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Log-Periodic Patch Antenna With Tunable
FrequencyM. F. Ismail
1, M. K. A. Rahim
2, F. Zubir
3, O. Ayop
4
Radio Communication Engineering Department
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
81310 Skudai Johor, Malaysia
mfaizal69@live.utm.my1 , mkamal@fke.utm.my
2 , farid@fke.utm.my
3 , osman@fke.utm.my
4
Abstract — This paper describes the design and analysis of a Log-
Periodic Microstrip Antenna Array operating between 3.3
Gigahertz (GHz) and 4.5 GHz. A five square patches fed by inset
feed line technique are connected with a single transmission line
by a log-periodic array formation. By applying five PIN Diodes
at the transmission line with a quarter-wave length radial stub
biasing, four different sub-band frequencies are configured byswitching ON and OFF the PIN Diode. Simulation as well as
measurement results with antenna design is presented and it
shows that a good agreement in term of return loss. The
simulated radiation pattern and realized gain for every sub
bands also presented and discussed.
Keywords- Log-periodic, Microstrip antenna, Reconfigurable,
PIN Diode
I. I NTRODUCTION
Reconfigurable antennas have received a great deal of
attention for their applications in wireless communication inrecent years. Compared to conventional antennas,reconfigurable antennas provide the ability to dynamically
adjust various antenna parameters such as operating frequency
[1], polarization [2], radiation pattern [3], and/or two or more
of parameters [4] in single antenna. In [1], the frequency
reconfigurability is achieved when the RF switches are
inserted with log periodic aperture fed microstrip antenna. The
five bands are selected from a wideband frequency by
switching ON and OFF state at desired patches. The
polarization reconfigurable also has been presented in [2]. A
square patch with two cross-shaped diagonal slots has been
designed with three types of reconfigurable polarization which
are a linear, right-handed and left handed. In [3] the author has presented the pattern reconfigurable from a planar array
microstrip antenna with separated transmission line design.
The most remarkable feature of this antenna is that two or
more parameters of the antenna can be reconfigurable. In [4],
a novel both pattern and frequency reconfigurable annular slot
antenna is presented. The antenna has three different
frequencies by controlling the matching stubs, which are
fabricated on the opposite side of the board. And it also has a
reconfigurable radiation pattern, which is controlled by the dc
voltage of the PIN diodes on the slot.
In this paper, the concept of frequency reconfigurable is
study from a combination of RF switching and the wideband
antenna. This proposed antenna is designed from the
combination of five elements using log-periodic techniquewith a scaling factor of 1.05. Compared to others a wideband
frequency reconfigurable antenna like monopole as reportedin [5], the log-periodic antenna is easier to select the required
band because of each element radiates at the different
frequency bands. This antenna used one switching for each patches instead using two switches for single frequency for
dipole antenna as reported in [6]. The Computer Simulation
Technology (CST) software is used to carry out the simulation
process for the reconfigurable antenna. The simulation results
are compared with measurement results in terms of return loss
while other parameters are also discussed such as radiation pattern, gain and half-power beam width.
II. A NTENNA DESIGN
All The concept of a reconfigurable antenna is
investigating by changing the switches of PIN diode to ON or
OFF. This antenna can perform a frequency range from 3.3
GHz until 4.5 GHz with four different sub bands. Figure 1
shows the proposed log-periodic microstrip antenna with
frequency reconfigurable. Five square patches with quarter-
wave length radial stub are connected with a single
transmission line in a single substrate. The patches are printed
on a FR-4 substrate with a thickness of 1.6 mm, dielectric
constant of 4.5 and loss tangent of 0.019.
The design principle for log-periodic wideband microstrip
antenna requires scaling of dimensions from period to period
so that the performance is periodic with the logarithm of frequency. The patch length (lp), the width (wp) and the insetfeed ( I ) are related to the scaling factor (τ ) by equation 1 [7].
The dimension of the first patch (higher frequency) is 16.32
mm x 16.32 mm. The space between each patch is a half
wavelength apart thus giving a forward fire radiation pattern
and reducing mutual coupling effect. The dimension of
ground plane is 130 mm x 100 mm.
Proceedings of the 5th European Conference on Antennas and Propagation (EUCAP)
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where m = 1, 2, 3, ……
Figure 1. Geometry of purpose antenna where wp=16.31mm; ltx=11.32mm;
lt=95.2mm; ls=10.81mm; sl=130mm; sw=100mm; h=1.6mm; θ=60º
The reconfigurabilty is achieved when the RF PIN diodes
are integrated at the feeding line of microstrip antenna to act
as a switch and to control the ON/OFF mode. For simulation,
the switches in RF systems are represented by an open or
short of the transmission line. Therefore, metal stripes of 3mm
x 1mm have been used to represent a switch and located at the
transmission line of patches. Hence, the ON state is
representing by that metal stripe and the absence of the metal
stripe is representing the OFF state. The same configuration
also presented in [3] and [5]. The five patches require five
switches PIN diode. The wideband operation is achieved
when all switches are in ON state. By controlling the switch atthe transmission line of patch, the required frequency band
could be achieved. The PIN diode switch conditions are
shown in Table 1. In simulation process, the ohmic losses are
assumed to be zero by using the ideal substrate and perfect
electric conductor.
TABLE I. PIN DIODE CONDITION
No of PIN
Diode
WideBand Band 1 Band 2 Band 3 Band 4
D1 O O X X X
D2 O O O X X
D3 O X O O X
D4 O X X O O
D5 O X X X O
O : PIN Diode ON
X : PIN Diode OFF
For fabricated antenna, when +9 volts DC is applied to each
PIN diode, it becomes a forward bias (ON state) while 0 voltsDC is applied, the PIN diode become OFF states or no bias.
The quarter-wave length radial stub is located at the middle
length of patch to connect from PIN diode to the DC and it’s
operating as a RF choke. The capacitor also placed at the
transmission line before connect to the SMA port to block the
DC signal from going into the signal generator.
III. SIMULATION A ND MEASUREMENT R ESULT
The prototype of the proposed reconfigurable frequency
antenna was fabricated using conventional photolithographytechnique. Figure 2 shows photograph of the fabricated
antenna structure with biasing circuit. The antenna structure
was tested on vector network analyzer (VNA). Figure 3 to 5
show the simulated as well as measured return loss
characteristics of the antenna with different band frequencies.
Figure 3 shows the bandwidth at -10dB Return loss of the
antenna without reconfigurable between simulation and
measurement. It shows that the operating frequency is
between 3.3 GHz until 4.5 GHz. The results also agree well
for the reconfigurable antenna between simulation and
measurement as shown in Table 2.
Figure 2. Photograph of the fabricated antenna
Figure 3. Simulated and measured return loss of log-periodic antenna
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Figure 4. Simulated return loss for each bands
Figure 5. Measured return loss for each bands
TABLE II. COMPARISON OF R ETURN LOSS FOR EACH BANDS
Antenna Parameter fL (GHz) fH (GHz) BW (%)
All Band Sim 3.33 4.38 27.5
Mea 3.34 4.38 27.19
Band 1 Sim 3.93 4.4 11.3
Mea 4.04 4.36 7.62
Band 2 Sim 3.75 4.08 8.44
Mea 3.73 3.98 6.5
Band 3 Sim 3.47 3.87 10.9
Mea 3.55 3.83 7.6
Band 4 Sim 3.32 3.58 7.54
Mea 3.35 3.60 7.20
The simulated realized gain for each state of PIN Diode is
plotted in Figure 6. The antenna operates from 3.3 GHz to 4.5
GHz with realized gain between 3 dB to 6 dB for each bands.
Since the log periodic technique enables one patch radiated at
single frequency hence, the gain is equally to a single patch.
The radiation patterns of the log-periodic antenna are shown
in figure 7. The patterns are taken at each sub band which is
3.5 GHz, 3.6 GHz, 3.8 GHz and 4.0 GHz while the radiation
pattern for each bands of reconfigurable antenna are plotted inFigure 8. The half power bandwidth of the antenna is taken
from the middle frequency of each band. The HPBW for log
periodic antenna is 76.3º while for Band 1, Band 2, Band 3
and Band 4 is 98.2º, 95.2º, 95.4º and 74.4º respectively. The
increase of beam angle at high frequency might be due to the
increased of the active region length at high frequency.
Figure 6. Simulated realized gain for each bands
(a)
(b)
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(c)
(d)
Figure 7. Simulated radiation pattern in E-plane and H-plane for log-
periodic antenna at (a) 3.5 GHz (b) 3.6 GHz (c) 3.8 GHz (d) 4.0 GHz
(a)
(b)
(c)
(d)
Figure 8. Simulated radiation pattern in E-plane and H-plane for
Reconfigurable Antenna at (a) Band 1 (b) Band 2 (c) Band 3 (d) Band 4
IV. CONCLUSIONS
The proposed frequency reconfigurable log-periodic
antenna has been design and simulated. It has been
demonstrated that the required frequency band could be
achieved by controlling the PIN diode switch. Four sub-bands
in which four groups of patches were selected from a
wideband frequency are obtained. For different group patches
selection, others sub-band could be achieved. For each
frequency band, a good return loss, gain and radiation pattern
have been obtained. The proposed antenna could be used for
cognitive radio that requiring wideband sensing and dynamic
band switching.
ACKNOWLEDGMENT
The authors thank to the Ministry of Higher Education
Malaysia (MOHE), Ministry of Sceince, Technology and
Innovation Malaysia (MOSTI), Research Management Centre
(RMC) and Radio Communication Engineering Department,
Universiti Teknologi Malaysia (UTM) for the supporting theresearch works.
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R EFERENCES
[1] M.R. Hamid, P. Gardner, P.S. Hall “Frequency Reconfigurable LogPeriodic patch Array” Electronic Letters, Vol.46; No.25, 2010.
[2] G. Monti, L. Corchia, and L. TarriconeJ. “Patch Antenna with
Reconfigurable Polarization” Progress In Electromagnetics ResearchC, Vol. 9, 13-23, 2009
[3] M. T. Ali, T. A. Rahman, M. R. Kamarudin and M. N. Md Tan “A
Planar Antenna Array With Saperated Feed Line For Higher Gain andSidelobe Reduction” Progress In Electromagnetics Research C, Vol. 8,
69-82, 200. [4] Symeon Nikolaou, B. Ramana, Cesar Lugo, C. Ileana, Dane C.
Thompson, E.Ponchak et al . “Pattern and Frequency Reconfigurable
Annular Slot Antenna Using PIN Diodes.” IEEE Transactions onAntennas and Propagation, Vol. 54, No. 2, February 2006: 439—448.
[5] A. H. Ramadan, K. Y. Kabalan, A. El-Hajj, S. Khoury and M. Al-Husseini “A Reconfigurable U-Koch Microstrip Antenna for Wireless
Applications.” Progress In Electromagnetics Research, PIER 93, 355-
367, 2009[6] Mirkamali, A., and Hall, P.S.: ‘Wideband frequency reconfiguration of
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[7] M.K.A. Rahim, M.R. Ahmad, A. Asrokin, M.Z.A.A. Aziz, “The design
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