i

, NBS

' PUBLICATIONS

NBSIR 78-876

TRANSIENTS IN RESISTIVELY LOADED ANTENNAS AND

THEIR COMPARISON WITH CONICAL ANTENNAS AND TEM HORNS

Motohisa Kanda

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80303

100

U56

78-875

1978

c. 2

March 1978

MATIONAI. BUREAU

07 BTAKDARJDS

UBBART

NBSiR 78-876 OCT 5 1981

TRANSIENTS IN RESISTIVELY LOADED ANTENNAS AND

THEIR COMPARISON WITH CONICAL ANTENNAS AND TEM HORNS

Motohisa Kanda

Electromagnetics Divi s

i qn^

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80303

1? «. ^ ^4

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

March 1978

s
(i
CONTENTS

Page

ABSTRACT c. 1

I. INTRODUCTION 1

II. THE RECEIVING AND TRANSMITTING TRANSIENT RESPONSES 2

III. THE EFFECTIVE LENGTH AND THE DRIVING-POINT IMPEDANCE OF A

RESISTIVELY LOADED LINEAR ANTENNA 3

IV. THE EFFECTIVE LENGTH AND THE DRIVING-POINT IMPEDANCE OF A

CONICAL ANTENNA 5

V. THE ANALYSIS FOR A TEM HORN 6

VI. FREQUENCY DOMAIN RESULTS 8

VI. 1 Resistively Loaded Linear Antenna 9

VI. 2 TEM Horn 10

VI. 3 Conical Antenna 10

VII. TIME DOMAIN RESULTS 10

VII. 1 Resistively Loaded Linear Antenna 10

VII. 2 TEM Horn .... 11

VII. 3 Conical Antenna 11

ACKNOWLEDGMENT 12

REFERENCES 13

FIGURE CAPTIONS 14

»

iii

TRANSIENTS IN RESISTIVELY LOADED ANTENNAS AND

THEIR COMPARISON WITH CONICAL ANTENNAS AND TEM HORNS

Motohisa Kanda

Electromagnetics Division

National Bureau of Standards

Boulder, Colorado 80302

The receiving and transmitting transient responses for a relatively short, linear antenna with continuous resistive loading are investigated theoretically and experimentally. The

antenna considered is a nonconducting cylinder with continuously

deposited, varying-conductivity, resistive loading.

The current distribution, the corresponding effective length,

and the driving point impedance are calculated by use of the

method of moments and compared with the Wu-King approximation.

The receiving and transmitting transient responses are calculated

in the frequency domain using the results of the effective length

and driving point impedance. The use of FFT then allows the

determination of transient fields for a known input waveform.

The receiving and transmitting transient responses for a conical

antenna and a TEM horn are also investigated theoretically to

compare with the transient response of the resistively loaded

antenna

.

Time domain measurements were performed using a time domain

antenna range with a time domain automatic network analyzer. The

agreements between theory and experiments of the receiving and

transmitting transient responses for the resistively loaded

antenna, the conical antenna, and the TEM horn are very good.

The receiving transient response of the resistively loaded

antenna indicates that an impulse shape of 70 ps duration is well

preserved. This provides the unique capability of this antenna to

measure fast, time-varying, transient fields with minimal pulseshape distortion due to nonlinear amplitude or phase characteristics.

Key words: Conical antenna; EMP; FFT; loaded antenna; method of

moments; TEM horn; time domain measurements; transients in resistivity.

I. INTRODUCTION

Recent study related to electromagnetic pulse (EMP) phenomena has focused

strong attention on the subject of transient EM fields. Antenna structures

which are able to preserve time-domain waveform of EMP need to be inherently

broadband and non-dispersive. One such antenna which has been successfully

fabricated is a linear antenna with continuously tapered resistive loading [1,

2, 3, 4].

In the previous papers by the author [3, 4], the current distributions on the resistively loaded linear antenna were calculated by solving the wave
equation nximerically using the method of moments [5]. Using the current distribution obtained by the method of moments, other quantities of interest, such as the input admittance, the near-field and far-field radiation patterns, and the

radiation efficiency, were calculated and compared with the results calculated

from the Wu-King current distributions [1]. To verify the theoretical results,

several resistively loaded linear antennas were fabricated, and their CW receiving characteristics were examined theoretically and experimentally. The CW

receiving characteristics were examined using both a TEM cell [6] and a nearfield extrapolation range [7] to cover the frequency range from 5 kHz to 5 GHz.

The purpose of the present paper is to theoretically and experimentally

investigate the receiving and transmitting transient responses for a relatively

short, linear antenna with continuous resistive loading. The antenna considered

is a nonconducting cylinder with continuously deposited, varying-conductivity,

resistive loading.

The current distribution, the corresponding effective length, and the

driving point impedance of the resistively loaded linear antenna are calculated

by use of the method of moments [5] and compared with the Wu-King approximation

[1]. The receiving and transmitting transient responses of the resistively

loaded linear antenna are calculated in the frequency domain using the results

of the effective length and the driving point impedance. The use of the fast

Fourier transform' (FFT) then allows the determination of transient fields for a known input waveform. As a comparison, the receiving and transmitting transient

responses for a conical antenna and a TEM horn are also investigated theoretically.

Finally, the time domain measurements were performed using a time domain

antenna range with a time domain automatic network analyzer. The comparison

between theoretical and experimental results of the receiving and transmitting

transient responses for the resistively loaded linear antenna, a conical antenna, and a TEM horn are also given in this paper.

II. THE RECEIVING AND TKANSMITTING TRANSIENT RESPONSES

rad The radiated electric field E- (f) from a linear antenna at distance r in

9

the far-field region is given by [8]

rad

(f) - j

60 V^(f)

F(f) (1) zAf) + z o S r

2
where F(f) is the field characteristic of an antenna with an antenna impedance

Z (f), V (f) is the driving voltage of a generator with an impedance Z , f is a

o o g

frequency, and k is a wave nxamber. The transmitting transfer function of the

antenna is then defined as E^d -jkr

s,(f) ^ v7F) - j z (f? ^ Z

^ • o o g

When the same antenna is used for receiving, the received voltage V (f ) across a load impedance Z^ is given by

-h (f)E^''''(f)Z- -

Z (f ) ^ Z, ' O L

inc where E (f) is a normal incident field to an antenna with an effective length

h^(f). The receiving transfer function of the antenna is then defined as

V (f) -h (f) Z ^ E^^^f) ^o^^^ h

Here a field characteristic F(f) and an effective length h^(f) are related

through the Rayleigh-Carson reciprocity theorem [8],

F(f) = kh^(f). (5)

Therefore, for the analysis of general transient phenomena in the far-field

region, it should be noted that a transmitting transient response is simply the

time derivative of a receiving transient response.

III. THE EFFECTIVE LENGTH AND THE DRIVING-POINT IMPEDANCE

OF A RESISTIVELY LOADED LINEAR ANTENNA

For a linear antenna with continuous resistive loading where the internal

impedance per unit length Z (z) is given by

the approximate current distribution is found to be of a traveling wave in

nature [1], i.e..

3
I (z) =

•z^ ' 60iJ;(l-j/kh)

e-^^l^l . (7) h

The symbols have the following meanings: a is a radius of an antenna, h is a half physical length of a dipole antenna, k is a wave number.

T s 2 sinh - - C(2ka,2kh) - jS(2ka,2kh) ^ kh ^^'^ ^

and C(a,x) and S(a,x) are the generalized cosine and sine integrals.

In the previous papers by the author [3, 4], the current distribution on

the resistively loaded linear antenna for different frequencies is calculated by

solving the one-dimensional wave equation nximerically using the method of

moments [5]. The detailed discussion on the subject is given elsewhere by the

author [4]. Here, to simplify the integral equation, it is assumed that a wire

radius, a, is much smaller than a wavelength, X, i.e., a << X, so that the

current can be considered to flow in a filament along the z-axis rather than on

the surface of a cylinder.

The numerical solutions using the method of moments and the analysis based

on the approximations by Wu and King have been applied to a resistively loaded

linear antenna. The resistive antenna elements are made by depositing a linearly tapered thin film alloy on a glass rod. For a dipole configuration, a glass rod, 15 cm long and 0.254 cm in diameter, is used as a substrate for the

deposited element. The resistive loading profile and the photograph of the

resistively loaded dipole antenna are, respectively, shown in figures 1(a) and

Kb).

The magnitude and the phase of the current distributions on the resistively

loaded antenna are calculated using both the method of moments and the Wu-King

approximation [1], and are shown in figure 2 at 1 GHz along with experimental

result.

The effective length, h^(f), of the resistively loaded linear antenna is

calculated by

z -h

Using the approximate current distribution given in eq (7), the effective length

h^Cf) and the driving-point impedanc

antenna are calculated and given by

h^Cf) and the driving-point impedance Z^(f) of the resistively loaded linear

4
h (f) = -|- d-jkh-e"^^) (9)

k h

and

Z^(f) = 60^1-^). (10)

The effective length and the driving-point impedance are shown in figures 3 and

4, respectively.

The more exact analyses for the effective length and the driving-point

impedance of the resistively loaded linear antenna were performed by numerically

integrating eq (8) for the current aistribution obtained by the method of

moments, and are also shown in figures 3 and 4, along with experimental results.

The results of the effective lengths and the driving-poing impedances

obtained from both the approximate current distributions and the moment method

results are used in eq (1) and (3) to calculate the receiving and transmitting

transient responses in the frequency domain. The use of the FFT then allows the

determination of transients fields for a known input waveform.

The effective length, h^(f), of a conical antenna can be derived from its

radiation field using the Rayleigh-Carson receiprocity theorem. The drivingpoint impedance, Z^(f), of a conical antenna is given by the ratio of the frequency domain representation of the voltage applied at the antenna terminal to

the frequency domain representative of the resultant current flowing into the

antenna terminal. The detailed analyses of the effective length, h^(f), and the

driving-point impedance, Z^(f), of a conical antenna were performed by C. W.

Harrison, Jr., and C. S. Williams, Jr. [9], and are given below.

IV. THE EFFECTIVE LENGTH AND THE DRIVING-POINT

IMPEDANCE OF A CONICAL ANTENNA

h^(f) » 1 fe jkir-r — e - d

00 2n + 1 1

n+1

n + n h

n-1

(k£) (k£) (U)

5
and

1 - -

a

a-' The symbols have the following meanings:

I is the length of the antenna,

P^(cos 9) is the Legendre polynomial of order n,

(2) h^ (kJl) is the spherical Hankel function of the second kind.

•

' ? e Z =» "o— 5.n. cot —77 .

(12)

8 -j2ka — = e a

1 + j 2ttZ

2n + 1

n(n + 1)

P (cos 9 ) n o n=l

n=l

1 4. • 'o Y 2n + 1 " ^ 27rZ ^ n(n + 1

P (cos 9 ) n o

and

C,(ka)

h^^^(kil) n

h<2)(^,5,) . n ^(2)(^^)

n-1 ka n

The results of the effective length and the driving-point impedance given

respectively by eq (11) and (12) are used in eq (1) and (3) to calculate the

receiving and transmitting transient responses in the frequency domain. The use

of FFT then allows the determination of transient fields for a known input

waveform.

V. THE ANALYSIS FOR A TEM HORN

Since the concept of an effective length becomes ambiguous for a TEM horn,

the transmitting transient response in a TEM horn is calculated from the radiation field of a TEM horn. The receiving transient response is then determined

using the Rayleigh-Carson reciprocity theorem given in eq (5) in conjunction

with eq (1) and (3)

.

6
It is assumed that the horn flare angle and the plate widths are chosen so that the TEM horn guides only the Ttii mode by maintaining a constant characteristic impedance. Then, by neglecting the edge diffraction effect and fringe

fields, the linearly polarized spherical field at the aperture is assumed to be

2 -jk (/r^+x'^+y'^ - r ) r o o Ey(x',y',0)

° ^ Z= '» (13)

/r^ + x'^ + y'^ /r^ + y'^

Here, the orientation of the x'y'z' coordinates is shown in figure 6, in which

the source is assumed to be at a distance r from the center of the aperture.

The radiated electromagnetic fields, E (x,y, z), outside the aperture are

then evaluated by use of the plane-wave spectrum analysis technique [10]. That

is, since _ T _ j(k x'+k v')

S(k^,k)=|^// E(x',y',0)e ^ dx'dy', (14)

aperture

then

, 1 " _ "j (k x+k y+k z)

F^'^(x,y,z) =

j;^ // S(k^,k )e ^ ^ ^ dk^ dk (15)

2 2 2 2 2Tr 2 with k +k +k =k » (—) . These integrations were carried out by use of

X ^ Z A

an ITT algorithm.

The other and perhaps more conventional technique for calculating the

radiation field of a TEM horn is as follows. Given the aperture electric field,

E, in eq (13), one can determine an equivalent magnetic current, M, at the

aperture by

M » 2? X n (16)

By use of an electric vector potential ^, i.e.,

-ikr

aperture

Mf ds , (17)

one can determine the electric and magnetic fields through the following relationships :

7
E = - V X F (18)

and

H = -j(ue^F +^ V(V.f). (19)

As an example, the component becomes

E "^(x,y,2) -

1:;^ // M^(x',y') (jk^i) • -^-^ • f

dx'dy' (20)

aperture

These two techniques are used to calculate the radiation field from a TEM

horn in the frequency domain. The receiving characteristic of a TEM horn is

determined from the transmitting characteristic by use of the Rayleigh-Carson

reciprocity theorem given in eq (5) with eq (1) and (3)

.

VI. FREQUENCY DOMAIN RESULTS

In this section, the receiving and the transmitting characteristics of the

resistively loaded dipole, a conical antenna, and a TEM horn are given in the

frequency domain. The receiving and the transmitting characteristic are evaluated theoretically and compared with experiments.

The experiments are performed using a time domain antenna range with a time

domain automatic network analyzer (TDANA) . The transmitting characteristics of

antennas are determined experimentally by using the resistively loaded antenna

for a standard receiving antenna, since its receiving characteristic is well

defined theoretically as given in section VI. 1. On the other hand, the receiving characteristics are determined experimentally by using a conical antenna for

a standard transmitting antenna, since its transmitting characteristic is well

defined theoretically as given in section VI. 3. The TDANA measures the time

domain waveform of the impulse response.

The time domain waveform is then digitized and stored in the minicomputer

memory. By acquiring an ensemble of many waveforms, it is possible to perform

signal averaging within the minicomputer to improve the signal to noise ratio in

the measurements. The minicomputer then computes the receiving and the transmitting characteristics from the digitized, averaged waveform using the FFT.

8
VI. 1 Rests tively Loaded Linear Antenna

The magnitude and the phase of the transfer function of the receiving

characteristic for the resistively loaded linear antenna with 100 f2 load are calculated theoretically and are respectively shown in figures 5(a) and 5(b)

along with the experimental results. Generally, the agreement between theory

and the experimental result is very good.

It is found from figure 5 that the magnitude of the receiving transfer

function is relatively flat above 200 MHz, whereas it rolls off 6 dB per octave

below 200 MHz. The phase of the receiving transfer function is constant over

the frequency range from 100 kHz to 100 MHz. Although the relatively small

phase dispersion takes place above 100 MHz, the over-all phase degradation for

the entire frequency range from 100 kHz to 10 GHz is only 160 degrees.

VI. 2 TEM Horn

The magnitude of the receiving transfer function for a 36 cm long TEM horn

with 100 £2 load is calculated theoretically and is shown in figure 6 along with

the experimental results. The agreement between theory and the experimental

result is good except at frequencies below 50 MHz. The theoretical result for

the receiving transfer function of the TEM horn is based on the assumption that,

regardless of its operation frequency, the tangential electric field at the TEM

horn aperture is assumed to be a linearly polarized spherical wave as given in

eq (13). Moreover, the magnitude of the assumed linearly polarized spherical

wave at the horn aperture is assumed to be constant with frequency by ignoring

all the reflections both at the aperture and at the throat at the TEM horn. It

is, however, apparent from the results of reflection coefficient measurements

made for the TEM horn that the reflection, particularly at the horn aperture,

becomes very severe at 100 MHz ('>>0.98).

Therefore, the assumption of tue constant spherical field at the horn

aperture totally fails in the frequency range below 100 MHz. Moreover, it is

also apparent that particularly at the low end of the frequency range below

100 MHz, when the aperture size (21.6 cm in this case) becomes much smaller than

a half-wavelength, the assumption of a linearly polarized spherical wave at the

horn aperture may also fail. An improved theoretical model, which will take

into account the effects due to the aperture and the throat of the TEM horn,

will be developed and presented as the subject of a future paper.

9
VI. 3 Conical Antenna

The transfer function of the transmitting characteristics for a conical

antenna (2.7 m long, 8 degrees apex angle) is calculated theoretically and is

given in figure 7. In this figure, there are two curves, one of which corresponds to sunnnation up to 57 terms and the other corresponds to summation up to

139 terms in eq (11) and (12). Both the curves agree with each other very well, \ indicating that the convergence is very good for a numerical solution with a 57-

term summation. It is found from figure 7 that the transfer function of the

transmitting characteristic for the conical antenna is reasonably flat above

10 MHz.

.

'

ii

VII. TIME DOMAIN RESULTS

Once frequency domain solutions are determined, use of the FFT then allows

the determination of transient fields for a known input waveform. The experiments were performed by use of a time domain antenna range with a time domain

automatic network analyzer. The impulse generator generates extremely narrow

(70 ps) duration impulses with relatively flat spectrum amplitudes greater than

60 dByV/MHz up to 5 GHz as shown in figure 8.. This impulse was used both as a driving voltage for the investigation of

transmitting transient responses and as an incident impulse field for the investigation of receiving transient responses.

VII. 1 Resistively Loaded Linear Antenna

The receiving and the transmitting characteristics of the transient responses

for the resistively loaded linear antenna are calculated theoretically using the

FFT and shown respectively in figures 9(a) and 9(b) along with the experimental

results. Generally, the theoretical results based on the current distributions

by the method of moments and by the Wu-King approximation agree very well with

the experimental results.

As indicated in figure 9(a), the original 70 ps pulse was broadened due to some dispersion. Figure 9 also indicates clearly that the transmitting characteristic of the transient response is proportional to its receiving characteristic differentiated with respect to time, as expected from the Rayleigh-Carson

reciprocity theorem given in eq (5).

10
VII. 2 TEM Horn

The receiving and the transmitting characteristics of the transient responses

for the TEM horn are calculated theoretically and are shown in figure 10 along

with the experimental results. The agreement between the theory and the experiments is very good, although the theory developed in Sec. V fails at frequencies

below 100 MHz. Since the lowest frequency points included in the FFT analysis

is 20 MHz, the deficiency in the theory at the frequency range between 20 MHz

and 100 MHz, which corresponds to only 5 frequency points in the FFT analysis,

does not seem to affect much the time domain waveform.

VII. 3 Conical Antenna

The transmitting characteristic of the transient response for the conical

antenna is calculated theoretically and given in figure 11 along with the experimental result. The theoretical calculations for the time domain waveform using

the 57-term summation agree very well with that using the 139-term summation.

VIII. CONCLUSION

The receiving and transmitting transient responses of the resistively

loaded linear antenna, the TEM horn, and the conical antenna are investigated

theoretically and experimentally using the FFT technique. The receiving transient response of the resistively loaded linear antenna indicates that the shape

of a 70 ps impulse is well preserved.

The results of theoretical and experimental investigations indicate that

the receiving and transmitting transient responses of a relatively short linear

antenna with continuously tapered resistive loading can be analyzed very well

theoretically. Since its receiving transient response is well behaved, the

resistively loaded linear antenna should find very wide applications as a standard receiving antenna for the measurements of fast, time-varying, transient

electromagnetic fields with minimal pulse-shape distortion due to nonlinear

amplitude or phase characteristics.

11
ACKNOWLEDGMENT

The author wishes to thank A.R. Ondrejka for careful time domain measurements

and B.K. Bender for computer assistance. Acknowledgment should also be extended

to Dr. P.F. Wacker, F.X. Ries and C.K.S. Miller for many stimulating discussions

and encouragement during the course of this work.

12
REFERENCES

[l] Wu, T. T. and King, R. W. P., The cylindrical antenna with nonref lecting

resistive loading, IEEE Trans. Antennas Propagat., AF-13 , No. 6, pp.

369-373 (May 1965).

[2] Shen, L. C, and King, R. W. P., The cylindrical antenna with nonreflecting

resistive loading, IEEE Trans. Antennas Propagat., AP-13 , No. 6, p. 998

(Nov. 1965).

[3] Kanda, M. , The characteristics of a relatively short broadband linear

antenna with tapered resistive loading. International lEEE/AP-S Symposium

Digest, Stanford, California (June 1977)

[4] Kanda, M. , A relatively short cylindrical broadband antenna with tapered

resistive loading for picosecond pulse measurements, to be published in

IEEE Trans. Antennas Propagat. (May 1978).

[5] Harrington, R. F. , Field Computation By Moment Methods (The Macmillan Co.,

New York, 1968)

[6] Crawford, M. L. , Generation of standard EM fields using TEM transmission

cells, IEEE Trans. Electromagnetic Compat., EMC-16 , No. 4, pp. 189-195,

(Nov. 1974).

[7] Bowman, R. R. , Calibration techniques for electromagnetic hazard meters;

500 MHz to 20 GHz, Nat. Bur. Stand. Internal Report 75-805 (April 1976).

[8] King, R. W. P., The Theory of Linear Antenna (Harvard University Press,

Massachusetts, 1956).

[9] Harrison, Jr., C. W., and Williams, Jr., C. S., Transients in Wide-Angle

Conical Antennas, IEEE Trans. Antennas Propagat., AP-13 , po. '236-246,

(March 1965).

[10] Kerns, D. M. , Plan-wave scattering-matrix theory of antennas and antennaantenna interactions: formulation and applications, J. Res. Nat. Bur.

Stand., 8QB , No. 1, pp. 5-49 (Jan. -March 1976).

13
FIGURE CAPTIONS

Figure 1 Dipole with continuously tapered resistive loading.

a) Resistive loading profile

b) Photographs of resistively loaded dipole

Figure 2 Current distribution of resistively loaded dipole at 1 GHz.

Figure 3 Effective length of resistively loaded dipole.

Figure 4 Driving-point impedance of resistively loaded dipole.

a) Real part (resistance)

b) Imaginary part (reactance)

Figure 5 Receiving transfer function of resistively loaded dipole.

a) Magnitude

b) Phase

Figure 6 Receiving transfer function of TEM horn.

Figure 7 Transmitting transfer function of conical antenna.

Figure 8 Time domain measurement.

a) Time domain picosecond impulse

b) Spectrum amplitude of picosecond impulse

Figure 9 Transient response of resistively loaded antenna. .

a) Receiving characteristic

b) Transmitting characteristic

Figure 10 Transient response of TEM horn.

a) Receiving characteristic

b) Transmitting characteristic

Figure 11 Transmitting transient response of conical antenna.

14
_J J

1 J

1 ,

I K —• DESIRED RESISTIVE LOADING PROFILE •

I X ACTUAL RESISTIVE LOADING PROFILE /

III•

I

III

/t/

/

•

102

10^

10'

ANTENNA END-^^

J ' ' I ! \ I L 0,01 0.02 0.03 0.04 0.05 0.06 0.07

POSITION ALONG ANTENNA (m)

Dipole with continuously tapered resistive loading

a) Resistive loading profile.

15
Figure 1. Dipole with continuously tapered resistive loading,

b) Photographs of resistively loaded dipole.

16
17

o o o . o ^ n CM r—

(y) 33N\/iSIS3il

19
-10

-10'

\

L. \

-10'

-10

-10'

-10'

I 1 1 1 1 ii|—I—I 1 1 1 1 1 1|—I

I 1 1 1 1 m

C=0.54pF \.

-X MOMENT METHOD

• • WU-KING'S THEORY

o o EXPERIMENT

' t t t I I il

I 1—t_Li

IMHz lOMHz lOOMHz IGHz

FREQUENCY

Figiire 4. Driving-point impedance of resistively loaded dipol*

b) Imaginary part (reactance)

.

20
• X • X

O ax

O • X

9

I— 32 —

Z — OS LU LU S • a. O =5 X

X • o

O

C3

3=o

o

ocn

I o

I o o

I oCOi o

I o

>-

o

o.

•o

<uo

0) ^

CO •H

caM

o

(3O

t4U

o6

9

«4>4 U

a

c

(0 lU 4J 3 e c

•H 00

u

m

3

6fl

(9P) NOIiONnj ilBiSNVyi JO 3aniIN9VW

21
J • 1 1

1 o o o O o

o a U) o en CM CM o

o

o

COO

(U

oa •H

03<UU

«Moe

o

V4

(U

M-lGOG

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u

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0) 0$

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&0

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Pl4

IDm

CO PU

(33^930) NOIiONnj HSJSNVyi AO 3SVHd

22
(9P) NOIlDNflJ ^HJSNVyi iO HQnilNSVW

23
•5C

-60

-70

-30

-90

TOO

no

^ -120

o

UJS -130

COo

I—o

-140

150

-1 60

-170

- 9

180

1 MHz 10 MHz

o

CONICAL ANTENNA

TRANSFER FUNCTION OF

TRANSMITTING CHARACTERISTICS

O 57 TERMS

X 139 TERMS

100 MHz

\

1 GHz 10 GHz

FREQUENCY

Figure 7. Transmitting transfer function of conical antenna.

24
I I

25
26
I i i I I I I I r

» »

i i i I ^ '

< 0.0 0.5 1.

TIME (ns)

Figure 9. Transient response of resistively loaded antenna,

a) Receiving characteristic.

27
T \ 1 I I I I r

0.0 0.5 1.0

^ TIME (ns)

Figure 9. Transient response of resistively loaded antenna,

b) Transmitting characteristic.

28
1 I I \ I I I I I TEM HORN

RECEIVING CHARACTERISTICS

f f i I I t f t i 0.0 0.5 ' 1.0

TIME (ns)

Figure 10. Transient response of TEM horn.

a) Receiving characteristic.

29
30
t I I I I I 1 I I

I ! I 0.0 0.5 KO

TIME (ns)

Figure 11. Transmitting transxent response of conical antenna.

31
NBS-lUA (REV. 7.73>

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 78-876

2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Transients In Resistively Loaded Antennas and Their

Comparison with Conical Antennas and TEM Horns

5. Publication Dace | March 1978

6. Performing Organization Code '

276.03 ^

7. AUTHOR(S)

Kanda, Motohisa

8. Performing Organ. Report No. 2763281

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Taslc/Work Unit No.

11. Concracc/Granc No.

12. Spoasoring Organizacioa Name aad Complete Address (Street, City, State, ZIP)

Same as #9.

13. Type of Report & Period

Covered

14. oponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or leas [actual stamnaTy ol most sigrtilicant information. It document includes a si^tilicant bibliography or l iterature survey, mention it here.) ^

I The receiving and transmitting transient responses for a relatively short, linear

J antenna with continuous resistive loading are investigated theoretically and experi- j mentally. The antenna considered is a nonconducting cylinder with continuously depos- i ited, varying-conductivity, resistive loading,

j The current distribution, the corresponding effective length, and the driving point

j impedance are calculated by use of the method of moments and compared with the Wu-King

; approximation. The receiving and transmitting transient responses are calculated in

the frequency domain using the results of the effective length and driving point impedance. The use of FFT then allows the determination of transient fields for a known

input waveform. The receiving and ^transmitting responses for a conical antenna and a TEM horn are also investigated theoretically to compare with the transient response of

the resistively loaded antenna.

Time domain measurements were performed using a time domain antenna range with a time domain automatic network analyzer. The agreements between theory and experiments

of the receiving and transmitting transient responses for the resistively loaded antenna, the conical antenna, and the TEM horn are very good.

The receiving transient response of the resistively loaded antenna indicates that

an impulse shape of 70 ps duration is well preserved. This provides the unique capability of this antenna to measure fast, time-varying, transient fields with minimal

^pulse-shape dJ.stortion due to nonlinear amplitude or phase characteristics.

17. KEY VORDS (aix^ to twelve entries; alphabetical order; capitalize only Iti9 Brst tetter of Ae tirat key word unless a proper name; separated by semicolons) conical antenna; EMPj FPT; loaded antenna; method of moments;

TEM horn; time domain measurements; transients in resistivity.

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