Triangular slot circular patch antenna for circular polarization reconfigura

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME
188
TRIANGULAR SLOT CIRCULAR PATCH ANTENNA FOR CIRCULAR
POLARIZATION RECONFIGURABILITY
Uma Shankar Modani1
, Anubhav Kanwaria2
1
(Govt. Engg. College, Ajmer, Rajasthan, India)
2
(Govt. Engg. College, Ajmer, Rajasthan, India)
ABSTRACT
This paper proposes a reconfigurable microstrip patch antenna with polarization states being
switched between left hand circular polarization (LHCP) and right hand circular polarization
(RHCP). The CP mode has been excited by perturbation element which is a triangular slot in the
circular patch. Two PIN diodes are symmetrically placed on each side of triangular slot to alter the
current direction around the patch, which determines the polarization state. By changing the state of
the PIN diode, the antenna has been made to switch between twp states of circular polarization. This
polarization reconfigurable patch antenna covers IEEE 802.11 outdoor band and has good agile
polarization performance with nearly 48MHz CP bandwidth and minimum axial ratio near to 1dB.
The minimum axial ratio frequency for LHCP and RHCP are same as 5.80GHz.
Keywords: Axial ratio, Circular polarization, Microstrip antenna, Reconfigurable antenna.
1. INTRODUCTION
RECONFIGURABLE antennas play an important role in modern wireless communication
systems, such as personal communications service (PCS) and wireless local area network (WLAN).
Reconfigurability may be present in resonant frequency, radiation pattern and/or polarization state
[1– 4]. Reconfigurable antennas with polarization diversity can realize frequency reuse, which
expands the capability of communication systems, and are useful when the operating frequency band
is limited [5, 6]. In addition, since a polarization diversity antennas can also alleviate the harmful
influence caused by multipath effects [7], therefore a polarization control is required from linearly
polarized to circularly polarized or a right-handed CP (RHCP) to a left-handed CP (LHCP) or vice
versa. Circular polarized microstrip patch antenna using dual feed which symmetrically excite two
orthogonal modes with 90 degree phase difference, needs a complicated feeding network [8– 10]
therefore single feed circularly polarized antennas are currently receiving much attention, because it
allows a reduction in the complexity, weight and the RF loss of any antenna feed and is desirable in
situations where it is difficult to accommodate dual orthogonal feeds with a power divider network
INTERNATIONAL JOURNAL OF ELECTRONICS AND
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 4, July-August, 2013, pp. 188-197
© IAEME: www.iaeme.com/ijecet.asp
Journal Impact Factor (2013): 5.8896 (Calculated by GISI)
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IJECET
© I A E M E

189
[11, 12]. The patch with a single point feed detunes degenerate modes of a symmetrical patch by
perturbation segments. Many, electrically controllable antennas have been researched with
switchable circularly polarization using perturbation technology such as switching slots [13– 16],
switching feeding point [17–20], and a switching corner truncations [21–23].
In this paper, a single feed reconfigurable microstrip patch antenna with an annular triangular
shaped slot has been proposed. The antenna has a simple configuration on a planar substrate.
2. ANTENNA DESIGN
Fig. 1 shows the geometry of the proposed single-fed circular microstrip patch antenna with
an annular triangular slot. The antenna consists of an inner equilateral triangle and outer circular
patch on Roger 5880 substrate with the thickness of 1.6mm and a relative dielectric constant of 2.2.
These two patches are connected by two pin diodes which are symmetrically placed with opposite
polarities at a point P which is 10.5mm apart from the top vertex of inner triangular patch along the
gap.
Fig. 1 Geometry of proposed antenna
The feeding point of the antenna is located at F which is 17.5mm apart from the center of the
patch on the negative X axis.
Table I Dimensions of the Radiating Patch Geometry
Parameters Dimensions (mm)
R(radius) 47.0
S(side) 43.2
P(position o f diode) 10.5(from top vertex)
G(gap) 1.0
Ground size 110 × 110

190
Fig. 2 shows the configurations of the prototype antenna. For the simulation purpose, the ON
condition of PIN diode has been realized by the presence of conductor and OFF condition of the
diode has been realized by the absence of conductor. In this way, the diode is assumed as ideal. The
design process involves resonating inner equilateral triangle near to 5.80GHz band and then
optimizing parameter mentioned in TABLE I for better results which include good matching, nearly
same minimum axial ratio point for LHCP and RHCP mode, and better gain performance.
(a) (b)
Fig. 2 Geometry of the simulated prototype antenna: (a) LHCP mode. (b) RHCP mode
The antenna polarization is controlled by switching the bias voltage between the triangular
patch and the outer circular patch. As the Diode D1 off and D2 is ON, the antenna has LHCP mode
and when Diode D2 off and D1 is ON, the antenna presents RHCP mode. The proposed antenna is
simulated with the aid of Ansoft HFSS software. The simulated return loss and axial ratio plot of the
proposed antenna have been shown in Fig. 3 and associated results are shown in TABLE II.
4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50
Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
ReturnLoss(dB)
RETURN LOSS
m1
m2
Curve Info
LHCP
RHCP
Name X Y
m1 5.8025 -25.7164
m2 5.8025 -24.7289
(a)

191
5.76 5.78 5.79 5.79 5.80 5.82 5.83
Freq [GHz]
0.50
1.00
1.50
2.00
2.50
3.00
3.50
AxialRatio(dB)
AXIAL PLOT
m1
m2
Curve Info
LHCP
RHCP
Name X Y
m1 5.8000 0.8680
m2 5.8000 1.0294
(b)
Fig. 3 Rectangular plot (a) Return loss plot for LHCP and RHCP mode (b) Axial ratio plot for LHCP
and RHCP mode
TABLE III: RESULTS OF DESIGN ANTENNNA IN TWO MODES
Parameters Return Loss (dB) Impedance BW (MHz/%) FL(GHz) FU(GHz)
LHCP 5.802GHz -25.71 541/9.32% 5.442 5.983
RHCP 5.802GHz -24.72 533/9.23% 5.444 5.977
The design exhibits circular polarization reconfigurability around 5.80GHz resonant bands
for nearly 48MHz bandwidth. Minimum axial ratio for LHCP mode is .868dB at 5.80GHz with total
gain of 2.058dB while for RHCP mode minimum axial ratio is 1.029dB at 5.80GHz with total gain
1.774dB as shown in Fig. 3 and Fig. 4. It has also been shown in Fig. 4 that the total gain radiation
patterns are having almost same shape for both the modes.
0.00
2.00
4.00
6.00
90
60
30
0
-30
-60
-90
-120
-150
-180
150
120
Radiation Pattern 4
m1
Curve Info
Gain Total (dB)
Name Ang Mag
m1 0.0000 2.0580
(a)

192
0.00
2.00
4.00
6.00
90
60
30
0
-30
-60
-90
-120
-150
-180
150
120
gain plot
m1 Curve Info
Gain Plot (dB)
Name Ang Mag
m1 0.0000 1.7745
(b)
Fig. 4 Total gain radiation pattern (dB) at Minimum axial ratio point, 5.80GHz, for E plane
(a) LHCP mode (b) RHCP mode
Around polarization band and at minimum axial ratio point, the polarization ratio radiation
pattern plot has been shown for both the modes in Fig. 5, which indicates that the proposed antenna
is left hand circularly polarized (LHCP) in most part of the curve for LHCP mode and right hand
circularly polarized in most part of the curve for RHCP mode.
-18.00
-6.00
6.00
18.00
90
60
30
0
-30
-60
-90
-120
-150
-180
150
120
Pr LHCP
Curve Info
PR LHCP (dB)
PR RHCP (dB)
(a)
-18.00
-6.00
6.00
18.00
90
60
30
0
-30
-60
-90
-120
-150
-180
150
120
gain plot1
Curve Info
PR RHCP (dB)
PR LHCP (DB)
(b)
Fig. 5 Polarization ratio radiation pattern for E plane at 5.80GHz (a) LHCP mode (b) RHCP mode

193
The proposed antenna possesses positive gain at all planes in both the modes when theta (Ѳ)
is 0 degree for desired polarization reconfigurable band extending from 5.770GHz to 5.882GHz and
high gain is observed when ‘Ѳ’ is around 40 degree as shown in Fig. 6.
5.72 5.74 5.76 5.78 5.80 5.82 5.84 5.86 5.88
Freq [GHz]
1.70
1.80
1.90
2.00
2.10
2.20
2.30
2.40
2.50
2.60
TotalGain(dB)
gain plot thetazero
m1
m2
Curve Info
LHCP
RHCP
Name X Y
m1 5.8025 2.0534
m2 5.8025 1.7646
(a)
5.72 5.74 5.76 5.78 5.80 5.82 5.84 5.86
Freq [GHz]
6.15
6.20
6.25
6.30
6.35
6.40
6.45
6.50
6.55
TotalGain(dB)
gain plot thetazero 40
m1
m2
Curve Info
LHCP
RHCP
Name X Y
m1 5.8025 6.3190
m2 5.8025 6.4888
(b)
Fig. 6 Total gain rectangular plot (a) Ѳ is 0 degree (b) Ѳ is 40 degree
3. STUDY OF VARIOUS PARAMETERS OF PROPOSED ANTENNA DESIGN
In this section, the antenna design parameters are varied and the effects of these variations on
the return loss and axial ratio of the antenna have been observed. For this study, the antenna design
shown in Fig. 2(a) has been used. Return loss curve has shown four resonating bands with third band
being the main resonant mode. Their matching is tightly controlled by feed position, position of
diode and outer circular patch radius which directly affects -10dB bandwidth also. It has been
observed that as feed moves along negative X axis, lower band matching increases and higher band
matching reduces. The affect of other parameters, varying one and keeping other constant have been
studied.
3.1 Variation In The Position Of Diode (P)
The position ‘P’ has been varied keeping all other parameters same as shown in Table I and
the results of return loss plots and axial plots for three values have been shown in Fig. 7. As diode
position move farther from top vertex of inner equilateral triangle, the matching of first and third

194
band increases while the second and fourth band matching disturbs, therefore bandwidth decreases.
Reverse effect has been observed when diode position P is decreased. It has been shown that P at
10.5mm distance offers best trade off, between AR bandwidth and minimum axial ratio. Also,
minimum axial ratio point at P of 9.5mm is same for both the modes.
4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50
Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
ReturnLoss(dB)
RETURN LOSS
m1
m2
m3
Name X Y
m1 5.7850 -19.6816
m2 5.8025 -25.7164
m3 5.7675 -22.2229
Curve Info
P 9.5 mm
P 10.5 mm
P 11.5 mm
(a)
5.72 5.74 5.76 5.78 5.80 5.82 5.84
Freq [GHz]
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
AxialRatio(dB)
AXIAL PLOT
m1
m2 m3
Curve Info
P 9.5 mm
P 10.5 mm
P 11.5 mm
Name X Y
m1 5.7675 1.4360
m2 5.8000 0.8680
m3 5.8150 0.8270
(b)
Fig. 7 Rectangular plot for variation in position of diode (P) (a) Return loss plot (b) Axial ratio plot
3.2 Variation In Radius Of Circular Patch (R)
The Radius ‘R’ has been varied keeping all other parameters same as shown in Table I and
the result of return loss plots and axial plots for three values have been shown in Fig. 8. Parameter R
affect design antenna attributes opposite to P parameter. As radius increases higher band matching
increases and lower band matching disturbs as shown in Fig.8 (a). In contrast to parameter P, patch
radius greatly affects minimum axial ratio value with leftwards movement of axial ratio band.
Minimum axial ratio value improvement from 1.28dB to 0.46dB has been observed as patch radius
varies from 46.5mm to 47.5mm as shown in Fig. 8(b) but observed total gain at circularly polarized
band also decreases to less than 1.50dB as shown in Fig. 9. Therefore, patch radii of 47mm has been
chosen with the optimum gain and minimum axial ratio of 2.053dB and .868dB respectively. The
other parameter such as peak directivity, peak gain and radiation efficiency are shown in TABLE III.

195
4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50
Freq [GHz]
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
ReturnLoss(dB)
RETURN LOSS
m1m2
m3
Name X Y
m1 5.8200 -26.4596
m2 5.8025 -25.7164
m3 5.7850 -24.3543
Curve Info
R 46.5 mm
R 47.0 mm
R 47.5 mm
(a)
5.76 5.77 5.78 5.79 5.80 5.81 5.82 5.83
Freq [GHz]
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
AxialRatio(dB)
AXIAL PLOT
m1
m2
m3
Curve Info
R 46.5 mm
R 47 mm
R 47.5 mm
Name X Y
m1 5.8050 1.2801
m2 5.8000 0.8680
m3 5.7850 0.4613
(b)
Fig. 8 Rectangular plot for variation in radius of circular patch (R) (a) Return loss plot (b) Axial ratio
plot
5.76 5.77 5.78 5.79 5.80 5.81 5.82 5.83
Freq [GHz]
1.20
1.40
1.60
1.80
2.00
2.20
2.40
2.60
TotalGain(dB)
gain plot thetazero1
Curve Info
R 46.5 mm
R 47 mm
R 47.5 mm
Fig. 9 Total gain rectangular plot for variation in radius of circular patch (R) at circular polarized
band

196
TABLE III: SIMULATED RESULTS OF ANTENNA PARAMETERS
Parameters Peak
Directivity
Peak Gain Radiation
Efficiency
Mode Minimum axial ratio point
LHCP 5.80GHz 5.907 5.889 99.68
RHCP 5.80GHz 6.097 6.093 99.94
4. CONCLUSION
A single probe-fed polarization reconfigurable microstrip antenna with a triangular slot has
been proposed for polarization diversities. It has been shown that the polarization of the proposed
antenna can be controlled between left hand circular polarization and right hand circular polarization
states by switching the PIN-diodes located near to the top vertex of equilateral triangular slot inside
the main circular patch. The proposed simple polarization reconfigurable planar antenna can be
applicable for WLAN communication terminals with polarization diversities.
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