2008_Design and analysis of TEM horn antennas for ultra-wideband technology

Ultra-Wideband Technology

Ying Suo, Jinghui Qiu, Yeshu Yuan

School of Electronics and Information Technology Harbin Institute of Technology, Harbin, 150001, China

suoyingsing@126.com

Abstract—TEM horn antennas for utra wideband (UWB) system applications are proposed in which offer unique advantages by their own structure characters. To realize ultra wideband and high gain operations, some antennas are designed and compared in this paper. By optimization, two classes of antennas can both reaize the same radia character, get a satisfied gain and the bandwidth is enough for practical operation. As the UWB antenna, the group deay time is considered speciay. The simulation results and analyses at 1~18 GHz frequency band of the TEM horn antenna are presented.

method without using resistive material is necessary to resolve this problem.

In this paper, two classes of TEM horn antenna are simulated and optimized. From 1 GHz to 18GHz the return loss is better than -10dB, and the gain is above 10dB from 3GHz to 18GHz. Radiation performance with structure and dimension change are analyzed in this paper.

II.

STRUCTURE OF BASIC TEMHORN ANTENNA

The basic TEM horn antenna is a simple design, consisting of two triangular metal plates and a feeding structure, and in order to match the impedance of the TEM horn antenna, which I.INTRODUCTION

is a balanced structure to an unbalanced coaxial line, a tapered

Using of ultra-wideband antenna technologies for balun structure is needed. Just neglecting the feeding structure electromagnetic compatibility (EMC) measurement systems, at this position, the horn antenna mainly contains three the UWB radar systems, UWB communication systems and in parametric variations: a,l and h which influence the radiation both military and civilian applications continues to increase. In characters of the antenna. As shown in Fig.1 below, the order to cover the whole frequency range (30 to 1000 MHz) in parameter ais the height of the triangular metal plates, the lcommunication testing, several narrowband antennas are used denote the hemline length of the triangular metal plates, while in general. To overcome the disadvantage of the coupling in the h signify the height separation between the two plates. For many narrowband antennas, development of an efficient and the radiated characteristic antenna requirement in the high accurate broad-band antenna is necessary. The transverse frequency band, a small field angle of the TEM horn is needed electromagnetic (TEM) horn antenna is suitable for this [5]. For this antenna, the current distribution on the metal plate purpose due to its wide bandwidth, directional radiation is mainly consisting of longitudinal current in the z-axis pattern and little distortion characteristics [1]. The TEM horn direction. So the small field angle horn can be considered as antenna is the main radiation of creating electromagnetic open-end transmission line. While the transmission line can be pulse, and is also the feeding source of the pulse reflection equivalent to many pieces small of electric dipoles and plane antenna. There is an interest in using TEM horn antenna magnetic dipoles, and the superposed field of the radiation to realize ultra-wideband characters for its good performance, field is such as uniform aperture distribution and a corresponding high −s(z−z′)

cJGTOTJGaperture efficiency and low cross polarization [2]. TEM horn μ02JGe

′,s)=dEzzsdm(,[ yx(z′,s)−cdpy(z′,s)] (1) antenna is a high power ultra-wideband microwave antenna, 4πzc

and it has simple structure, easy to processing, as an important constituent of the ultra-wideband system, can get extensive use.

TEM horn antenna is used as pulse radiation antenna, and as a result, people sometimes attached much importance to the time domain parameter character. But the frequency domain character is also important. To realize the ultra-wideband

lperiments character mentioned above, many researches and ex

have been utilized in different method. Paper [3] proposed the antenna with resistive pad. To reduce the distortion and the reflection at open end, paper [4] proposed the antenna with resistive sheet. However, these antennas used resistive l

Fig.1 TEM horn antenna without feeding structure material so that they had low efficiency. An alternative design

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2008Asia-PacificSympsoiumonElectromagneticCompatibility&

InternationalZurichSymposiumonElectromagneticCompatibility,19–22May2008,Singapore

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19thInternationalZurichSymposiumonElectromagneticCompatibility,19–22May2008,Singapore

Using parameter r in place of parameter z accordingly, and by integral transformation, the time domain radiation equation of the TEM horn antenna on the axis becomes

OTET(r,tr)=−y

the phase velocity change seriously in low frequency band,

and the signal transmission is stable in high frequency band.

V0hc

[δ(tr)+[−u(tr)+u(tr−2l/c)]](2)

r4πcfg2l

By the method of conformal mapping, the characteristic

impedance of the TEM horn antenna is given by

­120lnª°¬8hw+w(4h)º¼ w/h<1 (3) Zc=®°¯120ln[wh+1.393+0.677ln(wh+1.444)]w/h≥1

where w and h are separately expressing the width and height

of the antenna bore.

The software CST MWS based on time-domain finite integration technique is used to simulate the basic TEM horn antenna. In simulated model, the parameter a is 450mm, equals to 1.5 󰀂L, the parameter l employs 180mm, which is 0.6 󰀂L, and the parameter h is 60mm, mentioned here that 󰀂L is corresponding to low frequency end. The feeding of the discrete port chooses 150󰀃 to realize impedance matching, and the distance between the two metal plates at the feeding port is 2mm.

In CST MWS, the incident voltage is the time derivative of Gaussian of pulse:

Fig.3 Radiation patterns at selected frequencies

󰀍󰀒󰀍󰀋󰀒󰀋󰀕󰀒󰀕󰀍󰀋󰀕󰀍󰀒󰀕󰀃󰀋󰀋󰀒󰀍󰀋Frequency(GHz)group delay (ns)ª

Vin(t)=−t−t0exp«−(t−t0)

tp2t2«p¬

−10

2

º

» (4) »¼

III.

󰀍󰀒󰀃󰀋where tp=3×10s, t0=2×10s.

Fig.2 illustrates the return loss of the basic TEM horn antenna. Obviously, the return loss is better than -10dB from 1 GHz to 18GHz frequency band, and better than -13dB from 1.8GHz to18GHz. For the symmetrical structure of basic TEM horn antenna, the x-z plane radiation pattern can illustrate the whole radiation pattern as shown in Fig.3. The radiation pattern at 1GHz, 3GHz, 5GHz and 10GHz are given below. It can be seen that in low-frequency the radiate character deteriorates seriously. While fortunately the deterioration situation vanishes quickly. And the gain of the TEM horn antenna is above 10dB from 3GHz to 18GHz, so it can satisfy some high gain directing operation. Fig.4 shows the group delay time of the basic TEM horn antenna. It illustrates that 󰀋󰀕󰀍󰀋S11ÄdBÅ−10

Fig.4 Group delay time of basic TEM horn antenna

DESIGN AND SIMULATION OF TEMHORN $NTENNA

WITH FLOORBOARD

󰀕󰀃󰀋󰀕󰀐󰀋󰀕󰀊󰀋󰀋󰀎FrequencyÄGHzÅ󰀍󰀃 󰀍󰀌For reducing the dimension of the TEM horn antenna, a

new TEM horn antenna model which changes one of the triangular metal plates into a floorboard with the dimension of 610×254 mm2 is built and simulated. This change can not only simplify the structure, but also cut down to half its height. So based on the structure mentioned above, the character of the new model is also good and more attractive in fabrication. Fig.5 shows a TEM horn antenna with a floorboard. The TEM horn antenna includes a triangular metal plate, a floorboard and the coaxial-line feeding part. It uses the standard 75󰀃coaxial-line. The TEM horn antenna can realize the impedance conversion from 75󰀃 coaxial- line to the 377󰀃 of the bore resistance. The feeding structure is very important to calculate the resistant of the TEM horn antenna.

Fig.6 illustrates the return loss of the simulation result of the antenna, and it can completely meet the need for the use of ultra-wideband. As the unsymmetrical structure, the radiate pattern correspondingly alters. The main radiation direction should at the field angle between the triangular metal plates and the triangular metal plates, as illustrate in Fig.7, main lobe direct at theta=80º approximately. The directivity character at

Fig.2 Return loss of the basic TEM horn antenna

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2008Asia-PacificSympsoiumonElectromagneticCompatibility,19–22May2008,Singapore

1 GHz is not good, but the gain is superior to 10 GHz and is similar to the TEM horn without floorboard.

For any TEM horn antenna, the characteristic impedance is influenced by the height of the triangular metal plates and the hemline length of the triangular metal plates, as a result, methods for accurately designing these parameters to match the impedance become considerable importance. When the parameter m (distance between the floorboard and the peak of triangular metal plate) changes weakly, the characteristic impedance will alter severely. So a group of TEM horn 1-10 GHz frequency range with the m changes are given, and the input resistance of the coaxial-line chooses 75󰀃. As can be seen in Fig.8, the parameter m needs a very accurate calculation and fabrication dual to the severe deterioration of return loss. It increases the manufacture difficulty to some degree, and working accuracy need further improved.

Fig.9 shows the group delay time of the TEM horn antenna with floorboard. It can be seen the phase velocity change seriously from 1GHz to 4 GHz in low frequency, and the signal transmission is stable in high frequency. m=2mm󰀋󰀕󰀒󰀕󰀍󰀋S11ÄdBÅm=2.5mmm=1mm󰀕󰀍󰀒󰀕󰀃󰀋󰀕󰀃󰀒󰀕󰀐󰀋󰀋󰀃󰀊󰀎󰀌󰀍󰀋FrequencyÄGHzÅFig.8 The return loss with different m 󰀃󰀒󰀃󰀋Group delayÄnsÅ󰀍󰀒󰀍󰀋󰀒󰀋󰀕󰀒󰀋󰀒󰀍󰀋)UHTXHQF\\Ä*+]ÅFig.5 The model of TEM horn antenna with a floorboard

󰀋󰀕󰀒S11ÄdBÅ󰀕󰀍󰀋󰀕󰀍󰀒󰀕󰀃󰀋󰀕󰀃󰀒󰀕󰀐󰀋󰀋󰀎FrequencyÄGHzÅ󰀍󰀒󰀃󰀋Fig.9 The group delay time of TEM horn antenna with floorboard

󰀍󰀃󰀍󰀌IV.CONCLUSION

Fig.6 The return loss of the TEM horn antenna

two kind of TEM horn antenna are proposed, which has approximately the 18 times octave bandwidth, constant group delay time, high gain and the acceptable gain flatness. Return loss of the two TEM horn antenna can be both better than -10dB from 1 GHz to 18GHz. And the gain is above 10dB from 3GHz to 18GHz. The group delay time are discussed.

ACKNOWLEDGMENT

The authors would like to express their sincere gratitude to CST Ltd., Germany, for providing the CST Training Center (North East China Region) at our university with a free package of CST MWS software.

REFERENCES

[1]

J. R. T. Johnk, M. Taylor, T. J. O’Hara, “Efficient and Accurate Testing of an EMC Compliance Chamber using an Ultra-wideband Measurement System,” IEEE International Symposium on EMC, vol.1 13-17, pp.302-307 August 2001󰀡

Fig.7 The radiation pattern at selected frequencies

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19thInternationalZurichSymposiumonElectromagneticCompatibility,19–22May2008,Singapore

[2]

[3]

Sergei P. Skobelev, Per-Simon Kildal, “Analysis of Conical Quasi-TEM Horn with a Hard Corrugated Section,” IEEE Transactions on Antennas and Propagation, vol.51, No.10, pp.2723-2731, October 2003.

E. A. Theodorou, M. R. Gorman, P. R. Rigg, and F. N. Kong, “Broadband pulse-optimized antenna,” Proc. Inst. Elect. Eng. Microwaves Opt. Antennas, pt. H, vol. 128, no. 3, pp. 124–130, Jun. 1981.

[4]

[5][6]

K. L. Shlager, G. S. Smith, and J. G. Maloney, “TEM horn antenna for pulse radiation: An improved design,” Microw. Opt. Technol. Lett., vol. 12, no. 2, pp. 86–90, Jun. 1996

Everett G. Farr. A Simple Model of Small-Angle TEM Horns. Sensor and Simulation NotesèNote 340. 1992:1~23

CST Ltd, CST MICROWAVE STUDIO@ 5 User’s Manual , 200󰀐.

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