Time-domain Antenna Research Articles

A Novel All-Metal Four-Port Time-Domain Antenna With Enhanced Radiation Field

A Novel All-Metal Four-Port Time-Domain Antenna With Enhanced Radiation Field

Miniaturized Time-Domain Antenna With Improved Low-Frequency Radiation Performance

A miniaturized end-fire antenna with improved low-frequency radiation performance (RP) is proposed for time- domain applications. Through a novel resistive loading (RL) method, the proposed time-domain antenna (TDA) has a compact size of 0.176 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> ) × 0.156 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ), and improved low-frequency RP. Note that, this improvement does not mean the improvement of radiation efficiency, but means the enhancement of the radiation in forward and the reduction of the radiation in backward. Furthermore, the size of the proposed TDA is reduced by 78% as compared with the traditional antipodal Vivaldi antenna (AVA). In order to provide a certain reference for the design of end-fire TDAs, the mechanism of the novel RL technique is explored according to the design. Measured results show that the bandwidth of the proposed TDA is 0.168 ∼ 3 GHz (179%). Due to the compact size and good time-domain performance, the proposed TDA can be a good candidate for time-domain applications such as ground penetrating radar (GPR), Through-Wall Radar (TWR) and high-power pulsed source (HPS). Meanwhile, the novel RL technique can be a prior solution for the miniaturization and low-frequency RP improvement for end-fire TDAs.

High power balanced TEM horn antenna for ultra wide band radiator

AbstractA balanced transverse electromagnetic (TEM) horn type antenna is designed and developed for a 120 kV, 66 Ω high power ultra wideband (UWB) radiator. This antenna consists of a coaxial to parallel plate unzipper BALUN followed by an exponentially tapered TEM horn structure. Analysis of this antenna in time and frequency domain is performed using CST Microwave Studio. This antenna is having a power handling capacity of 1000 MW, with percentage bandwidth of 167%. This antenna has a gain of ~10 dB at 1 GHz frequency. Return loss performance of better than −10 dB is observed in 150 MHz to 1 GHz frequency range. Effective radiation of short pulses (&lt;5 ns) with very fast rise time (300–500 ps) has been demonstrated using this high‐power antenna. Practical results at 220 MW power are presented in this article. Directional performance of this antenna is practically established through peak power patterns in horizontal and vertical plane.

Time-modulated linear array synthesis with optimal time schemes for the simultaneous suppression of sidelobe and sidebands

AbstractAn efficient analysis of time-modulated array (TMA) toward realizing less-attenuating radiation patterns with simultaneously suppressed sidelobe and sidebands is presented in this paper. In this framework, an optimal outer element-controlled time sequence is derived. The proposed time scheme, along with optimized array excitations, is profitably applied for the desired solution. TMAs are considered unconventional alternatives to the phased arrays. The desired array radiation features can be attained by periodically enabling and disabling the array elements through high-speed switches. Despite the advantages of architectural simplicity and real-time reconfigurability of periodic time sequences, time-domain antenna arrays inherently generate unavoidable sideband radiations (SRs). The undesired SRs obtained at multiple harmonics around the carrier frequency of the array resembles power loss in unintended directions. This paper aims to minimize the SRs as well as the sidelobe level (SLL) for an efficient analysis of time-modulated linear array (TMLA) with high-directive radiation patterns. The starting instants and the period of on-times are optimized to generate a unique shifted time scheme for the edge elements of the TMLA to reduce the sideband levels (SBLs). The array excitations and the uniform spacing between the elements are also optimized together with the shifted time scheme for the coveted solution. Other methods of suppressing SLLs and SBLs with shifted pulse schemes and sub-sectioned pulse schemes are also presented for a fair comparison. Modified versions of the particle swarm optimization algorithm (PSO) are applied for the desired solutions. The optimal results attained by wavelet mutation-based novel PSO is compared with the conventional PSO and the modified novel PSO-based results. The representative results are reported, and the superior performance abilities of the proposed method compared to other published studies are assessed.

Experiment on Direction of Arrival Estimation of Atmospheric Spark Discharge Plasma Using Combined Time-Domain Antenna

Apart from interfering in the communication system of an aircraft, electromagnetic pulses (EMPs) radiated from spark discharge plasma, which is generated during high-speed flight, can also be utilized in passive detection. In order to validate this idea, an experiment on direction of arrival (DOA) estimation of a spark discharge plasma target using its radiated EMPs is carried out in this paper. A combined time-domain antenna is designed based on the model of spark discharge process and is used to receive the radiated EMPs during the experiment. According to the experimental results, the DOA estimation system with combined antenna is able to obtain the direction information of a spark discharge plasma. Results also show that the estimation performance of elevation angle is better when the actual elevation angle of the discharge plasma target is higher, while the estimation performance of azimuth is opposite. The azimuth angle of a target has very little influence on the DOA estimation. Moreover, the estimation error can be reduced effectively by increasing the aperture size of receiving array. The previously mentioned results provide an approach to locate the discharge plasma source using radiated EMPs with passive detection techniques.

Extrapolation of Electromagnetic Response from Linear Antennas in Time Domain without Late-Time Instabilities in Numerical Solution of EFI Equation

The paper presents a new hybrid method relied upon to solve integral equations of the electric field in time domain and to model linear antennas with pulse excitation. The method consists in a mixed, numerical-analytical description of the process that helps maintain the stability of calculations during the late time phase. As described in the analytical part, the modified spherical Bessel function of the first kind allows for extrapolation with a high degree of accuracy and loworder expressions. The modified spherical Bessel functions of the first kind are of the oscillating character, and their combination with the exponential factor makes them convenient for extrapolation of the answer of the antenna with pulse excitation. New functions are introduced to computational practice.

Time-Domain Characterization of the Radiation Pattern of the Terahertz Photoconductive Antennas

We present a novel method to characterize the radiation pattern of the terahertz photoconductive antennas in time-domain. The method uses a modified version of the terahertz time-domain spectroscopy system, where we use the basics of physical optics and the optical path compensation principle using the delay line in the system in order to detect the spatial distribution of the terahertz radiation of the photoconductive antennas in two major planes. Using this method, we investigate two terahertz photoconductive antennas, namely dipole and spiral antennas, and compare the measurement results with simulations in time-domain. The comparison of the calculation and measurement results shows good agreement, where we measure an average and maximum optical path difference error of 4.7 and 8%, which results in an average and maximum half-power beam width error of 1.87 and 3.2°, respectively. We believe that the proposed method will be useful for predicting the system level performance of the terahertz time-domain spectroscopy systems in real-life applications.

Novel Features of Classical Electrodynamics and Their Connection to the Elementary Charge, Energy Density of Vacuum and Heisenberg’s Uncertainty Principle—Review and Consolidation

The paper provides a review and conciliation of the results pertinent to the energy and action associated with electromagnetic radiation obtained using classical electrodynamics and published in several journal papers. The results presented in those papers are based on three systems that generate electromagnetic radiation, namely, frequency domain antennas, time domain antennas and decelerating (or accelerating) charged elementary particles. In the case of radiation generated by a frequency domain antenna, the energy dissipated as radiation within half a period, U, satisfies the order of magnitude inequality U ≥ hv → q ≥ e where q is the magnitude of the oscillating charge in the antenna, e is the elementary charge, v is the frequency and h is the Planck constant. In the case of transient radiation fields generated by time domain antennas or the radiation emitted by decelerating (or accelerating) charged elementary particles, the energy dissipated by the system as radiation satisfies the order of magnitude inequality Uτr ≥ h/4π → q ≥ e where U is the energy dissipated as radiation by the system τr, is the duration of the energy emission and q is either the charge in the current pulse in the case of the time domain antenna or the charge of the elementary particle giving rise to the radiation. These results are derived while adhering strictly to the principles of classical electrodynamics alone. These results were interpreted in different papers in different ways using different assumptions. In this paper, we provide a unified interpretation of the results, and combining these results with two simple quantum mechanical concepts, expression for the elementary charge as a function of other natural constants and the energy density of vacuum is derived. The expressions predict the elementary charge to an accuracy higher than about 1%.

Study on frequency and impulse response of novel triple band notched UWB antenna in indoor environments

In this paper, a novel fork shaped structure backed plane is added to a simple UWB (ultra wideband) slot antenna to enhance the impedance bandwidth as well as create triple band notched characteristics for Impulse Radio (IR) UWB applications. This fork-shaped structure is connected to a rectangular radiating patch at four different points through the cylindrical pins. The proposed antenna with this fork-shaped structure shows a very wide impedance bandwidth which spans from 2.5 up to more than 20 GHz and offers triple band-notched properties in WiMAX, WLAN and X-band downlink satellite communication spectrums. Moreover, the proposed antenna shows good radiation features such as gain, radiation efficiency and radiation patterns. A comprehensive investigation on the antenna time domain performance is also performed throughout the paper, and the effect of the proposed antenna on the two popular excitation pulses including modulated Gaussian (MG) and square root raised cosine (SRRC) pulses is fully investigated. A frequency-domain measurement setup is applied to measure time domain characteristics of the proposed antenna. Also, the realistic indoor multipath propagation channel characteristics when the proposed antennas are applied as the transmitter and receiver antennas are studied. Sub-band divided ray tracing method is used to simulate channel characteristics.

Simulation Study of an Impulse Radiation Antenna Array

A picosecond-pulse electric field, matching ultra-wideband antenna, can be applied to biomedical noninvasive therapy. Its effect depends largely on the electric field intensity on the target. Because the amplitude enhancement of a picosecond-pulse source is restricted by many factors, ultra-wideband time-domain antenna research has become important. Here, the intensity of the electromagnetic radiation propagated by the antenna was greatly improved by arraying the antenna feed structure. For targeted focusing, an ellipsoidal reflective surface is commonly utilized, but this structure limits the formation feasibility of the feed structure. Here, the feed structure and the reflector were arrayed at the same time, while satisfying the time and spatial consistency of the electromagnetic waves at the target, the intensity of the electric field at the target was greatly improved, and the size of the focal spot was reduced simultaneously. A Gaussian pulse with a 1-V amplitude and a 200-ps width was used as the excitation source. Using this antenna array, a focal spot less than $1\times 1\times 1$ cm was formed at the target. Also, with the increased number of elements in the antenna array, the electric field intensity of the target increased. The relationship between the field intensity at the target and the number of combined antennas is discussed. The increased field strength eventually levels off, which is also consistent with the theory.

Modified Cross Correlation Green’s Function With FDTD for Characterization of MIMO Antennas in Nonuniform Propagation Environment

A finite-difference time-domain-based technique for evaluating envelope correlation coefficient (ECC) and mean effective gain (MEG) of multiple-input multiple-output (MIMO) antennas operating in real-life nonuniform propagation environment is introduced. The proposed algorithm is based on the formulation of a modified cross correlation Green’s function (CGF), which directly incorporates the specific angular distribution functions and cross-polarization discrimination parameters. Thus, the proposed technique based on modified CGF is able to calculate ECC/MEG for MIMO antennas in nonuniform propagation scenario, directly from the time-domain antenna currents. This avoids the troublesome determination of far-field antenna pattern at each working frequency and the consequent postprocessing, as required in the conventional approach. Numerical examples using thin-wire half-wavelength dipole antennas and printed microstrip-fed slot antennas are provided to show the effectiveness of the proposed technique for characterizing MIMO antennas in nonuniform propagation environment.

Electrical Balance Duplexer Field Trials in High-Speed Rail Scenarios

Electrical balance duplexers (EBDs) present a potential alternative to the fixed-frequency duplexing filters used for frequency division duplexing in cellular handset radio frequency front ends. However, the transmit-to-receive (Tx–Rx) isolation can be affected by interaction between the antenna and the environment, and therefore, the EBDs balancing impedance must adaptively track time-domain antenna impedance variation. A rail scenario presents a potentially demanding use case for an EBD, as fast moving trains in the vicinity of the antenna may cause dynamically changing reflections, which can be received as self-interference. In this paper, measured dynamic antenna reflection coefficients at 745 and 1900 MHz from train mounted antennas are included in the EBD circuit simulations in order to investigate the resulting variation in Tx–Rx isolation, and determine requirements for balancing impedance adaptation. This paper also presents the results from rail-based field trials of a hardware prototype EBD, which implements real-time antenna impedance tracking. Results show that the rail scenario does result in variation in Tx–Rx isolation, but that rebalancing the EBD at the intervals of 5 ms was sufficient to maintain >50 dB isolation for ~95% of the time.

Computational Analysis and Verifications of Characteristic Modes in Real Materials

Despite its long history, the theory of characteristic modes (TCMs) has only been utilized in antenna design for perfect electric conductors (PECs). This is due to computational problems associated with dielectric and magnetic materials. In particular, the symmetric form of the Poggio–Miller–Chan–Harrington–Wu–Tsai (PMCHWT) surface formulation for the method of moments (MoM) solves for both external (real) and internal (nonreal) resonances of a structure. The external resonances are the characteristic modes (CMs), whereas the internal resonances are not. This paper proposes a new postprocessing method capable of providing unique and real CMs in all physical mediums, including lossy magnetic and dielectric materials. The method removes the internal resonances of a structure by defining a minimum radiated power, which is found through utilizing the physical bounds of the structure. The CMs found using the proposed method are verified through the use of an MoM volume formulation, time domain antenna simulations, and experiments involving multiple antenna prototypes.

Effects of lossless cavity-backing on power spiral antenna in time-domain

Effects of lossless cavity-backing on time-domain performance of a two-arm combined equiangular/power spiral antenna are discussed. The impact of cavity depth is studied and guidelines for achieving low pulse distortion are established. The resistive arms' termination is found to be necessary to achieve a compromise between good time and frequency performances at the expense of efficiency at low frequencies. Developed antenna with diameter to depth ratio of 8:1 has wide-angle fidelity factor of 90% while maintaining VSWR 5 dBic, and axial ratio <2.2 dB. Presented results show that the proposed antenna is viable candidate for many applications including pulsed and continuous-wave through-wall imaging, electronic attack/support measures, and ground penetrating radar. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:677–681, 2015

Two-Dimensional Time-Domain Antenna Arrays for Optimum Steerable Energy Pattern with Low Side Lobes

This document presents the synthesis of different two-dimensional time-domain antenna arrays for steerable energy patterns with side lobe levels. The research is focused on the uniform and nonuniform distributions of true-time exciting delays and positions of antenna elements. The uniform square array, random array, uniform concentric ring array, and rotated nonuniform concentric ring array geometries are particularly studied. These geometries are synthesized by using the well-known sequential quadratic programming. The synthesis regards the optimal true-time exciting delays and optimal positions of pulsed antenna elements. The results show the capabilities of the different antenna arrays to steer the beam in their energy pattern in time domain and how their performance is in frequency domain after the synthesis in time domain.

Modeling the Transient Radiated and Received Pulses of Ultra-Wideband Antennas

In this paper, we propose a method for modeling the transient radiated and received pulses of ultra-wideband (UWB) planar aperture antennas. The proposed method is able to analytically model the angle-dependent pulse distortion of the antennas. The method relates the input pulse of an antenna to its transient radiated fields, and the incident transient fields to its output pulse. This method needs to estimate the antenna's aperture field distribution from time-domain antenna measurements. Using the proposed method, the received pulses from three different antennas-a ridged-horn, a dielectric loaded horn, and a Vivaldi antenna-are modeled and compared with the measured received pulses. A comparison of pulse shape, amplitude, and energy shows very good agreement. Different input pulses are also examined for the experimental evaluation of the proposed method. The method allows designers to analytically estimate the antenna effect on transmitted pulse enabling the inclusion of pulse distortion by the antenna into the ultra-wideband transceiver design.

Low Complexity Transmitter Architectures for SFBC MIMO-OFDM Systems

Multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with space-frequency block coding (SFBC) have a high computational complexity since the number of inverse fast Fourier transforms (IFFTs) required scales in direct proportion to the number of antennas at the transmitter. This paper proposes to generate the SFBC encoded signals of the various antennas in time domain by exploiting the time-domain signal properties and signal correlations among the various transmitter antennas, achieving a significant reduction in computational complexity. In particular, it is demonstrated that the time domain SFBC encoded signals of the various antennas can be obtained from the time domain signal of the first antenna. Therefore, the proposed scheme requires only one IFFT irrespective of the number of transmission antennas. In addition, a low-complexity peak-to-average power ratio (PAPR) reduction scheme is presented based on the proposed transmitter architectures.

UWB time‐domain antennas beam scanning

AbstractUltra‐wideband (UWB) antenna is indispensable in impulse radar that transmits and receives short electromagnetic pulse signals and preserves the waveform well. Phased array antenna systems cannot meet the demand of the system. Optical true‐time delay techniques open the possibility of ultra‐wide bandwidth antenna systems, while at the same time meeting the stringent weight and size requirements. Continuously tunable true‐time delay techniques can provide continuous beam scanning. With advanced optoelectronic technique, fast wavelength tuning speed is possible. To detect and track moving‐target [Bi and Ren, Prog Electomagn Res 87 (2008), 15–41)], UWB time‐domain antenna array beam scanning is studied in this article. First, the theory of time‐domain antenna array scanning is analyzed, some useful conclusions are achieved. Then, an experiment system of UWB time‐domain antenna array scanning is built, which includes an antenna array, fiber‐optic true‐time delay device, and other equipments. Finally, the theoretical and experimental results combined to are made to validate the theory of UWB time‐domain antenna array beam scanning. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1110–1112, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25102

Transient Response of Straight Thin Wires Located at Different Heights Above a Ground Plane Using Antenna Theory and Transmission Line Approach

Transient electromagnetic field coupling to straight thin wires parallel to each other and located at different heights above a perfectly conducting or dielectric ground plane is analyzed using wire antenna theory and a transmission line method. The time-domain antenna theory formulation is based on a set of the space-time Hallen integral equations. The transmission line approximation is based on the corresponding time-domain Telegrapher's equations. The space-time integral equations arising from the wire antenna theory are handled by the time-domain Galerkin-Bubnov scheme of the indirect boundary element method. The time-domain Telegrapher's equations are solved using the finite-difference time-domain method. Time-domain numerical results obtained with both approaches are compared to the results computed via NEC 2 code combined with an inverse Fourier transform procedure. Some illustrative comparisons of results obtained by means of antenna theory and transmission line approach are presented throughout the paper.

超宽带时域天线阵列延时控制扫描实验

超宽带时域天线阵列延时控制扫描实验