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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 

a printed log periodic dipole array’, Microw. Opt. Technol. Lett., 2010,

52, pp. 2310–2311

[7]  M.K.A. Rahim, M.R. Ahmad, A. Asrokin, M.Z.A.A. Aziz, “The design

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