Showing papers on "Dipole antenna published in 2009"

Method and apparatus for adaptive tuning of wireless power transfer

Abstract: Exemplary embodiments are directed to wireless power transfer. A transmit antenna generates an electromagnetic field at a resonant frequency of to create a coupling-mode region within a near field of the transmit antenna. A receive antenna receives the resonant frequency when it is within the coupling-mode region and resonates substantially near the resonant frequency. One, or both, of the transmit and receive antennas are tunable antennas that can be adaptively tuned. The adaptive tuning is accomplished by detecting a mismatch at the tunable antenna and generating a mismatch signal responsive to a voltage standing wave ratio at the tunable antenna. A resonance characteristic of the tunable antenna can be modified by adjusting a capacitance of a variable capacitor network connected to the tunable antenna.

Wireless power transfer in public places

Abstract: Exemplary embodiments are directed to public wireless-power-transmission. A device disposed in or on a publicly placed structure and a user neighboring device includes a repeater antenna with a loop antenna and a capacitive element. The public wireless-power-transmitting device includes a transmit antenna to wirelessly transfer power by generating a near-field radiation at a resonant frequency within a coupling-mode region and an amplifier for driving the transmit antenna. When in the coupling-mode region, the repeater antenna couples with the near-field radiation generated by the transmit antenna and develops an enhanced coupling-mode region about the repeater antenna with a repeated near-field radiation that is stronger than the near-field radiation of the transmit antenna within the enhanced coupling-mode region. Power may be wirelessly transferred from the enhanced coupling-mode region to a receiver device including a receive antenna.

Non-Foster Impedance Matching of Electrically-Small Antennas

Abstract: Electrically-small antennas present high-Q impedances characterized by large reactances and small radiation resistances. For such antennas, the effectiveness of passive matching is severely limited by gain-bandwidth theory, which predicts narrow bandwidths and/or poor gain. With receivers, the inability to resolve this impedance mismatch results in poor signal-to-noise (S/N) ratio, as compared to using a full-size antenna. With transmitters, the consequence is poor power efficiency. However, in many applications full-size antennas are impractical, and a means is required to effectively match their electrically-small counterparts. This paper presents the technique of non-Foster impedance matching, which employs active networks of negative inductors and capacitors to bypass the restrictions of gain-bandwidth theory. We first review the origins and development of non-Foster impedance matching, and then present experimental results for the non-Foster impedance matching of electrically-small dipoles and monopoles. For receivers, our best measurements on the antenna range demonstrate up to 20 dB improvement in S/N over 20-120 MHz; for transmitters, we show a power efficiency improvement which exceeds a factor of two over an 5% bandwidth about 20 MHz with an average signal power of 1 W to the radiation resistance.

Optical antenna thermal emitters

Abstract: Optical antennas are a critical component in nanophotonics research1 and have been used to enhance nonlinear2,3 and Raman4 cross-sections and to make nanoscale optical probes5. In addition to their ‘receiving’ properties, optical antennas can operate in ‘broadcasting’ mode, and have been used to modify the emission rate6 and direction7 of individual molecules. In these applications the antenna must operate at frequencies given by existing light emitters. Using thermal excitation of optical antennas, we bypass this limitation and realize emitters at infrared frequencies where sources are less readily available. Specifically, we show that the thermal emission from a single SiC whisker antenna is attributable to well-defined, size-tunable Mie resonances8. Furthermore, we derive a fundamental limit on the antenna emittance and argue theoretically that these structures are nearly ideal black-body antennas. Combined with advancing progress in antenna design, these results could lead to optical antenna emitters operating throughout the infrared frequency range. Single SiC whiskers can be made into infrared emitters by thermal excitation. The broadband thermal emission is coupled to the electromagnetic resonances of the whisker, allowing relatively narrowband emission at infrared frequencies. The emission frequency can be tuned by adjusting the size of the whiskers.

Antennas for Over-Body-Surface Communication at 2.45 GHz

Abstract: In this paper, the on-body performance of a range of wearable antennas was investigated by measuring |S 21| path gain between two devices mounted on tissue-equivalent numerical and experimental phantoms, representative of human muscle tissue at 2.45 GHz. In particular, the study focused on the performance of a compact higher mode microstrip patch antenna (HMMPA) with a profile as low as lambda/20. The 5- and 10-mm-high HMMPA prototypes had an impedance bandwidth of 6.7% and 8.6%, respectively, sufficient for the operating requirements of the 2.45-GHz industrial, scientific, and medical (ISM) band and both antennas offered 11-dB higher path gain compared to a fundamental-mode microstrip patch antenna. It was also demonstrated that a 7-dB improvement in path gain can be obtained for a fundamental-mode patch through the addition of a shortening wall. Notably, on-body HMMPA performance was comparable to a quarter wave monopole antenna on the same size of groundplane, mounted normal to the tissue surface, indicating that the low-profile and physically more robust antenna is a promising solution for bodyworn antenna applications.

A Broadband Dual-Polarized Magneto-Electric Dipole Antenna With Simple Feeds

Abstract: A novel dual-polarized magneto-electric dipole antenna excited by two -shaped strips is presented. The antenna achieves a common impedance bandwidth of 65.9% (SWR < 2) at both input ports. The antenna has excellent performance in isolation, which is more than 36 dB between the two input ports, and the gain of the antenna is about 9.5 dBi. The radiation pattern and bandwidth over the operating frequency band are very stable.

Programmable antenna with programmable impedance matching and methods for use therewith

Abstract: A programmable antenna includes a fixed antenna element and a programmable antenna element that is tunable to one of a plurality of resonant frequencies in response to at least one antenna control signal. A programmable impedance matching network is tunable in response to at least one matching network control signal, to provide, for instance, a substantially constant load impedance. A control module generates the antenna control signals and the matching network control signals, in response to a frequency selection signal.

Transmitters for wireless power transmission

Abstract: Exemplary embodiments are directed to wireless power transfer. A wireless power transmitter includes a transmit antenna configured as a resonant tank including a loop inductor and an antenna capacitance. The transmitter further includes an amplifier configured to drive the transmit antenna and a matching circuit operably coupled between the transmit antenna and the amplifier. The transmitter also includes a capacitor integrating the antenna capacitance and a matching circuit capacitance.

Impedance Characterization of RFID Tag Antennas and Application in Tag Co-Design

Abstract: In this paper, an experimental methodology for the characterization of the impedance of balanced RF identification (RFID) tag antennas is presented, and the application of the proposed method in RFID tag co-design is demonstrated. The balanced tag antenna is considered as a two-port network and the impedance of the antenna is characterized using network parameters. In the measurement, the antenna is connected to the two ports of a vector network analyzer through a test fixture. The influence of the test fixture is deembedded by using a port-extension technique and the antenna impedance can be extracted directly from the measured S -parameters. The proposed method is useful in practical RFID applications for co-designing the RFID tag with the attached platforms for enhancing the tag performance. An example of co-designing an ultra-high-frequency RFID tag with a plastic Sushi plate is demonstrated. The co-designed tag antenna achieves conjugate matching with the application-specific integrated circuit so that the reading range of the RFID tag is greatly enhanced.

Small Square Monopole Antenna With Inverted T-Shaped Notch in the Ground Plane for UWB Application

Abstract: In this letter, we present a novel printed monopole antenna for ultrawideband (UWB) applications. The proposed antenna consists of a square radiating patch with two rectangular slots and a ground plane with inverted T-shaped notch, which provides a wide usable fractional bandwidth of more than 120% (3.1212.73 GHz). The proposed antenna is simple and small in size. Simulated and experimental results obtained for this antenna show that it exhibits good radiation behavior within the UWB frequency range.

Conformal Ingestible Capsule Antenna: A Novel Chandelier Meandered Design

Abstract: This paper investigates a conformal antenna for the ingestible bio-telemetric capsule system. This system has the potential to provide real-time biological information from within the human body via a radio frequency link. The balanced planar meandered dipole (concept used for antenna miniaturization through space-filling) is discussed along with the offset planar meandered dipole, which facilitates better matching. The conformal chandelier meandered dipole antenna (CCMDA), which is an extension of the offset planar meandered dipole and envelopes the capsule surface, is then investigated. The return loss, input impedance, and radiation pattern characteristics of the CCMDA are discussed in detail at the operating frequency of 1.4 GHz. Additionally, electrical components (specifically the batteries) are modeled inside the capsule to investigate their effects on the conformal antenna performance in free space. The capsule antenna is then inserted into a simple box model (a simplification of the human torso) and a 4-mm precision human-body model (Ansoft) where the detuning effects are observed and discussed. Finally, a circularly polarized receiver antenna design consisting of orthogonal dipoles is suggested which provides polarization diversity and is miniaturized to fit into a personal digital assistant (PDA) for portability of the data telemetric link.

Cross resonant optical antenna.

Abstract: We propose a novel cross resonant optical antenna consisting of two perpendicular nanosized gold dipole antennas with a common feed gap. We demonstrate that the cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa. The cross antenna structure therefore opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.

A Broadband Center-Fed Circular Patch-Ring Antenna With a Monopole Like Radiation Pattern

Abstract: A center-fed circular microstrip patch antenna with a coupled annular ring is presented. This antenna has a low profile configuration with a monopole like radiation pattern. Compared to the center-fed circular patch antenna (CPA), the proposed antenna has a large bandwidth and similar radiation pattern. The proposed antenna is fabricated and tested. It resonates at 5.8 GHz, the corresponding impedance bandwidth and gain are 12.8% and 5.7 dBi, respectively. Very good agreement between the measurement and simulation for the return loss and radiation patterns is achieved.

Equivalent-Circuit Analysis of a Broadband Printed Dipole With Adjusted Integrated Balun and an Array for Base Station Applications

Abstract: A printed dipole with an integrated balun features a broad operating bandwidth. The feed point of conventional balun structures is fixed at the top of the integrated balun, which makes it difficult to match to a 50-Omega feed. In this communication, we demonstrate that it is possible to directly match with the 50-Omega feed by adjusting the position of the feed point of the integrated balun. The printed dipole with the hereby presented adjustable integrated balun maintains the broadband performance and exhibits flexibility for the matching to different impedance values, which is extremely important for the design of antenna arrays since the mutual coupling between antenna elements commonly changes the input impedance of each single element. An equivalent-circuit analysis is presented for the understanding of the mechanism of the impedance match. An eight-element linear antenna array is designed as a benchmarking topology for broadband wireless base stations.

A Circularly Polarized Antenna With Wide Axial Ratio Beamwidth

Abstract: A novel circularly polarized (CP) antenna with wide angular coverage is presented. The proposed antenna is formed by two bowtie patch antennas and two electric dipoles. It can achieve an impedance bandwidth (SWR < 1.6) of 41% and a 3-dB axial ratio bandwidth of 33%. For this design, very stable and symmetrical radiation patterns are obtained. In the axial ratio passband, the 3-dB beamwidth is 85degplusmn2deg with a gain of 6.3 dBi plusmn0.3 dBi. The cross polarization is lower than -15 dB over a wide range of angles. For the entire half-power beamwidth, the axial ratio can be kept below 3 dB.

The Long Wavelength Array

Abstract: The Long Wavelength Array (LWA) will be a new multipurpose radio telescope operating in the frequency range 10-88 MHz. Upon completion, the LWA will consist of 53 phased array ldquostationsrdquo distributed over a region about 400 km in diameter in the state of New Mexico. Each station will consist of 256 pairs of dipole-type antennas whose signals are formed into beams, with outputs transported to a central location for high-resolution aperture synthesis imaging. The resulting image sensitivity is estimated to be a few millijanskys (5 sigma, 8 MHz, two polarizations, 1 h, zenith) in 20-80 MHz; with resolution and field of view of (8 '', 8deg) and (2'', 2 deg) at 20 and 80 MHz, respectively. Notable engineering features of the instrument, demonstrated in this paper, include Galactic-noise limited active antennas and direct sampling digitization of the entire tuning range. This paper also summarizes the LWA science goals, specifications, and analysis leading to top-level design decisions.

On-Chip Integrated Antenna Structures in CMOS for 60 GHz WPAN Systems

Abstract: We present several on-chip antenna structures that may be fabricated with standard CMOS technology for use at millimeter wave frequencies. On-chip antennas for wireless personal area networks (WPANs) promise to reduce interconnection losses and greatly reduce wireless transceiver costs, while providing unprecedented flexibility for device manufacturers. We present the current state of research in on-chip integrated antennas, highlight several pitfalls and challenges for on-chip design, modeling, and measurement, and propose several antenna structures that derive from the microwave and HF communication fields. We also describe an experimental test apparatus for performing measurements on RFIC systems with on-chip antennas at The University of Texas at Austin.

An Ultrawideband Diversity Antenna

Abstract: A compact diversity antenna operating at an ultrawideband (UWB) frequency range of 3.1-5 GHz is proposed for use in portable devices. The antenna printed on a printed circuit board (PCB) slab consists of two notched triangular radiating elements with two feeding ports. A ground plane is etched on the reverse side of the PCB. The shape of the ground plane is optimized to improve the isolation between the ports as well as impedance matching. The simulated and measured results show that across the operating bandwidth, the antenna can achieve a broad impedance bandwidth with good performance in terms of isolation of -2 dBi, and efficiency of > 70%. The correlation between the radiation patterns shows consistent diversity performance across the UWB bandwidth. A method to derive thetransfer function of the antenna has been proposed, which can be used to obtain the radiated pulses in the time domain. Furthermore, a parametric study is conducted to provide antenna engineers with useful information for designing and optimizing the antenna.

Novel Planar UWB Monopole Antenna With Triple Band-Notched Characteristics

Abstract: A novel spade-shaped ultrawideband (UWB) printed planar monopole antenna with triple band-notched characteristics is proposed. By employing a hook-shaped defected ground structure (DGS) in each side of the ground plane, embedding an Omega-shaped slot on the radiating patch as well as adding a semi-octagon-shaped resonant ring on the back side of the antenna, triple notched frequency bands are achieved. The proposed antenna has been successfully simulated, fabricated, and measured. Effects of the key parameters on the frequency ranges of the notched bands are also investigated. The measured impedance bandwidth defined by VS WR < 2 of 10.1 GHz (2.9-13 GHz), with the triple notched bands of 3.3-3.9, 5.2-5.35, and 5.8-6.0 GHz, is obtained. Measured group delay and transmission characteristics indicate that the antenna has good transient response. Furthermore, the proposed antenna shows the merit of insensitivity to both finite ground size and fabrication tolerances.

The Analysis of a Reconfigurable Antenna With a Rotating Feed Using Graph Models

Abstract: This letter investigates a new reconfigurable antenna technique based on the rotation of a slot. The surface currents are redistributed for each slot position. The antenna is simulated, fabricated, and tested. The return loss frequency tuning matches the simulated data. The antenna radiation pattern remains unchanged for different slot positions. Finally, the process for automatic rotation and control of the slot is investigated using graph models.

Bandwidth Enhancement of Novel Compact Single and Dual Band-Notched Printed Monopole Antenna With a Pair of L-Shaped Slots

Abstract: A dual band-notched printed ultrawideband monopole antenna is presented, with a modified ground plane. By using this modified element including a pair of variable L-shaped slots, cut in the ground plane, additional resonances are excited and hence the bandwidth is increased up to 130%. To generate single and dual band-notched characteristics, we use inverted U- and fork-shaped parasitic structures, respectively, instead of changing the patch or feedline shapes. By properly adjusting the dimensions of these capacitive-coupled elements, not only one or two controllable notch resonances are achieved, but also the lower-edge frequency of the band is decreased. The measured results show that the proposed dual band-notched monopole antenna offers a very wide bandwidth from 2.2 to 13.4 GHz (143%), defined by 10-dB return loss, with two notched bands, covering all the 5.2/5.8-GHz WLAN, 3.5/5.5-GHz WiMax and 4-GHz C bands. Impedance, radiation, efficiency and gain characteristics of the antenna are also discussed.

Antenna array with metamaterial lens

Abstract: An antenna array comprises two or more antenna elements. Each of the two or more antenna elements is configured to scan within a field of view. Each of the two or more antenna elements is further configured to transmit or receive a signal. The antenna array also comprises a metamaterial lens coupled to the two or more antenna elements. The metamaterial lens is configured to distribute the signal according to a sinc-like distribution over an aperture of the antenna array.

A Dual-Polarized Magneto-Electric Dipole With Dielectric Loading

Abstract: A plusmn45degdual-polarized magneto-electric dipole loaded with dielectric substrate is presented. This antenna is composed of shorted-circuited patches and planar dipoles and is fed by four Gamma-shaped probes. The height of a prototype antenna operated at 1.9 GHz is only 24 mm (0.15lambdao). A wide impedance bandwidth of 24.9% is achieved. The average gain is about 8.2 dBi and the isolation between the two ports is higher than 29 dB over the operating bandwidth. It is demonstrated that the antenna performance can be improved by adding metallic side walls.

Foldable and Stretchable Liquid Metal Planar Inverted Cone Antenna

Abstract: A mechanically flexible planar inverted cone antenna (PICA) for ultrawideband (UWB) applications is presented. It can be both folded and stretched significantly without permanent damage or loss of electrical functionality. The antenna is manufactured with a process in which conductors are realized by injecting room temperature liquid metal alloy into micro-structured channels in an elastic dielectric material. The elastic dielectric material together with the liquid metal enables bending with a very small radius, twisting, and stretching along any direction. Port impedance and radiation characteristics of the non-stretched and stretched antenna are studied in simulations and experiments. The presented antenna has a return loss better than 10 dB within 3-11 GHz and a radiation efficiency of > 70% over 3-10 GHz, also when stretched. Tests verify that stretching up to 40% is possible with maintained electrical performance. The presented antenna is useful for example for body-worn antennas and in applications in harsh environments where mechanical flexibility helps improve durability.

Broadband Microstrip Antenna With Left-Handed Metamaterials

Abstract: A novel type of microstrip antenna is proposed for compact wideband wireless applications. The antenna is composed of six unit cells of left-handed metamaterial (LHM) and a dipole element. The dipole is directly connected to three of six LHM unit cells, which are arranged in a 2 times 3 antenna array form. In this aspect, the proposed antenna is regarded as LHM loaded dipole antenna. The antenna is matched with a stepped impedance transformer and rectangular slot in the truncated ground plane. The coupled LH resonances and simultaneous excitation of different sections of unit cells and dipole result into broad bandwidth. The proposed antenna has a maximum gain of -1 dBi at 2.5 GHz. The measured return loss indicates 63% bandwidth for |S11| < -10 dB over the band of 1.3-2.5 GHz. The overall size of LHM loaded antenna is lambda0/2.87 times lambda0/11.27 times lambda0/315.80 at the center frequency. The radiation of the electrically small LHM unit cells is also demonstrated by the simulated radiation pattern, which is an important concept for the antenna miniaturization.

Near-field direct antenna modulation

Abstract: NFDAM systems provide a unique solution for transmitting highly secured direction-dependent data and hence preventing eavesdroppers from properly demodulating the signal. A 60-GHz proof-of-concept chip was designed and measured.

Characteristics of Cavity Slot Antenna for Body-Area Networks

Abstract: Antennas and the propagation characteristics for body-area networks have become an active area of research. In this paper, a cavity slot antenna is proposed for onbody communications at 2.45 GHz. First, the antenna characteristics (input impedance, radiation pattern, and efficiency) are calculated by the finite-difference time-domain method. The results show that the proposed antenna has a relatively high efficiency of more than 50% even in the vicinity of the human body. Next, the onbody radio wave-propagation characteristics are investigated through numerical simulation and experimental measurements of the electric-field distributions around a phantom with a simplified shape of a human arm. Both sets of results are then compared and discussed. Finally, good agreement between the measured and the calculated results is confirmed.

Multiband Printed Monopole Slot Antenna for WWAN Operation in the Laptop Computer

Abstract: A multiband printed monopole slot antenna promising for operating as an internal antenna in the thin-profile laptop computer for wireless wide area network (WWAN) operation is presented. The proposed antenna is formed by three monopole slots operated at their quarter-wavelength modes and arranged in a compact planar configuration. A step-shaped microstrip feedline is applied to excite the three monopole slots at their respective optimal feeding position, and two wide operating bands at about 900 and 1900 MHz are obtained for the antenna to cover all the five operating bands of GSM850/900/1800/1900/UMTS for WWAN operation. The antenna is easily printed on a small-size FR4 substrate and shows a length of 60 mm only and a height of 12 mm when mounted at the top edge of the system ground plane or supporting metal frame of the laptop display. Details of the proposed antenna are presented and studied.

High-Gain Yagi-Uda Antennas for Millimeter-Wave Switched-Beam Systems

Abstract: A high-efficiency microstrip-fed Yagi-Uda antenna has been developed for millimeter-wave applications. The antenna is built on both sides of a Teflon substrate (epsivr = 2.2) which results in an integrated balun for the feed dipole. A 7-element design results in a measured gain of 9-11 dB at 22-26 GHz with a cross-polarization level of 90 % ) and is suitable for mm-wave radars and high data-rate communication systems.

A Note on the Mutual-Coupling Problems in Transmitting and Receiving Antenna Arrays

Abstract: In antenna arrays, mutual coupling between antenna elements is well known as an undesired effect, which degrades the performance of array signal-processing algorithms. The compensation of such an undesired effect has been a popular research topic throughout the years. Various approaches for mutual-coupling compensation have been developed, and they can easily be found in the open literature. In general, the mutual-coupling problems for a transmitting and receiving array are different, even if the physical geometry of the array remains unchanged. However, it seems that antenna engineers are not well aware of such differences in the analysis of receiving antenna arrays. In this note, the mutual-coupling problems in transmitting and receiving antenna arrays are revisited. The differences between the mutual coupling and mutual impedances for transmitting and receiving antenna arrays are explained. It is concluded that the mutual-coupling problems of transmitting and receiving arrays are in general different, and hence different mutual impedances should be used for mutual-coupling analysis and compensation.