Source Antenna Research Articles

Investigation of a high power electromagnetic pulse source

A high power electromagnetic pulse source with a resonant antenna driven by a compact power supply was investigated in this paper. To match the impedance of the resonant antenna and initial power source, a compact power conditioning circuit based on electro exploding opening switch (EEOS) and pulsed transformer was adopted. In the preliminary experiments, an impulse capacitor was used to drive the system. With the opening of the EEOS at the current of 15 kA flowing trough the primary of the transformer, the resonant antenna was rapidly charged to about -370 kV within a time of about 100 ns. When the switch in the resonant antenna closed at the charging voltage of about -202 kV, the peak intensity of the detected electric field at a distance of about 10 m from the center of the source was 7.2 kV∕m. The corresponding peak power of the radiated electromagnetic field reached 76 MW, while the total radiated electromagnetic energy was about 0.65 J. The total energy efficiency of the resonant antenna was about 22% which can be improved by increasing the closing rapidity of the switch in the antenna.

Collaborative Relay Beamforming Strategies for Multiple Destinations with Guaranteed QoS in Wireless Machine-to-Machine Networks

The Machine-to-Machine (M2M) communications allow information exchange between machine devices, which can be carried out without any human interaction. However, there are a large number of small and low-power machine devices in the wireless M2M networks. To guarantee the quality of service (QoS) requirements of the destination devices, we study the amplify-and-forward (AF) relay beamforming, where multiple relay M2M devices can transmit signals from the source M2M device to multiple destination M2M devices. In this paper, we propose two iterative strategies to jointly optimize the source antenna selection and the collaborative relay beamforming weights with the aid of perfect channel state information (CSI). The aim of the proposed strategies is to maximize the worst-case received signal-to-interference-and-noise ratio (SINR) under two different types of relay power constraints, which are the total relay power constraint and individual relay power constraints, respectively. Using the semidefinite relaxation (SDR) technique, the optimization problem of collaborative relay beamforming can be formulated as a semidefinite programming (SDP) problem, which can be optimally solved. Simulation results validate our theoretical analysis and demonstrate that after several iterations, the performance of the proposed iterative strategies can obtain near-optimal performance.

Performance Analysis of Optimal Single Stream Beamforming in MIMO Dual-Hop AF Systems

This paper investigates the performance of optimal single stream beamforming schemes in multiple-input multiple-output (MIMO) dual-hop amplify-and-forward (AF) systems. Assuming channel state information is not available at the source and relay, the optimal transmit and receive beamforming vectors are computed at the destination, and the transmit beamforming vector is sent to the transmitter via a dedicated feedback link. Then, a set of new closed-form expressions for the statistical properties of the maximum eigenvalue of the resultant channel is derived, i.e., the cumulative density function (cdf), probability density function (pdf) and general moments, as well as the first order asymptotic expansion and asymptotic large dimension approximations. These analytical expressions are then applied to study three important performance metrics of the system, i.e., outage probability, average symbol error rate and ergodic capacity. In addition, more detailed treatments are provided for some important special cases, e.g., when the number of antennas at one of the nodes is one or large, simple and insightful expressions for the key parameters such as diversity order and array gain of the system are derived. With the analytical results, the joint impact of source, relay and destination antenna numbers on the system performance is addressed, and the performance of optimal beamforming schemes and orthogonal space-time block-coding (OSTBC) schemes are compared. Results reveal that the number of antennas at the relay has a great impact on how the numbers of antennas at the source and destination contribute to the system performance, and optimal beamforming not only achieves the same maximum diversity order as OSTBC, but also provides significant power gains over OSTBC.

Electrically small Huygens source antenna for linear polarisation

We study the possibility of creating a Huygens source antenna for linear polarisation with good matching to a 50 Ω feeding cable. For this purpose, we design two identical radiating elements, both comprising one electric and one magnetic dipole. The dimensions of these radiating elements are optimised numerically to obtain equally strong radiation from the electric and magnetic dipoles. The optimised prototype is then manufactured and its radiation properties are measured.

On Capacity Scaling of Multi-Antenna Multi-Hop Networks: The Significance of the Relaying Strategy in the “Long Network Limit”

The sum-capacity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$C$</tex></formula> of a static uplink channel with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> single-antenna sources and an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> -antenna destination is known to scale linearly in <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> , if the random channel matrix fulfills the conditions for the Marcenko-Pastur law: if each source transmits at power <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$P/n$</tex></formula> , there exists a positive <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$c_{0}$</tex></formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\lim_{n \ura{} \infty}C/n=c_{0}$</tex></formula> almost surely. This paper addresses the question to which extent this result carries over to multi-hop networks. Specifically, an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$L+1$</tex></formula> -hop network with <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex> </formula> non-cooperative source antennas, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n$</tex></formula> fully cooperative destination antennas, and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> relay stages of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$n_{\cal R}$</tex></formula> (cooperative or non-cooperative) relay antennas each is considered. Four relaying strategies are assessed based on the interrelationship between two sequences. For each considered strategy <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm XF}$</tex></formula> , there exists a sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(c_{L}^{\rm XF})_{L=0}^{\infty}$</tex> </formula> , such that <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$c_{L}^{\rm XF}=\lim_{n \ura{} \infty}R^{\rm XF}_{L}/n$</tex></formula> almost surely, where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$R^{\rm XF}_{L}$</tex></formula> denotes the supremum of the set of sum-rates that are achievable by the strategy over <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex> </formula> hops. This sequence depends on the sequence <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(P_{L})_{L=0}^{\infty}$</tex> </formula> , where <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$P_{L}$</tex></formula> corresponds to the power of the source stage and each of the relay stages in an <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L\!+\!1$</tex></formula> -hop network. Results are summarized as follows: <orderedlist continuation="restarts" numeration="bullet" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <listitem><para>Decode &amp; forward (DF): For <formula formulatype="inline"><tex Notation="TeX">$n_{\cal R}=n$</tex></formula>, <formula formulatype="inline"><tex Notation="TeX">$c^{\rm DF}_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>, if also <formula formulatype="inline"><tex Notation="TeX">$P_{L}$</tex></formula> is constant with respect to <formula formulatype="inline"> <tex Notation="TeX">$L$</tex></formula>.</para></listitem></orderedlist>

H− radio frequency source development at the Spallation Neutron Source

The Spallation Neutron Source (SNS) now routinely operates nearly 1 MW of beam power on target with a highly persistent ∼38 mA peak current in the linac and an availability of ∼90%. H(-) beam pulses (∼1 ms, 60 Hz) are produced by a Cs-enhanced, multicusp ion source closely coupled with an electrostatic low energy beam transport (LEBT), which focuses the 65 kV beam into a radio frequency quadrupole accelerator. The source plasma is generated by RF excitation (2 MHz, ∼60 kW) of a copper antenna that has been encased with a thickness of ∼0.7 mm of porcelain enamel and immersed into the plasma chamber. The ion source and LEBT normally have a combined availability of ∼99%. Recent increases in duty-factor and RF power have made antenna failures a leading cause of downtime. This report first identifies the physical mechanism of antenna failure from a statistical inspection of ∼75 antennas which ran at the SNS, scanning electron microscopy studies of antenna surface, and cross sectional cuts and analysis of calorimetric heating measurements. Failure mitigation efforts are then described which include modifying the antenna geometry and our acceptance∕installation criteria. Progress and status of the development of the SNS external antenna source, a long-term solution to the internal antenna problem, are then discussed. Currently, this source is capable of delivering comparable beam currents to the baseline source to the SNS and, an earlier version, has briefly demonstrated unanalyzed currents up to ∼100 mA (1 ms, 60 Hz) on the test stand. In particular, this paper discusses plasma ignition (dc and RF plasma guns), antenna reliability, magnet overheating, and insufficient beam persistence.

Opportunistic Relaying for MIMO Amplify-and-Forward Cooperative Networks

We consider a wireless relay network with multiple antenna terminals over Rayleigh fading channels, and apply distributed space-time coding (DSTC) in amplify-and-forward (A&F) mode. The A&F scheme is used in a way that each relay transmits a scaled version of the linear combination of the received symbols. It turns out that, combined with power allocation in the relays, A&F DSTC results in an opportunistic relaying scheme, in which only the best relay is selected to retransmit the source's space-time coded signal. Furthermore, assuming the knowledge of source-relay CSI at the source node, we design an efficient power allocation which outperforms uniform power allocation across the source antennas. Next, assuming M-PSK or M-QAM modulations, we analyze the performance of the proposed cooperative diversity transmission schemes in a wireless relay networks with the multiple-antenna source and destination. We derive the probability density function (PDF) of the received SNR at the destination. Then, the PDF is used to determine the symbol error rate (SER) in Rayleigh fading channels. We derived closed-form approximations of the average SER in the high SNR scenario, from which we find the diversity order of system R min{N s , N d }, where R, N s , and N d are the number of the relays, source antennas, and destination antennas, respectively. Simulation results show that the proposed system obtain more than 6 dB gain in SNR over A&F MIMO DSTC for BER 10?4, when R = 2, N s = 2, and N d = 1.

High-responsivity, low-noise, room-temperature, self-mixing terahertz detector realized using floating antennas on a GaN-based field-effect transistor

Using only optical lithography, we have fabricated a GaN/AlGaN high-electron mobility transistor with distinctive source and drain antennas electrically isolated from the electron channel. Working at room temperature, it efficiently detects terahertz radiation via self-mixing, with a responsivity (3.6 kV/W) exceptionally high for a III-V device and with a noise (40pW/Hz) just above the thermal limit. Performance improves at 77 K. While the device itself is micrometer-sized, our modeling indicates the asymmetric antennas induce a rather localized (&amp;lt;200 nm) region of strong self-mixing. Thus, a nanometer-scale active region is achieved by design and without recourse to electron-beam lithography.

Cocrystallization of coordinative and inorganic lanthanide centers showing dual emission via linked or unlinked antenna

In this paper, we report the design and synthesis of two pyridyl-substituted tripodal ligands, 3-TPyMNTB (tris(((pyridin-3-ylmethyl)benzimidazol-2-yl)methyl)amine) and 4-TPyMNTB (tris(((pyridin-4-ylmethyl)benzimidazol-2-yl)methyl)amine). Reaction of these two ligands with Eu(III)/Tb(III) picrate salts gives mononuclear complexes [Eu(3-TPyMNTB)(pic)3]·2H2O (1) and [Tb(3-TPyMNTB)(pic)3]·2H2O (2), respectively. While reaction with Eu(III)/Tb(III) nitrate salts leads to cocrystallization of a coordinative motif and an inorganic salt in one single-crystal, namely, [Eu(3-TPyMNTB)(NO3)3]·0.5[Eu(NO3)3(H2O)4]·3CH3CN (3), [Tb(3-TPyMNTB)(NO3)3]·0.5[Tb(NO3)3(H2O)4]·3CH3CN·1.5C2H5OH (4), [Eu(4-TPyMNTB)(NO3)3]·[Eu(NO3)3(H2O)3]·3CH3CN·0.5H2O (5) and [Tb(4-TPyMNTB)(NO3)3]·[Tb(NO3)3(H2O)3]·3CH3CN·0.5H2O (6). In these cocrystals, the organic ligand-coordinated motif [Ln(3(4)-TPyMNTB)(NO3)3] and the nitrate anion-bonded motif [Ln(NO3)3(H2O)n] (Ln = Eu(III) or Tb(III), n = 3 or 4) provide two Eu(III)/Tb(III) centers which coexist in the same crystal lattice. Of most interest, both coordinative and inorganic centers can be excited by the absorption of the organic ligand, that is, the double luminescent centers in the cocrystalline systems can be sensitized by the same antenna source. Therefore, both Dexter and Forster mechanisms are proposed to be involved in the emission process, in which the energy transfer is conducted either through direct bond linkages or through space from unlinked organic antennae.

Employing Power Allocation to Enhance Zero Forcing Scheme Advantages over Multi-Antenna Multiple Relay Networks

A multi-antenna multiple relay (MAMR) network is considered and a variation of two-hop zero-forcing amplify-forward relaying method is proposed. Deploying ZF method together with application of diagonal power allocation matrices at the relays, it is shown that the overall MAMR network is simplified to M independent single antenna multiple relay (SAMR) networks, where M is the number of source and destination antennas. This enables to incorporate network beamforming proposed for SAMR networks. Accordingly, using the BER as the performance metric, we present simulation results to show the proposed approach outperforms the common ZF method addressed in the literature.

About Change of Impulse Outskirts during Propagating in Dispersive Media

Abstract While propagating waves in the dispersive plasma, the absorption of the energy of electromagnetic waves significantly influences on the statistical characteristics of the scattered radiation. The absorption may cause the deformation of the power of radiation spectrum while discussing the asymmetric problem. In the point of view of the practical usage, it is interesting to discuss the cases when the source and receiver antennas are located on the different sides of chaotically inhomogeneous absorptive layers. The statistical modeling will be fulfilled for different coefficient of the absorption.

Outage Performance of Cooperative Relay Selection with Multiple Source and Destination Antennas over Dissimilar Nakagami-&lt;i&gt;m&lt;/i&gt; Fading Channels

Outage Performance of Cooperative Relay Selection with Multiple Source and Destination Antennas over Dissimilar Nakagami-&lt;i&gt;m&lt;/i&gt; Fading Channels

Compact Metamaterial-Based Substrate-Integrated Luneburg Lens Antenna

A compact and small electric-size aperture directive broadband Luneburg lens antenna is presented. The substrate-integrated lens antenna is based on embedding a Vivaldi antenna source inside a parallel-plate waveguide to illuminate a Luneburg lens operating in X-band. The focusing condition of the lens, requiring a gradient refractive index, is achieved through the use of complementary nonresonant metamaterial structures. Numerical simulations are performed to determine the suitable unit cells geometry with respect to the wave launcher inserted into the parallel-plate waveguide. A prototype fabricated using standard printed circuit board techniques has been measured in an anechoic chamber. The electric field distribution inside the antenna system has also been explored using a two-dimensional near-field microwave scanning setup. A good qualitative agreement is observed between simulations and experiments. It has been shown from both far- and near-field measurements that the proposed planar antenna presents good focusing properties.

Delay spread of electromagnetic waves along random rough surface

This paper is concerned with a numerical analysis of propagation characteristics of electromagnetic waves traveling along two-dimensional (2D) random rough surface (RRS). Ray searching algorithm is based on 2D discrete ray tracing method, and the field distribution corresponding to each searched ray is computed by using source and image diffraction coefficients. Numerical computations are carried out for total field distributions along RRS as well as delay profiles at an arbitrary observation point which is far from a source antenna. Detailed discussions are made on the effect of directivity of source or receive antenna to the delay spreads of received powers.

Design and fabrication of a composite-antenna-structure for broadband frequency with microwave absorber

Here we design, fabricate, and study a composite-antenna-structure (CAS) with excellent electrical and mechanical properties. The CAS, consisting of a glass/epoxy face sheet and a honeycomb core, acts as a basic mechanical structure in which a spiral type antenna is embedded. To increase the signal intensity, a carbon fiber plate is used as the bottom sheet. This reflector interrupts radiation, causing the wave from the antenna source to flow to the end of the arms without sufficient radiation. To overcome this problem, a microwave absorber is used for unwanted radiation to reduce the effect of the reflector. We measured the antenna performance by the return loss, axial ratio, gain, and radiation pattern. The structure showed a bandwidth of 0.5–2 GHz and a gain of 5–9 dBi, with circular polarization characteristics and a reflection loss below −10 dB within the desired frequency band.

Pulse Distortion and Mitigation Thereof in Spiral Antenna-Based UWB Communication Systems

A dispersion of two-arm planar equiangular and Archimedean spiral antennas is investigated. Frequency domain characterization of spiral antennas-based ultra-wideband link is conducted computationally and experimentally. The time domain performance is obtained by post processing frequency domain data using the inverse fast Fourier transform. Effects of source pulse shape and antenna's geometrical parameters on the dispersive properties of the channel are discussed and relevant conclusions regarding the low-distortion spiral antenna are presented. Finally, a theoretical pre-distortion compensation method based on a frequency-dependent delay removal technique is employed to enhance the performance of spiral antennas as pulse radiators.

Effects of the airwave in time-domain marine controlled-source electromagnetics

In marine time-domain controlled-source electromagnetics (CSEM), there are two different acquisition methods: with horizontal sources for fast and simple data acquisition or with vertical sources for minimizing the effects of the airwave. Illustrations of the electric field as a function of space and time for various source antenna orientations, based on analytical formulation of the electric field in two half-spaces, provide insights into the properties of the airwave and the nature of diffuse electric fields. Observing the development of the electric field over time and space reveals that diffusive fields exhibit directionality. Therefore, techniques that have thus far mostly been applied to wavefields can be adapted for CSEM. Examples range from the well-known up-down decomposition to beam steering. Vertical sources have the advantage of not creating an airwave. On the other hand, it is quite difficult to achieve perfect verticality of the source antenna. Results, using a numerically modeled data set to analyze the impact of the airwave on a signal from a subsurface reservoir in the case of a slightly dipping vertical source, indicate that already for a dip of [Formula: see text], the airwave contributes 20% to the complete electric field in our configuration of reservoir depth, water thickness, and conductivity values.

Average rate performance of two-way amplify-and-forward relaying in asymmetric fading channels

A two-way relaying (TWR) system is analyzed, where two source terminals with unequal numbers of antennas exchange data via an amplify-and-forward relay terminal with a single antenna. In the system considered herein, the link quality between the sources and relay can generally be asymmetric due to the non-identical antenna configuration, power allocation, and relay location. In such a general setup, accurate bounds on the average sum rate (ASR) are derived when beamforming or orthogonal space time block coding is employed at the sources. We show that the proposed bounds are almost indistinguishable from the exact ASR under various system configurations. It is also observed that the ASR performance of the TWR system with unequal numbers of source antennas is more sensitive to the relay location than to the power allocation.

Design and realisation of an electrically small Huygens source for circular polarisation

The authors study the possibilities of realising circularly polarised Huygens source antennas combining electric and magnetic dipoles. The required combinations of dipoles are first studied analytically. Radiating elements comprising both electric and magnetic dipoles in a single element, namely, chiral particles, are then chosen as a way to realise the required dipole radiators. The use of elements that have equally strong electric and magnetic dipoles in a single element greatly simplifies the realisation and feeding of these antennas. The designed antennas are studied numerically and finally the radiation properties of the antennas are verified with measurements. The numerical and experimental results confirm that the antennas have radiation characteristics similar to a Huygens source.

Effects of Multiple Antennas on Outage Performance of Decode-and-Forward Cooperative Networks with Relay Selection

In this paper, we consider multiple source and destination antennas based on relay selection scheme to improve the end-to-end outage performance for decode-and-forward cooperative networks. We derive an exact closed-form expression of the outage probability for the proposed system over a Rayleigh fading channel and describe the diversity-multiplexing tradeoff of the system. We then analyze the effects of the number of source and destination antennas on the outage probabilities and diversity-multiplexing tradeoffs.