A Reconfigurable Compact Antenna for DVBH
Application
Yang Kang(1), Haipeng Mi(1), Zhijun Zhang(1), Wenhua Chen(1), Zhenghe Feng (1),
(1) Department of Electronic Engineering, Tsinghua University, China, 100084
Email: kangy05@mails.tsinghua.edu.cn, mhp@mails.tsinghua.edu.cn, zjzh@tsinghua.edu.cn,
chenwh@mail.tsinghua.edu.cn, fzh-dee@tsinghua.edu.cn.
Abstract- This paper presents a novel design of compact
antenna that covers the frequency from 470MHz to 770MHz
(DVBH application). The design is based on a monopole antenna
and a reconfigurable matching network. The antenna has a
dimension of 28.4×21.6×17.5 mm3. It is installed into a device
with a volume of 115×74×16 mm3. The matching network
consists of switches, capacitors and inductors, and can be
reconfigured to eight schemes. Accordingly, the antenna can be
dynamically tuned to eight different frequency bands within the
whole band. These separate bands combine to cover the ISDB-T
frequency range, with good antenna performance.
Keywordscompact
antenna;
reconfigurable antenna; DVBH.
I.
matching
network;
INTRODUCTION
Modern communication is pushing for wider bandwidth and
compacter size out of antennas. For Digital Video
Broadcasting - Handheld (DVBH) application, the frequency
range is quite low, from 470MHz to 770MHz, and the
bandwidth is relatively wide that is nearly 50% of the center
frequency. Besides, the strict requirement of the antenna
dimension makes the antenna design more difficult. Due to the
effects of integrated components and the grounded metal shell,
the EM interference is severe. It is a challenge to design a
wideband and compact antenna with good performance in
small devices.
It is hard to implement a single antenna covering a wide
bandwidth, especially at such a low frequency. There have
been a lot of solutions to deal with this problem. One solution
is to use varactor to tune antenna [1-6]. The antenna resonance
frequency is tuned by the tuning circuits, which consist of
varactor and other components. By changing the voltage
loaded on the varactor, the antenna can be tuned to different
frequency bands. However, varactor-tuned antennas have
intrinsic shortcomings. The varactor tuned antenna is very
sensitive to the biased voltage, so that resonance frequency is
difficult to control accurately. Other solutions have also been
presented, such as reconfigurable 1 antennas using variable
capacitor [7], parasite element [8], PIN diode switches [9], etc.
These methods can dynamically control the resonance
frequency and cover wideband frequency with good antenna
performance. However, they have disadvantages such as
Project 60771009 supported by NSFC
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complicated structure and large size for implementation, high
biased voltage requirement, high manufacturing cost, etc.
This paper presents a reconfigurable compact antenna tuned
by a multi-states matching network, which consists of
switches, capacitors and inductors. By turning the switches,
the matching network can form eight different circuit schemes.
Accordingly, the antenna can achieve eight resonance
frequencies respectively within the ISDB-T band of 470MHz
to 770MHz.
II.
ANTENNA SYSTEM DESIGN
A. Antenna Structure
The proposed antenna system is composed of a monopole
antenna and a matching network. It is mounted on a metal box,
which is a grounded metal shell of a portable device, as shown
in Fig. 1. The dimension of the metal box is 115×74×16 mm3.
There are two perpendicular recesses along edges of the corner
where the antenna locates, with dimensions of 32×15×10 mm3
and 59×8×10 mm3 respectively.
The first part of the antenna element sits in the recess; the
tail part of the element hangs out of the device with 6.6mm
clearance, so that the effect from the metal ground can be
reduced. The feeding point is at the top surface of the metal
shield. The antenna element is made of copper wires, with a
diameter of 0.8 mm and a total length of 122.5 mm. The total
space occupied is 28.4×21.6×17.5 mm3, as shown in Fig. 2.
The measured result indicates that the antenna has its own
resonance frequency of 720MHz.
B. Matching Network
The most commonly used matching components are
inductor and capacitor. They are both used in this design. The
matching network consists of three switches, three inductors
and one capacitor. The matching circuit is shown in Fig. 3.
The antenna element is connected to the serially connected
inductors. The other port of the serial inductors is connected to
the feeding point and a shunted inductor or capacitor. Using
three separate switches, the circuit can be reconfigured to
eight schemes. By properly selecting the component values,
the antenna can achieve eight different resonances.
In order to select the suitable values of the matching
components, the first step is to tune the antenna to the lowest
frequency, which is 470MHz in this case, because it is more
ICMMT2008 Proceedings
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difficult for the antenna to achieve good performance at lower
frequency than at higher frequency, especially for such a
compact antenna.
4
18
.
6
16.2
6.
4
9.
4
Fig. 1. Grounded Metal Shell Model
loss less than -6dB. The detailed lumped component values
and the antenna resonance frequency are presented in Table I.
The simulation result verified that the matching network can
effectively tune the antenna resonance frequency and
accordingly make the antenna cover the required bandwidth.
In some frequency bands, such as from 470MHz to 500MHz,
from 680MHz to 720MHz, the return loss parameter is greater
than -6dB. It is because the number of lumped components
used is limited, so that the whole bandwidth of 300MHz is
difficult to cover ideally. If adding more components into the
matching circuit, it is possible to achieve more separate bands
and cover the required bandwidth better. However, adding
components may increase the circuit complexity and reduce
antenna efficiency. These factors should be considered and
dealt with in practical applications.
13.5
28.4
26
Fig. 2. Antenna Element Structure
Fig. 4. Simulation Model of Matching Network
Fig. 3. Matching Network Circuit Scheme
III.
ANTENNA SIMULATION
The antenna simulation has been performed on HFSS. The
size of the metal box and antenna element are the same as
discussed above. The dimension of the lumped components is
0.8×1.6 mm2. The serially connected inductors are selected as
22nH and 12nH. The shunted capacitor and inductor are
selected as 8.2pF and 6.8nH respectively.
In the simulation model, the serially connected inductors are
simplified as one inductor, whose value can be set to 12nH,
22nH, 34nH or 0nH. The shunted capacitor or inductor can be
connected into the circuit by adding a metal sheet. The
dimension of the feeding point is 0.2 × 0.8 mm2. The shunted
capacitor and inductor, and the feeding point are connected to
the metal ground. The structure of the matching network is
presented in Fig. 4.
The simulated results of return loss are shown in Fig. 5. If
set -6dB as a reference, most parts of the frequency band
between 470MHz to 770MHz is ideally covered, with return
Fig. 5. Simulated Return Loss
Table I
PARAMETERS OF COMPONENTS AND CORRESPONDING RESONANCE
FREQUENCY
Series
L=34nH
L=34nH
L=22nH
L=22nH
L=12nH
L=12nH
L=0nH
L=0nH
Shunt
L=6.8nH
C=8.2pF
L=6.8nH
C=8.2pF
L=6.8nH
C=8.2pF
L=6.8nH
C=8.2pF
Frequency
500-520MHz
560-570MHz
540-560MHz
600-630MHz
580-610MHz
640-680MHz
650-680MHz
720-760MHz
IV.
EXPERIMENTAL RESULTS
In order to verify the simulation result, a circuit composed
of two inductors and one capacitor is fabricated. By replacing
the component with a suitable one, the matching circuit can be
changed to eight structures. The most distinct advantage of
this simple circuit is that it occupies a very small area that
would hardly cause any influence on the antenna performance.
The measured return loss values under eight matching
circuit schemes are presented as Fig. 6. The measured result
agrees with the simulated one, although there is some
frequency shift. The relative shift of the resonance frequency
is within an allowable range. In practical applications, it is
only need to make small adjustment of the component values
in order to correct the frequency.
Fig. 7-9 present the 2D radiation patterns. Here are the
measured results for three frequency bands: 480MHz,
610MHz and 750MHz. At each frequency, two polarizations
(V and H) and three planes (X-Y, X-Z, Y-Z) are measured.
Standard dipole antennas at corresponding frequencies were
used as references, whose gain is 1.5dBi. Each figure shows
the radiation pattern on one cut-plane when the receiving
antenna is horizontally and vertically polarized respectively.
advantages of the matching network is that it can tune the
antenna to many resonance frequencies with simple circuit
structure and small footprint. By increasing the number of
matching components, which is a tradeoff between antenna
efficiency and the matching circuit’s complexity, the antenna
can be tuned to more frequencies. In this way, the antenna can
cover broader bandwidth. Therefore, the proposed principle
for antenna matching network has extensive application in
modern wireless communications.
(a)
(b)
Fig. 6. Measured Return Loss.
V.
CONCLUSION
A novel reconfigurable compact antenna tuned by matching
network is proposed. The antenna element has its own
resonance frequency of 720MHz. The matching network
controls the antenna resonance frequency. It is composed by
switches, inductors and capacitors. By selecting suitable
values of the lumped components, the antenna can be
dynamically tuned to eight different resonance frequencies,
with ideal return loss lower than -6dB (equivalent to VSWR of
3:1). All these separate frequency bands combine to cover the
DVBH band from 470MHz to 770MHz.
The experimental results of the return loss and radiation
patterns have been presented. They have verified that the
antenna has good performance. One of the most important
(c)
Fig. 7. Radiation Pattern at 480MHz
(a)X-Y plane, (b)X-Z plane, (c)Y-Z plane
(a)
(a)
(b)
(b)
(c)
Fig. 9. Radiation Pattern at 750MHz
(a)X-Y plane, (b)X-Z plane, (c)Y-Z plane
(c)
Fig. 8. Radiation Pattern at 610MHz
(a)X-Y plane, (b)X-Z plane, (c)Y-Z plane
REFERENCES
[1]
[2]
[3]
[4]
[5]
Zlatoljub D. Milosavljevic, “A Varactor-Tuned DVB-H Antenna,”
International Workshop on Antenna Technology: Small and Smart
Antennas Matematerials and Applications, 2007. IWAT '07, pp. 124-127,
21-23 Mar. 2007.
Claudio M. Montiel, Lu Fan, and Kai Chang, “A Novel Active Antenna
with Self-Mixing and Wideband Varactor-Tuning Capabilities for
Communication and Vehicle Identification Applications,” IEEE
Transactions on Microwave Theory and Techniques, vol. 44, No. 12, pp.
2421-2430, December 1996.
Dong-Hyuk Choi and Seong-Ook Park, “A Varactor-Tuned ActiveIntegrated Antenna Using Slot Antenna,” IEEE Antennas and Wireless
Propagation Letters, vol. 4, pp. 191-193, 2005.
Julio A. Navarro, Yong-Hui Shu, and Kai Chang, “Broadband
Electronically Tunable Planar Active Radiating Elements and Spatial
Power Combiners Using Notch Antennas,” IEEE Transactions on
Microwave Theory and Techniques, vol. 40, pp. 323-328, No. 2,
February 1992.
Nader Behdad and Kamal Sarabandi, “A Varactor-Tuned Dual-Band Slot
Antenna,” IEEE Transactions on Antennas and Propagation, vol. 54, pp.
401-408, No. 2, February 2006.
[6]
[7]
[8]
[9]
Nader Behdad and Kamal Sarabandi, “Dual-Band Reconfigurable
Antenna With a Very Wide Tunability Range,” IEEE Transactions on
Antennas and Propagation, vol. 54, pp. 409-416, No. 2, February 2006.
James T. Aberle, Sung-Hoon Oh, David T. Auckland, and Shawn D.
Rogers, “Reconfigurable Antennas for Portable Wireless Devices,” IEEE
Antennas and Propagation Magazine, vol. 45, pp. 148-154, No. 6,
December 2003.
Chih-Ming Su, Liang-Che Chou, Chun-I Lin and Kin-Lu Wong,
“Embedded DTV Antenna for Laptop Application,” IEEE Antennas and
Propagation Society International Symposium, vol. 4B, pp. 68- 71, 2005.
Dimitrios Peroulis, Kamal Sarabandi and Linda P. B. Katehi, “A Planar
VHF Reconfigurable slot Antenna,” IEEE Antennas and Propagation
Society International Symposium, vol. 1, pp. 154-157, 2001.