vie to?“

KM

MAR j 2 J90Q

A BROADBAND, ISOTROPIC, REAL-TIME, ELECTRIC-FIELD SENSOR (BIRES]

USING RESISTIVELY LOADED DIPOLES

Motohisa Kanda

Francis X. Ries

Donald R. Belsher

~2>t V . , n MHI

NBSIR 79-1622 /(

'

'

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

December 1979

NBSIR 79-1622

A BROADBAND, ISOTROPIC, REAL-TIME, ELECTRIC-FIELD SENSOR (BIRES)

USING RESISTIVELY LOADED DIPOLES

Motohisa Kanda

Francis X. Ries

Donald R. Belsher

Electromagnetic Fields Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

December 1979

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

LIST OF TABLES iv

LIST OF FIGURES . iv

1. INTRODUCTION... 1

2. A RESISTIVELY LOADED DIPOLE 3

2.1 Theoretical Considerations 3

2.2 Fabrication of Continuously Tapered, Resistively Loaded

Antennas 4

2.3 Receiving Characteristics of the Resistively Loaded

Dipole 5

2.4 Far-Field Radiation Patterns * 6

3. BROADBAND, ISOTROPIC, REAL-TIME, ELECTRIC-FIELD SENSOR

(BIRES) ' 7

3.1 Design Configurations 7

3.2 Frequency Response 8

3.3 Tangential Sensitivity 8

3.4 Dynamic Range 9

3.5 Isotropy 10

4. CALIBRATION OF ANTENNA FACTOR 11

4.1 Calibration Technique 11

4.2 Antenna Factors 13

5. CONCLUSIONS 14

6 . ACKNOWLEDGMENT 15

7. REFERENCES 15

i i i
LIST OF TABLES

^age

Table 1. Tangential sensitivities of BIRES 17

Table 2. Dynamic ranges of BIRES 18

LIST OF FIGURES

Figure 1. Resistive loading profile 19

Figure 2. Resistively loaded dipole 20

Figure 3. Receiving transfer function of resistively

loaded dipole 21

Figure 4(a). Radiation patterns of resistively loaded

dipoles at 100 MHz 22

Figure 4(b). Radiation patterns of resistively loaded

dipoles at 1 GHz 23

Figure 4(c). Radiation patterns of resistively loaded

dipoles at 2.5 GHZ 24

Figure 4(d). Radiation patterns of resistively loaded

dipoles at 5 GHz 25

Figure 4(e). Radiation patterns of resistively loaded

dipoles at 10 GHz 26

Figure 5. Broadband, isotropic, real-time, electricfield sensor (BIRES) .. 27

Figure 6. Block diagram of BIRES switching system 28

Figure 7. Power gain, noise figure, and output power

at 1-dB gain compression point of the broadband

shaping amplifier 29

Figure 8. Linearity of BIRES at 750 MHz 30

Figure 9(a). Isotropy of BIRES at 450 MHz 31

Figure 9(b). Isotropy of BIRES at 550 MHz 32

Figure 9(c). Isotropy of BIRES at 650 MHz 33

Figure 9(d). Isotropy of BIRES at 750 MHz 34

Figure 9(e). Isotropy of BIRES at 850 MHz 35

Figure 9(f). Isotropy of BIRES at 950 MHz 36

Figure 9(g). Isotropy of BIRES at 1 GHz 37

i v
Figure 10. Sketch of pyramidal horn dimensions in wavelengths 38

Figure 11(a). Antenna factors of BIRES for low-level

measurements... 39

Figure 11(b). Antenna factors of BIRES for high-level

measurements 40

v
'
A Broadband, Isotropic, Real-Time, Electric-Field Sensor (BIRES)

Using Resistively Loaded Dipoles

Motohisa Kanda, Francis X. Ries and Donald R. Belsher

Electromagnetic Fields Division

National Bureau of Standards

Boulder, Colorado 80303

A broadband, isotropic, real-time/ electr ic-f ield

sensor (BIRES) developed by the National Bureau of

Standards (NBS) consists of three resistively loaded

dipoles mounted orthogonally to each other. It has the

capability of measuring a complete description of

frequency, polarization, magnitude, and phase

information of the incident electromagnetic (EM)

field. The typical tangential sensitivity of the BIRES

is 13 to 16 yV/m with a usable dynamic range of 125

to 144 dB for various bandwidths in the frequency range

of 10 MHz to 1 GHz. The isotropic response, isotropy,

of the BIRES is obtained by calculating the Hermitian

magnitude of the incident .electric field, and its

variation is found to be less than ± 1 dB.

Key words: Broadband; dynamic range; electric-field

sensor;- Hermitian magnitude; isotropy; resistively

loaded dipole; tangential sensitivity.

1. INTRODUCTION

Recently, there has been a steady increase in the use of

microwave energy for commercial, industrial, consumer, and

military applications. This has created a need to measure the

electromagnetic (EM) field strength in near- and far-field

regions over a broadband frequency range of any polarization

emanating from various sources operating at many different

frequencies and traveling in any direction. For this reason,

various types of EM sensors have been developed.

The National Bureau of Standards (NBS) has developed several

energy density meters (EDMs), which consist of three orthogonal

dipoles with diode detectors connected between the arms of the

dipoles. There are also several kinds of commercially available

radiation monitors ( RMs ) , composed of three orthogonal elements

consisting of thin-film thermocouples deposited on a plastic
substrate. In these devices, the detected signals from the

orthogonal elements of the field sensor (a dipole with a diode or

with a thermocouple) are proportional to the square of the

corresponding electr ic-f ield strengths, which can then be readily

converted into units of mW/cm .

However, EDMs and RMs measure only the Hermitian magnitude

of an electr ic-f ield strength and destroy its frequency and phase

information. Frequency, phase, and magnitude information of an

EM field are particularly essential for short duration, impulsive

EM measurements. Since an EDM with a beam lead Schottky barrier

diode and an RM with a high input impedance voltmeter consist of

electrically short dipoles with high impedance loads, their

responses are relatively flat over the frequency range below the

first dipole resonance frequency [1], However, near the first

dipole resonance frequency, the responses of these devices

generally increase, and accurate EM-f ield-intensity measurements

will not be possible. For this reason, a broadband, isotropic,

real-time, electric-field sensor (BIRES) using resistively loaded

dipoles was considered.

A resistively loaded dipole developed by NBS has several

unique properties which make this antenna useful as a BIRES. The

dipole has linear magnitude and phase response over a broadband

frequency range typically between 10 MHz and 1 GHz. These

characteristics provide the unique capability for measuring fast,

time-varying EM fields with minimal pulse-shape distortion due to

nonlinear amplitude or phase characteristics. The dipole also

has a relatively effective filtering action so that EM signals

outside the frequency range from 10 MHz to 1 GHz will be

rejected. This characteristic prevents any outband response.

This antenna system provides a substantial improvement over

the previous antennas used for EM energy density measurements.

The antenna will provide magnitude, phase, polarization, and

frequency information of the EM environment. It has the ability

2
to measure electric-field strengths (i.e., magnitude, phase,

polarization, and frequency) over 10 MHz to 1 GHz in quick

succession, a procedure prohibited until now because of the need

to physically change antennas.

The purpose of this paper is to discuss the basic

characteristics of a BIRES using resistively loaded dipoles.

Section 2 discusses briefly the theoretical concepts and the

characteristics of a resistively loaded dipole. The design

considerations for a BIRES using resistively loaded dipoles are

then given in section 3. The calibration of the BIRES in terms

of its antenna factor is given in section 4.

2. A RESISTIVELY LOADED DIPOLE

2.1 Theoretical Considerations

If a cylindrical antenna has a tapered resistive loading

such that the internal impedance per unit length Z

1 (z) is a particular function of position along the antenna, Wu and

King [2,3] found that a pure outward traveling wave can exist on

an antenna of finite length, h, and radius, a. That is, if the

impedance loading is given by:

Z (z) =

60t|>

where :

( 1 )

ip = 2 [si

“1 h

inh — - C(2ka,2kh) - jS(2ka,2kh)

a J

1

^

kh

(1 - ej2kh

)

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

integrals, then the approximate current distribution for the onedimensional wave is a traveling wave such that:

3
I ( 2 ) z

( z)

V

o

60^(1 - j/kh)

I z | \ - jk | z

tt] *

The solution e

+ ^l z l does not satisfy the original wave

equation. Since the frequency dependence of Z

1 (z) appears only

in the form of a logarithm for small kh, the antenna has much

broader frequency characteristics than an antenna with lumped

resistors located at quarter-wavelengths from the ends of the

antenna [4,5]

In the present study, the resistively loaded dipole was

analyzed theoretically using the method of moments [6]. Detailed

theoretical analyses on this subject are given elsewhere by the

first author [7,8,9].

2.2 Fabrication of Continuously Tapered, Resistively Loaded Antennas

The resistive antenna elements are made by depositing,

starting at the center and proceeding outward toward the ends, a thin alloy film of varying resistivity as shown in figure 1.

This alloy, which consists of approximately 70 percent nickel,

15 percent chromium, 10 percent iron, and 2 percent titanium, has

a very high resistivity and a very low temperature coefficient.

A glass rod, 15 cm long and 0.7 cm in diameter, was chosen as a substrate for the deposited element. This becomes a half-wave

dipole; i.e., kh = ir/2 at 1 GHz. The desired resistive loading

profile, which turns out to be a relatively weak function of

frequency, is calculated and is shown in figure 1. Typically,

the resistive loading required is about 5 kft/m at the driving

point, about 10 kft/m at the midpoint, and infinite at the end

of the antenna. Knowing the resistivity of the alloy used, it is

possible to calculate the required thin-film thickness of the

alloy. Typically, this thickness is about 240 nm at the driving

point, 100 nm at the midpoint, and zero at the end of the

antenna. The photograph of the resistively loaded dipole antenna

is shown in figure 2.

4
2.3 Receiving Characteristics of the Resistively Loaded Dipole

The theoretical results for the receiving transfer function

of the resisitvely loaded dipole were obtained using the method

of moments [6] in the frequency domain. Figure 3 shows these

results along with the experimental results. Here, the receiving

transfer function is defined as a ratio of the output voltage of

the antenna to the normal incident electric-field strength. It

is found from figure 3 that the resistively loaded dipole has a frequency response that is flat to ± 3 dB from 200 MHz to over

3 GHz, whereas its frequency response rolls off at -6 dB per

octave below 200 MHz.

The transient response of the resistively loaded antenna was

also evaluated experimentally on the time-domain antenna range

with a time-domain automatic network analyzer ( TDANA ) . The TDANA

measures the time-domain waveform of the impulse response of the

antenna. The duration of the impulse used in the theory and the

experiments is typically 100 ps. The time-domain waveform is

then digitized and stored in a 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

spectrum amplitude from the digitized, averaged waveform using

the fast Fourier transform ( FFT ) . The frequency response thus

obtained experimentally is also shown in figure 3. The

theoretical and experimental results are in generally good

agreement. Figure 3 indicates that the receiving characteristic

of the resistively loaded dipole is well behaved. The antenna

should find very wide application as a standard receiving antenna

for the measurements of fast, time-varying, transient EM fields.

5
2.4 Far-Field Radiation Patterns

The electric field of the resistively loaded antenna for the

far-field regions is rigorously given by:

E (r) = j

u> sin 6 A

0 Z

/ r

2 + z2 + 2rz' cos 0 jwy sin 0 h -jk — o , e

2

/ 1 ( z ' ) - - --

-h

Z / r

2 + z2 + 2rz' cos 6

d z

(3)

This integration is carried out numerically using the current

distribution I„(z) obtained by the method of moments, z

Using the current distribution given by the Wu-King

approximation in eq (2), the far-field radiation patterns can

also be calculated analytically, yielding [2]:

f = jVo

# F(kh,e)

0 r

( 1 - j/kh ) r

(4)

where :

f (kh,0

)

-jkh sin2 0+(l+cos2 0)-[j2cos0 sin(kh cos0 )+(l+cos2 0)cos(kh cos0)]e

kh sin3 0

-jkh

The experiments to obtain the radiation pattern were

performed using a near-field calibration range for the frequency

range between '700 MHz and 5 GHz. The experimental and

theoretical results of the far-field radiation patterns are shown

in figures 4(a), 4(b), 4(c), 4(d), and 4(e) for several

frequencies. As shown in figures 4(a) and 4(b), the radiation

patterns of the resistively loaded antenna are well behaved at

frequencies below 1 GHz, kh < n/2, and are very similar to

6
those of a metal dipole with the same electrical length,

2h = 15 cm. As frequency increases above 1 GHz, kh > tt/2, the

radiation patterns of a 15 cm long, metal dipole split and result

in many sidelobes as shown in figures 4(c), 4(d), and 4(e).

However, figure 4(c) indicates that the 15 cm long,, resistively

loaded dipole still has a well-behaved electric-field pattern up

to 2.5 GHz, kh = 2 .5 ( tt/2 ) . At 5 GHz, kh = 5(tt/2), the

radiation pattern of the resistively loaded dipole splits and

results in sidelobes as shown in figure 4(d). For further

reference, the radiation pattern of the resistively loaded

antenna at 10 GHz, kh = 10(tt/2), is shown in figure 4(e). It

was thus found that the 15 cm long, resistively loaded dipole

discloses a well-behaved, radiation pattern up to 2.5 GHz,

kh = 2. 5 (tt/2); whereas a 15 cm long, metal dipole has a wellbehaved electric-field pattern only up to 1 GHz, kh = tt/2, as

expected

.

3. BROADBAND, ISOTROPIC, REAL-TIME, ELECTRIC-FIELD SENSOR (BIRES)

3.1 Design Configurations

A BIRES consists of three resistively loaded dipoles. The

protective mount is made of a polycarbonate core, nylon dipole

holders, and epoxy fiber glass tubing for the main support. The

housing provides for mounting orthogonally the three dipoles, a set of three baluns, and a set of three coaxial cables in a fixed, relative direction as shown in figure 5.

In order to provide an output voltage of at least 2 pV at

the BIRES output for an electric-field strength of 15 pV/m

meter, a shaping amplifier, a booster amplifier, and a 30-dB

attenuator are incorporated in a coaxially switched system. A

block diagram of the BIRES switching system is shown in

figure 6. For the BIRES frequency response to be flat over the

frequency range from 10 MHz to 1' GHz, a shaping amplifier is

always used. This amplifier provides additional gain at those

7
frequencies where the frequency response of the resistively

loaded dipole falls off.

For measurements of low-level, electr ic-f ield strengths

below 300 mV/m, both shaping and booster amplifiers are used to

provide a proper output, at least 2 yV at an electric-field

strength of 15 yV/m. For the measurement of high-level,

electric-field strengths above 300 mV/m, a shaping amplifier with

a 30-dB attenuator is used in the switching system. The entire

setup is shown in figure 6.

It is found that the frequency response of each resistively

loaded dipole has a 6-dB roll-off below 200 MHz as shown in

figure 3. For the overall frequency response of the B IRES to be

flat over a frequency range from 10 MHz to 1 GHz, a shaping

amplifier is used to compensate a 6-dB roll-off below 200 MHz.

The typical power gain of the shapinq amplifier is shown in

figure 7. The detailed frequency response of the BIRFS at lowand high-level settings is given in terms of the antenna factor

section 4.

It is common practice to make performance comparisons among

various antenna systems based upon input signal sensitivity. One

common criterion is tangential sensitivity, usually defined as

that input signal which increases the antenna output power by a factor of 2 (i.e., (S+N)/N = 2 or S/N = 1). The signal-to-noise

ratio, S/N, of the antenna system can be estimated as:

3.2 Frequency Response

3.3 Tangential Sensitivity

S

N

(5)

ant

n + (1 - n )T + T ]b*

o amp

8
The symbols have the following meanings: k is Boltzmann's

constant ( 1 . 38xlO-2 ^JK

- -*- ) , Tant is the antenna temperature in

kelvins, n is the antenna radiation efficiency, TQ

is the

ambient temperature in kelvins, Tamp

is the effective input noise

temperature of a field effect transistor (FET) amplifier in

kelvins, and B is the bandwidth in hertz. Here, T .n+(l-n)T

is the noise contribution due to the antenna system. If the

antenna is surrounded by a 290-K environment, the noise

temperature contributed by the antenna system would be 290 K

regardless of its radiation efficiency, n

.

To estimate the the tangential sensitivities of the BIRES at

various frequencies, the noise figures of the broadband, shaping

amplifier were measured using an automated noise figure meter and

are shown in figure 7. At the same time, the losses due to the

balun and the 7.6 m long RG 8A/U cable were also measured using

an automated network analyzer. The tangential sensitivities of

the BIRES with various bandwidths and frequencies are calculated

using eq (5) and are summarized in table 1. The typical

tangential sensitivities of the BIRES are 13 to 16yV/m for

various bandwidths in the frequency range from 10 MHz to 1 GHz.

3.4 Dynamic Range

The dynamic range of the BIRES is limited by the broadband,

shaping amplifier. Typical power gain variations and the output

power at the 1-dB gain compression point are shown in figure 7.

The output power at the 1-dR gain compression point of the

shaping amplifier essentially limits the dynamic range of the

BIRES and decreases approximately 20 dB per decade from 20 MHz to

200 MHz. This 20-dB decrease results because the amplifier gain

is specially tailored to provide additional gain (20 dB per

decade) at those frequencies where the antenna response falls

off. To achieve a 20-dB gain roll-off for 20 MHz to 200 MHz, a

9
20-dB per decade, low-pass filter was added at the final stage of

the amplifier so that the noise figure (typically 4 dB) is not

degraded. The filter does, however, degrade the output power at

the 1-dB gain compression point to approximately -20 dBm. The

low amplifier output at the 1-dB gain compression point limits

the maximum measurable electric field to about 8 V/m at 30 MHz

and 1 V/m. at 200 MHz as indicated in table 2. To increase the

maximum electric field that can be measured by the BIRES, a 3-dB

attenuator is added for the high-level, electric-f ield

measurements. The maximum electric field that can be measured by

the BIRES with a 30-dB attenuator (high level) at various

frequencies is given in table 2. The relation between the

incident electric-field strength and the output of the BIRES at

750 MHz is shown in figure 8. The overall dynamic range of the

BIRES with and without a 30-dB attenuator (high level and low

level) as a function of bandwidth is given below:

To achieve isotropy of response for EM radiation measurements, the resistively loaded dipoles are mounted orthogonally to

each other. Three' separate rf signal outputs from mutually

orthogonal dipoles are then fed into a receiver, e.g., a field

intensity meter, a spectrum analyzer, etc. The Hermitian magnitudes are meaningful measures of the intensity of complicated

electric fields having reactive near-field components, multipath

components, and arbitrary polarization. In isotropic media, the

Hermitian magnitude of the electric-f ield strength is defined as:

O 152 db (100 Hz RW)

142 dB (1 kHz BW)

132 dB (10 kHz BW)

125 dB (50 kHz BW)

O

O

o

3.5 Isotropy

( 6 )

10
in a rectangular coordinate system.

The radiation patterns of each resistively loaded dipole are

measured in an anechoic chamber at frequencies between 450 MHz

and 1 GHz and are shown in figures 9(a), 9(b), 9(c), 9(d), 9(e),

9(f), and 9(g). The overall radiation patterns of the HIRES are

calculated using eq (6) and are also shown in these figures. The

overall variation in isotropic response with respect to angle is

within ± 1 dB.

4. CALIBRATION OF ANTENNA FACTOR

4.1 Calibration Technique

The BIRES is immersed in a calculable, standard EM field in

order to calibrate it. Calibrating fields above 450 MHz are

produced in an anechoic chamber by a series of standard-gain

pyramidal horns.

To establish a standard field at frequencies above 450 MHz,

the radiated field intensity is calculated in the near zone of

standard-gain horn antennas. These antennas consist of a series

of rectangular pyramidal horns. It is desirable to calibrate the

BIRES in far-zone, plane-wave fields. To keep the proximity

correction to less than 0.05 dB, the separation distance required

between a rectangular pyramidal horn and the BIRES must be on the

order of 32 D

2 /X where D is the largest dimension of the

pyramidal horn and X is the wavelength. The anechoic room

available for the measurements does not, however, meet this

requirement. Therefore, a complication known as near-zone gain

reduction arises when field strength is calculated near a transmitting antenna. Unlike a field traveling in a waveguide,

the EM field across a horn aperture has a somewhat spherical

(rather than planar) wavefront. The phase at the rim of the horn

lags that at the center, causing a nonequiphase front across the

11
aperture, which reduces the effective gain in the near-field

(Fresnel) region. A further reduction occurs, even for an

equiphase aperture, due to the difference in distance between the

various elements in the radiating aperture and the on-axis field

point in question. Both of these "defects" reduce the power

density to less than that predicted by the simple far-zone,

inverse-square relation of a distant point source.

Larsen [10] has generated simple polynomial expressions,

similar to the various algebraic equations which have been

published for approximating the Fresnel integrals, to determine

the near-zone gain reduction factors, R

H and RE

, for pyramidal

horns. The pertinent horn dimensions used in the equations are

shown in figure 10, where the dimensions have been normalized to

wavelengths by letting:

A L = — , and D = — EX X

Here :

a, b, £ and £ = horn dimensions (meters) given in figure 10,

H E

d = distance in front of the horn aperture to an on-axis field

point (meters), and X = free-space wavelength (meters).

After defining :

a = A

2 and 6 t

the two gain reduction factors, R^ due to the H-plane flare of

horn and R E due to the E-plane flare of horn, expressed in dB,

are given by:

Ru = (0.01a) (1 + 10.19a + 0.51a2 - 0.097a 3

) (7)

H

12
and

R = ( 0 . 1

3

2

) (2.31 + 0.0533) . (8)

hi

Finally, the theoretical gain of the horn (near zone or far

zone), expressed in dB, is given by:

GAIN = 10 log ( AB ) + 10.08 - R - R . (9)

H E

4.2 Antenna Factors

The antenna factors of the BIRES are determined by immersing

the antenna in the known field generated with standard-gain

pyamidal horns in an anechoic chamber for the frequency range

from 450 MHz to 1 GHz as described in subsection 4.1, and are

shown in figure 11.

The antenna factor K, expressed in dB, is defined as:

K = 20 log ( E /V) , (10)

where :

E

g = standard ele-ctr ic-f ield strength (volt/m) generated by a standard-gain pyramidal horn in an anechoic chamber, and

V = rf voltage at the output of the RIRES into a 50-g load

( receiver )

.

An unknown field strength, E in dB above 1 yV/m, may be

measured with the calibrated BIRES by using the expression:

E K + M (ID
where :

K = antenna factor (dB)

,

and

M = metering circuit indication (dB above 1 mV) of a calibrated 50-ft receiver.

It is estimated that the standard fields can be established

in an anechoic chamber by rectangular pyramidal horns over the

frequency range from 450 MHz to 1 GHz with an uncertainty less

than ± 1.0 dB [10] by carefully measuring the power delivered to

the horns. By estimating the mismatch error between the BIRRS

and a 50-ft load receiver to be ± 1.0 dB, the antenna factors of

the BIRES given thus have a ± 3-dB uncertainty, including ± 1-dB

variation in its isotropic response.

5. CONCLUSIONS

The prototype development and evaluation of a BIRES have

been discussed in this paper. The BIRES, which consists of three

resistively loaded dipoles mounted orthogonally to each other,

allows measurement of three polarization components of broadband

electric fields for the frequency range from 10 MHz to 1 GHz.

The three separate rf signal outputs from these dipoles provide a complete description of frequency, polarization, magnitude, and

phase information of the incident electric field.

The typical tangential sensitivity of the BIRES is 13 to

16 mV/m with a typical usable dynamic range from 125 to 144 dB

for various bandwidths at a frequency range from 10 MHz to

1 GHz. The isotropy of response of the BIRES can be obtained by

arithmetically evaluating the Hermitian magnitudes of the

incident electric field. The variation with respect to angle in

isotropy of response is found to be less than ± 1 dB. The

antenna factors of the BIRES are determined by immersing the

antenna in the standard electric fields produced in the anechoic

14 -
chamber by rectanqular, pyramidal horns for the frequency range

from 4 50 MHz and 8 50 MHz. The antenna factors below 4 50 MHz were

not determined due to experimental difficulties. However, the

evaluation of each component of the HIRES, namely the resistively

loaded dipoles, baluns, 30-dR attenuator, shapinq and booster

amplifiers, and coaxial switches, indicates that the antenna

factors of the RIRES are estimated to be flat to within ± 3 dB,

and to have a ± 3-dR uncertainty, including the nonisotropic

response

Since the HIRES has a linear maqnitude and phase response

over a broadband frequency range from 10 MHz to 1 GHz, it has the

unioue capability to measure fast, time-varying, complicated EM

fields

VII. ACKNOWLEDGMENT

The authors wish to thank D. G. Melquist, E. B. Larsen, and

W. D. Baumgartner for careful experimental assistance.

VIII. REFERENCES

[1] Kanda, M. , The characteristics of broadband, isotropic,

electric-field and magnetic-field probes, NBSIR 77-868,

Nat. Bur. of Stand. (TJ.S.) (Nov. 1077).

[2] Wu, T. T., and King, R. W. P., The cylindrical antenna with

resistive loading, IEEE mrans. Antennas Propagat. AP-13,

No. 6, 369-373 (May 1965).

[3] Shen, L. C., and King, R. W. P., The cvlindrical antenna

with nonreflecting resistive loading, IEEE Trans. Antennas

Propaqat. AP-13 , No. 6, 998 (Nov. 1965).

[4] Altshuler, E. E., The traveling-wave linear antenna, IEEE

Trans. Antennas Propagat. AP-Q , No. 4, 324-329 (July 1961).

Iizuka, K., The traveling-wave V-antenna and related

antennas, IEEE Trans. Antennas Propagat. AP-9 , No. 2,

236-243 (March 1967).

[ 5 ]
[6] Harrington, R. E., Field Computation by Moment Methods

(McMillan Company, New York, 1968).

[7] Kanda, M., The characteristics of a relatively short

broadband linear antenna with tapered resistive loading.

International IEEE/AP-S Symposium Digest, Stanford,

California (June 1977).

[8] Kanda, M. , A relatively short cylindrical broadband antenna

with tapered resistive loading for picosecond pulse

measurements, IEEE Trans. Antennas Propagat. AP-26, No. 3,

439-447 (May 1978) .

[9] Kanda, M. , Transients in resistively loaded antennas, and

their comparison with conical antennas and TEM horns,

Internat ional/AP-S Symposium Digest, University of

Maryland, MD (May 1978).

[10] Larsen, E. B., Techniques for producing standard EM fields

from 10 kHz to 10 GHz for evaluating radiation monitors.

Symposium on Electromagnetic Fields in Biological Systems,

Ottawa, Canada (June 1978).

16
Table

1.

Tangential

sensitivities

of

BIRES E^z • . o —»

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o o o o z lI X o r— CM LO LO 1

uj r" f— ^ CD O *3- CO CO co CO i~5 ' ' ' ' 1 ' 1 •- L_ O

£5ni co

IS) . „ > NZ --—-» s z 1

y—«s X—V y S o t—1

-•

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POSITION

ALONG

DIPOLE

(cm)
Fig.

2.

Resistively

loaded

dipole.
Nl

CDO

N

nzCD

O

o

N

HZO

o

>-CD

O'

UJ

ct:

( a p ) NOiiDNfij j3jsn\/ji jo a a n i i novw

21

Fig.

3.

Receiving

transfer

function

of

resistively

loaded

dipole.
FAR-FIELD, 100 MHz

« LOADED DIPOLE (THEORETICAL,

Fig. 4(a). Radiation patterns of resistively loaded dipoles at 100 MHz.
FAR-FIELD, 1 GHz

Fig. 4(b). Radiation patterns of resistively loaded dipoles at 1 GHz.
FAR-FIELD, 2.5 GHz

* LOADED DIPOLE (THEORETICAL,

MOMENT METHOD) • LOADED DIPOLE (THEORETICAL,

Fig. 4(c). Radiation patterns of resistively loaded dipoles at 2.5 GHz.
FAR- FI ELD , 5 GHz

Fig. 4(d). Radiation patterns of resistively loaded dipoles at 5 GHz

25
FAR- FIELD, 10 GHz

• * LOADED DIPOLE (THEORETICAL,

MOMENT METHOD)

•— LOADED DIPOLE (THEORETICAL,

WU-KING)

Fig. 4(e). Radiation patterns of resistively loaded dipoles at 10 GHz.

26
Fig.

5.

Broadband,

isotropic,

real-time,

electric-field

sensor

(BIRES).
VO

CT>

28

Block

diagram

of

BIRES

switching

system.
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>-

C_)

O'

UJ

cn

1_L_

(gp) Ni\/9 ygidiidNV

29

Fig.

7.

Power

gain,

noise

figure,

and

output

power

at1

dB

gain

compression

point

of

the

broadband

shaping

amplifier.
lOOmV

X

30V11OA lfldino

30
MRB

31

Fiq.

9(a).

Isotropy

ofR

IRES

at

450

MHz
MRS

32

Fiq.

9(h).

Tsotropv

of

RIFFS

at

550

MHz
MRE

uc• CT •H

fe.

33

Isotropy

of

BIRFS

at6

50

MHz
34

Fiq.

9(d).

Isotropy

of

RIFES

at

750

MHz
35

Isotropy

of

BIRRS

at

8

50

MHz
< HO > 30nindWd 3A I ld"13d

\

36

Fiq.

0(f).

Tsotropv

of

BIRRS

at

0

50

MHz
MR6

tr

O'.0~ •H

a,

37

Isotropy

of

HIRES

at1

GHz
Fig. 10. Sketch of pyramidal horn dimensions in wavelengths.

38
X

CHANNEL

Y

CHANNEL

Z

CHANNEL

oooo

X

X

oo o

(ap) U013VJ VNN31NV

o

OJ

39

Fig.

11(a).

Antenna

factors

of

BIRES

for

low-level

measurements.
o

cr> oo udcnj UD 1*0 UD UD

(ap) bOlOVJ VNN31NV

40

Fig.

11(b).

Antenna

factors

of

BIRES

for

high-level

measurements.
NBS-1 14A (REV. 9-78)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 79-1622

tSoVt. Accession No, 3. Recipient'* Accession No.

4. TITLE AND SUBTITLE

A Broadband, Isotropic, Real-time, Electric-field

Sensor (BIRES) Using Resistively Loaded Dipoles

5. Publication Date December 1979

7. AUTHOR(S)

Motohisa Kanda, Francis X. Ries and Donald R. Belsher

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. Project/Task/Work Unit No.

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

, L. 11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP) 13. Type of Report & Period Covered

Same as Item 9.

15. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.)

A broadband, isotropic, real-time, electric-field sensor (BIRES)

developed by the National Bureau of Standards (NBS) consists of three

resistively loaded dipoles mounted orthogonally to each other. It has

the capability of measuring a complete description of frequency,

polarization, magnitude, and phase information of the incident

electromagnetic (EM) field. The typical tangential sensitivity of the

BIRES is 13 to 16 yV/m with a usable dynamic range of 125 to 144 dB for

various bandwidths in the frequency range of 10 MHz to 1 GHz. The

isotropic response, isotropy, of the BIRES is obtained by calculating

the Hermitian magnitude of the incident electric field, and its variation

is found to be less than + 1 dB.

17. KEY WORDS (six to twelve entries ; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons ' Broadband; dynamic range; electric-field sensor; Hermitian magnitude;

isotropy; resistively loaded dipole; tangential sensitivity.

18. AVAILABILITY Pjf Unlimited

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20402, SD Stock No. SN003-003-

I I Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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