# A Novel High-Performance Patch Radiator

Authors: N. S. Raghava; Asok De
Journal: International Journal of Microwave Science and Technology
 (2008)

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## Abstract

A novel two-layer highly efficient directive E-shaped patch radiator is described. By modifying the geometry of a rectangular patch and  by introducing two slits, the size of the original rectangular patch is reduced. Further reduction in the size is achieved by stacking E-shaped patches. Both gain and efficiency of this modified antenna is increased by 16%. It is also observed that by introducing EBG structure, the bandwidth of the antenna is increased by 10.5% approximately.


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## Body

## 1. Introduction

Microstirp patch  antennas (MSAs) [1–3] have attractive  features
such as low weight, low profile planar configurations, ease of fabrication, and
integration with RF devices which are being used for many applications due to
key advantages over conventional antennas. However, there are several
applications where even the physically small size of a conventional MSA is
still too large. One such application is handset of mobile communication. Although
the above said features are compatible with the mobile communication
technology, the operational frequency is too low. Also the practical
limitations of these MSAs are low gain and low efficiency. Thus, several
techniques have been proposed to alleviate these problems, such that
effectively the size of the radiator is reduced. One such method is to use a
thicker substrate with low-permittivity constant, which is not acceptable for
mobile communications. Other proposed methods include using high dielectric
constant material [4], multiple resonances, and modifying the geometry of patch
antennas [5–9]. However, using high dielectric constant material, the
efficiency was poor and the bandwidth is narrow due to surface wave excitation.
Modifying the geometry of the patch [10, 11] instead gives better results. Size
of the microstrip patch antenna can be reduced by using high-permittivity
substrate or shorting posts at the cost of bandwidth, gain, and efficiency.It is difficult to achieve high
gain and high efficiency from simple rectangular MSA. To fulfill these
requirements, the geometry of a rectangular patch antenna has to be modified as
discussed below. A pair of slits is inserted into an appropriate radiating edge
of the rectangular patch antenna. These slots reduce the size of the original
rectangular patch because the length of the current path around the slots is
increased [12]. To achieve this, a rectangular microstrip antenna of size 105 mm
× 44 mm is considered and is fed with a microstrip line at the center of the
long edge of the antenna. Two parallel narrow slots of length and width 43.25 mm
× 1 mm are inserted symmetrically into the radiating edge of a normal
rectangular patch resembling the English letter E.  Also to achieve bandwidth enhancement [13, 14],
a patch is etched on one side of a
dielectric substrate micro machined [15] with a rectangular lattice of holes on
the ground plane. These lattices of holes act as electromagnetic bandgap (EBG)
structure.Two designs of
microstrip patch antennas are studied. First, antenna design has an E-shaped
stacked microstrip antenna loaded with three shorting posts. Second, design has
an E-shaped antenna with electromagnetic bandgap (EBG) structure etched on the other
side of the substrate.


## 2. Proposed New Designs

The designs proposed incorporate novel methods for
additional, independently radiating resonances within the structure. Also they
are fabricated on  thick substrate with low dielectric constants which have enough bandwidth for 3G applications.


### 2.1. Antenna Design-I

A conventional
rectangular microstrip antenna’s  resonant frequency  can be  reduced by placing a
shorting post at the center of the edges. However, this shorted rectangular
patch antenna has low gain and efficiency. To improve these parameters, a
stacked E-shaped patch is used in the first design.The
geometry of loaded stacked  E-shaped patch antenna (LSESP) consists of two identical E-shaped patches (ESPs). The design of the antenna consists of two
air dielectrics of 18 mm height each. The first ESP is placed at 18 mm above the
ground plane, and the second ESP is stacked on the first patch at 36 mm from the
ground plane. Two shorting posts are connected from the ground to the lower
patch at the points (52.5,−11) and (−52.5,−11), and the third post is connected
from the lower to the upper patch at the point (0,22) as shown in Figure1.Figure 1
Top view of LS ESP antenna.The excitation
for the antenna is given by a microstrip line feed to the lower patch.


### 2.2. Antenna Design-II

In the second design, the antenna consists of a single
dielectric layer on which E-shaped patch is etched on one side.On the other side, a 265 mm× 110 mm rectangular metallic
ground plane is constructed.  Slots of
2.5 mm × 2.5 mm square holes spaced 5 mm apart forming a 52 × 21 matrix have been
made on the ground plane. There are no slots in the area just below the patch.
This rectangular ground plane acts as EBG [16] ground plane. The excitation for
the antenna is given by a microstrip line feed to the patch as shown in Figure 2.Figure 2
Top view of EBG ESP.


## 2.1. Antenna Design-I

A conventional
rectangular microstrip antenna’s  resonant frequency  can be  reduced by placing a
shorting post at the center of the edges. However, this shorted rectangular
patch antenna has low gain and efficiency. To improve these parameters, a
stacked E-shaped patch is used in the first design.The
geometry of loaded stacked  E-shaped patch antenna (LSESP) consists of two identical E-shaped patches (ESPs). The design of the antenna consists of two
air dielectrics of 18 mm height each. The first ESP is placed at 18 mm above the
ground plane, and the second ESP is stacked on the first patch at 36 mm from the
ground plane. Two shorting posts are connected from the ground to the lower
patch at the points (52.5,−11) and (−52.5,−11), and the third post is connected
from the lower to the upper patch at the point (0,22) as shown in Figure1.Figure 1
Top view of LS ESP antenna.The excitation
for the antenna is given by a microstrip line feed to the lower patch.


## 2.2. Antenna Design-II

In the second design, the antenna consists of a single
dielectric layer on which E-shaped patch is etched on one side.On the other side, a 265 mm× 110 mm rectangular metallic
ground plane is constructed.  Slots of
2.5 mm × 2.5 mm square holes spaced 5 mm apart forming a 52 × 21 matrix have been
made on the ground plane. There are no slots in the area just below the patch.
This rectangular ground plane acts as EBG [16] ground plane. The excitation for
the antenna is given by a microstrip line feed to the patch as shown in Figure 2.Figure 2
Top view of EBG ESP.


## 3. Results and Discussions

To simulate the structures,  IE3D software [17] is
used,  which is based on method of moments.  The first design is used to provide
high gain and efficiency, whereas the second design provides larger bandwidth
as discussed below. The various parameters of ESP and LS ESP have been
tabulated in Table 1.Table 1
Comparison of ESP and
LS ESP antennas.
Antenna
designResonant
frequency
(GHz)VSWRRadiation
efficiency
(%)Antenna
efficiency
(%)Gain
(dBi)Directivity
(dBi)3 dB beam widthESP1.981.1683.2182.789.3410.1560.27,
65LS
ESP2.251.1699.8399.309.819.8438.04, 69.91ESP2.601.3610097.710.7210.8235.69, 64.57LS
ESP2.841.1010097.1112.4412.5734.16, 48.54As seen from Table1, both resonant frequencies of ESP
antenna have been increased in case of LS ESP as shown in Figure 3. Radiation
and antenna efficiency are increased by 16% in case of first resonant frequency,
and in case of second resonant frequency both of them are almost the same as
shown in Figures 4 and 5. Also, the gain and directivity of the LS ESP have been
increased by 16% in second resonant frequency. Further, the 2D patterns of the ESP and
LS ESP are shown in Figures 7 and 8.Figure 3
SimulatedS-parameters
of the ESP and LS ESP.(a)-(b) Radiation patterns of the ESP at
1.977 GHz and 2.601 GHz.
(a)(b)(a)-(b)
Radiation patterns
of the LS ESP at 2.25 GHz and 2.841 GHz.
(a)(b)Figure 6
3D view of the E-shaped patch.Figure 7
2D pattern of the ESP at 1.977 GHz.Figure 8
2D pattern
of the LS ESP at 2.84 GHz.The impedance bandwidth calculated by the EBG ESP antenna is
10.5% more than the bandwidth provided by the simple E-shaped patch radiator.
TheS-parameters of the EBG ESP antenna are as shown in Figure 9.Simulated dB[S(1,1)] and Ang[S(1,1)] versus frequency of  ESP EBG.
(a)(b)



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*Source: 562193-2008-08-04.xml*