Octagonal Shaped Annular Ring Pattern Reconfigurable Antenna Designs
for Cognitive Radio Application
Abstract— An Octagonal shaped Annular Ring pattern reconfigurable antenna is proposed for cognitive radio applications which
gives Omni-directional and directional pattern at 1.3 GHz. The antenna has the frequency switching capability at 1.5 GHz, 3.2
GHz, 4.8 GHz and 6.8 GHz with the use of a single PIN diode. Further, the antenna is modified by inserting a slotted square
shape in an octagonal ring. With the use of two diodes, the proposed antenna shows the pattern diversity at 3.2 GHz and 4.6 GHz
with the gain of 6.23 dBi. Also, the antenna shows the frequency switching for 1.5 GHz, 3.1 GHz, 4 GHz, 4.3 GHz, 4.8 GHz and
6.8 GHz with the different states of the PIN diode. The proposed antennas can be used for RFID, S and C band applications.
Keywords— Radiation Pattern, Reconfigurable, Octagonal, PIN Diodes, Cognitive Radio
Received: August 16, 2021. Revised: March 21, 2022. Accepted: April 22, 2022. Published: May 19, 2022.
1. Introduction
ECENTLY, reconfigurable antennas have increased the
research interest for their multifunctionality and degree of
freedom in the wireless communication systems [15-18].
Frequency-reconfigurable systems maintain radiations and
polarization properties constant while varying their operational
frequencies [1], [2]. The various radiator has been intended to
function either as pattern reconfigurable, frequency
reconfigurable or polarization reconfigurable [3]. Further
designs are associates with hybrid kinds of reconfigurable
structures, like the antenna discussed in [4] that have different
formats of frequency and polarization reconfigurability.
Pattern reconfigurable antennas have shown great interest
in having their advantages to receive and transmit signals with
desired directions. The pattern reconfigurability can be
achieved by using various approaches, like switching
connection conditions, switching the feed network as well as
switching the load. Though, there are no limited methods to
design the pattern reconfigurable featured antenna structures.
To realize pattern reconfigurable featured antennas effectually
prompted much research subsequently. In [5] A frequency and
pattern reconfigurable antenna is discussed in which the
radiator comprises of a square conducting patch having a row
of shorting through its center. This structure fed
perpendicularly with the coaxial connector at the center of the
patch which gives two resonant modes at two different
frequencies. With TMz100 mode resonance, the antenna
radiates having a broadside radiation pattern and also
resonates in a quasi-radial gives omni-directional pattern. The
two frequencies are controlled and reconfigured by using
varactors loaded with open-circuited stubs. The stubs act as
microstrip transmission lines.
In order to incorporate pattern switching, we can add
parasitic elements to the radiators [6-13]. In [14], two parasitic
elements were added on both sides of the patch in the designed
antenna. Through changing the states of diodes which works as
a switch on the parasitic elements, two parasitic elements and
the driven element govern the radiation properties. Pattern
reconfiguration also can be accomplished using co-located
radiating aperture, element phase shifting. In [19] a frequency-
reconfigurable bow-tie antenna is proposed which has two
arms. These are printed on both sides of the dielectric
substrate. The operating frequency band can be switched by
changing the operative electrical length of the bow-tie arms
using six PIN diodes. A biasing circuit was designed having
two low pass filters which isolated the dc from RF signals.
[20] a slot-ring antenna was proposed in which 16 PIN diodes
are placed inside the slots and 4 ports are used to feed the
radiator. By switching the diodes, the antenna array gives the
reconfigurability for the C band and L band. Two dc biasing
circuits were simulated to control the switching between ports.
ABHA SHARMA1,2, SONAM GOUR1,3, AMIT RATHI1,*
1Department of Electronics & Communication, Manipal University Jaipur, Jaipur, Rajasthan, INDIA
2Department of Electronics & Communication, Arya Institute of Engineering & Technology Jaipur, Rajasthan,
INDIA
3Department of Electronics & Communication. Poornima College of Engineering, Jaipur, Rajasthan,
Engineering, Jaipur, Rajasthan, INDIA
R
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2. Antenna Design
The proposed design has printed on double-sided FR-4
substrates which have dielectric constant ɛr = 4.4 (tanδ =
0.035) with dimensions 60 x 60 x 1.5 mm3 as shown in Figure
1. A rectangular-shaped conducting element mounted on FR-4
substrate. An octagonal ring structure cut out from the
radiating patch. The antenna is fed using a micro strip line.
Fig. 1 Structure of Octagonal Ring microstrip antenna
The proposed antenna gives the return loss at frequencies of
1.3 GHz, 4.8 GHz and 6.8 GHz which is shown in Figure 2.
Fig. 2 Return Loss plot of Octagonal Ring microstrip antenna
To control the PIN diode to provide switching at port, a
(KODAK SR44) button battery of 1.5 V was applied. A
Skyworks SMP1345-079LF PIN diode [1] has been used.
Figure 3 shows the simulated circuit design for the PIN diode.
The equivalent circuit of the PIN diode is fundamental to
provide the switching to the simulated design. In On state of
the diode, the serial inductance (Ls) is 0.7 nH impacts on the
resonant frequency and in OFF state the capacitance of 0.33
pF and resistance of 3KΩ is provided.
Fig. 3 Equivalent circuit diagram of PIN diode in forward bias and
reverse bias
Fig. 4 Return Loss plot of Octagonal Ring microstrip antenna (ON
State)
Fig. 5 Return Loss plot of Octagonal Ring microstrip antenna (OFF
State)
In the ON state of the diode, the proposed design resonates
at 1.5 GHz, 3.2 GHz and 6.8 GHz frequencies and at the OFF
state it gives resonance at 1.3 GHz, 3.8 GHz and 6.8 GHz
which shows the switching at 1.3 GHz and 6.8 GHz as
presented in Figure 4.
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Fig. 6 Return Loss plot of Octagonal Ring micro strip antenna (ON &
OFF State
(a)
(b)
Fig. 7 Radiation Patterns plot of Octagonal Ring microstrip antenna
(ON-OFF State) (a) at 1.3 GHz and (b) at 4.6 GHz
Due to the octagon shape, the path of current distribution
changed which causes the change in the radiation pattern. At
1.3 GHz, in ON state of diode, antenna gives an eight shaped
directional radiation pattern while in OFF state it is broad
directional as shown in Figure 7 (a). at 4.6 GHz, the antenna
radiates in omni-directional with ON condition of diode and
OFF mode it gives broad radiation pattern as shown in Fig. 7
(b).
Table 1 shows the results in terms of radiation pattern and
gain for different states of diodes.
TABLE 1 RESULTS ANALYSIS OF OCTAGONAL RING MICRO STRIP ANTENNA
State of diode
Radiation
Pattern
Gain
ON
Directional
4.6 dBi
OFF
Omni-
Directional
4.8 dBi
In the next proposed design, we have just inserted a
square ring-shaped ring into the octagonal patch. Due to a
change in the direction of the current, now the proposed
designed antenna provides the switching at multiple
frequencies 1.3 GHz, 1.5 GHz, 4 GHz, 4.3 GHz, 4.8 GHz and
6.8 GHz with using two PIN diodes as shown in Figure 8.
Fig. 8 Structure of Octagonal Ring Square slotted micro strip antenna
Fig. 9 Return Loss plot of Octagonal Ring Square slotted microstrip
antenna (ON-ON State)
When both diodes are in ON mode, the antenna shows the
resonance at two frequencies 3.15-3.22 GHz, 4.31-4.44 GHz
shown in Figure 9.
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Fig. 10 Return Loss plot of Octagonal Ring Square slotted microstrip
antenna (ON-OFF State)
Now at diode D1 is turned ON and D2 is in OFF state, 1.50-
1.54, 4.06-4.40 GHz, 6.73-6.96 GHz three bands are obtained
with the bandwidth of 4%, which is shown in Figure 10.
Fig 11 Return Loss plot of Octagonal Ring Square slotted microstrip
antenna (OFF-ON State)
Figure 11 shows three bands at 1.33-1.40, 3.85-4.11 and
4.75-4.88 GHz when diode D1 is OFF and diode D2 is ON.
Also 1.32-1.37, 3.96-4.05 GHz bands are obtained when
diode D1 and D2 both are in OFF state with the bandwidth of
500 MHz and 900 MHz respectively as shown in Figure 12.
Figure 12 Return Loss plot of Octagonal Ring Square slotted
microstrip antenna (OFF-OFF State)
Figure 13 Return Loss plot of Octagonal Ring Square slotted
microstrip antenna Comparative Analysis
Figure13 shows the comparative results of all four states of
the diode for the proposed design. The proposed design shows
the pattern diversity at 3.2 GHz and 4.6 GHz with the gain of 6
dBi which is depicted in Figure14 for all states of the diode.
(a)
(b)
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Fig. 14 Radiation Patterns plot of Octagonal Ring Square slotted
microstrip antenna (ON-OFF State) (a) at 3.2 GHz, (b) at 4.6 GHz
When D1 is ON and D2 is at OFF state as well as D1 and
D2 are ON, the radiation pattern at the frequency of 3.2 GHz
shows the main lobe is in the downward direction and when
both diodes are in OFF state, showing the main lobe in an
upward direction from 0 degree to 45 degree.
Similarly, at 4.6 GHz, the change in the state of diode shows
the change in main lobe direction having the shape of eight.
A comparative analysis of the proposed antenna is shown in
Table 2 The proposed antenna shows the frequency and
pattern diversity for 1.5 GHz, 3.2 GHz and 4.6 GHz which can
be used in Cognitive Radio applications. With the switching at
3.1 GHz, 4 GHz, 4.3 GHz, 4.8 GHz and 6.8 GHz, the
proposed design can be used in C band applications.
TABLE 2 RESULTS ANALYSIS OF OCTAGONAL RING SQUARE SLOTTED MICRO
STRIP ANTENNA
State of diode
Frequency
Bands
Bandwidth
Gain
ON-ON
3.15-3.22 GHz,
4.31-4.43 GHz
70 MHz
120 MHz
4.71 dBi
ON-OFF
1.50-1.54 GHz
4.00-4.40GHz,
6.73-6.96 GHz
40 MHz
400 MHz
5.17 dBi
OFF-ON
1.33-1.40 GHz
3.85-4.11 GHz
4.75-4.88 GHz
70 MHz
260 MHz
130 MHz
4.52 dBi
OFF-OFF
1.32-1.37 GHz
3.96-4.05 GHz
50 MHz
90 MHz
6.23 dBi
3. Conclusions
TABLE 3 RESULTS COMPARISONS WITH PREVIOUS WORK
REF
[5]
[19]
[20]
[6]
This
Paper
Substrate
Roger
Duroid
5880
-
Rogers
RT/
Duroid
5880
FR-4
FR-4
Dielectric
Constant
2.2
2.65
2.2
1.4
4.4
Substrate
Height
1.575 mm
1 mm
0.79
mm
1.6,
0.6 mm
1.5 mm
Frequency
Bands
(GHz)
2.68 To
3.51
2.4,
3.5, 5.5
1.76,
5.71
2.2 to
2.4
1.5, 3.2,
3.1, 4, 4.3,
4.6,4.8 &
6.8
Reconfigur
ation
Method
Varactor
Diode, Use
of Shorting
Pins and
Stubs
6 PIN
Diodes
16
PIN
Diodes
2 PIN
Diodes
2 PIN
Diodes
Reconfigur
ation
Frequency
& Pattern
Freque
ncy
Freque
ncy
Pattern
Frequency
& Pattern
Applicatio
ns
Cognitive
Radio
Application
s
Blueto
oth,
WiMA
X, And
WLAN
L and
C
Band
Applic
ations
Bluetoo
th and
Mobile
Commu
nication
Mobile
Communic
ations, C
Band
Applicatio
Applic
ations
s
ns, and
Cognitive
Radio
Applicatio
ns
Table 3 shows the comparison with previous studies which
shows proposed antenna with having two diodes provides the
switching for multi bands can be used for different
applications such as mobile communications, cognitive radio
applications, radar and C band applications.
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