Circular Microstrip Antenna and Properties Improvement

EL5056 & ET4056 - Elektronika Frekuensi Radio Lanjut

Program Studi Teknik TelekomunikasiSekolah Teknik Elektro dan Informatika

Institut Teknologi Bandung

1

Circular Patch

x

y

h

a

2

Circular Patch: Resonance Frequency

a PMCFrom separation of variables:

( ) ( )cosz mE m J kφ ρ=

Jm = Bessel function of first kind, order m.

0z

a

E

ρρ =

∂=

∂( ) 0mJ ka′ =

3

Circular Patch: Resonance Frequency (cont.)

mnka x′=a PMC

(nth root of Jm′ Bessel function)

2mn mnr

cf xπ ε

′=

Dominant mode: TM11

11 112 r

cf xaπ ε

′=11 1.842x′ ≈

4

Fringing extension: ae = a + Δa

11 112 e r

cf xaπ ε

′=

“Long/Shen Formula” :

a PMC

a + Δa

ln 1.77262r

h aah

ππε

⎡ ⎤⎛ ⎞Δ = +⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦21 ln 1.7726

2er

h aa aa h

ππ ε

⎡ ⎤⎛ ⎞= + +⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦or

Circular Patch: Resonance Frequency (cont.)

5

Circular Patch: Patterns(based on magnetic current model)

( )( )( )

1

1

1cosz

J kρE ρ,φ φ

J ka h

⎛ ⎞⎛ ⎞⎟⎜ ⎟⎜⎟⎜= ⎟⎜⎟⎜ ⎟⎜⎟⎟⎝ ⎠⎜⎝ ⎠

(The edge voltage has a maximum of one volt.)

a

yx

E-plane

H-plane

In patch cavity:

The probe is on the x axis.

2a

rεh

infinite GP and substrate

0 rk k ε=

x

The origin is at the center of the patch.

6

Circular Patch: Patterns (cont.)( ) ( ) ( ) ( )0

1 1 00

2 tanc cos sinRθ z

EE r,θ ,φ πa k h φ J ' k a θ Q θη

=

( ) ( )( )

( )1 001

0 0

sin2 tanc sin

sinRφ z

J k a θEE r,θ ,φ πa k h φ P θη k a θ

⎛ ⎞⎟⎜ ⎟=− ⎜ ⎟⎜ ⎟⎜⎝ ⎠

( ) ( )( ) ( )( )( ) ( )0

2cos 1 cos

tan secTE jN θ

P θ θ Γ θ θk hN θ jN θ θ

⎡ ⎤−⎢ ⎥= − = ⎢ ⎥−⎢ ⎥⎣ ⎦

( ) ( )( )

( )( )( )0

2 cos1

tan cos

r

TM

r

εj θN θ

Q θ Γ θ εk h N θ j θN θ

⎛ ⎞⎟⎜ ⎟− ⎜ ⎟⎜ ⎟⎟⎜⎝ ⎠= − =

−

( ) ( )tanc tanx x / x=where

( ) ( )2sinrN θ ε θ= −7

Circular Patch: Input Resistance

( )( )

21 0

21

in edge

J kR R

J kaρ⎡ ⎤

≈ ⎢ ⎥⎢ ⎥⎣ ⎦

a

0ρ

8

Circular Patch: Input Resistance (cont.)

12edge r

sp

R eP

⎡ ⎤= ⎢ ⎥

⎢ ⎥⎣ ⎦

( ) ( )( )

( ) ( ) ( ) ( )

/ 22 2

0 00 0

2 22 21 0 0

tanc8

sin sin sin

sp

inc

P k a k hN

Q J k a P J k a d

ππ θη

θ θ θ θ θ θ

=

⎡ ⎤′⋅ +⎢ ⎥⎣ ⎦

∫

( ) ( )1 /incJ x J x x=

where

Psp = power radiated into space by circular patch with maximum edge voltage of one volt.

er = radiation efficiency

9

Circular Patch: Input Resistance (cont.)

20

0

( )8sp cP k a Iπη

=

CAD Formula:

43c cI p= ( )

62

0 20

kc k

k

p k a e=

= ∑ 0

2

43

64

85

107

12

10.400000

0.0785710

7.27509 10

3.81786 10

1.09839 10

1.47731 10

eee

e

e

e

e

−

−

−

−

== −=

= − ×

= ×

= − ×

= ×

10

Feeding Methods

Some of the more common methods for feeding microstrip antennas are shown.

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Feeding Methods: Coaxial Feed

Advantages:simple easy to obtain input match

Disadvantages: difficult to obtain input match for thicker substrates, due to probe inductance. significant probe radiation for thicker substrates

2 0cosedgexR R

Lπ⎛ ⎞= ⎜ ⎟

⎝ ⎠

12

Feeding Methods: Inset-Feed

Advantages:simpleallows for planar feeding easy to obtain input match

Disadvantages: significant line radiation for thicker substratesfor deep notches, pattern may shown distortion.

13

Feeding Methods: Proximity (EMC) Coupling

Advantages:allows for planar feeding less line radiation compared to microstrip feed

Disadvantages:requires multilayer fabricationalignment is important for input match

patch

microstrip line

14

Feeding Methods: Aperture Coupled Patch (ACP) Advantages:

allows for planar feeding feed radiation is isolated from patch radiationhigher bandwidth, since probe inductance problem restriction is eliminated and a double-resonance can be created.allows for use of different substrates to optimize antenna and feed-circuit performance

Disadvantages: requires multilayer fabricationalignment is important for input match

patch

microstrip line

slot

15

Improving Bandwidth

Some of the techniques that has been successfully developed are illustrated here.

(The literature may be consulted for additional designs and modifications.)

16

Improving Bandwidth: Probe Compensation

L-shaped probe:

capacitive “top hat” on probe:

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Improving Bandwidth: SSFIPSSFIP: Strip Slot Foam Inverted Patch (a version of the ACP).

microstrip substrate

patch

microstrip line slot

foam

patch substrate

• Bandwidths greater than 25% have been achieved.

• Increased bandwidth is due to the thick foam substrate and also a dual-tuned resonance (patch+slot).

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Improving Bandwidth: Stacked Patches

• Bandwidth increase is due to thick low-permittivity antenna substrates and a dual or triple-tuned resonance.

• Bandwidths of 25% have been achieved using a probe feed.

• Bandwidths of 100% have been achieved using an ACP feed.

microstrip substrate

driven patch

microstrip lineslot

patch substratesparasitic patch

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Improving Bandwidth: Stacked Patches (cont.)

-10 dB S11 bandwidth is about 100%

stacked patch with ACP feed3 4 5 6 7 8 9 10 11 12

Frequency (GHz)

-40

-35

-30

-25

-20

-15

-10

-5

0

Ret

urn

Loss

(dB

)

MeasuredComputed

20

Improving Bandwidth: Parasitic Patches

Radiating Edges Gap Coupled Microstrip Antennas (REGCOMA).

Non-Radiating Edges Gap Coupled Microstrip Antennas (NEGCOMA)

Four-Edges Gap Coupled Microstrip Antennas (FEGCOMA)

Bandwidth improvement factor:REGCOMA: 3.0, NEGCOMA: 3.0, FEGCOMA: 5.0?

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Improving Bandwidth: Direct-Coupled Patches

Radiating Edges Direct Coupled Microstrip Antennas (REDCOMA).

Non-Radiating Edges Direct Coupled Microstrip Antennas (NEDCOMA)

Four-Edges Direct Coupled Microstrip Antennas (FEDCOMA)

Bandwidth improvement factor:REDCOMA: 5.0, NEDCOMA: 5.0, FEDCOMA: 7.0

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Improving Bandwidth: U-shaped slot

The introduction of a U-shaped slot can give a significant bandwidth (10%-40%).

(This is partly due to a double resonance effect.)

“Single Layer Single Patch Wideband Microstrip Antenna,” T. Huynh and K. F. Lee, Electronics Letters, Vol. 31, No. 16, pp. 1310-1312, 1986.

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Improving Bandwidth: Double U-Slot

A 44% bandwidth was achieved.

“Double U-Slot Rectangular Patch Antenna,” Y. X. Guo, K. M. Luk, and Y. L. Chow, Electronics Letters, Vol. 34, No. 19, pp. 1805-1806, 1998.

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Improving Bandwidth: E-Patch

A modification of the U-slot patch.

A bandwidth of 34% was achieved (40% using a capacitive “washer” to compensate for the probe inductance).

“A Novel E-shaped Broadband Microstrip Patch Antenna,” B. L. Ooi and Q. Shen, Microwave and Optical Technology Letters, Vol. 27, No. 5, pp. 348-352, 2000.

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Multi-Band Antennas

General Principle:

Introduce multiple resonance paths into the antenna. (The same technique can be used to increase bandwidth via multiple resonances, if the resonances are closely spaced.)

A multi-band antenna is often more desirable than a broad-band antenna, if multiple narrow-band channels are to be covered.

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Multi-Band Antennas: Examples

Dual-Band E patch

high-band

low-band

low-band

feed

Dual-Band Patch with Parasitic Strip

low-band

high-band

feed

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Miniaturization

• High Permittivity• Quarter-Wave Patch• PIFA• Capacitive Loading• Slots• Meandering

Note: miniaturization usually comes at a price of reduced bandwidth.

General rule: maximum obtainable bandwidth is proportional to the volume of the patch (based on the Chu limit.)

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Miniaturization: High Permittivity

It has about one-fourth the bandwidth of the regular patch.

L

W E-plane

H-plane

1rε =4rε =

L´=L/2

W´=W/2

(Bandwidth is inversely proportional to the permittivity.)

29

Miniaturization: Quarter-Wave Patch

L

W E-plane

H-plane

Ez = 0

It has about one-half the bandwidth of the regular patch.

W E-plane

H-plane

short-circuit vias

L´=L/2

30

Miniaturization: Planar Inverted F Antenna (PIFA)

A single shorting plate or via is used.

This antenna can be viewed as a limiting case of the quarter-wave patch, or as an LC resonator.

side view

feedshorting plateor via top view

/ 4dL λ<

31

PIFA with Capacitive Loading

The capacitive loading allows for the length of the PIFA to be reduced.

feedshorting plate top view

side view

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Miniaturization: Slotted Patch

The slot forces the current to flow through a longer path, increasing the effective dimensions of the patch.

top view

linear CP

0o ±90o

33

Miniaturization: Meandering

Meandering forces the current to flow through a longer path, increasing the effective dimensions of the patch.

feed

via

meandered quarter-wave patch

feed

via

meandered PIFA

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Improving Performance: Reducing Surface-Wave Excitation and Lateral Radiation

Reduced Surface Wave (RSW) Antenna

SIDE VIEW

zb

hx

shorted annular ring

ground plane feed

aρ0

TOP VIEW

a

ρo

b

feed

D. R. Jackson, J. T. Williams, A. K. Bhattacharyya, R. Smith, S. J. Buchheit, and S. A. Long, “Microstrip Patch Designs that do Not Excite Surface Waves,” IEEE Trans. Antennas Propagat., vol. 41, No 8, pp. 1026-1037, August 1993.

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Reducing surface-wave excitation and lateral radiation reduces edge diffraction.

RSW: Improved Patterns

space-wave radiation (desired)

lateral radiation (undesired)

surface waves (undesired)

diffracted field at edge

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-90

-60

-30

0

30

60

90

120

150

180

210

240

-40

-30

-30

-20

-20

-10

-10-90

-60

-30

0

30

60

90

120

150

180

210

240

-40

-30

-30

-20

-20

-10

-10

conventionalconventional RSWRSW

Measurements were taken on a 1 m diameter circular ground plane at 1.575 GHz.

RSW: E-plane Radiation Patterns

MeasurementTheory

37

Reducing surface-wave excitation and lateral radiation reduces mutual coupling.

RSW: Mutual Coupling

space-wave radiation

lateral radiation

surface waves

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Reducing surface-wave excitation and lateral radiation reduces mutual coupling.

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

0 1 2 3 4 5 6 7 8 9 10

Separation [Wavelengths]

S12 [

dB]

RSW - MeasuredRSW - TheoryConv - MeasuredConv - Theory

RSW: Mutual Coupling (cont.)

“Mutual Coupling Between Reduced Surface-Wave Microstrip Antennas,” M. A. Khayat, J. T. Williams, D. R. Jackson, and S. A. Long, IEEE Trans. Antennas and Propagation, Vol. 48, pp. 1581-1593, Oct. 2000.

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ReferencesGeneral references about microstrip antennas:

Microstrip Antenna Design Handbook, R. Garg, P. Bhartia, I. J. Bahl, and A. Ittipiboon, Editors, Artech House, 2001.

Microstrip Patch Antennas: A Designer’s Guide, Rodney B. Waterhouse, Kluwer Academic Publishers, 2003.

Microstrip and Printed Antenna Design, Randy Bancroft, Noble Publishers, 2004.

Microstrip Antennas: The Analysis and Design of Microstrip Antennas and Arrays, David M. Pozar and Daniel H. Schaubert, Editors, Wiley/IEEE Press, 1995.

Advances in Microstrip and Printed Antennas, K. F. Lee, Editor, John Wiley, 1997.

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References (cont.)

General references about microstrip antennas (cont.):

Millimeter-Wave Microstrip and Printed Circuit Antennas, P. Bhartia, Artech House, 1991.

The Handbook of Microstrip Antennas (two volume set), J. R. James and P. S. Hall, INSPEC, 1989.

Microstrip Antenna Theory and Design, J. R. James, P. S. Hall, and C. Wood, INSPEC/IEE, 1981.

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References devoted to broadband microstrip antennas:

Compact and Broadband Microstrip Antennas, Kin-Lu Wong, John Wiley, 2003.

Broadband Microstrip Antennas, Girish Kumar and K. P. Ray, Artech House, 2002.

Broadband Patch Antennas, Jean-Francois Zurcher and Fred E. Gardiol, Artech House, 1995.

References (cont.)

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