Patch antenna

OVERVIEW

• DEFINITION

• GEOMETRY

• ADVANTAGES AND DISADVANTAGES

• FEEDING TECHNIQUES

• BASIC PROPERTIES

• BANDWIDTH IMPROVEMENT

• RADIATION PATTERN

• IMPROVING PERFORMANCE

• MAIN APPLICATIONS

• CONCLUSIONS

• REFERENCES

WHAT IS MICROSTRIP ANTENNA

ALSO CALLED AS ‘PATCH ANTENNAS’

One of the most useful antennas at microwave

frequencies( f>1 Ghz)

It consists of a metal ‘patch’ on top of a grounded

dielectric substrate

The patch may be in variety of shapes but circular

and rectangular are the most common

OVERVIEW OF MICROSTRIP ANTENNA (CONT.)

GEOMETRY OF RECTANGULAR PATCH ANTENNA

Typically h is much smaller than operating wavelength but not smaller than .05 of

wavelength

ADVANTAGES OF PATCH ANTENNA

Light weight and low volume

Easy to fabricate(use etching & photolithography)

Easy to feed(coaxial cable,microstrip line etc.)

Easy to use in an array or incorporate with other

microstrip circuit elements

Mechanically robust when mounted on a rigid

surface

DISADVANTAGES OF PATCH ANTENNA

Narrow bandwidth

Low efficiency limited by *conductor & dielectric and **surface

wave losses

Low gain

Radiation from feeds and junctions

Low power handling capacity

*Conductor and dielectric losses are more severe for thinner

substrates

**Surface wave losses become more severe for thicker

substrates(unless air or foam is used)

FEEDING TECHNIQUES

MICROSTRIP FEED :

• EASY TO FABRICATE

• SIMPLE TO MATCH BY

CONTROLLING THE INSET POSITION

• RELATIVELY SIMPLE TO MODEL

FEEDING TECHNIQUES(CONTD.)

QUARTER WAVELENGTH FEED

Z1 CAN BE ALTERED BY

CHANGING WIDTH OF

QUARTER WAVELENGTH

STRIP

FEEDING TECHNIQUES(CONTD.)

COAXIAL OR PROBE FEED

• EASY TO FABRICATE

• LOW SPURIOUS RADIATION

• FEED CAN BE PLACE AT ANY DESIRED

LOCATION TO MATCH IMPUT

IMPEDANCE

• NARROW BANDWIDTH

• FOR THICKER SUBSTRATES,THE

INCREASED PROBE LENGTH MAKES

Zin MORE INDUCTIVE

FEEDING TECHNIQUES(CONTD.)

APERTURE COUPLING FEED

• THE RADIATING PATCH AND THE MICROSTRIP FEED

LINE ARE SEPARATED BY THE GROUND PLANE

• THE AMOUNT OF COUPLING FROM

THE FEED LINE TO THE PATCH IS

DETERMINED BY THE SHAPE, SIZE

AND LOCATION OF THE APERTURE.

• LOW SPURIOUS RADIATION

• DIFFICULT TO FABRICATE

• NARROW BANDWIDTH

FEEDING TECHNIQUES(CONTD.)

PROXIMITY COUPLING

• FEED LINE IS BETWEEN THE TWO SUBSTRATES AND THE RADIATING PATCH IS

ON TOP OF THE UPPER SUBSTRATE.

• ELIMINATES SPURIOUS RADIATION

• HIGH BANDWIDTH

• DIFFICULT TO FABRICATE

• Length of feeding stub and

width-to-length ratio of patch

is used to control the match

BASIC PROPERTIES OF PATCH ANTENNA

RESONANCE FREQUENCYThe resonance frequency is controlled by the patch length and the substrate

permittivity.

The calculation can be improved by adding a“fringing length extension” ΔL to each

edge of the patch to get an “effective length” Le .

RESONANT FREQUENCY(CONTD.)

BANDWIDTH

• The bandwidth is directly proportional to substrate

thickness h.

• The bandwidth is inversely proportional to εr (a foam

substrate gives a high bandwidth).

• The bandwidth is directly proportional to the width W.

RESULTS:

• By using a thick foam substrate, bandwidth of about

10% can be achieved.

• By using special feeding techniques (aperture coupling)

and stacked patches, bandwidth of over 50% have been

achieved.

BANDWIDTH IMPROVEMENT

U-SLOT

The introduction of a U-shaped slot

can give a significant bandwidth

(10%-40%).

DOUBLE U-SLOT

A 44% bandwidth was achieved.

BANDWIDTH IMPROVEMENT(CONTD.)

A bandwidth of 34% was achieved

RESONANT INPUT RESISTANCE

• The resonant input resistance is almost independent of the

substrate thickness h.

• The resonant input resistance is proportional to εr.

• The resonant input resistance is directly controlled by the

location of the fed point. (maximum at edges , zero at center

of patch.)

RADIATION PATTERN

• The E-plane pattern is typically broader than the H-

plane pattern.

• The truncation of the ground plane will cause edge

diffraction, which tends to degrade the pattern

RADIATION PATTERN(CONTD.)

E - P L A N E

P AT T E R N

H - P L A N E

P AT T E R N

IMPROVING PERFORMANCE

By Reducing Surface-Wave Excitation and LateraL Radiation by

decreasing dielectric thickness and permittivity

IMPROVING PERFORMANCE(CONTD.)

Reducing surface-wave excitation and lateral radiation

reduces mutual coupling.

MAIN APPLICATIONS

1. MOBILES AND SATELLITES

2. GLOBAL POSITIONING SYSTEM(GPS)

3. RADIO FREQUENCY

IDENTIFICATION(RFID)

4. WORLDWIDE INTEROPERABILITY

FOR MICROWAVE ACCESS(WiMAX)

5. MEDICAL APPLICATIONS

6. RADAR APPLICATIONS

CONCLUSION

• A THEORITICAL AS WELL AS PRACTICAL ASPECT OF MICROSTRIP

PATCH ANTENNA IS PRESENTED

• Lower gain and low power handling capacity can be

overcome through an array configuration.

• Particular microstrip patch antenna can be designed for each

application and different merits are compared with

conventional microwave antenna.

REFERENCES

• C.A. Balanis, Antenna theory: analysis and design, 2nd ed., John Willey and & Son, Inc., 1997

• James j., and P.S. Hall (Eds), Handbook of microstrip antenna, Peter Peregrinus, London, UK, 1989.

• J. D. Kraus, R. J. Marhefka, “Antenna for all applications” 3rd Ed., McGraw-Hill, 2002.

• P.Subbulakshmi , R.Rajkumar : “ Design and characterization of corporatefeed rectangular microstrip patch antenna array antenna”,IEEE InternationalConference on Emerging Trends in Computing, Communication andNanotechnology,549-552, (ICECCN 2013)

• WWW.ANTENNA-THEORY.COM