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Design of Twin inverted
L shape Microstrip antenna using HFSS

P.C.Praveen Kumar1,Department of ECE,GITAM
University.

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Dr.P.Trinatha Rao2,Department of ECE,
GITAM University.

 

Abstract: In the proposed work, a novel
design of twin inverted L compact and small size micro strip antenna is designed.
The radiating structure consists of two inverted L shaped structures in
coalesced form on FR-4 substrate with dielectric constant of 4.4 and fed with
probe feed with size of 50×10×1 mm3. The proposed antenna is resonates
at 12.5GHz with impedance bandwidth of 14.5%.The gain and efficiency of the
proposed antenna are above -28 dB and 97% respectively across the entire
operating band.

Keywords:
inverted L
antenna, FR-4, Radiation pattern, Gain.

1. Introduction:

Modern communication systems are smaller in size and
robust day by day. Therefore, the need of scale down, wideband and smaller
patch antennas are in demand. Micro strip patch antennas are widely used as
they offer compactness, low profile, light weight and capability to easily
integrate with circuits.

However, the micro strip patch antenna is limited by
its narrow operating bandwidth. The  major challenges for researchers is an
improvement of bandwidth and size reduction of the antenna as both are
generally mutually conflicting properties.

High Frequency Structure Simulator
(HFSS)is a commercial finite element
method solver for
electromagnetic structures from Ansys.  It is one of
several commercial tools used for antenna design,
and the design of complex RF electronic circuit elements including filters, transmission lines,
and packaging. HFSS uses a numerical technique called

 

the finite element method1. This is procedure where a
structure is subdivided into much smaller subsection called finite element. The
finite element used by HFSS are tetrahedra and entire collection of tetrahedral
is called mesh. Solution is found for the fields within the finite element and
these fields are interrelated so that Maxwell’s equations are satisfied across
interelement buildings4. Yielding a field solution for the entire original
structure. Once the field solution has found the s matrix solution is
determined.

In this proposed with flame retardant – 4( FR-4)
material is used as substrate, denotes that
safety of flammability of FR-4 is in compliance with the standard UL94V-06.
FR-4 is created from the constituent materials like epoxy resin, woven glass
fabric reinforcement, brominated
flame retardant with adopted specifications of relative permittivity
of 4.4 , relative permeability of 1,dielectric loss tangent of 0.02 and mass
density of 1900.

            There
are various impedance matching and feeding techniques used to achieve wide
bandwidth 5-9. Using some narrow slots or removing some portion from the
resonators such as patch loaded with slot provides a compact antenna with
enhanced bandwidth.

In this proposed  paper, a novel twin inverted L shaped wideband
patch antenna is presented. As per the available literature, not much work done
in this area. The proposed antenna structure is probe fed with wave port  and realized using two inverted L shaped
patches. This structure increases the periphery of the patch which increases
the effective length. This increment in the length increases the antenna size,
to reduce the antenna size we fold the both side edges like inverted L shape. This
folding causes the shift of resonance frequency towards the upper side. The
antenna parameters such as radiation pattern, bandwidth, gain and efficiency
are calculated by HFSS. The antenna structure is described in Sections 2. The
measured results and discussions are presented in Section 3 followed by
conclusion in Section 4.

2. Antenna Structure

The geometry of the proposed antenna is
shown in the figure no.1.The figure no.1a shows the top view of the proposed
antenna witch clearly represents every patch in the design. figure no.1b shows
the side view of the proposed antenna. The side view clearly shows how the
patch is mounted on the substrate in z axis at Z=1mm.

     (a)

(b)

Figure.1 Geometry of the proposed
antenna (a) top view and (b) side view.

The proposed antenna is printed on the
substrate,FR4 material is used as the substrate with the dimensions length
,width and height L X W X
H as 75mm X 20mm X
1mm respectively which is cited in Table no.1.The proposed antenna is designed
and mounted on the top of the substrate in Z-axis with thickness  of the substrate of 1mm and the thickness of
the radiating copper patch is of 0.1mm.The dimensions of the proposed antenna
is made with L1 X W1 X
H1
as 50mm X
10mm X
1mm
respectively. The RP1 is the rectangular patch 1 with L X
W
as 1mm X
10mm
in XY axis. One end of the patch is connected to RP2 and the other end is
connected to WP1.RP2 is the rectangular patch 2 with LXW
as 50mm X
1mm
on the XY axis .The RP2 is decides total length of the proposed antenna. The
actual length of the Rectangular path of the proposed antenna is RP2+ILP1+ILP2.
It comes around 82mmX 1mm.To place the proposed antenna in Mobile communication
Instruments, the length of the antenna will becomes complex and complicated to
withstand. To overcome length issue the author is planned to reduce the length
by folding the two side edges of the rectangular patch in inverted L shape. The
folding in the left hand side  of RP2
with the dimensions of 1mm X 8mm folding in
XY plane RP3 has formed   and 8mm X
1mm in XY plane RP5 has formed. RP3 and RP5 folding forms Inverted L shape
patch(ILP1) in the Left hand side. The folding in the right hand side  of RP2 with the dimensions of 1mm X
8mm
folding in XY plane RP4 has formed   and
8mm X
1mm in XY plane RP6 has formed. RP4 and RP6 folding forms Inverted L shape
patch (ILP2) in the right hand side. The folded arm inverted L shaped patch
gives better results compared to unfolded rectangular patch. In the proposed
antenna input signal is fed with wave feeding method.  WP is the wave port feeding patch which is
placed ZX plane with 2mm X 2mm patch dimensions
which is matched with the input impedance of 50?.The wave feed method is simple
to design as compared with co-axial feeding method. The design parameters of
the proposed antenna is tabulated in table no.1.

Table 1: Design
Parameters of the proposed antenna

S.No

Parameters

Size

1

LxWxH

75X20X1mm3

2

L1xW1xH1

50X10X1mm3

3

Substrate

FR-4(?r
= 4.4)

4

Wp( wave port)

2×2
mm2

5

Rp1

10
mm

6

Rp2

50
mm

7

Rp3

8
mm

8

Rp4

8
mm

9

Rp5

8
mm

10

Rp6

8
mm

11

ILP1

8×8
mm2

12

ILP2

8x8mm2

 

 

3.
Results and Discussions

The proposed antenna is made to
simulate at  different resonant
frequencies with different frequency setups. Initially the antenna is made to
simulate at 700MHz solution frequency with the frequency setup from 1GHz to 4
GHz.
The return loss S11(dB) of the proposed antenna from frequencies
1GHz to 4GHz is plotted as shown in figure no.2. The graph is drawn between
frequency and return loss(S11). The Frequency is plotted in X-axis in GHz and
return loss is plotted in Y-axis in dB. In the plot point m1
represents the minimum return loss with is -6.84dB at 4GHz and m2 is
the second minimum return loss with is -5.62DB at 1.3GHz. It is traced that the return
loss is less than -7dB throughout the frequency of 1 to 4GHz which is not
suitable for the antenna to radiate the signal. The antenna
will comes to active working condition and gives better results when it
generates -10dB of return loss(S11) 1-2. The plotted graph in the
figure no.2 is decaying from 3GHz to 4GHz and the plot shows that it further
decays even more that 4GHz.

Figure.2 Return loss of the
Proposed antenna form   1GHz to 4GHz.

To investigate the antenna
working, the antenna is made to simulate with the frequency setup from 1GHz to
100GHz.
The return loss S11(dB) of the proposed antenna from frequencies
1GHz to 100Ghz is plotted as shown in figure no.3. The graph is drawn between
frequency and return loss(S11). The Frequency is plotted in X-axis in GHz and
return loss is plotted in Y-axis in dB.

In
the plot point m1 represents the minimum return loss point with  -6.90dB at 4.08GHz,the point m2
represents the second minimum return loss point 
with -12.24dB at 11.88GHz, the point m3 represents the third
minimum return loss point  with -28.83DB
at 22.48GHz, the point m4 represents the forth minimum return loss
point  with -33.81dB at 30.56GHz and the
point m5 represents the fifth minimum return loss point  with -26.28dB at 58.48GHz.It is traced that the proposed
antenna gives better results with the simulation frequency more than 11GHz.

Figure.3 Return loss of the
Proposed antenna from   1GHz to 100GHz.

From
all the reference points in the figure no.3, point m4 gives high
return loss of -33.81dB at 30.5GHz of frequency. This is very high frequency to
operate. Among all the reference points, reference point m2 gives better
results -14.24 dB at 11.88GHz. To investigate the proposed antenna farther, the
antenna is made to simulate with the solution frequency of 12.5GHz with the
resonance frequency from 11GHz to 14GHz.The return loss of the proposed antenna
from 11GHz to 14GHz is as shown in figure no.4.

Figure.4 Return loss of the
Proposed antenna from  11GHz to 14GHz.

The
figure no.4 is plotted frequency in GHz in X-axis and Return loss(S11) in dB in
Y-axis. The  minimum return loss(S11) is
-12.53DB at 11.94GHz which is represented as m1 in figure  no.4. It is the better return loss (S11)
for the proposed antenna.

The
bandwidth of the proposed antenna plotted in figure no.5.Bandwidth is
calculated for the proposed antenna between the lower frequency band and upper
frequency band between 11GHz and 14GHz which has return loss of -10dB. In the
figure no.5 the reference point m1 shows the lower frequency band at
11.07GHz which has return loss (S11) of -10dB and the reference
point m2 shows the upper frequency band at 12.89GHz which has return
loss (S11) of -10dB. The difference between the m1 and m2 is the
bandwidth. The plot shows the bandwidth of the proposed antenna is around
1.82GHz which has represented on the X-axis of the plot.

Figure.5 Bandwidth of the Proposed
antenna.

The
VSWR for the proposed antenna is plotted in figure no.6. The frequency in GHz
is plotted on the X-axis and the VSWR in dB is plotted on the Y-axis. The plot
shows that VSWR is below 6 for the entire frequency band of 11GHz to 14GHz.In
the plot the reference point m1 shows the minimum VSWR point of the
plot. The proposed antenna has the minimum VSWR of 4.18 at 11.94GHz which has
represented by m1.

Figure.6 VSWR of the Proposed
antenna.

The impedance bandwidth is the ordinary
bandwidth of the antenna.  Normally this is defined as the range of
frequencies over which the return loss is acceptable.  Percentage is
referring to a quantity more commonly called fractional bandwidth (FBW).
 This is simply the absolute bandwidth (or impedance bandwidth) divided by
the center frequency of the antenna.

FBW = BW / fc                                      – (1)

BW=1.82GHz

fc=( sweep frey min+ sweep freq max)/2  – (2)

fc=(11GHz+14GHz)/2   fc=12.5GHz

FBW=1.82GHz/12.5GHz=14.56%

Taking the Gain in all the 360? we are getting
the average gain of around 28dB by investigating all the
parameters of the proposed antenna from 11GHz to 14GHz frequency band with
solution frequency of 12.5GHz, it is came to know that the Maximum radiation
intensity is of 0.0629763(W/sr), peak directivity is of  0.878769, peak gain is of 0.838597, Peak
Realized Gain is of 0.791427. For the proposed antenna from the wave port, it
is made to give incident power of 1W from the external source, it is traced
that  0.943722 W of power is accepted by
the proposed antenna and 0.90058 W of power is radiated by the proposed antenna
to the free space. By taking the accepted power and radiated power in to
account, the antenna is getting the radiation efficiency of  0.974286(97%).The detailed antenna parameters
of proposed antenna is enlisted in Table no.2.

Table .2 Antenna
parameters of Proposed Antenna.

S.No

        Quantity

Value

1

Max U

0.0629763(W/sr)

2

Peak Directivity

0.878769

3

Peak Gain

0.838597

    4

    Peak Realized Gain

0.791427

5

Radiated Power

0.90058(W)

6

Accepted Power

0.943722(W)

7

Incident Power

0.999967(W)

8

Radiation Efficiency

0.974286

9

Front to Back Ratio

1.03463

10

Decay Factor

-0

 

The
3D radiation pattern of proposed antenna is plotted in figure no.7.

Figure.7.3D
radiation pattern.

 

The 3D radiation pattern is drawn on
spherical coordinate system. The 3D Radiation pattern is in the shape of donut,
which is the ideal radiation pattern of the isotropic antenna.

 

Figure.8
3D Radiation pattern rectangular plot.

The 3D radiation pattern with reference to
rectangular coordinate system is plotted in the figure no.8.

 

 

figure
.9 2D Radiation pattern.

The proposed antenna 2D radiation
pattern on polar plot is shown in the 
figure no.9. In the polar plot the magnitude of the signal is
represented on the circles and phase angle of the signal is represented by phase
plot.The 2D radiation pattern for all 360? plane is giving the shape of 8.  

The proposed antenna and 3D radiation
pattern  is drawn on the single plot
is  as shown in figure no.10.The figure
shown how the signal is radiating from the proposed antenna. The signal is
radiating from the proposed antenna at the center.

figure.10 Proposed
antenna with radiation pattern.

4.Conclusion

In
the proposed paper, a novel, compact and small size patch antenna is designed.
The present study infers that the resonant frequencies and bandwidth are
controlled by using twin inverted L shaped patches to the reference antenna.
The effective size of the antenna is significantly reduced by folding the edges
as inverted L shape. With this structure we are getting impedance bandwidth of 14.50%
with the gain of -28dBi. Producing the good results between the range of 11GHz
to 14GHz. The radiation pattern is stable for the entire frequency band The
antenna performance can be further improved by optimizing the width and length
of the antenna and feeding systems. The antenna operates in X-band and can be
suitably used for various microwave devices operating in this range, primarily
for satellite communications.

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