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Author

T A Milligan

Bio: T A Milligan is an academic researcher. The author has contributed to research in topics: Slot antenna & Reconfigurable antenna. The author has an hindex of 1, co-authored 1 publications receiving 816 citations.

Papers
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Book
01 Mar 1985
TL;DR: Aperture Distributions and Arrays Synthesis as discussed by the authors is a technique used to synthesize antenna arrays, which are then used to measure the distance from the source to the sink. But it requires the antenna array to be symmetric.
Abstract: Preface. 1. Properties of Antennas. 2. Radiation Structures and Numerical Methods. 3. Arrays. 4. Aperture Distributions and Arrays Synthesis. 5. Dipoles, Slots, and Loops. 6. Microstrip Antennas. 7. Horn Antennas. 8. Reflector Antennas. 9. Lens Antennas. 10. Traveling Wave Antennas. 11. Frequency-Independent Antennas. 12. Phased Arrays. Index.

816 citations


Cited by
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Journal ArticleDOI
TL;DR: This Letter shows that antenna designs can be transferred to the optical frequency regime by replacing lambda by a linearly scaled effective wavelength lambda(eff)=n(1)+n(2) lambda/lambda/lambda(p), with lambda(p) being the plasma wavelength and n(1), n( 2) being coefficients that depend on geometry and material properties.
Abstract: In antenna theory, antenna parameters are directly related to the wavelength lambda of incident radiation, but this scaling fails at optical frequencies where metals behave as strongly coupled plasmas. In this Letter we show that antenna designs can be transferred to the optical frequency regime by replacing lambda by a linearly scaled effective wavelength lambda(eff)=n(1)+n(2)lambda/lambda(p), with lambda(p) being the plasma wavelength and n(1), n(2) being coefficients that depend on geometry and material properties. It is assumed that the antenna is made of linear segments with radii R << lambda. Optical antennas hold great promise for increasing the efficiency of photovoltaics, light-emitting devices, and optical sensors.

1,094 citations

Journal ArticleDOI
01 Nov 2006
TL;DR: This work provides an extensive overview of applications and design challenges for WUSNs, challenges for the underground communication channel including methods for predicting path losses in an underground link, and challenges at each layer of the communication protocol stack.
Abstract: This work introduces the concept of a Wireless Underground Sensor Network (WUSN). WUSNs can be used to monitor a variety of conditions, such as soil properties for agricultural applications and toxic substances for environmental monitoring. Unlike existing methods of monitoring underground conditions, which rely on buried sensors connected via wire to the surface, WUSN devices are deployed completely belowground and do not require any wired connections. Each device contains all necessary sensors, memory, a processor, a radio, an antenna, and a power source. This makes their deployment much simpler than existing underground sensing solutions. Wireless communication within a dense substance such as soil or rock is, however, significantly more challenging than through air. This factor, combined with the necessity to conserve energy due to the difficulty of unearthing and recharging WUSN devices, requires that communication protocols be redesigned to be as efficient as possible. This work provides an extensive overview of applications and design challenges for WUSNs, challenges for the underground communication channel including methods for predicting path losses in an underground link, and challenges at each layer of the communication protocol stack. � 2006 Elsevier B.V. All rights reserved.

667 citations

Journal ArticleDOI
TL;DR: Experimental evidence is presented that a single low-loss dielectric subwavelength sphere of moderate refractive index radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres, and these Kerker scattering conditions only depend on a/λ.
Abstract: Magnetodielectric small spheres present unusual electromagnetic scattering features, theoretically predicted a few decades ago. However, achieving such behaviour has remained elusive, due to the non-magnetic character of natural optical materials or the difficulty in obtaining low-loss highly permeable magnetic materials in the gigahertz regime. Here we present unambiguous experimental evidence that a single low-loss dielectric subwavelength sphere of moderate refractive index (n=4 like some semiconductors at near-infrared) radiates fields identical to those from equal amplitude crossed electric and magnetic dipoles, and indistinguishable from those of ideal magnetodielectric spheres. The measured scattering radiation patterns and degree of linear polarization (3–9 GHz/33–100 mm range) show that, by appropriately tuning the a/λ ratio, zero-backward (‘Huygens’ source) or almost zero-forward (‘Huygens’ reflector) radiated power can be obtained. These Kerker scattering conditions only depend on a/λ. Our results open new technological challenges from nano- and micro-photonics to science and engineering of antennas, metamaterials and electromagnetic devices. The absence of forward or backward scattered radiation by magnetodielectric spheres was predicted decades ago, yet direct measurements have remained elusive. Geffrin et al. present unambiguous evidence of such scattering effects in the gigahertz range for a sub-wavelength dielectric sphere.

539 citations

Journal ArticleDOI
TL;DR: Based on the channel analysis, the MI waveguide technique for communication is developed in order to reduce the high path loss of the traditional EM wave system and the ordinary MI system and reveals that the transmission range of the MIWaveguide system is dramatically increased.
Abstract: The main difference between the wireless underground sensor networks (WUSNs) and the terrestrial wireless sensor networks is the signal propagation medium. The underground is a challenging environment for wireless communications since the propagation medium is no longer air but soil, rock and water. The well established wireless signal propagation techniques using electromagnetic (EM) waves do not work well in this environment due to three problems: high path loss, dynamic channel condition and large antenna size. New techniques using magnetic induction (MI) create constant channel condition and can accomplish the communication with small size coils. In this paper, detailed analysis on the path loss and the bandwidth of the MI system in underground soil medium is provided. Based on the channel analysis, the MI waveguide technique for communication is developed in order to reduce the high path loss of the traditional EM wave system and the ordinary MI system. The performance of the EM wave system, the ordinary MI system and our improved MI waveguide system are quantitatively compared. The results reveal that the transmission range of the MI waveguide system is dramatically increased.

516 citations

Journal ArticleDOI
TL;DR: In this article, the performance of an optoelectronic terahertz (THz) beam system was described, where the transmitter operation was based on the repetitive, sub-picosecond laser excitation of a Hertzian dipole antenna embedded in a charged coplanar line.
Abstract: The performance of an optoelectronic terahertz (THz) beam system is described. The transmitter operation is based on the repetitive, subpicosecond laser excitation of a Hertzian dipole antenna embedded in a charged coplanar line. With this transmitter electromagnetic beams of 1/2 cycle THz pulses at a repetition rate of 100 MHz are produced. The associated optoelectronic receiver is gated in synchronism with the excitation of the transmitter by subpicosecond pulses from the same laser source. With this receiver, the 10-nW beams of THz pulses were observed with a signal-to-noise ratio greater than 10000:1. Several sources contributing to the noise of the receiver are discussed, together with ways to reduce them. With an integration time of 125 ms, a signal-to-noise ratio of 1 is obtained for a THz beam with an average power of 10/sup -16/ W. The receiver operates in the sampling mode and has a time resolution of 0.5 ps. >

488 citations