Content uploaded by V. I. Koshelev
Author content
All content in this area was uploaded by V. I. Koshelev on Oct 10, 2017
Content may be subject to copyright.
213
ISSN 0020-4412, Instruments and Experimental Techniques, 2017, Vol. 60, No. 2, pp. 213–218. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © V.P. Gubanov, A.M. Efremov, V.I. Koshelev, B.M. Kovalchuk, V.V. Plisko, V.V. Rostov, A.S. Stepchenko, 2017, published in Pribory i Tekhnika Eks-
perimenta, 2017, No. 2, pp. 61–67.
A Source of High-Power Pulses of Ultrawideband Radiation
with a Nine-Element Array of Combined Antennas
V. P. Gubanov, A. M. Efremov, V. I. Koshelev*, B. M. Kovalchuk, V. V. Plisko,
V. V. Ro stov, and A. S. Stepchenko
Institute of High Current Electronics, Russian Academy of Sciences,
Siberian Branch, (IHCE SB RAS), Tomsk, 634055 Russia
*e-mail: koshelev@lhfe.hcei.tsc.ru
Received March 23, 2016
Abstract—The design and research results for a high-power source of ultra-wideband radiation with a nine-
element array excited by a bipolar high-voltage pulse with 2-ns duration are presented. The radiation pulses
with an effective potential of 1 MV at a pulse repetition rate of 100 Hz were obtained.
DOI: 10.1134/S0020441217020063
INTRODUCTION
To derive pulses of ultrawideband (UWB) radiation
with an effective potential of rEp (the product of the
peak electric-field strength and the distance in the far-
field region) at the megavolt level, arrays of combined
antennas excited by bipolar voltage pulses are widely
used [1]. The results of research on a UWB source with
an effective radiation potential of 1.7 MV based on the
excitation of a 16-element array with a bipolar pulse of
2-ns dur ation were presented in [2]. The lifetim e of the
source was 1 hour of continuous operation at a pulse
repetition rate of 100 Hz; it was limited by partial
breakdowns of coaxial cables with polyethylene insu-
lation. To ensure the electric strength, the wave trans-
former and the power divider were filled with trans-
former oil.
Later [3], in a UWB source with a four-element
antenna array excited by bipolar pulses of 3 ns dura-
tion, it was suggested to use coaxial cord-insulated
cables that were filled with SF6 gas. In addition, to
increase the efficiency of the energy transfer from the
bipolar pulse generator to the antenna array and
reduce the source dimensions, a bipolar pulse former
with a wave impedance reduced to 12.5 Ω and the
direct charging of the former line from a Sinus-160
monopolar pulse generator, i.e., without using an
intermediate peaking stage, was developed in [3].
One of the objectives of this work was to study the
possibility of obtaining shorter bipolar pulses of 2-ns
duration and 100-kV amplitude using the proposed
method. The work presents the results of studying a
UWB source with a nine-element array, which is
excited by a bipolar pulse of 2-ns duration, using gas
insulation of the entire feeder system, thus making it
possible to increase the source lifetime.
1. THE SOURCE OF ULTRAWIDEBAND
RADIATION PULSES
Figure 1 shows the appearance of the UWB source.
The source includes a bipolar pulse generator that
consists of a monopolar pulse generator, 1, and bipolar
pulse former, 2, a wave transformer, 3, a power divider,
4, and a nine-element antenna array, 5, which is con-
nected to power divider, 4, with coaxial cord-insulated
ELECTRONICS AND RADIO
ENGINEERING
Fig. 1. The source of ultra-wideband radiation with a nine-
element antenna array: (1) monopolar pulse generator; (2)
bipolar pulse former; (3) wave transformer; (4) power
divider; and (5) nine-element antenna array.
1234
5
214
INSTRUMENTS AND EXPERIMENTAL TECHNIQUES Vol. 60 No. 2 2017
GUBANOV et al.
cables. The wave transformer, the power divider, and
the cables are filled with SF6 gas under a pressure of 5
atm.
2. THE BIPOLAR VOLTAGE PULSE
GENERATOR
The bipolar pulse generator consists of a monopo-
lar pulse generator and a bipolar pulse former.
A Sinus-160-30 high-voltage pulse generator was used
as the monopolar pulse generator. This is a modified
version of the Sinus-160 generator [4]. The wave
impedance of the forming line in the modified version
of the generator was decreased from 40 to 30 Ω and the
stored energy was increased from 3.4 to 4.6 J at a
charging voltage of 350 kV.
The equivalent circuit of the bipolar voltage-pulse
generator is shown in Fig. 2. The monopolar-pulse
generator consists of a forming line, FL0, and a spark
gap, S0. This line was charged from the secondary
winding of a Tesla transformer to a voltage of –350 kV
with a pulse repetition rate of 100 Hz. The bipolar-
pulse former was assembled according to the open-
ended line scheme [4], which includes the FL2–FL5
lines, a peaking spark gap, S1, a cutting-off spark gap,
S2, and the load resistance of Rl = 12.5 Ω.
When switching the spark gap S0, a charging-volt-
age pulse was fed to the forming line, FL2, via the
transmitting line, FL1, through a limiting resistor, R0.
Using the resistor, R0, makes it possible to reduce volt-
age oscillations in the FL0–S0–R0–FL1–FL2–S1–S2
circuit after forming a bipolar pulse and reduce the
erosion of electrodes of the spark gaps, which
increases their service life. When the S1 spark gap trig-
gers near the charging-voltage maximum on the FL2
line and S2 triggers with a relative delay equal to the
double travel time along the FL3 line a bipolar voltage
pulse is formed in the transmitting line, FL5, at whose
end a load is mounted.
The circuit was simulated using PSpice software.
The spark gaps were switched almost perfectly. The
spark-gap switching time, i.e., the time during which
the spark-gap resistance changes from 10 kΩ to 0.1 Ω,
was set equal to 2, 1, and 1 ns for S0, S1, and S2, respec-
tively. The FL1 transmission line represents the set of
lines with a wave impedance from 45 to 88 Ω, which is
equivalent to the coaxial junction from the S0 spark
gap to the FL2 line.
The estimated pulses of the charging voltage, U1, in
the FL2 line (curve 1) and the output pulses of bipolar
voltage, U2, in the FL5 line (curve 2) are shown in Fig. 3.
The maximum charging voltage in the FL2 line reaches
330 kV during 4.6 ns. The amplitude, U2, and duration
of the estimated output bipolar pulse amplitude and
duration are ±150 kV and 1.7 ns, respectively.
Figure 4 shows the design of the bipolar-voltage-
pulse former. Three coaxial lines, FL2–FL4, the right
side of FL1, the peaking spark gap, S1, and the cutting-
off spark gap, S2, are placed inside the brass frame in a
nitrogen medium under a pressure of 25–45 atm. The
diameters of the inner conductors of the FL2–FL4
lines are equal to 70, 70, and 55 mm, respectively. The
insulator of the FL4 line and the bushing insulator of
FL5 are made of caprolon as a single unit. The param-
eters of the lines are indicated in Fig. 2.
Fig. 2. The equivalent circuit of the bipolar-pulse generator: (FL0–FL5) coaxial lines; (S0–S2) spark gaps; (R0) limiting resistor;
(Rl) load; and (U1, U2) outputs of estimated voltage pulses.
S
0
S
1
U
1
U
2
S
2
FL
0
2.25 ns/30
FL
2
0.34 ns/6.25
FL
3
0.34 ns/6.25
FL
4
0.34 ns/6.25
FL
5
FL
1
R
0
6
R
l
12.5
350 kV
1.5 ns/12.5
Fig. 3. The estimated pulses of the charging voltage, U1, in
the FL2 line (1) and the output bipolar-voltage pulse, U2,
in the FL5 line (2).
2468t, ns
U, kV
400
300
200
100
0
100
200
2
1
INSTRUMENTS AND EXPERIMENTAL TECHNIQUES Vol. 60 No. 2 2017
A SOURCE OF HIGH-POWER PULSES 215
The ends of the inner conductors of the FL2 and
FL3 lines with a thickness of 2 mm are the electrodes
of the S1 ring spark gap and 2-mm-thick disc 2 and
insert 1 at the frame are the electrodes of the spark gap,
S2. All electrodes of S1 and S2 are removable and made
of copper. The gaps in the spark gaps S1 and S2 are 1.5
and 0.75 mm, respectively. The inner conductors of
the FL2–FL4 lines are connected to each other by leak-
age inductances, 3, that are intended to remove the
residual charge on the electrodes after the spark gaps
operate.
The charging pulse was fed to the FL2 line via the
FL1 line from the Sinus-160-30 generator through a
caprolon insulator (not shown in Fig. 4). When the S1
spark gap operated followed by the S2 gap (with a
delay) a bipolar voltage pulse was formed, which was
output through the bushing insulator by the FL5
matched transmission line into the load (not shown in
Fig. 4). SF6 gas under a pressure of 5 atm was used as
insulation in the right part of the FL5 transmitting line.
A water line with loss served as the load of the FL5
transmitting line when adjusting the generator of bipo-
lar pulses.
A voltage divider with coupled lines, D2, was used
to record the output bipolar voltage pulse in the FL5
line. The confidence time interval of measuring the
output pulse by the divider is determined by the double
wave travel time along the FL5 line; it equals 5.7 ns.
The divider was calibrated by feeding a bipolar voltage
pulse of 2-ns duration to the input of the FL5 line from
a low-voltage generator. Pulses at the line output and
an attenuated pulse from the divider output were
recorded with a Tektronix TDS 6604 oscilloscope with
a bandwidth of up to 6 GHz using attenuators. The
experiment revealed the good agreement of the pulse
shapes at the line output and of the restored pulse with
an attenuation factor of 78 from the D2 voltage divider.
The D1 capacitance divider is intended for recording
the charging voltage in the FL2 line.
The charging voltage of the FL2 line with the
above-described interelectrode gaps and a pressure in
the S1 and S2 spark gaps of 43 atm was 250 kV, while
the charging time was 3.4 ns (Fig. 5). The amplitudes
of negative U– and positive U+ half-waves of the output
bipolar voltage pulse Ug(t), shown in Fig 6, were –85
and +100 kV, respectively. The duration of the bipolar
Fig. 4. The structure of the bipolar pulse former: (1) insert; (2) disc; (3) leakage inductance; and (D1, D2) voltage dividers.
FL1D1D2
S1S2
FL2FL3FL4
FL5
1233
Fig. 5. A pulse of the charging voltage in the line FL2
obtained from the divider, D1, output.
2 1 0 1 2 3 t, ns
U, kV
300
200
100
0
100
Fig. 6. An output bipolar voltage pulse, Ug, formed at the
D2 divider output.
Ug, kV
100
50
0
50
100
1012t, ns
216
INSTRUMENTS AND EXPERIMENTAL TECHNIQUES Vol. 60 No. 2 2017
GUBANOV et al.
pulse was determined at the levels of 0.1U+ and 0.1U–
with the linear approximation of the fronts before
crossing the zero line; it equaled τp = 2 ns. The pulse
amplitude is less than the estimated one because of the
simplification of the current-switching process in cal-
culations and triggering of the spark gaps at a voltage
that is lower than the maximum charging voltage.
During the pulse duration, an energy of 0.8 J is
transmitted into the load that amounts to 18% of the
energy accumulated in the forming line FL0. The stan-
dard deviation of the amplitudes U– and U+ relative to
the average value does not exceed 3–4%. As the pres-
sure in the pulse former increases, the charging time of
the FL2 forming line and the instability of the ampli-
tudes U– and U+ increase. In this case, the maximum
charging voltage in the FL2 line is reached at a
charging time of 5.2 ns.
3. THE WAVE TRANSFORMER
AND POWER DIVIDER
The wave transformer is a coaxial line with a resis-
tance that changes from 12.5 to 5.56 Ω. The resistance
of the wave transformer was calculated using the
expression for a compensated exponential junction [5]
,
where L is the junction length and ρ0 and ρL are the
initial and final junction resistances. The transformer
length is L = 90 cm and equals 1.5 τpc, where c is the
speed of light. Figure 7 shows the estimated perfor-
mance S21 of the wave transformer. In the frequency
band from 0.2 to 1 GHz, the estimated loss does not
exceed 1%.
A numerical simulation of the power divider char-
acteristics, S21, was performed. The results are pre-
(
)
(
)
⎧⎫
−−
=−
⎨⎬
⎩⎭
0
0
ρ
ρ( ) ρ exp ln 0.133sin 2π
ρ
L
Lx Lx
xLL
sented at Fig. 8. The estimated characteristics, S21
(curve 1), is close to the ideal characteristic (curve 2).
Curve 2 corresponds to decreasing the voltage-pulse
amplitude in a nine-channel power divider without a
loss by three times.
To connect the power divider with the elements of
the antenna array, a cord-insulated cable of the
PK 50-17-51 type was used. The design of the cables
made it possible to pump SF6 gas into the feeder sys-
tem under a pressure of 5 atm, which increased its
electric strength.
To measure the characteristics of the feeder system,
a low-voltage bipolar pulse of 2-ns duration was fed to
its input. The pulse at the output of each channel of the
divider was recorded with the oscilloscope. Figure 9
shows the oscillogram, 1, of a pulse at the wave-trans-
former input and oscillogram, 2, of a pulse at the out-
Fig. 7. The estimated characteristics, S21, of the wave
transformer.
0 0.2 0.4 0.6 0.8 f, GHz
S21, dB
1.6
1.2
0.8
0.4
0
Fig. 8. The simulated characteristics, S21, of the power
divider (1) compared with the characteristic of an ideal
divider without loss (2).
0 0.2 0.4 0.6 f, GHz
S21, dB
9.56
9.55
9.54
1
2
Fig. 9. The pulses at the input (1) and output (2) of the
nine-channel power divider.
0123t, ns
U, rel. its
1.0
0.5
0
0.5
1.0
2
1
INSTRUMENTS AND EXPERIMENTAL TECHNIQUES Vol. 60 No. 2 2017
A SOURCE OF HIGH-POWER PULSES 217
put of the divider averaged over all nine channels
(multiplied by three). The wave transformer and the
power divider reduce the amplitude of the first lobe of
a bipolar pulse by 4%.
4. THE ANTENNA ARRAY
The antenna array consists of nine (3 × 3) com-
bined 30 × 30-cm antennas fastened to a metal frame
(Fig. 1). The array elements are combined into vertical
sections by three elements in each section. The neigh-
boring elements in a vertical section are galvanically
coupled to one another. The distance between the
centers of sections equals 36 cm. The array aperture is
102 × 90 cm.
A combined antenna [6, 7] optimized for radiation
of bipolar voltage pulses with a 2-ns duration was used
as the array element. The matching band of a single
combined antenna in the level of the voltage standing
wave ratio (VSWR) of ≤2.5 or less is within 0.2–1.1
GHz (Fig. 10). The antenna peak-power radiation
pattern is close to a cardioid pattern in the H- and E-
plane. The half-height pattern width in the H-plane
equals 90°, while in the E-plane it is 75°. The width of
the array radiation pattern in the both planes is three
times smaller.
To record the electromagnetic pulses, the receiving
antenna was used, which is half of a TEM-horn with
dimensions of the earth plate of 20 × 120 cm and a
mouth of 9.5 × 2 cm. The wave impedance in the horn
mouth is 50 Ω. Calculation of the frequency depen-
dence of the effective length of this antenna was car-
ried out in [8]. The effective length of the antenna, he,
in a frequency band of 0.15–3 GHz is 1 cm.
Figure 11 shows the dependence of the product of
the peak field strength, Ep, on the distance, r, from the
radiator to the observation point. The horizontal seg-
ment of the curve corresponds to the far-field region.
It is seen from Fig. 11 that distances larger than 10 m
can be considered the far-field region where the effec-
tive radiation potential is measured.
5. THE RADIATION OF POWERFUL
ULTRAWIDEBAND PULSES
Figure 12 shows an oscillogram of a pulse radiated
by the array. The effective radiation potential was
1 MV at the amplitude of a bipolar voltage pulse
Ugmax = 100 kV. The efficiency of the radiator with
respect to the peak field strength was rEp/Ug max = 10.
Research on the influence of the bipolar-voltage-
pulse shape on the effective potential of radiation was
previously conducted. The pulse shape changed when
changing the pressure in the spark gaps of the bipolar-
pulse former. Figure 13 shows the dependences of the
Fig. 10. The voltage standing-wave ratio of a single
antenna.
0 0.25 0.50 0.75 1.00 f, GHz
1
2
3
4
5
V
SWR
Fig. 11. The dependence of the product of the peak field
strength, Ep, at the distance r on the distance r.
246810r, m
rEp, rel. units
0.84
0.88
0.92
0.96
1.00
Fig. 12. The oscillogram of a radiation pulse of a source
with a nine-element antenna array.
012345t, ns
rE, MV
1.0
0.5
0
0.5
1.0
218
INSTRUMENTS AND EXPERIMENTAL TECHNIQUES Vol. 60 No. 2 2017
GUBANOV et al.
effective radiation potential and its standard deviation,
σ, on the pressure in the spark gaps of the bipolar-
pulse former. The maximum effective radiation poten-
tial was reached at a nitrogen pressure of 36 atm.
Tests on the stability and source lifetime at a pulse
repetition rate of 100 Hz were conducted. In the
experiments, the amplitude of an electromagnetic
pulse, rEp, and its standard deviation, σ, were mea-
sured. Averaging was performed over 1000 pulses.
The results of the first hour of operation are presented
in Fig. 14. After a 2-hour break for cooling the monop-
olar-pulse generator and a pressure reduction in the
former by 1–2 atm, the source continued to work with
high stability of the radiation parameters at a pulse
repetition rate of 100 Hz during the second hour.
The continuous work time of the source is usually lim-
ited to 5 hours [3] and is due to the erosion of dis-
charger electrodes.
CONCLUSIONS
Based on the excitation of a nine-element array of
combined antennas by a bipolar voltage pulse with a
100-kV amplitude and a 2-ns duration, a powerful
source of ultrawideband radiation with the effective
potential rEp = 1 MV at the efficiency with respect to
the peak field strength rEp/Ug max = 10 has been cre-
ated. A feeder system with gas insulation was used in
this source. The continuous operation of the source
during 1 hour at a pulse repetition rate of 100 Hz with
high stability of radiation and the possibility of con-
tinuing to operate after a 2-hour cooling break was
demonstrated.
REFERENCES
1. Belichenko, V.P., Buyanov, Yu.I., and Koshelev, V.I.,
Sverkhshirokopolosnye impul’snye radiosistemy (ultraw-
ideband Pulse Radio Systems), Novosibirsk: Nauka,
2015.
2. Gubanov, V.P., Efremov, A.M., Koshelev, V.I.,
Koval’chuk, B.M., Korovin, S.D., Plisko, V.V., Step-
chenko, A.S., and Sukhushin, K.N., Instrum. Exp.
Tec h., 2005, vol. 48, no. 3, p. 312.
3. Andreev, Yu.A., Efremov, A.M., Koshelev, V.I.,
Koval’chuk, B.M., Plisko, V.V., and Sukhushin, K.N.,
Instrum. Exp. Tech., 2011, vol. 54, no. 6, p. 794.
4. Andreev, Yu.A., Gubanov, V.P., Efremov, A.M.,
Koshelev, V.I., Korovin, S.D., Kovalchuk, B.M.,
Kremnev, V.V., Plisko, V.V., Stepchenko, A.S., and
Sukhushin, K.N., Laser Part. Beams, 2003, vol. 21,
no. 2, p. 211. doi 10.1017/S0263034603212088
5. Fel’dshtein, A.L., Yavich, L.R., and Smirnov, V.P.,
Spravochnik po elementam volnovodnoi tekhniki
(A Handbook on Waveguide Technique Elements),
Moscow: Sovetskoe Radio,1967.
6. Koshelev, V.I., Buyanov, Yu.I., Andreev, Yu.A., Plisko, V.V.,
and Sukhushin, K.N., Proc. IEEE Pulsed Power Plasma
Sci. Conf., Las Vegas, 2001, vol. 2, p. 1661.
7. Andreev, Yu.A., Buyanov, Yu.I., and Koshelev, V.I.,
J. Commun. Technol. Electron., 2005, vol. 50, no. 5,
p. 535.
8. Andreev, Yu.A., Koshelev, V.I., and Plisko, V.V., Proc.
5th All-Russ. Sci.-Techn. Conf. “Radiolocation and
Radiocommunication”, Moscow, 2011, p. 77.
Translated by M. Kromin
Fig. 13. The dependences of the effective radiation poten-
tial, rEp, and its standard deviation, σ, on the pressure, p,
in the spark gaps of the former.
32 34 36 38 40 42
rEp, MV σ, %
p, atm
0.95
1.00
1.05
1.10
4
8
12
16
Fig. 14. The dependences of the effective radiation poten-
tial, rEp, and its standard deviation, σ, on the number of
pulses.
rEp, kV σ, %
Number of pulses, 105
01.2 2.4 3.6
1030
1040
1050
1060
1070
1080
4
6
8
10
12
14
