compact broadband coplanar capacitive coupled probe fed microstrip antenna for wireless applications

IJETR, 2012; Vol 1(2): July-2012 (009 - 013) International Standard Serial Number: 2278 - 6082

Available online on www.ijetr.com

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COMPACT BROADBAND COPLANAR CAPACITIVE COUPLED PROBE FED MICROSTRIP

ANTENNA FOR WIRELESS APPLICATIONS

Dr. Ravi M. Yadahalli1*

,

Nandini Ammanagi2, Neelamma K Patil

3

1P.E.S. Institute of Technology & Management, Shivamogga, Karnataka, India

2V.E.S. Institute of Technology, Mumbai, India

3K.L.Es College of Engineering & Technology, Belgaum, Karnataka, India

ABSTRACT

In this paper, the design of a compact broadband capacitive feed

microstrip antenna with open end meandering slots in the radiating

patch is presented. The three identical narrow open end meandering

slots are embedded in the radiating patch of the antenna. Effects of

varying the length of meandering slots on the input characteristics of

the antenna have been investigated and discussed.

KEYWORDS: Microstrip Patch Antenna; Coplanar Capacitive Coupled

feed; Impedance bandwidth; meandering slot.

INTRODUCTION

In modern wireless communication systems,

more and more attention is paid for the

development of small size, broadband antennas.

Printed Microstrip antennas (MSAs) are attractive,

as they are small in size, low in cost, and easy to

integrate with printed circuit configuration.

Many studies to increase the bandwidth of the

microstrip patch antennas have been extensively

investigated [1, 2]. Recently, an ultra-wideband

microstrip antenna was achieved by using a

capacitive coupled probe feed [3, 4]. To

accommodate such antennas in wireless

communication systems, it is necessary to reduce

the size of such antennas. Many techniques have

been reported for reducing the size of microstrip

antennas [5, 6, 7]. Meandering of the radiating

patch by loading several slits in the non-radiating

edge is proven to be one of the effective methods

in reducing the size of the microstrip antennas [8,

9, 10]. It is found that the narrow meandering slots

increase the effective electrical length of the patch,

which in turn reduces the size of the antenna

operated at a given frequency.

In this paper, a capacitive fed compact

broadband microstrip antenna with meandered

slots in its radiating patch for wireless applications

Correspondence Author

Dr. Ravi M. Yadahalli

P.E.S. Institute of Technology &

Management, Shivamogga,

Karnataka, India

Email: [email protected]

International Journal of Engineering & Technology Research


is presented. The proposed antenna consists of a

rectangular patch which is fed by a capacitive

probe feed. Three identical narrow open

are embedded in the antenna’s radiating patch.

These meandered slots are aligned with an equal

spacing of L/4 parallel to the rectangular patch’s

radiating patch. Parametric study was carried out

by varying the length of meandered slots. The

proposed antenna is simulated using IE3D which is

Method of Moments (MOM) based

Electromagnetic (EM) software [11].

2. Antenna Design

Initially a reference antenna (RA) which is a

rectangular microstrip antenna was designed for 6

GHz using a coplanar capacitive coupled probe

feed. Reference antenna uses glass epoxy substrate

having εr = 4.4 and h = 1.56 mm and Fig.1 shows

the geometry of the reference antenna. Table 1

shows the optimized dimensions of reference

antenna. The configuration is basically a suspended

microstrip antenna in which radiating patch and

the feed strip are etched on the substrate of

thickness “h” mm. A long pin SMA connector is

used to connect the feed strip which is capacitively

coupled to the radiating patch. The length and

width of the radiating patch is designed for center

frequency of 6 GHz. The Capacitive feed strip is

basically a rectangular microstrip capacitor formed

from a truncated microstrip transmission

all its open ends are represented by terminal or

edge capacitances.

International Journal of Engineering & Technology Research

is presented. The proposed antenna consists of a

tch which is fed by a capacitive

probe feed. Three identical narrow open-end slots

are embedded in the antenna’s radiating patch.

These meandered slots are aligned with an equal

spacing of L/4 parallel to the rectangular patch’s

study was carried out

by varying the length of meandered slots. The

IE3D which is

Method of Moments (MOM) based

Initially a reference antenna (RA) which is a

angular microstrip antenna was designed for 6

GHz using a coplanar capacitive coupled probe

feed. Reference antenna uses glass epoxy substrate

= 4.4 and h = 1.56 mm and Fig.1 shows

the geometry of the reference antenna. Table 1

d dimensions of reference

antenna. The configuration is basically a suspended

microstrip antenna in which radiating patch and

the feed strip are etched on the substrate of

thickness “h” mm. A long pin SMA connector is

s capacitively

coupled to the radiating patch. The length and

width of the radiating patch is designed for center

frequency of 6 GHz. The Capacitive feed strip is

basically a rectangular microstrip capacitor formed

from a truncated microstrip transmission line and

all its open ends are represented by terminal or

Fig.1. Geometry of Coplanar Capacitive fed

microstrip antenna.

(a) Top View (b) Cross-sectional View

Table1. Dimensions of capacitive coupled probe

feed microstrip antenna

Parameter

Length of the radiator patch (L)

Width of the radiator patch (W)

Length of the feed strip (s)

Width of the feed strip (t)

Separation of the feed strip from

the patch (d)

Air gap between substrate (g)

Relative dielectric constant (

Thickness of substrate (h)

Later, the radiating patch is meandered using

three identical narrow meandering slots (L

Fig. 2 shows coplanar capacitive coupled probe fed

microstrip antenna with meandered slots in its

radiator patch. The meandered slots are aligned

with an equal spacing of L/4 parallel to the

radiating edge. The width of the meandering slot is

Ws = 1 mm.

Fig. 2. Geometry of coplanar capacitive coupled

probe fed microstrip antenna with meandering

slots in its radiating patch

(a) Top View (b) Cross-sectional View

ISSN: 2278 - 6082

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Fig.1. Geometry of Coplanar Capacitive fed

sectional View

Table1. Dimensions of capacitive coupled probe


Dimension

Length of the radiator patch (L) 11.33 mm

Width of the radiator patch (W) 15.21 mm

Length of the feed strip (s) 1.2 mm

Width of the feed strip (t) 3.7 mm

Separation of the feed strip from 1.7 mm

substrate (g) 4 mm

Relative dielectric constant ( ) 4.4 mm

1.56 mm

the radiating patch is meandered using

three identical narrow meandering slots (Ls, Ws).

Fig. 2 shows coplanar capacitive coupled probe fed

microstrip antenna with meandered slots in its

The meandered slots are aligned

with an equal spacing of L/4 parallel to the

radiating edge. The width of the meandering slot is

Fig. 2. Geometry of coplanar capacitive coupled

probe fed microstrip antenna with meandering

sectional View

International Journal of Engineering & Technology Research ISSN: 2278 - 6082


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3. PARAMETRIC STUDY

To understand how dimension of the

meandered slots will affect the center frequency,

impedance bandwidth and size reduction of

antenna, a parametric study was carried out using

IE3D simulation software version 14.1. The

simulated data of the proposed antenna were

noted by varying the Ls from the 9.21 mm to 14.21

mm, which are tabulated in Table 2. It may be

noted from the table that the reference antenna

(RA) with Ls = 0 mm resonates for 6.2 GHz having a

bandwidth of 2.6% (−10 dB return loss) and this

may confirmed from Fig.3. Also, it is also amply

evident from the table that the resonant frequency

of the antenna decreases gradually with the

increase in the slot length from 9.21 mm to 14.21

mm.

Table 2. Dimensions of capacitive coupled probe


Length of

meandering

slot

Ls (mm)

Resonant

frequency

fr (GHz)

Bandwidth

(MHz)

Size

Reduction

(%)

0 6.2 2600 -

9.21 5.39 192 14.55

10.21 5.36 202 15.07

11.21 5.2 226 17.60

12.21 5.34 258 13.39

13.21 5.34 264 13.39

14.21 5.33 267 13.42

Initially, as the slot length Ls increases from 0 to

9.21 mm, the resonant frequency of the antenna

slightly lowers from 6.2 GHz to 5.39 GHz giving a

size reduction of 14.55 % when compared to RA.

The bandwidth at this slot length is found to be

decreased from 90.32% to 3.56%. Again, as the slot

length increases from 9.21 mm to 10.21 mm, the

resonant frequency of the antenna decreases to

5.36 GHz giving a size reduction of 15.07%.

Moreover, it also observed that the bandwidth of

the antenna is 202 MHz.

Later when Ls = 11.21 mm, the resonant

frequency of the antenna lowers still further and

resonates at frequency, which is 1.19 times the

resonant frequency of the RA giving a size

reduction of 17.60%. However, the bandwidth of

the antenna is increased from 3.76 % to 4.23%.

This can be confirmed from Fig.4, which shows the

return loss characteristics of the proposed

antenna. Further increase in the length of the

meandered slots will not affect the center

frequency anymore.

Fig.3. Return loss characteristics of a capacitive

coupled microstrip antenna without meandering

slots

Fig.4. Return loss characteristics of a capacitive

coupled microstrip antenna with meandering slots

The radiation pattern at the resonant frequency 6.2

GHz of reference antenna has been taken for the

both H-plane and E-plane which are platted in



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Fig.5. The co-polarised radiation pattern at the

resonant frequency of the proposed antenna has

been taken i.e., for 5.2 GHz which is as shown in

Fig.6.

Fig.5. Radiation pattern of the reference antenna

Fig.6. Radiation pattern of the proposed antenna

4. Conclusion

In this paper, the design of a compact capacitive

fed microstrip antenna suspended above the

ground plane is presented. The meandered slots

were etched in the radiating patch of the

microstrip patch antenna to achieve size reduction.

Simulation results show that the proposed antenna

with meandered slots in its radiating patch

resonates at 5.2 GHz providing a size reduction of

17.60% with a bandwidth of 226 MHz.

REFERENCES

[1] S N Mulgi, R M vani, B S Makal, P V Hunagung

and S F Farida, “Enhancement of bandwidth of

rectangular microstrip antenna by feeding and gap-

coupling techniques”, Progress in Electromagnetic

Research Symposium 2000. pp.623, 2000.

[2] Kumar G and Ray K P (2003), Broadband

Microstrip Antennas, Artech House, Norwood , MA

[3] “Design Studies of Ultra-WidebandMicrostrip

Antennas with a Small Capacitive Feed”, Veeresh G.

Kasabegoudar, Dibyant S. Upadhyay, and K. J. Vinoy;

International Journal of Antennas and Propagation,

Volume 2007, pp.1-8.

[4] “A Coplanar Capacitively Coupled Probe Fed

Microstrip Antenna for Wireless Applications”

Veeresh G. Kasabegoudar and K. J. Vinoy, The 2009

International Symposium on Antennas and

Propagation (ISAP 2009) October 20-23, 2009,

Bangkok, Thailand.

[5] Fujimutho K, Henderson A, Hirasawa K and

James J R (1987) , Small Antennas, Research Studies

Press, London, UK

[6] Kan H K and Waterhouse R B (1999), “Size

Reduction Technique for shorted patches”, Electron.

Lett., Vol. 35, pp.948-949

[7] Wong K L (2000), Compact and Broadband

Microstrip Antennas, John Wiley & Sons.



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[8] S. Dey and R Mitra, Compact microstrip patch

antenna, Microwave Opt Technol Lett 13 (1996), 12-

14.

[9] Kuo J S and Wong K L. ‘A Compact microstrip

antenna with meandered slots in the ground plane’,

Microw. Opt. Technol. Lett., 2001, 29, pp. 95-97.

[10] Prabhakar H V, U K Kummuri, R. M. Yadahalli

and V Munnappa, ‘Effect of various meandering

slots in rectangular microstrip antenna ground plane

for compact broadband operation’, Electronics

Letters, 2007, 43, pp.

[11] IE3D release 14.1, Zeland Software Inc, 2011.

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compact broadband coplanar capacitive coupled probe fed microstrip antenna for wireless applications

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