Journal of Electrical Engineering & Technology (2019) 14:339–345
https://doi.org/10.1007/s42835-018-00033-5
ORIGINAL ARTICLE
Design and Fabrication of VHF Band Small Antenna Using Composite
Right/Left‑Handed Transmission Lines
Hee Jae Jun2 · Jonghyup Lee1 · Seongro Choi1 · Yong Bae Park1
Received: 18 July 2018 / Revised: 7 September 2018 / Accepted: 16 September 2018 / Published online: 4 January 2019
© The Korean Institute of Electrical Engineers 2019
Abstract
This paper presents a small VHF antenna using a composite right/left-handed (CRLH) transmission lines. The proposed
antennas have 3 and 7 unit cells that consist of interdigital capacitors and shunt spiral inductors. The size of the antenna with
3 unit cells is 0.039λ × 0.025λ × 0.0008λ (72.9 × 47.5 × 1.52 mm3) at 161 MHz and its peak gain is − 33 dBi. To enhance the
gain, the antenna with 7 unit cells is fabricated. Its size is 0.089λ × 0.025λ × 0.0008λ (167.2 × 47.5 × 1.52 mm3) at 161.4 MHz
and its peak gain is − 26.5 dBi. The radiation pattern of both antennas is omni-directional. The electrical size in kr of each
antenna is 0.055 and 0.11, respectively. The effects of frequency characteristic of lumped elements on the impedance matching are discussed.
Keywords Composite right/left handed transmission line · VHF antenna · Zeroth-order resonance
1 Introduction
The military communications in the VHF band typically use
monopole antennas, dipole antennas, and whip antennas [1,
2]. The size of those antennas is proportional to the wavelength so that they have disadvantage in terms of mobility
and convenience in the VHF band. In order to overcome
these disadvantages, the small antennas are needed in the
VHF band.
There are many types of miniaturized antennas [3, 4].
Recently, small antennas using composite right/left-handed
transmission line (CRLH TL) have been extensively studied
[5–11]. CRLH TL shows LH property at low frequency and
Hee Jae Jun and Jonghyup Lee equally contributed first authors.
* Yong Bae Park
yong@ajou.ac.kr
Hee Jae Jun
hjjun@moasoftware.co.kr
Jonghyup Lee
indestructible@ajou.ac.kr
Seongro Choi
axwzs4869@ajou.ac.kr
1
Department of Electrical and Computer Engineering, Ajou
University, Suwon, South Korea
2
MOASOFT Corporation, Seoul, South Korea
RH property at high frequency. As the frequency is changed
from low to high, the propagation constant is changed from
negative to positive, and CRLH TL structure has a size-independent zeroth-order resonant frequency and the antenna can
be made smaller using the CRLH TL [12–15]. The small
antennas using CRLH TL have been investigated intensively
in the UHF band. However, the study of the VHF antennas
using CRLH TL seems to be lacking.
In this work, the antenna based on CRLH TL is designed
at VHF band. The proposed antennas have 3 and 7 unit
cells that consist of interdigital capacitors and shunt spiral inductors. The size of the antenna with 3 unit cells is
0.039λ × 0.025λ × 0.0008λ (72.9 × 47.5 × 1.52 mm 3) at
161 MHz and its peak gain is − 33 dBi. To enhance the
gain, the antenna with 7 unit cells is fabricated. Its size is
0.089λ × 0.025λ × 0.0008λ (167.2 × 47.5 × 1.52 mm3) at
161.4 MHz and its peak gain is − 26.5 dBi. The electrical
size in kr of each antenna is 0.055 and 0.11, respectively.
The ‘k’ is the wavenumber. The physical size ‘r’ is the radius
of the smallest hemi-sphere that can enclose the antenna.
Usually, antennas with sizes less than 0.2 in kr are considered to be very small antennas. Therefore, our proposed
antennas are very small. The effects of frequency characteristic of lumped elements on the impedance matching are
also discussed.
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2 Design of CRLH TL Antenna
Figure 1 shows an equivalent circuit of a CRLH transmission
line. Since a left-handed (LH) transmission line consists of
a series capacitor and a shunt inductor, there is magnetic
flux between the series capacitors and it generates a parasitic series inductance in the transmission line. A parasitic
parallel capacitance is also generated by the top conductor
and the ground plane. Because of these phenomena, the LH
transmission line structure has also RH property. CRLH TL
has a zeroth-order resonant frequency in which the propagation number (β) becomes zero so that the antennas using the
CRLH TL can be made smaller. The zeroth-order resonant
frequency is determined by the shunt resonant frequency in
the case of open termination [11]:
1
𝜔sh = √
.
CR LL
(1)
Figure 2 shows the unit cell of the proposed CRLH
transmission line. It consists of an interdigital capacitor and a shunt spiral inductor. The interdigital capacitor
has a series capacitance (­ CL). The shunt inductance (­ LL)
is made of spiral inductor and via. The shunt capacitance
­(CR) and series inductance ­(LR) are parasitic components
as described above. The zeroth-order resonance of the unit
cell is designed at 160 MHz through optimization using
the Ansys HFSS software. The substrate is Taconic TLY5(εr = 2.2) with thickness of 1.52 mm and Table 1 shows
optimized dimensions of the unit cell. The size of the unit
cell is 0.013λ × 0.025λ × 0.0008λ (23.6 × 47.5 × 1.52 mm3).
The inductance of the spiral inductor (­ LL) is 99.6 nH and the
shunt capacitance (­ CR) is 9.93 pF. The spiral inductor is connected to ground plane by via. Figure 3 shows the structure
of the CRLH TL antenna. The antenna is designed using
the Ansys HFSS software. It consists of 3 unit cells and the
size is 0.039λ × 0.025λ × 0.0008λ (72.9 × 47.5 × 1.52 mm3)
Fig. 1 Equivalent circuit of CRLH TL
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Fig. 2 Unit cell of CRLH TL
at 161 MHz. The electrical size in kr of the antenna is 0.055.
The simulated return loss characteristic of the antenna is
shown in Fig. 4. The zeroth-order resonant frequency
is 161 MHz. The fractional bandwidth of the antenna at
zeroth-order resonant frequency is 0.18%. The resonant
frequency of − 1 mode is 119 MHz. Figure 5 illustrates
with 3 unit cells at 161 MHz the electric field distributions
at zeroth-order resonant frequency. It is seen that there is
no phase difference of the field due to zero phase constant
(β = 0). Figure 6 shows the simulation results of normalized
Table 1 Dimensions of the unit cell
Design parameter
Value
Substrate thickness
Dielectric constant
idc
Lc
s
wc
Number of IDC’s finger
Spiral inductor turns
Via radius
ws
Pitch
Rin
lw
1.52 mm
2.2
1 mm
19 mm
0.7 mm
33.3 mm
20
5
0.2 mm
4 mm
1.2 mm
0.4 mm
0.6 mm
Journal of Electrical Engineering & Technology (2019) 14:339–345
341
Fig. 3 The structure of CRLH TL antenna with 3 unit cells
5
return loss (dB)
0
-5
Fig. 6 Simulated normalized radiation pattern of CRLH TL antenna,
N=3
-10
-15
-20
100
110
120
130
140
150
160
170
180
frequency / MHz
Fig. 4 Return loss of CRLH TL antenna with 3 unit cells
Fig. 7 The structure of CRLH TL antenna with 7 unit cells
Fig. 5 Electric field distribution of CRLH TL antenna
radiation pattern of the antenna. The antenna has an omnidirectional radiation pattern and its peak gain is − 33 dBi.
To enhance the gain, we design the antenna with more unit
cells of CRLH TL. Figure 7 shows the CRLH TL antenna
with 7 unit cells. Its real size is 0.089λ × 0.025λ × 0.0008λ
(167.2 × 47.5 × 1.52 mm3) and its electrical size in kr is
0.11. The antenna gain can be enhanced by increasing the
number of unit cells because the gain of small antennas
is proportional to antenna’s size. However, an impedance
mismatch occurs if the number of the unit cells increases.
Figure 8 shows input impedances of the 3 cell antenna and
the impedance mismatched 7 cell antenna. Note that the 3
cell antenna has a zeroth-order resonance at 161 MHz but
the 7 cell antenna does not have a zeroth-order resonance
near 160 MHz. Two inductors are used for the L-section
impedance matching of the proposed 7 cell antenna. Figure 9 illustrates the simulated return loss before and after
applying the L-section matching. The zeroth-order resonant
frequency is 163 MHz. The zeroth-order resonant frequency
is almost equal to that of the three-cell antenna. Figure 10
shows simulation results of the normalized radiation pattern.
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5
return loss (dB)
0
-5
-10
-15
3 Cell
7 Cell
-20
130
140
150
160
170
180
frequency / MHz
Fig. 8 Return loss of the 3 cell antenna and the impedance mismatched 7 cell antenna
5
Fig. 10 Simulated normalized radiation pattern of CRLH TL antenna,
N=7
return loss (dB)
0
-5
-10
-15
Before Matching
After Matching
-20
130
140
150
160
170
180
frequency / MHz
Fig. 9 Return loss of CRLH TL antenna with 7 unit cells
The antenna has omni-directional pattern and its peak gain
is − 26.5 dBi. The gain is enhanced by 6.5 dBi compared
with 3 unit cells.
3 Fabrication and Measurement
Figure 11 shows the fabricated antennas. The L-section
matching network with CTC Ceratech CI-B1608-271 series
chip inductor with a value of 270 nH and CTC Ceratech
CI-B1608-181 shunt inductor with a value of 180 nH is used
for impedance matching.
Figure 12 shows the simulated and measured return loss
of the antenna with 3 unit cells. The comparison between
simulation and measurement shows a good agreement. Note
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Fig. 11 Photograph of fabricated antenna
that the return loss is − 10.58 dB at 161 MHz. Figure 13
illustrates the simulated and measured return loss of the
including calculation result antenna with 7 unit cells. It seen
that the zeroth-order resonant frequencies are almost equal at
around 161.4 MHz, but the measured data has a wider bandwidth than the simulation result. The fractional bandwidth of
Journal of Electrical Engineering & Technology (2019) 14:339–345
343
5
10
0
8
-5
)
6
-10
Impedance (
return loss (dB)
real-sim
4
-15
real-meas
2
simulation
measurement
-20
100
110
120
130
140
150
160
170
0
150
180
155
160
165
170
175
180
frequency / MHz
frequency / MHz
(a) real part
Fig. 12 Return loss of fabricated antenna with 3 unit cells
-50
5
-100
Impedance (
)
0
return loss (dB)
-5
-10
-150
-15
imag-sim
imag-meas
-20
-25
-30
130
-200
simulation
150
155
measurement
140
160
165
170
175
180
frequency / MHz
150
160
170
(b) imaginary part
180
frequency / MHz
Fig. 14 Input impedance of fabricated antenna with 7 unit cells
Fig. 13 Return loss of fabricated antenna with 7 unit cells
series chip inductor(270nH)
600
)
400
Impedance (
fabricated antenna is 2.97%, and that of simulated antenna is
0.24%. In order to analyze this error, the impedances of the
antenna and lumped elements are measured and compared
with ideal impedances. Figure 14 shows the measured and
simulated input impedance of the 7 cell antenna. It is seen
that the real part of the measured input impedance is smaller
than that of the simulated input impedance and the imaginary parts of them are almost the same. Figures 15 and 16
depict the actual impedances extracted from measurements
of the series inductor and the shunt inductor, respectively.
We measured the impedance of the antenna without the
lumped element using network analyzer. Then, we measured
the impedance of the antenna with the lumped element. By
subtracting the impedance of the antenna without the lumped
element from that with the lumped element, we can extract
200
0
-200
real(extraction)
imag(extraction)
ideal
-400
150
155
160
165
170
175
180
frequency / MHz
Fig. 15 Extracted impedance of series chip inductor
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Journal of Electrical Engineering & Technology (2019) 14:339–345
Table 2 Performance comparison between 3 cell antenna and 7 cell
antenna
paraller chip inductor(180nH)
600
Size (kr)
Resonant frequency (MHz)
Return loss (dB)
Fractional BW (%)
Gain (dBi)
Impedance (
)
400
200
0
imag(extraction)
ideal
-400
150
155
160
165
170
175
7 cell antenna
0.055
161
− 10.58
0.18
− 33
0.11
161.4
− 23.78
2.97
− 26.5
should be considered for the impedance matching. Table 2
shows the antenna performance comparison between 3 cell
antenna and 7 cell antenna.
real(extraction)
-200
3 cell antenna
180
frequency / MHz
4 Conclusion
Fig. 16 Extracted impedance of shunt chip inductor
the actual impedance of the lumped element and obtain its
frequency characteristic. Note that the actual impedances
deviate from the ideal impedances in terms of frequency.
Figure 17 shows the measured data and the calculated data.
The calculated data is acquired by using the measured input
impedance of the antenna without the lumped element and
the extracted impedances of two inductors. The comparison
between calculated data and measured data shows a good
agreement since the actual impedances are used for the
analysis. We have figured out that the actual impedance is
different from the ideal impedance of the lumped element.
It means that the impedance mismatch occurs if we use the
ideal values of lumped elements for the impedance matching. Therefore, the frequency dependent characteristic of
lumped elements and the actual impedance of the antenna
5
The small antennas using CRLH TL has been designed
and fabricated at VHF band. The proposed antennas have
3 and 7 unit cells which consist of interdigital capacitors
and shunt spiral inductors. The antenna with 3 unit cells has
size of 0.039λ × 0.025λ × 0.0008λ (72.9 × 47.5 × 1.52 mm3)
at 161 MHz and its peak gain is − 33 dBi. The
size of 7 cell antenna is 0.089λ × 0.025λ × 0.0008λ
(167.2 × 47.5 × 1.52 mm3) at 161.4 MHz and its peak gain
is − 26.5 dBi. Increasing the number of unit cells, the gain of
antenna has been enhanced. The effects of frequency characteristic of lumped elements on the impedance matching
also have been discussed. The antenna based on CRLH TL
can overcome the physical limitation of the conventional
military antenna. Therefore, the proposed antennas can be
used for military communication in the VHF band.
Acknowledgements This work has been supported by the Future Combat System Network Technology Research Center program of Defense
Acquisition Program Administration and Agency for Defense Development (UD160070BD).
0
References
return loss (dB)
-5
-10
-15
-20
measurement
-25
-30
150
calculation
155
160
165
170
175
frequency / MHz
Fig. 17 Return loss of fabricated antenna with 7 unit cells
13
180
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Hee Jae Jun received B.S and
M.S. degree in the department of
Electrical and Computer Engineering from the Ajou University, Suwon, Rep. of Korea, in
2016 and 2018, respectively. He
is currently with MOASOFT
Corporation. His research interests include electromagnetic
field scattering analysis and
metamaterial antennas .
345
Jonghyup Lee received B.S
degree in the department of
Electrical and Computer Engineering from the Ajou University, Suwon, Rep. of Korea, in
2017. He is currently working on
M.S. course in the department of
Electrical and Computer Engineering, Ajou, University,
Suwon, Rep. of Korea. His
research interests include metamaterial antennas .
Seongro Choi received B.S
degree in the department of
Electrical and Computer Engineering from the Ajou University, Suwon, Rep. of Korea, in
2017. He is currently working on
M.S. course in the department of
Electrical and Computer Engineering, Ajou, University,
Suwon, Rep. of Korea. His
research interests include metamaterial antennas .
Yong Bae Park received B.S.,
M.S., and Ph.D. degrees in electrical engineering from the
Korea Advanced Institute of Science and Technology, South
Korea, in 1998, 2000, and 2003,
respectively. From 2003 to 2006,
he was with the Korea Telecom
Laboratory, Seoul, South Korea.
In 2006, he joined the School of
Electrical and Computer Engineering, Ajou University, South
Korea, where he is now a Professor. His research interests
include electromagnetic field
analysis, metamaterial antennas,
and electromagnetic interference and compatibility .
13