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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Frequency (GR,)

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Frequency (GR,)

Frequency (GR,)

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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

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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.

References: [I] S. Yang, C. Zhang, H. K. Pan, A. E. Fathy, and V. K. Nair,

"Frequency-recontigurable antennas for multiradio wireless

platforms," IEEE Microw. Mag., vol. 10, no. I, pp. 66-83, Feb.

2009.

[2] T.Wu, R. L. Li, S. Y. Eom, S. S. Myoung, K. Lim, J. Laskar, S. 1. Jeon, and M. M. Tentzeris, "Switchable quad-band antennas tor

cognitive radio base station applications," IEEE Trans. Antennas Propagat., vol. 58, no. 5, pp. 1468-1476, May 2010.

[3] A. F. Sheta and S. F. Mahmoud, "A widely tunable compact patch antenna," IEEE Antennas Wireless Propag. Lett., vol. 7, pp. 40-

42,2008.

1301

[4] T. Y. Han and C. T. Huang, "Reconfigurable monopolar patch

antenna," lET Electron. Lett., vol. 46, no. 3, pp. 199-200, Feb.

2010.

[5] A. Tariq, and H. Ghafouri-Shiraz, "Frequency-reconfigurable

monopole antennas," IEEE Trans. Antennas Propagat., vol. 60, no. 1, pp. 44-50, Jan 2012.

[6] H. B. El-Shaarawy, F. Coccetti, R. Plana, M. El-Said, and E. A.

Hashish, "Novel reconfigurable defected ground structure resonator on coplanar waveguide," IEEE Trans. Antennas Propag., vol. 58, no. 11, pp. 3622-3628, Nov. 2010.

[7] [Online]. Available: www.avagotech.comldocs/AVOI-0593EN

[8] Ansoft High Frequency Structure Simulator (HFSS). ver. 11,

Ansoft Corp., 2006.