TEM Horn Research Articles

TEM喇叭短脉冲响应特性与张角的依赖关系

TEM喇叭短脉冲响应特性与张角的依赖关系

PRINTED TEM HORN ANTENNA FED BY BALANCED MICROSTRIP LINE

In this paper, a new kind of printed TEM horn antenna with high-gain fed by balanced microstrip line is proposed. The radiation part of the antenna (printed on the FR4 epoxy substrate) is composed of two symmetrical triangular metal foil branches fed by balanced microstrip line. The antenna has been simulated by CST MICROWAVE STUDIO r software and the simulated results show that the proposed antenna is a kind of traveling wave antenna. Besides, an equivalent adopted V-shaped antenna model is proposed to describe the radiation characteristic of the antenna. The simulated and measured results indicate that in the frequency ranging from 1.64GHz to 9GHz, the re∞ection coe-cient of the antenna is less than i6dB and in the work frequency band, the average gain value is over 8.2dB. The antenna gain will be improved greatly by extending the length of the dielectric slab appropriately (in the main radiation direction) without in∞uencing the bandwidth. The measured and simulated results have a good consistency. This antenna will have wide application in the UWB fleld.

TEM horn antenna for near‐field microwave imaging

AbstractAntennas capable of sending and receiving ultra‐wideband pulses are required for radar‐based microwave breast imaging.This article describes a TEM horn antenna designed to operate over a 2–12 GHz band with specific radiated near‐field characteristics. Simulations and experimental measurements are presented, including detection of objects representing tumors. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1164–1170, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25136

Detection of super-high-frequency partial discharge by using neural networks

A system has been developed for the detection of super-high-frequency (SHF) partial discharge (PD) at frequencies up to 6 GHz. The system consists of three antennas for capturing PDs and a fast digital oscilloscope for sampling data. One of the antennas is a disk-cone antenna with frequency range below 710 MHz. The other two half TEM horn antennas have been designed and constructed for the frequency range 716 MHz - 5 GHz. To extend the frequency range up to 6 GHz, a methodology has been developed by compensating amplitude-response to frequency-magnitude. The compensation is realised by using multilayer feed-forward neural networks to equalise on amplitude-response. A direct sampling method is used to log the captured PD data. This PD detection system has been implemented to measure PDs at a 400 kV electrical substation (Strathaven, Scottish Power Ltd).

Constant Impedance TEM Horn Antenna: Aperture and Characteristic Impedance’s Impacts on Axial Electric Field

TEM horn antenna with constant characteristic impedance (CCI TEM horn antenna) is a widely used ultra-wideband (UWB) antenna. Considering the peak-to-peak value of the axial electric field (Vpp), how to design such antenna’s characteristic impedance (Z c) has not been involved in previous research. The relationship between Vpp and antenna aperture as well as characteristic impedance is numerical analyzed. The simulation and experimental results show that the optimal aperture is existed to maximize Vpp when the antenna’s length is fixed at the axis. More over, Vpp of the antenna with optimal aperture reaches the maximum value when the characteristic impedance is 280 ohm.

Frequency‐independent performance of elliptic profile TEM horns

AbstractThe TEM horn with elliptic E‐plane profile has been shown to give extremely wide bandwidth performance as far as VSWR and gain is concerned. In this article, the variation in radiation pattern versus frequency is explored, and it is shown that, dependant on choice, E‐plane or H‐plane radiation patterns that are virtually independent of frequency can be obtained. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 607–612, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24109

TEM HORN ANTENNA FOR ULTRA-WIDE BAND MICROWAVE BREAST IMAGING

A novel TEM horn antenna placed in a solid dielectric medium is proposed for microwave imaging of the breast. The major design requirement is that the antenna couples the microwave energy into the tissue without being immersed itself in a coupling medium. The antenna achieves this requirement by: 1) directing all radiated power through its front aperture, and 2) blocking external electromagnetic interference by a carefully designed enclosure consisting of copper sheets and power absorbing sheets. In the whole ultra-wide band the antenna features: 1) good impedance match, 2) uniform field distribution at the antenna aperture, and 3) good coupling efficiency.

Extreme performance TEM horn

AbstractPreviously, a TEM horn with ultra wideband performance had been described. The horn made use of an elliptic plate separation profile, while the plate width was determined by an optimal impedance function and the characteristic impedance equations for microstrip. In this article, it is shown that if the impedance equations for parallel plate waveguide are employed in the calculation of the plate width, extreme bandwith of more than 70:1 for a VSWR of 2:1 can be achieved. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2121–2125, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23550

FDTD analysis of ground-penetrating radar antennas with shields and absorbers

One of the most critical hardware components of a ground-penetrating radar (GPR) is the antenna system. Important parameters of antennas, such as antenna bandwidth, radiation waveform and cross coupling determine the GPR system performance. The modified TEM horn antenna with distributed resistor load is presented in this paper, and the radiation properties of the antenna with the shields and absorbers are studied through the three-dimensional finite-difference time-domain (FDTD) scheme. Simulations show that the direct signal coupled from the transmitter is decreased by means of the shields and absorbers. Therefore, using the antenna in the GPR system can improve the signal-to-clutter ratio and the dynamic range of the system.

Hyper‐wide band TEM horn array design for multi band ground‐penetrating impulse radar

AbstractThe array configuration of the partially dielectric‐loaded TEM (PDTEM) horn structure that can maintain very broadband antenna characteristics over a bandwidth ratio greater than 50:1 is proposed to obtain an efficient impulse signal radiation for ultra‐wide band radar and communication systems. It is shown that proper array combinations of TEM horn antennas can remarkably improve the impulse radiation performance yielding high gain and low input reflection levels over the hyper‐wide operational band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 76–81, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23007

유전자 알고리즘을 이용한 광대역 TEM 혼 안테나 설계

본 논문에서는 유전자 알고리즘을 이용하여 시간 영역 측정에 사용할 광대역 TEM 혼 안테나를 개발하였다. 안테나 개발에 고려된 설계 목표로는 <TEX>$2{\sim}10\;GHz$</TEX>의 주파수 영역에서 -10 dB 이하(VSWR<2)의 입력단 반사 손실과, 대역폭 내에서 높은 복사 이득 그리고 낮은 이득 편차이다. 또한 TEM 혼 안테나의 전체 크기를 줄이며 휴대가 용이하도록 하기 위해 안테나 본체와 급전부를 연결할 광대역의 balun을 설계하였다. 제작된 TEM 혼 안테나의 주파수 영역 측정 결과 <TEX>$2{\sim}10\;GHz$</TEX>에서 -10 dB 반사 손실을 만족하며, 기존의 삼각 플레이트 형태의 TEM 혼 안테나와 비교하였을 때 그 부피가 80 % 감소하였다. 안테나의 broadside 이득 값은 <TEX>$2{\sim}10\;GHz$</TEX> 대역에서 12 dBi 기준으로 이득 편차가 6 dB 이하를 만족한다. 안테나의 시간 영역 측정 결과 group delay의 변화폭은 0.4 ns 이하를 만족하며, 펄스 측정시 송신과 수신 신호의 상승 시간은 각각 58.5 ps와 66.5 ps로 대략 10 % 이내의 변화를 보였다. In this paper, we propose a broadband TEM horn antenna optimized using a genetic algorithm. The characteristics required for the TEM horn are the broad matching bandwidth from 2 GHz to 10 GHz and high gain in broadside with a small gain deviation within that bandwidth. In addition, a broadband balun is designed to improve the portability and to reduce the total size of the antenna. The measured return loss of the proposed TEM horn with the broadband balun is less than -10 dB(VSWR<2) from 2 GHz to 10 GHz. Compared to a conventional triangular type TEM horn, the proposed antenna shows about 80 % reduced volume and gives the broadside gain about 12 dBi with a gain deviation less than 6 dB from 2 GHz to 10 GHz. The time domain measurement shows less than 0.4 ns group delay and the pulse measurement using the transmitting signal with the rising time of 58.5 ps shows the received pulse with the rising time of 66.5 ps, which is less than 10 % rising time variation.

Mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques

Summary Two ground penetrating radar (GPR) techniques were used to estimate the shallow soil water content at the field scale. The first technique is based on the ground wave velocity measured with a bistatic impulse radar connected to 450 MHz ground-coupled antennas. The second technique is based on inverse modeling of an off-ground monostatic TEM horn antenna in the 0.8–1.6 GHz frequency range. Data were collected on a 8 by 9 m partially irrigated intensive research plot and along four 148.5 m transects. Time domain reflectometry, capacitance sensors, and volumetric soil samples were used as reference measurements. The aim of the study was to test the applicability of the ground wave method and the off-ground inverse modeling approach at the field scale for a soil with a silt loam texture. The results for the ground wave technique were difficult to interpret due to the strong attenuation of the GPR signal, which is related to the silt loam texture at the test site. The root mean square error of the ground wave technique was 0.076 m 3 m −3 when compared to the TDR measurements and 0.102 m 3 m −3 when compared with the volumetric soil samples. The off-ground monostatic GPR measured less within-field soil water content variability than the reference measurements, resulting in a root mean square error of 0.053 m 3 m −3 when compared with the TDR measurements and an error of 0.051 m 3 m −3 when compared with the volumetric soil samples. The variability between the two GPR measurements was even larger with a RSME of 0.115 m 3 m −3 . In summary, both GPR methods did not provide adequate spatial information on soil water content variation at the field scale. The main reason for the deviating results of the ground wave method was the poor data quality due to high silt and clay content at the test site. Additional reasons were shallow reflections and the dry upper soil layer that cannot be detected by the ground wave method. In the case of off-ground GPR, the high sensitivity to the dry surface layer is the most likely reason for the observed deviations. The off-ground GPR results might be improved by using a different antenna that allows data acquisition in a lower frequency range.

TEM horn antenna with an elliptic profile

AbstractA variety of profiles for the cross section of wideband TEM horns have been proposed, employing an optimal impedance function or exponential taper in order to minimize reflection losses. In this article, an elliptic longitudinal sectional profile, combined with an optimal impedance function, is proposed and evaluated.© 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1548–1551, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22488

Compensation of the effects of antenna dispersion on UWB waveforms via optical pulse-shaping techniques

To our knowledge, we present the first experimental demonstration of compensation of antenna dispersion effects on impulsive ultra-wideband (UWB) signals. By extracting the RF spectral phase from a time-domain impulse response measurement of a pair of ridged TEM horn antennas, we utilize a photonic-synthesis technique for arbitrary electromagnetic signal waveforms to generate a signal ''matched'' to the antenna pair. We demonstrate that the received waveform is compressed and exhibits reduced ringing levels, as compared to the impulse response of the system. Our technique is reprogrammable and we believe the technique will be applicable to a variety of antennas operating in the UWB communications band of 3.1-10.6 GHz.

Research on ultra-wide band planar Vivaldi antenna array

Planar Vivaldi antenna, with attractive performance compared with conventional TEM horn antennas, was introduced and used to form array. Normalized radiation energy pattern was adopted to characterize the transmit and receive behavior of ultra-wide-band (UWB) antenna array. Finite-difference time-domain (FDTD) was used to analyze the array. Radiation energy pattern in H plane was measured in outdoor region, for the difficulty of installing, E plane pattern was not measured. Measured and simulated results indicate that the planar Vivaldi antenna array can be used in the practical UWB radar and communication system, which can increase the gain, as it has narrow beam width. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2117–2120, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21873

A Chebyshev Tapered TEM Horn Antenna

An exponential TEM horn antenna with Chebeyshev impedance taper is designed and constructed. The results show improved directivity of the antenna and a wider range of frequencies with a VSWR less than two, over the entire band. DOI: 10.2529/PIERS060902041831

Experimental Field Statistics Validation in a Cubic Reverberation Chamber with Mechanical Mode Stirring &amp; Bistatic Illumination

The paper gives an critical overview of measurements carried out in the cubic reverberation chamber at Royal Military Academy (2,5 ×2,5 ×2,5m 3 ). The room is equiped with a mechanical mode stirrer illuminated simultaneously by two small cross-polarized ultra-wideband TEM horns. The frequencies of interest are between 800 MHz and 2,5 GHz. Though the whole validation of the chamber as immunity testing facility is still in progress, the results presented here point out that what could firstly be seen as a drawback - the cubic shape - can be effectively overcome by carefully designing the mode stirrer. Spatial homogeneity of the field, stirring efficiency ratio at different frequencies and CDF at the expected LUF (least usable frequency) are presented and critically commented.

A novel UWB feeding mechanism for the TEM horn antenna, reflector IRA, and the vivaldi antenna

This work proposes a method for feeding a balanced IRA with an unbalanced transmission line. This method is based on the current distribution on the surface of the antenna. The method of moments (MoM) simulations show that for the IRAs, there are some areas with low current density in comparison to the current density of the feeding points, almost over the entire frequency range. The coaxial cable is attached to the antenna's body all the way from the feeding point to an area of low current density, and extends out of the antenna structure at that point. This tremendously reduces the current density on the body of the coaxial cable. As a result, the current balance between two parts of the antenna is not disturbed. This method is applied to the TEM horn antenna, the reflector IRA, and the Vivaldi antenna. The TEM horn antenna was simulated using the HEMI software, and was fed by an unbalanced coaxial cable, both directly at the feeding point and using this method. This method was also applied to the reflector impulse-radiating antenna. Also, the Vivaldi antenna was fed both by considering the low-current density area and direct feeding. The E-plane far-field pattern of the new feeding method had good agreement with the result generated by the HEMI software for the balanced-fed antenna.

A Compact Source of Subgigawatt Subnanosecond Pulses

The system comprises a nanosecond solid-state opening switch (SOS) generator that charges resonantly a short pulse-forming line (PFL) through a decoupling inductor, one or two pulse-compression stages based on high-pressure gas spark gaps (SGs), a matched load and several built-in voltage and current probes. Weighing less than 50 kg, the pulser provides up to 160-kV subnanosecond pulses at a 37.5-/spl Omega/ load at a repetition rate of up to 300 Hz. The pulsewidth can be regulated from 2 ns down to 300 ps without SG depressurization. The rise- and fall times are 180 and 100 ps, respectively. Alternatively, unipolar or bipolar output can be provided. The latter was formed by a synchronous operation of SGs located at the beginning and at the end of a PFL; thus, an active conversion of unipolar to bipolar output was realized. The load peak-to-peak voltage was almost two times as high as the amplitude of the unipolar pulse. In the active converter, a virtually identical electrical field stress across the switching SGs was achieved, which alone provided its stable operation. Circuit analysis accounting for distributed character of the components and numerous parasitic parameters is presented. Voltage and current measurement means were developed and time-domain calibrated. Waveforms probed at different locations of the pulser system, from the SOS generator to the load, are presented. The experimental results are in fair agreement with PSpice simulations used for the hardware design. Life test of a one-stage compressor with two types of electrode systems was performed, and the results are reported. The pulser was tested with a TEM horn antenna. The effective potential (field multiplied by distance) of this radiation source is 640 kV in far field.

Simulation of ultra‐wideband indoor propagation

AbstractA comprehensive simulation of ultra‐wideband signal propagation in indoor environments is presented. The simulation is based on time‐domain electromagnetic modeling of transmitting and receiving antennas and the analysis of wave propagation through indoor channels using the time‐domain uniform theory of diffraction. The antennas are a pair of TEM horns which are modeled as arrays of vee dipoles. The analysis of these antennas is performed directly in the time domain, without the need for transforming the solutions from the frequency domain to the time domain. The frequency dependence of materials utilized in the structure on the indoor channel is accounted for in the channel simulation. The simulation results are compared with the corresponding measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 103–108, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20221