Post on 03-Oct-2016
20th Iranian Conference on Electrical Engineering, (ICEE2012), May 15-17,2012, Tehran, Iran
Novel Frequency Reconfigurable Microstrip Monopole Antenna for
Multi-Radio Wireless Applications
Hamid Boudaghi, Mohammadnaghi Azarmanesh, and Hossein Mardani Microelectronics Research Laboratory, Urmia University, Urmia, Iran
st_h.boudaghi@urmia.ac. ir, m.azarmanesh@urmia.ac. ir, h.mardani@urmia.ac.ir
Abstract: In this paper, a novel frequency reconjigurable monopole antenna with jive switchable states including an ultrawideband (UWB) state, three single band states and a dualband state is presented. The frequency reconjigurable capability of the antenna is achieved by using a switchable slotted structure on the ground plane. The antenna which supports most applicable frequency bands above 2 GHz can be used in multi-radio wireless systems. Reflection coefficient and radiation pattern measurements were performed for the fabricated antenna. Good agreement between simulated and measured results was obtained.
Keywords: Antenna, defected ground structure (DGS)
filter, PIN diode, reconfigurable antenna, ultrawideband
(UWB).
1. T ntrod uction
With the rapid development of electronics and wireless
communications, the demand for mobile devices
operating at different standards or for different
applications is extending. On the other hand, wireless systems are evolving toward multi-functionality. Multi
band or reconfigurable antennas are suitable candidates for providing multi-functionality. Although, multi-band
antennas have the capability of serving multiple
frequency bands with one antenna, but the crosstalk from
the neighbor bands makes them a weak choice in
comparison to reconfigurable antennas [I]. In order to
have reconfigurable antennas, different electrical or
electromechanical switches such as varactor diodes, PIN
diodes and RF-MEMS have been used. Among these
switching devices, PIN diodes are very reliable because
they have high switching speeds and low resistance and capacitance in the on and off states, respectively.
Most of frequency reconfigurable antennas are
antennas only capable to switch between different
narrowband modes [2]-[4]. In [2], a switchable quad-band antenna by using a MEMS switch has been proposed. By
controlling the states of switches, the patch antenna in [3] can operate in four different frequency bands. In this paper we propose a novel frequency reconfigurable
antenna with the capability to switch between UWB,
single band and dualband modes. The proposed antenna
has five different switchable states: 2.95-10.92 GHz in
UWB mode, 2.24-2.72 GHz, 3.32-3.79 GHz, and 5.15-5.9 GHz in single band mode and 2.11-2.8 GHz & 5.14-
5.9 GHz in dualband mode. The designed antenna which
uses a switchable slotted structure for reconfigurability
has a simple structure and compact size of 40 mm x 40 mm.
In Section 2, we describe the structure and design
principles of the proposed antenna. Section 3 shows the
simulation and measurement results for the
reconfigurable antenna and Section 4 contains the
conclusion.
2. Antenna Structure and Design
The configuration of the proposed reconfigurable antenna is depicted in Fig. I. The proposed antenna is constructed on a FR4 substrate with the relative dielectric
constant of 4.4 and thickness of 1.6 mm. The size of the
substrate is 40 mm x 40 mm. The radiating element is a
circular patch with radius of 10 mm which is fed with a
50-0 microstrip feedline with the length of 20 mm and
width of 2.86 mm. On the bottom of substrate, there is a
ground plane with 19 mm x 40 mm dimensions below the
feedline. To provide frequency reconfigurability, a switchable
structure of slots is used on the ground plane. This
structure which acts as a defected ground structure (DGS)
filter is designed to suppress frequencies outside the
desired band. The devised slots on the ground plane
change the inductance and capacitance of the input
impedance of the antenna. This causes a shift in resonant
frequency of the structure which is controllable by
changing the shape and size of the slots [5], [6]. The width of these slots is I mm.
To make the designed filter switchable and therefore
achieve a frequency reconfigurable antenna, four PIN
diodes were soldered inside the slots. For applying the
DC voltage to PIN diodes, metal strips with dimensions
of 2 mm x 0.6 mm were used inside the slots. Moreover,
for each PIN diode a 100 pF DC blocking capacitor was
978-1-4673-1148-9/12/$31.00©2012IEEE 1298
z
(3)
:or Swikhlog Structure �lOOPF
Metol Strip
PIN Diode
(b) Fig. I. Contlguration of the proposed recontlgurable monopole antenna;
(a) top view, (b) bottom view (Unit: mm).
placed in the slots to create the RF connection of the PIN
diode and also to isolate the RF signal from the DC. In
the introduced design, HPND-4005 beam lead PIN diodes
[7] were used. For biasing PIN diodes a 0.7 volts supply
is applied to metal strips. The PIN diodes exhibit an
ohmic resistance of 4.6 0 and capacitance of 0.0 17 pF in
the on and off states, respectively. By turning diodes on,
the metal strips are connected to the ground plane and
become a part of it. The desired frequency band can be
selected by varying the states of PIN diodes which
changes the total equivalent length of the slots. The
proper dimensions of the slots and positions of diodes DI
to D4 were found during the design procedure by various
simulations in order to obtain desired frequency bands
(Fig. I).
3. Simulated and Measured Results
The proposed reconfigurable antenna has been simulated by High Frequency Structure Simulator
software [8]. Two methods exist to simulate PIN diodes:
In first method, the PIN diode is modeled as a metal tape (with tape dimensions corresponding to the diode
dimensions) in the on state and for the off state this tape
is removed to have open circuit in slots; and in the second
method, PIN diode is modeled as a resistor/capacitor in
the on/off states, respectively; In this design, the second method are used. According to the technical datasheet of
the HPND-4005, PIN diodes are simulated as a 4.6-0
resistor and 0.017-pF capacitor in the on and off states, respectively. The antenna shown in Fig. 1 is then
implemented, and measurements are done. A photograph of the fabricated antenna is shown in Fig. 2.
(a)
(b) Fig. 2. Photograph of the tabricated antenna; (a) top view, (b) bottom
vIew.
Thin Bias wires are used to bias PIN diodes. A series resistor is placed before the power supply in order to
protect PIN diodes. Also, the SMA connector of the
antenna is connected to a DC blocker to protect network
analyzer against DC currents.
Fig. 3 shows the simulated and measured results of the input reflection coefficient for different states of the
antenna. As it is seen from this figure, a good agreement
exists between these results. For the proposed design, five
operating states were investigated, and their
corresponding diode states were shown in Table I.
By turning all diodes on, the bandpass filtering effect
is eliminated and the antenna will radiate in its UWB
mode. When diode D2 is off, depending on other diodes
biasing condition single band and dualband modes are achievable. As an example from Table I, we can see
when diodes D 1 and D2 are off and diodes D3 and D4 are
on, the antenna's operating frequency band is 5.15-5.9 GHz. Meanwhile, in state 5 in which all diodes are off
the antenna will operate in its dualband mode coverin�
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-20 -252
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Frequency (GR,)
6 7 Frequency (GR,)
6 7 Frequency (GR,)
Frequency (GR,)
Frequency (GR,)
muuuumi State 1 1m
10 11
11
11
... :-----�-
uuumu.imi State 5 lu.
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I---Simulated -Measured I Fig. 3. Simulated and measured retlection coetlicient of the antenna tor
ditTerent switching states.
TABLE T: Details of PIN Diode Combinations and Simulated and
Measured Frequency Bands in Each State
Diodes DI D2 D3 D4 Frequency Bands (GHz )
Simulated / Measured
State I on on on on 2.82-10.96/2.95-10.92
State 2 otT otT on on 5.02-5.96/5.15-5.9
State 3 on otT otT on 3.23-3.82/3.32-3.79
State 4 on otT otT otT 2.23-2.78 /2.24-2.72
State 5 otT otT otT otT 2.04-2.82 &5.04-5.85 / 2.11-2.8 & 5.14-5.9
2.11-2.8 GHz & 5.14-5.9 GHz frequency bands. Therefore, we can conclude that the frequency band is
5 dB
·15
·J5
·5 5 180
·J5
·15
, dB
'dB
-15
-J'
-5 5
-J'
-15
, dB
, dB
-15
-J5
-5 5 lBO
-J'
-15
, dB
2.4 GHz H-plane 2.4 GHz E-plallE' 90 90
270 270
Ca) 4.8 GHz H-lllallE' 4.8 GHz E-plane
90 90
270 270
(b) 9 GHz H-plane 9 GHz E-plane
90 90
270
(c)
- Co-Polarization (l\'le.,ured) ..... , Cross-Polarization (Measured) --- Co-Polarization (Simulated) -0-' Cross-Polarization (Simulated)
270
Fig. 4. Simulated and measured radiation patterns of the tested antenna
at (a) 2.4 GHz (state 4), (b) 4.8 GHz (state 1) and (c) 9 GHz (state 1).
controllable by electronically changing the condition of PIN diode switches embedded on the ground plane. The
frequency bandwidth obtained by switching between
different states can serve several wireless communications systems, including the WiMax (2.3-2.4
GHz, 2.5-2.7 GHz, 3.3-3.8 GHz; 5.15-5.85 GHz), WiFi
(2.4-2.48 GHz; 5.15-5.85 GHz) and UWB (3.1-10.6
GHz).From the results, good impedance matching with
less than 10 dB return loss is observed at all operating bands.
The proposed antenna tested in an anechoic chamber
in order to obtain its radiation characteristics. A dc power
supply was placed inside the chamber and covered with
absorbers during the measurements. The simulated and
measured radiation patterns in two operational states are
depicted in Fig. 4. The left and right pictures show H
plane (xz plane) and E-plane (yz plane) radiation patterns respectively. Good agreement between simulation and
measurement results has been seen. The H-plane patterns
are almost omnidirectional, but degradation in E-plane
1300
Frequency (GHz)
(a)
3.5
@' 3 "C ';;'2.5 '" I;,) 2·
1.5
Frequency (GHz)
(b) Fig. 5. Measured gain of the proposed antenna for different switching
states; (a) UWB, (b) single band and dual band modes.
patterns is observed. This degradation is due to the asymmetric structure of slots with respect to yz plane.
From an overall view of these radiation patterns one can see that the antenna behaves similar to the typical printed
monopole antennas.
The measured antenna gain in different states is
exhibited in Fig. 5. From Fig. 5(a), it is apparent that the
antenna shows a reasonably flat gain with an average of
3.3 dBi in UWB mode. Also, as shown in Fig. 5(b), the
antenna has an acceptable gain in single band and
dual band modes.
4. Conclusion
This paper presents a novel frequency reconfigurable
monopole antenna which can be used as an UWB or band selective antenna. The antenna uses a DGS filter to
deliver the frequency reconfigurable capability. The proposed antenna is simple to design and fabricate and
exploits 4 PIN diodes to switch on the desired frequency bands. The antenna is able to operate at five different
switching states with a reasonable return loss. Good
radiation patterns and acceptable gain values were
obtained for different operating states of the proposed
reconfigurable monopole antenna. The antenna IS
intended for use in multi-radio wireless applications.
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[4] T. Y. Han and C. T. Huang, "Reconfigurable monopolar patch
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