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International Journal of Electronics Engineering, 2 (2), 2010, pp. 295–298

Study o f Slo t Inser t ed Inver t ed Patc h —Rect angular  

Microst r ip Antenna for Wire less Appl ic at ions

P.A. Ambresh, P. M. Hadalgi, and P. V. Hunagund

 Department of P.G. Studies and Research in Applied Electronics, Gulbarga University, Gulbarga,

Karnataka-585106, India, E-mail: ambreshpa@rediffmail.com, hadalgipm@rediffmail.com.

 Abstract: In this article, an innovative design approach that improves the characteristics of conventional rectangular microstrip

antenna is presented. Antenna design adopts fundamental techniques such as direct contact probe feeding, inverted patch

structure with air packed dielectric substrate and slots inserted patch are the design conditions. The antenna has been fabricated

and measured for the EM-Study such as impedance bandwidth, return loss, radiation pattern and antenna gain measurement.

The antenna is designed for the Worldwide interoperability for Microwave access (WiMax) application operating in the

frequency range of 3.3– 3.5 GHz, RADAR application and European fixed satellite services (3-4 GHz) and is structured as

Slots Inserted Inverted Patch—Rectangular Microstrip Antenna (SIIP-RMSA). Measurement results show single band property

of SIIP-RMSA with an achievable impedance bandwidth of 7.93% (at 3.78 GHz), with the return loss (RL) of – 27 dB and

attained gain of 5.45 dB with 5% of size reduction. Keywords: Inverted Patch, Single Band, Microstrip Antenna, Radio Spectrum, Probe Fed, WiMax, EM-Study, European

Fixed Satellite Services.

1. INTRODUCTION

For decades the microstrip antenna has been intensively used

in the field of wireless communication and is found as a

class of new-style antenna which is developed in the early

1970 s. In contrast to the ordinary antennas, it exhibits a

variety of qualities such as low volume, light weight, low

profile, cost reliable, easy to conform with carrier and robust

when mounted on the rigid surfaces [1] – [3]. However, the

inherently narrow bandwidth and low gain [4] of this kind

of antenna tends to prohibit its wider applications. As it is

well-known, a simple conventional microstrip antenna has

impedance bandwidth of about 3% or less with respect to

centre frequency. Hence, this poses a problem for antenna

designer to meet the requirements such as to offer size

reduction, increment in gain, bandwidth of conventional

microstrip antenna, etc. [5]-[6]. There are plentiful and

renowned methods to increase the gain, bandwidth of 

antennas including increase of the substrate thickness, the

use of a low dielectric substrate, the use of air packed

dielectric substrate, various impedance matching and feedingtechniques, the use of multiple resonators and the use of slot

antenna geometry [7] – [13]. However, the bandwidth and

the size of an antenna are generally mutually ambiguous

properties, that is, upgrading one of the characteristics

normally results in degradation of the other.

2. ANTENNA DESIGN STRUCTURE

The design structure of Slots Inserted Inverted Patch —

Rectangular Microstrip Antenna (SIIP-RMSA) is depicted

in Fig. 1. The proposed antenna having width W and length

 L is supported by a FR4 dielectric superstrate with a dielectric

permittivity of єr and thickness h, with air packed dielectric

substrate єowith a thickness of ∆ is sandwiched between

the superstrate and ground plane. An Aluminium plate with

the dimension  Lg

and W g

with thickness of h1 is used as a

ground plane. Table 1 shows the optimized antenna design

parameters obtained for the proposed antenna. The proposedantenna is designed to operate in the frequency range 2 to

4 GHz. The artwork of the proposed antenna is carried out

by means of computer software AutoCAD 2006 to achieve

better accuracy and the fabrication is carried out using

photolithography method. The fabricated patch and the

ground plane were fixed firmly together with plastic spacers

along the four corners of the antenna. The patch also

integrates two horizontal and a vertical slots on the same

radiating element (patch), the slots are inserted in parallel

on the non-radiating and radiating edges of the patch

symmetrically with respect to the centerline ( x and  y-axis)

of the patch. When the energy is applied to the SIIP-RMSA,current flows in the patch and this current is not confined to

the edges of the slot but rather spread out over the patch.

The broader slots are selected because they are more efficient

in improving impedance bandwidth when compared to

narrow slots [14]. The dimensions of the slots are taken in

terms λ0, where λ0 is the free space wavelength. The patch

is fed by direct contact probe feeding method along the center

line of Y -axis at a distance f  p

from the top edge of the patch

as shown in Fig. 1. The feed point is selected based on the

equations as mentioned [15] along x and y-axis.

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296 International Journal of Electronics Engineering

The benefit of using air as dielectric medium below

inverted patch structure offers bandwidth increment,

penetration through the substrate can be avoided, to

accommodate the active devices and to have direct contact

of co-axial probe with respect to patch and the ground plane,

while the application of using superstrate with inverted patch

is to offer a gain enhancement and also it minimizes radiation

losses as there is no necessary of drilling a hole through the

patch. Use of parallel slots also reduces size of the patch.

On the other hand, the use of superstrate provides the

necessary protection for the patch from the environmental

effects. These techniques offer easy patch fabrication

especially for antenna array structures.

3. EXPERIMENTAL RESULTS AND DISCUSSION

The designed frequency for Conventional Microstrip

Antenna (CMSA) is 3.85 GHz. The impedance bandwidth

over return loss (RL) less than – 10 dB is measured for

2 – 4 GHz band of frequency. The measurements are taken

on Vector Network Analyzer (Rohde and Schwarz, Germany

make ZVK model 1127.8651). The plot showing the

variation of return loss (RL) versus frequency (GHz) of 

CMSA and SIIP-RMSA is presented in Fig. 2. The results

show that designed CMSA offers bandwidth at the expense

of return loss (3% at RL = – 15 dB), and gain of 3 dB. On

the other hand, when the slots are inserted on the same patchkeeping the feed point location fixed, it is found that the

antenna resonates at the lower frequency of 3.78 GHz, which

is fairly close to the designed frequency 3.85 GHz offering

increment in bandwidth of 7.93%, achieving return loss (RL)

of – 27 dB with an attained gain of 5.45 dB, and also 5% of 

size reduction. For the measurement of radiation pattern,

the antenna under test (AUT), i.e. the proposed antenna and

standard pyramidal horn antenna are kept in the far field

region. The AUT, which is the receiving antenna, is kept in

phase with respect to transmitting pyramidal horn antenna.

The received power by AUT is measured from 0° to 180°

with the rotational steps of 10°. Notably, as shown in Fig. 3,

the radiation characteristics of the proposed antenna display

good broadside radiation patterns. The 3 dB half power

beamwidth (HPBW) of SIIP-RMSA is found to be 42°.

Figure 4 shows the input impedance characteristics of SIIP-

RMSA having a single loop at the center of the Smith chart

fulfilling the property of better impedance matching and

single band property.

Fig. 1: View of Design Structure of SIIP-RMSA

Table 1

Optimized Antenna Design Parameters

Parameters CMSA SIIP-RMSA

(Dimensions in mm) (Dimensions in mm)

Length and Width

of Patch, ( L, W ) (17.76, 23.28) (17.76, 23.28)

Permittivity-FR4,

(єr ) 4.4 4.4

Thickness of 

superstrate, (h) 1.6 1.6

Permittivity of 

Air, (єo) 1 1

Air Gap, (∆) 8.5 8.5

Length and Width of 

ground plane, ( Lg, W 

g) (40, 40) (40, 40)

Aluminium

thickness, (h1) 1 1

Slot Length,

( Ls1

, Ls2

, Ls3

) – (17.14, 1.1, 17.14)

Slot Width,

(W s1

, W s2

, W s3

) – (2.86, 2.51, 2.86)

Slot Spacing, (S1, S2, (5.17, 4.01, 4.01,

S3, S4, S5, S6, S7) – 5.17, 1.68, 9.7, 1.68)

Feed Point

Location, ( fp) 4.2 4.2

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Study of Slot Inserted Inverted Patch—Rectangular Microstrip Antenna for Wireless Applications 297

Fig. 2: Variation of Return Loss ( RL) Versus Frequency (GHz) of CMSA and SIIP-RMSA

Fig. 3: Radiation Pattern of CMSA (3.85 GHz) and SIIP-RMSA (3.78 GHz)

Fig. 4: Plot of Variation of Input Impedance Versus Frequency

(GHz) of SIIP-RMSA

4. CONCLUSION

From the experimental study, it is found that the impedance

bandwidth of SIIP-RMSA is 7.93% by inserting the slots in

the radiating patch in comparison with conventional

rectangular microstrip antenna having impedance bandwidth

of 3%. By using superstrate and varying the slot length and

width, the gain enhancement of 5.45dB is achieved with 5%of size reduction. The improved impedance bandwidth, gain

and size reduction is achieved by inserting slots on the patch.

Designed antenna finds application in WiMax services,

RADAR application and European fixed satellite services

covering the frequency range of 3-4 GHz.

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