E-Shape Patch Antenna for Millimeter Wave Communication · Indexing in Process - EMBASE, EmCARE,...

Vol 04, Special Issue 01, 2013 International Journal of Engineering Sciences Research-IJESR

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E-Shape Patch Antenna for Millimeter Wave Communication K.NALINI1, A.SAI SUNEEL2, S.B.SRIDEVI3

1 M.Tech., Assistant Professor, Department of ECE, SE&T, SPMVV, Tirupati, India. 2 M.Tech., Assistant Professor, Department of ECE, SE&T, SPMVV, Tirupati, India. 3 M.Tech., Assistant Professor, Department of ECE, SE&T, SPMVV, Tirupati, India.

[email protected], [email protected], [email protected]

ABSTRACT

This paper describes, E-shape patch antenna is proposed for millimeter wave frequencies. Using this E-shape

structure, the patch antenna is designed for wide band operation at about 31GHz to 38GHz for millimeter wave

communication. Simulated and measured results for main parameters such as return loss, impedance, bandwidth,

radiation patterns and gain also discussed in this paper. The development of models of such antennas, with

simplicity in designing and feeding, can well meet millimeter wave wireless communication. The antenna is

fabricated on double-sided FR-4(𝜖𝑟=4.4) printed circuit board using etching technique, and the design has been

tested with the network analyzer. The comparison between current distribution pattern and measurement results

for return loss and radiation patterns will discussed in this paper.

Keywords: E-shape patch antenna, Microstrip antenna, feed technique

1. INTRODUCTION

An antenna (or aerial) is a transducer designed to transmit or receive electromagnetic waves. In other words,

antennas convert electromagnetic waves into electrical currents and vice versa. They are used with waves in the

radio part of the electromagnetic spectrum, that is, radio waves, and are a necessary part of all radio equipment. .

In air, those signals travel very quickly and with a very low transmission loss. The signals are absorbed when

moving through more conductive materials, such as concrete walls or rock. Antennas are used in systems such as

radio and television broadcasting, point-to-point radio communication, wireless LAN, cell phones, radar, and

spacecraft communication. Antennas are most commonly employed in air or outer space, but can also be operated

under water or even through soil and rock at certain frequencies for shorter distances.

There are two fundamental types of antenna directional patterns, which, with reference to a specific two

dimensional plane (usually horizontal [parallel to the ground] or vertical [perpendicular to the ground], are either

Omni-directional (radiates equally in all directions), such as a vertical rod (in the horizontal plane) or

Directional (radiates more in one direction than in other)

1.1. MICROSTRIP PATCH ANTENNA In its most basic form, a Microstrip patch antenna consists of a radiating patch on one side of a dielectric substrate

which has a ground plane on the other side as shown in Figure 1. The patch is generally made of conducting

material such as copper or gold and can take any possible shape. The radiating patch and the feed lines are usually

photo etched on the dielectric substrate.

Fig 1: Structure of a Microstrip Patch Antenna Fig 2: Common shapes of microstrip patch elements

In order to simplify analysis and performance prediction, the patch is generally square, rectangular, circular,

triangular, and elliptical or some other common shape as shown in Figure 2. For a rectangular patch, the length L

of the patch is usually 0.3333λ<L <0.5λ, where 𝜆0 is the free-space wavelength. The patch is selected to be very

thin such that t << λ (where t is the patch thickness). The height h of the dielectric substrate is usually 0.003 𝜆0≤

h ≤ 0.05λ. The Di-electric constant of the substrate Є0 is typically in the range 2.2 ≤ ≤ 12 Є0.

Microstrip patch antennas radiate primarily because of the fringing fields between the patch edge and the ground

plane. For good antenna performance, a thick dielectric substrate having a low dielectric constant is desirable

since this provides better efficiency, larger bandwidth and better radiation. However, such a configuration leads

to a larger antenna size. In order to design a compact Microstrip patch antenna, higher dielectric constants must

be used which are less efficient and result in narrower bandwidth. Hence a compromise must be reached between

antenna dimensions and antenna performance.

1.1.1. Advantages • Light weight and low volume.

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http://en.wikipedia.org/wiki/Transducer

http://en.wikipedia.org/wiki/Transmitter

http://en.wikipedia.org/wiki/Receiver_(radio)

http://en.wikipedia.org/wiki/Electromagnetic_radiation

http://en.wikipedia.org/wiki/Electromagnetic_spectrum

http://en.wikipedia.org/wiki/Radio_wave

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Television

http://en.wikipedia.org/wiki/Wireless_LAN

http://en.wikipedia.org/wiki/Cell_phone

http://en.wikipedia.org/wiki/Radar

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• Low profile planar configuration which can be easily made conformal to host surface.

• Low fabrication cost, hence can be manufactured in large quantities.

• Supports both, linear as well as circular polarization.

• Can be easily integrated with microwave integrated circuits (MICs).

• Capable of dual and triple frequency operations.

• Mechanically robust when mounted on rigid surfaces.

1.1.2. Disadvantages • Narrow bandwidth

• Low efficiency

• Low Gain

• Extraneous radiation from feeds and junctions

• Poor end fire radiator except tapered slot antennas

• Low power handling capacity.

• Surface wave excitation

1.2. E-patch antenna

E-shaped patch antenna is proposed for millimeter wave communication using this E-patch wide band patch

antenna is design for millimeter wave communication

1.3. Feed Techniques

Microstrip patch antennas can be fed by a variety of methods. These methods can be classified into two categories-

contacting and non-contacting. In the contacting method, the RF power is fed directly to the radiating patch using

a connecting element such as a microstrip line.

In the non-contacting scheme, electromagnetic field coupling is done to transfer power between the microstrip

line and the radiating patch. The four most popular feed techniques used are the microstrip line, coaxial probe

(both contacting schemes), aperture coupling and proximity coupling (both non-contacting schemes).

1.3.1. Microstrip Line Feed:

Fig 3: Microstrip Line Feed

The purpose of the inset cut in the patch is to match the impedance of the feed line to the patch without the need

for any additional matching element. This is achieved by properly controlling the inset position. Hence this is an

easy feeding scheme, since it provides ease of fabrication and simplicity in modeling as well as impedance

matching. However as the thickness of the dielectric substrate being used, increases, surface waves and spurious

feed radiation also increases, which hampers the bandwidth of the antenna. The feed radiation also leads to

undesired cross polarized radiation.

1.3.2. Coaxial Feed

The Coaxial feed or probe feed is a very common technique used for feeding Microstrip patch antennas. As seen

from Figure 4, the inner conductor of the coaxial connector extends through the dielectric and is soldered to the

radiating patch, while the outer conductor is connected to the ground plane.

Fig 4: Probe fed Rectangular Microstrip Patch Antenna

The main advantage of this type of feeding scheme is that the feed can be placed at any desired location inside the

patch in order to match with its input impedance. This feed method is easy to fabricate and has low spurious

radiation. However, its major disadvantage is that it provides narrow bandwidth and is difficult to model since a

hole has to be drilled in the substrate and the connector protrudes outside the ground plane, thus not making it

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completely planar for thick substrates ( h > 0.02λo ). Also, for thicker substrates, the increased probe length makes

the input impedance more inductive, leading to matching problems. It is seen above that for a thick dielectric

substrate, which provides broad bandwidth, the microstrip line feed and the coaxial feed suffer from numerous

disadvantages. The non-contacting feed techniques which have been discussed below, solve these problems.

1.3.3. Aperture Coupled Feed

In this type of feed technique, the radiating patch and the microstrip feed line are separated by the ground plane

as shown in Figure 5. Coupling between the patch and the feed line is made through a slot or an aperture in the

ground plane.

Fig 5: Aperture-coupled feed

The coupling aperture is usually centered under the patch, leading to lower cross polarization due to symmetry of

the configuration. The amount of coupling from the feed line to the patch is determined by the shape, size and

location of the aperture. Since the ground plane separates the patch and the feed line, spurious radiation is

minimized. Generally, a high dielectric material is used for the bottom substrate and a thick, low dielectric constant

material is used for the top substrate to optimize radiation from the patch. The major disadvantage of this feed

technique is that it is difficult to fabricate due to multiple layers, which also increases the antenna thickness. This

feeding scheme also provides narrow bandwidth.

1.3.4. Proximity Coupled Feed

This type of feed technique is also called as the electromagnetic coupling scheme. As shown in Figure 1.6, two

dielectric substrates are used such that the feed line is between the two substrates and the radiating patch is on top

of the upper substrate. The main advantage of this feed technique is that it eliminates spurious feed radiation and

provides very high bandwidth (as high as 13%), due to overall increase in the thickness of the microstrip patch

antenna. This scheme also provides choices between two different dielectric media, one for the patch and one for

the feed line to optimize the individual performances.

Fig 6: Proximity-coupled Feed

Matching can be achieved by controlling the length of the feed line and the width-to-line ratio of the patch. The

major disadvantage of this feed scheme is that it is difficult to fabricate because of the two dielectric layers which

need proper alignment. Also, there is an increase in the overall thickness of the antenna. The main advantage of

this feed technique is that it eliminates spurious feed radiation and provides very high bandwidth due to overall

increase in the thickness of the microstrip patch antenna.

Table 1: below summarizes the characteristics of the different feed techniques.

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2. E-PATCH ANTENNAS

2.1. Design of E- shaped patch Antenna.

The size of the antenna on the substrate should be very small. Conventional whip and helical antennas takes large

volume on the substrate. So in order to reduce the size of the antenna on the substrate, we use Microstrip antennas.

The objective of designing the E- shaped patch antenna is the miniaturization of antenna. E-shaped patch antenna

exhibit high gain and improve efficiency in a surprisingly small package. E-shaped patch antenna can be designed

to exhibit wideband capabilities in millimeter wave communication.

2.2. Selection of Antenna specifications The selection of antenna parameters is influenced by its practical applications. The antenna specifications are

chosen such that it meets all our requirements. The four antenna specifications to be chosen are:

Frequency of operation.

Feed technique.

Dielectric constant.

Thickness of dielectric substrate.

2.2.1 Frequency of Operation Bluetooth /ISM, WiMAX, WLAN takes the advantage of a license free frequency bands, i.e. Industrial Scientific

and Medical (ISM) bands. The ISM bands for long range communication has two resonant modes at 2.32GHz and

4GHz.

2.2.2 Feed Technique

Various feeding techniques were discussed in chapter 1. Here, we have chosen 50Ω Microstrip Feed line method

as our feeding technique as the matching is easier and the process is simpler.

2.2.3 Dielectric Constant

The substrate is chosen such that the antenna has a low Q-factor, as the Q-factor is inversely proportional to

bandwidth. Another factor taken into consideration when selecting a substrate is loss tangent (tan δ). The dielectric

loss tangent of FR4 substrate is 0.0245. Lower the loss tangent higher the bandwidth so a dielectric with low tan

δ value is preferred in order to have larger bandwidth.

VSWRQ

VSWRBW

*

1

2.2.4. Thickness of Substrate There are numerous substrates that can be used for the design of microstrip antennas, and their dielectric constants

are usually in the range of 2.2≤r≤12. The one that are most desirable for antenna performance are thick substrates

whose dielectric constant is in the lower end of the range because they provide efficiency, larger bandwidth,

loosely bound fields for radiation into space, but at the expense of larger element size. Thin substrates with higher

dielectric constants are desirable for microwave circuitry because they require tightly bound fields to ever, because

of their greater losses; they are less efficient and have relatively smaller bandwidths. Since microstrip antennas

are often integrated with other microwave circuitry, a compromise has to be reached between good antenna

performance and circuit design. Bandwidth is directly proportional to the thickness of the substrate. The thickness

chosen is 1.6mm.

2.3. Design of E-shaped shaped patch antenna without truncated patch lines

For the printed E- shaped patch antenna, a microstrip feed line technique is used and for the impedance adaptation,

a 7×8mm ground plane is also used. E-shaped patch antenna with truncated patch lines is designed for millimeter

wave band. Using the antenna specifications the dimensions are calculated. Thus the designed E-shaped patch

with a patchantenna with ground plane is simulated using an IE3D simulator.

Fig 7: Structure of E-shaped patch antenna Fig 8: dimensions of the antenna

The above figure 8. Depicts the top and profile structure of the patch antenna. Concrete dimension parameters are

shown in Figure 8: where, L1=3.7mm, L2=3mm, L3=1.5mm, L4=0.6mm, L5=1.2mm, L6=3.9mm, L7=2.5mm,

L8=1.8mm, L9=1.5mm.

2.3.1: Design Formulae

The width of the L-Shaped monopole antenna is obtained using the formulae

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𝑤

ℎ=

2

𝛱[𝐵 − 1 − ln(2𝐵 − 1) +

𝜀𝑟 − 1

2 ∗ 𝜀𝑟{ln(B − 1) + 0.39 −

0.61

εr}]

and ‘B’ is obtained using the below formulae

B=377𝛱

2𝑍̥ √𝜀𝑟

Where,

h= height of the substrate.

W=width of the parasitic patch which is an optimized value.

Є𝑟 = dielectric constant or relative permittivity.

𝑧𝑜= characteristic impedance.

The total length of the L-Shaped monopole antenna excluding the feed line is obtained using the formulae l=𝜆𝑔

4

Where,

𝜆𝑔= guided wavelength which is given as

𝜆𝑔= 𝜆˳

√𝜀𝑒𝑓𝑓

Є𝑒𝑓𝑓= 𝜀𝑟+1

2+

𝜀𝑟−1

2

1

√1+12𝐻

𝑊

2.3.2. Design of E-shaped Antenna without truncated patch lines

The design parameters of monopole antenna are

Resonant frequency: around 29 to 31GHz.

Dielectric constant value: 3.7

Thickness of the substrate:0.8

Loss tangent:0.0245

Type of feed: microstrip line feed.

2.4. Design of E-shaped patch antenna with truncated patch lines For the printed E- shaped patch antenna, a microstrip feed line technique is used and for the impedance adaptation,

a 7×8mm ground plane is also used. E-shaped patch antenna with truncated patch lines is designed for millimeter

wave band. Using the antenna specifications the dimensions are calculated. Thus the designed E-shaped patch

with a patch antenna with ground plane is simulated using an IE3D simulator.

Fig 9: structure of E-shaped patch antenna Fig 10: Top and profile structure of antenna

with truncated patch lines

The above fig2.3.Depicts the top and profile structure of the patch antenna. Concrete dimension parameters are

shown in Fig. 1(b), where, 𝑙1 = 3.7 mm, 𝑙2 = 0.8 mm, 𝑙3 = 2.5 mm, 𝑙4 = 1.75 mm, 𝑙5 = 1.8 mm, 𝑙6 = 0.6 mm and

all line width 𝑤1 =0.7

2.4.1. Design Formulae The length and width of the parasitic element are calculated using the formulae presented below

𝑤

ℎ=

2

𝛱[𝐵 − 1 − ln(2𝐵 − 1) +

𝜀𝑟 − 1

2 ∗ 𝜀𝑟{ln(B − 1) + 0.39 −

0.61

εr}]

and the parameter B is calculated using the formulae below

B=377𝛱

2𝑍̥ √𝜀𝑟

Where,

𝑧0 is the characteristic impedance which is calculated using the formulae

𝑧0=120𝛱

√𝜀𝑒𝑓𝑓[𝑤

ℎ+1.393+0.667 ln(

𝑤

ℎ+1.444)]

W=width of the parasitic element

h=height of the substrate

and the length of the parasitic element is calculated using the formulae

l=𝜆𝑔

4

Where,

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𝜆𝑔= guided wavelength which is given as

𝜆𝑔= 𝜆˳

√𝜀𝑒𝑓𝑓

Є𝑒𝑓𝑓= = 𝜀𝑟+1

2+

𝜀𝑟−1

2

1

√1+12𝐻

𝑊

2.4.2. Design of Monopole Antenna with a parasitic element

The design parameters of monopole antenna are

Resonant frequency: around 31 to 38GHz.

Dielectric constant value: 3.7

Thickness of the substrate:0.8mm

Loss tangent:0.0023

Type of feed: microstrip line feed.

3. SIMULATION AND EXPERIMENTAL RESULTS OF DIFFERENT STRUCTURES OF E SHAPED

WIDEBAND PATCH ANTENNA The antenna was designed using IE3D software. IE3D is based on Method of Moments.

3.1 Simulation of E-shaped patch antenna without truncated patch lines The E-shaped patch antenna without a truncated patch lines is fabricated on an quartz crystal substrate with a loss

tangent of 0.0023 and fed using 50Ω-microstrip feed line.

3.1.1 Structure of E-shaped patch Antenna without truncated patch lines

Fig 11: Structure of E-shaped patch antenna without truncated patch lines.

bn3.1.2 Results obtained for E-shaped patch antenna without truncated patch lines

When the feed is given to the E-Shaped Monopole antenna, reflection occurs at the port because of impedance

mismatching. It means that when a load is mismatched, not all of the available power from the generator is

delivered to the load. This loss is termed as return loss. It is given using the formulae

RL=-20log|Γ| dB

But, when the feed is perfectly matched return loss will be minimum.

RETURN LOSS VSWR

Fig 12: Return loss Vs Frequency plot Fig 13: VSWR Vs Frequency

From the graph it is observed that VSWR for Monopole antenna is 2 at a frequency of 2GHz

Where, )/()( olol ZZZZ

)1/()1( VSWR

Substituting the value of from equations we get ZoZVSWR l /

So since we have obtained a VSWR of <=2 the matching has been attained perfectly.

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Gain Efficiency

Fig 14: Gain Vs Frequency Fig 15: Efficiency Vs Frequency

The gain of the E-shaped patch antenna is maximum at 6.2dbi and minimum gain at 3.9dbi. The Antenna

efficiency is the ratio of Radiated power to the incident power. The Radiation efficiency is the ratio of Radiated

power to the input power. The antenna efficiency is found to be maximum at 35GHz and minimum at 35.5GHz

the radiation efficiency is found to be maximum at 35 GHz and minimum at 35.5 GHz.

Current distribution for 29GHz Current distribution for 36GHz

Fig 16: Current Distrubution at 30GHz Fig 17: Current Distrubution at 3GHz

Figure 16 and Figure 17 are the simulated surface-current distribution at 30 and 36GHz, respectively, which

demonstrate the basic idea of the wideband mechanism of the E-shaped patch antenna. Currents flow from the

feeding point to the top and bottom edges. These current path lengths determine the resonant frequency. The

current path length in Figure 16 represents a lower resonant frequency. The current path length Figure 17

represents a higher resonant frequency. The structure can be modeled as a dual resonant circuit. These two

resonant circuits couple together and form a wide bandwidth.

2D RADIATION PATTERN 30GHz 2D RADIATION PATTERN AT 36GHz

Fig 18: Radiation pattern at 30GHz Fig 19: Radiation pattern at 36 GHz

Figure 18 shows the radiation pattern at 30GHz, here calculating E-total radiation; E-theta is 0 and 90degrees.

Figure 19 shows the radiation pattern at 36GHz, here calculating E-total radiation; E-theta is 0 and 90degrees.

3D RADIATION PATTERN

Fig 20: 3D Radiation Pattern

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4. EXPERIMENTAL RESULTS

4.1 Fabrication and Testing

The antenna has been fabricated on FR4 substrate with εr of 4.4 and substrate thickness of 1.6mm. In order to

fabricate the given BTA structure we use CIRCUITCAM 5.0 to draw its layout. This layout is then exported to

BOARDMASTER which is interfaced with the cutter used i.e. LPKF Proto Mat C60 shown in figure 21.

Fig 21: LPKF Protomat C60

The 60,000-rpm programmable speed motor allows the use of an extended range of tools, including small

rectangular profiled end mills with diameters as small as 10 mils. Such tools have superior characteristics for RF

and microwave applications and allow maximum precision at minimum penetration into the substrate.

The high-speed motor also allows maximum density digital design with track/clearance geometries of 4 mil and

8 mil drill holes. The whole system is controlled by software. After designing the whole circuit with a conventional

circuit designer (Circuit CAM) it is possible to export the file to the software, connected with the machine. After

setting a few parameters (definition of the working area, maximum width or a single trace) and placing the right

mill/drill in the tool holder the process starts. The drilling process is straightforward while the milling phase

requires a great attention. In fact, before starting the machine, the milling depth must be set very accurately.

The fabricated antenna is shown in figure 22 and is tested using PNA network analyzer E8364B. This network

analyzer can test any millimeter wave antenna for frequency ranges of 10 MHz to 50GHz. The results obtained

using network analyzer is shown in figure 23.

4.2 Hardware Part of the Antenna:

Fig 22: photograph of antenna

4.3 Return Loss Curve obtained using network analyzer 4.4 VSWR Curve obtained using network analyzer

Fig 23: Return loss curve obtained using network analyzer Fig 24: VSWR curve obtained using network

analyzer

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From the figure 23 we can see that the return loss of -10 dB at 30.6 GHz-35.2GHz

From the figure 24 the VSWR of the antenna at 30.6- 35.2GHz the VSWR value is below

4.5 Return Loss Curve Obtained Using IE3D Simulator

Fig 25: Return loss for ie3d simulation

4.6 Comparison of measured and simulated results:

From the below table 2 it is analyzed that results obtained for E-patch antenna structure with εrof 4.4 through

software analysis using IE3D software are approximately equal to the results obtained through hard ware analysis

using network analyzer.

Table 2: Comparison between Measured and Simulated results

Parameter Simulation Measured

VSWR frequency band 31.3-36.8GHz 30.6-35.2GHz

Resonant frequency 31.3-36.8GHz 30.6-35.2GHz

Return loss -35DB -20dB

CONCLUSIONS An E-shape wideband patch antenna design for millimeter wave communication has been proposed. This patch

antenna is simplicity in design and low manufacturing cost. Main parameters such as the return loss, impedance

bandwidth, gains and the radiation patterns at some operating bands have been studied. The results indicate that

the constructed antenna shows satisfactory characteristics of wideband, which will meet millimeter-wave wireless

communication

ACKNOLEDGEMENTS

This paper is dedicated to my parents.

REFERENCES

[1] K.Hettak and G.Delisl, “Omni directional dual polarizeed antenna for wireless indoor applications at

millimeter waves” in proc.IEEE AP-S Int symp..jul.1999, pp.2054-2057.

[2] W-I.K wak, S.-O.Park, and j.s.kim, “A folded planar inverted –F antenna for GSM/DCS/BLUETOOTH tripple

band application” IEEE antenna wireless propag.lett.vol.5, pp.18-21, 2006.

[3] F.yang, student member, X.X.ZHANG, X.ye ,and y.rahmat-sammi, “wide band E-Shaped patch antennas for

wireless communications”

[4] Y.G.e.member IEEE, K.P.Essele,and, and T.S.BIRD,’’E-shaped patch antenna for high speed wireless

networks’’, IEEE Transaction.antennas propag...vol 52,no.12,pp.1094-1100,dec 2004

[5] Y.G.e.member IEEE, K.P.Essele, and, and, andT.S.BIRD,’’A compact E-shaped patch antenna with

corrugated wings,’’IEEE trans.antennas propag.., vol.54, no.8, pp.2411-2413, Aug.2006.

[6] Modern antenna design, second edition, 2005, Thomas. A. Milligan, IEEE press Wiley-interscience, A. John

Wiley &Sons, INC, Publication.

[7] Foundation for microstrip circuit design, T. C. Edwards. A Wiley-interscience, A. John Wiley &Sons, first

edition, 1983.

[8] High-Frequency circuit design and measurements, Peter C. L. Yip, Chapman and Hall University and

Professional division, First edition 1990.

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