The conditions for antenna diversity action are investigated. In terms of the fields, a condition is shown to be that the incident field and the far field of the diversity antenna should obey (or nearly obey) an orthogonality relationship. The role of mutual coupling is central, and it is different from that in a conventional array antenna. In terms of antenna parameters, a sufficient condition for diversity action for a certain class of high gain antennas at the mobile, which approximates most practical mobile antennas, is shown to be zero (or low) mutual resistance between elements. This is not the case at the base station, where the condition is necessary only. The mutual resistance condition offers a powerful design tool, and examples of new mobile diversity antennas are discussed along with some existing designs.

Antenna diversity in mobile communications

This paper presents a method for measuring signal backscattering from RFID tags, and for calculating a tag's radar cross section (RCS). We derive a theoretical formula for the RCS of an RFID tag with a minimum-scattering antenna. We describe an experimental measurement technique, which involves using a network analyzer connected to an anechoic chamber with and without the tag. The return loss measured in this way allows us to calculate the backscattered power and to find the tag's RCS. Measurements were performed using an RFID tag operating in the UHF band. To determine whether the tag was turned on, we used an RFID tag tester. The tag's RCS was also calculated theoretically, using electromagnetic simulation software. The theoretical results were found to be in good agreement with experimental data

Theory and measurement of backscattering from RFID tags

Radio-frequency identification (RFID) is a wireless data capturing technique that utilizes radio frequency (RF) waves for automatic identification of objects. RFID relies on RF waves for data transmission between the data carrying device, called the RFID tag, and the interrogator.

Chipless RFID: Bar Code of the Future

Artificial materials, metamaterials and plasmonic media have recently received tremendous attention from the scientific communities, media and the general public, following novel ideas and suggestions for their potential use in a variety of applications such as cloaking. Here we briefly review and highlight some of the available solutions for invisibility and cloaking that employ metamaterials and plasmonic materials at various frequencies. We briefly overview some of the different cloaking mechanisms recently proposed in the literature, such as plasmonic cloaking based on scattering cancelation, coordinate-transformation cloaking and anomalous localized resonances for cloaking, in particular providing some details for scattering-cancelation-based plasmonic cloaking. We mention the main analogies and differences among these various approaches and we discuss some possible ideas for realizations and applications of these results, with particular attention to the physical phenomena involved.

/pdf/plasmonic-and-metamaterial-cloaking-physical-mechanisms-and-1qz4kctf1n.pdf

Plasmonic and Metamaterial Cloaking: Physical Mechanisms and Potentials

A personal navigation system is proposed in the present paper. This system is based on the use of inertial sensors and will be a complement for the Global Positioning System in places where GPS signals are not available. Such places are indoors and outdoors without a clear visibility of the sky (urban canyons, places under dense foliage...). A known initial position is required for this method for it to be able to estimate the trajectory of the pedestrian using inertial sensors attached to the foot. The developed method and the approximations taken into account are explained. Finally, the results of several tests carried out are shown.

http://rua.ua.es/dspace/bitstream/10045/12578/1/JoPha_3_1_05.pdf

Pedestrian tracking using inertial sensors

Antennas with identical radiation patterns can differ in the manner and extent to which they modify an incident wave, i.e., in the way they scatter. This paper enlarges on the work of Dicke [1] on this subject, employing, as he does, a scattering representation based on spherical modes. However, the approach is more physical and includes antennas with nonreciprocal components and with N (local) ports. A canonical minimum-scattering antenna is defined as one which becomes "invisible" when the accessible waveguide terminals are open-circuited. The scattering matrix of such an antenna is shown to be unique once N arbitrary orthogonal radiation patterns have been specified. Neither an impedance nor an admittance matrix for such an antenna exists. It is demonstrated for a large class of antennas terminated by matched receivers that the scattered power is generally greater than the absorbed power, equality being attained for minimum-scattering antennas.

Minimum-scattering antennas

A Van Atta antenna array, which has a major lobe of the reradiated field in a direction retrograde to that of the incident wave for arbitrary directions of incidence, is analyzed in terms of the scattering matrix of the network interconnecting the antennas.

A note on reflector arrays

The uniqueness of the lossless feed network for a multibeam array

This communication reports the results of an experimental investigation of a new log-periodic (LP) antenna. Tbe antenna consists of an LP array of radial waveguides excited by a two-wire transmission line. The antenna exhibits a vertically polarized omnidirWtiOM1 radiation pattern which is essentially constant over the designed bandwidth. Much progress has been made in the development of frequency-independent antennas. The main features of this class of antennas are directional radiation patterns and impedance which are constant over a very m-ide bandwidth. These antennas are generally not capable of omnidirectional operation. Dyson [ 1 ] has shown that a logspiral antenna of the proper configuration would have an approximately Omnidirectional radiation pattern which is circularly polarized. The discone antenna, which does not belong to the log-periodic (LP) class, has an omnidirectional vertically polarized radiation pattern over an approximate 6 to 1 bandwidth [2], [3]. The purpose of this investigation was to determine whether the log-periodic principle could be applied to a structure to give omnidirectional and vertically polarized characteristics over a wider range of fiequencies than is now possible. The basic element chosen for such a structure was a pair of parallel circular disks which are closely spaced compared to the wavelength. Such a basic element, when excited at the center of the plates, operates as a radial waveguide in the lowest E-type mode [4], thus producing the desired far-field radiation patterns. The LP structure is composed of an array of such disks with the diameter of the plates and the spacing between them varying in a log-periodic manner. The elements are alternately connected to a narrow two-wire transmission line running through the center of the disks. The LP antenna is shown in Fig. 1. Tests were made on three models of the structure having values of the LP parameter 7 of 0.90, 0.96 and 0.98. The ratio of the plate spacing to the diameter u was held constant at 0.115. The antennas were designed to operate over a 3: 1 bandwidth (500 MHz to 1500 MHz). The diameter of the largest plate was approximately 0.4 wavelength and the height was approximately 0.93 wavelength at 500 MHz (T =0.96). Measurements of impedance, far-field radiation patterns, and polarization were made. For all models, the impedance was relatively constant over the designed frequency quency range, being within an SWR of 2: 1 relative to I5+,20 ohms. The far-field pattern measurements showed that the structure was omnidirectional within 3 dB over most of the designed bandwidth. Better omnidirectionality was obtained with r closer to 1 than when T was a lower value. Fig. 2(a) shows the typical azimuth variation. The eleManuscript received March 13, 1968; revised April 1, 1968 and July 8. 1968. This work was supported in part by the Small Industries Research Program through The Pennsylvania State University, and in part by National Science Foundation Traineeship Grant GE7919.1. Fig. 1. The log-periodic parallel plate antenna. vation patterns showed that the angle of maximum radiation occurred between 45 to 75 degrees with the axis of the antenna and scans with frequency. A typical elevation pattern is shown in Fig. 2(b). The polarization measurement, shown in Fig. 2(c), was made by changing the orientation of a linearly polarized transmitting antenna with respect to the axis of the test antenna. Zero degrees on Fig. 2(c) represents the point where the polarization of the transmitted wave was parallel to the axis of the test antenna, i.e., vertically polarized. Ninety degrees represents the point where the polarization of the transmitted wave was perpendicular to the axis of the test antenna, i.e., horizontal polarization. Thus the structure is, indeed, vertically polarized. More details of the experimental investigation may be found in [5]. The investigation indicated that the structure is capable of vertically polarized omnidirectional radiation and an impedance characteristic which are both relatively constant over a very wide bandwidth. However, the deviations from the desired omnidirectional characteristics indicate that the lowest E-type mode may not be the dominant one on the antenna at some frequencies. Near-field measurements indicate that higher-order modes are present. The nonpropagating modes will not affect the far-field radiation characteristics, but can account for the large reactive component of the input impedance. A comparison of the LP disk antenna with a discone antenna of the same bandwidth (3 to 1) indicates that the LP antenna is considerably larger in size. For a lower cutoff frequency of 500 MHz, the largest diameter of the LP antenna is 9 inches whereas the largest diameter of the discone antenna is 5.5 inches. The height of the LP antenna is 20 inches compared to 5 inches for the discone antenna. Theoretically, the LP disk antenna should be I capable of operation over a wider bandwidth than is obtainable with a discone antenna. L Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on October 2, 2009 at 07:12 from IEEE Xplore. Restrictions apply.

/pdf/the-influence-of-the-scattered-field-on-the-reradiation-2zwoukvog1.pdf

W. Kahn

Papers

Minimum-scattering antennas

A note on reflector arrays

The uniqueness of the lossless feed network for a multibeam array

The influence of the scattered field on the reradiation pattern of reflector arrays

Lossless interconnections of elements in a passive antenna array