabrication costs and are easily mass produced. They are thin and do not perturb the aerodynamics of a host automobile. Linear, circular, and dual polarization are achieved with simple changes in feed position. Beam steering is accomplished by varying the relative phase between radiating elements. In planar array, both horizontal and vertical beam can be combined to provide full scanning capabilities. Tunable ceramic phase shifters are used in these antennas. The dielectric properties of the ferroelectric material are changed by a bias voltage. In the case of health monitoring of civil structures, these antennas are used in conjunction with ferroelectric sensors. The sensors are fabricated with interdigital transducers printed on a piezoelectric polymer or ceramic type film. They are in turn mounted onto an ultra thin Penn State's novel RF antenna. The wave form measurements may be monitored at a remote location via the antenna in the sensors and the electronically steerable antenna outlined above.

Radiation by aperture antennas of arbitrary shape fed by a covered microstrip line

Abstract: Conformal antenna arrays are widely used in wireless communications. In order to design such arrays precisely a CAD tool which can handle complicated configurations is needed. A printed aperture antennas fed by a covered microstrip line in a triplate structure is an example of such arrays. The mixed potential integral equation (MPIE) CAD tool has been successfully used to investigate the behavior of the arbitrarily-shaped aperture antenna, fed by a covered microstrip line.

Propagation measurements for 1.9 GHz high-gain antenna design

Abstract: This paper addresses the benefits achievable with advanced base station antennas for 1.9 GHz personal communications services (PCS). High-gain antennas, multiple sub-aperture diversity combining, and adaptive array processing are all parts of the advanced antenna concept. A measurement program was carried out in urban and suburban environments to preview the performance achievable with large antennas. Results indicate that very tall narrow antenna subarrays can produce the desired high gain while minimizing the amount of beam-steering and beamforming required.

Pattern shaping for handset antennas

Abstract: Traditional handset designs for personal communications have used simple antennas and it appears that little attempt has been made to shape the radiation pattern in a systematic way. Although diversity designs have been discussed, e.g. by Jensen and Rahmat-Samii (see IEEE Trans. Antennas and Propagation, vol.42, p.1106-1113, 1994), and Ogawa and Uwano (see IEEE Trans. Antennas and Propagation, vol.42, p.1342-1345, 1994), a clear analysis of what constitutes a "good" handset pattern has not yet been made. The authors discuss these questions, suggest a classification for the possible structures, and present some work on modelling and measurements of prototypes for the new generation of systems working around 1.8-2 GHz. >