8/10/2019 circularly polarized antenna

1/2

case with 0

=

65 . However. other CP characteristics are similar to

those observed for 0 =

65 .

Centre

frequency

M M

Table

1: Com parison between proposed disk-sec tor microstrip

antennas (antenna 1 with

8

=

65

and antenna

2

with

0

= 70 ) an d reference antenn a (circularly-polarised

equilateral-triangular microstrip antenna with slit [4])

Maximum

dimensions area

h e a r P atc h C P Maximum

bandwidth received

powel-

of patch

inm nm'

MFIr

dBin

Antenna 1

Antenna 2

141

1944 48.4 1149 25 (1.3% ) -50.4

1889

51.6

1237 23 (1.2%) -50.0

1931

48.2

998

19

(1.0%) -50.3

Conclusions: A single-feed circularly-polarised disk-sector micros-

trip antenna has been experimentally investigated. The present

CP

design requires no perturbation elements to be introduced in the

patch, and the excitation of two near-degenerate orthogonal

modes for CP radiation is mainly controlled by the flare angle of

the patch, which is experimentally found to be 65 and

70 .

EE

1998

Eleclronics

Lerrcrs

Online

No

19981587

Wen-Hsiu Hsu and Kin-Lu Wong (Deparznwir

of E/wtr.ir.o/

Enginwring,

Nurional Sun

Yat-Sen University, Kcrohsiung,

Tciiiwm

Republic of China)

16 Septeniher

199%

References

1 J A ME S .

J R ,

and H A L L ,

P.s

(Eds.): 'Handbook of microstrip

antennas' (Peter Peregrinus, London. 1989)

2

WO N G . K . L . , and

L I N . Y

F.: 'Circularly polarised microstrip antenna

with tuning stub', Electron.

Letr. 1998.

34 pp.

831-832

3

W O N G , K L., HSU. w.H and wu. C.K : 'Single-ked circularly polarized

microstrip antenna with

a

slit ',

Mzcvoiv.

Opt.

Technol. Lett. 1998.

18 pp.

306-308

LU. J H , T A N G ,

c

L.. and W O N G ,

K . L

: 'Circular polarisation design of

single-feed eq uilatera l-triang ular microstrip ante nna', Election.

Let t . ,

1998,

34 pp.

319-321

4

Circularly polarised microstrip antenna array

using proximity coupled feed

W . K .

Lo, C.H. Chan

and K . M .

Luk

A

2 x 2 circularly polarised CP) microstrip antenna array using a

proximity coupled feed and sequential rotation is described. As

compared with a previously presen ted single-element circularly

polarised microstrip antenna with a cross-slot, the new array

achieves a much wider

impedance

bandwidth of

11.18' 1

and has

an axial ratio bandwidth of 4. I h. he rcturn

loss,

radiation

patterns anti axial ratio of the a n t c nna array were measured

and

are

prcsented.

Introduction:

Microstrip antennas have been investigated exten-

sively

because

of their advantages such as small size, low profile

and

low

cost. Circularly

polarised CP)

antennas

arc

particularly

useful for a number of radar an d mobile satellite comm unication

systems. It has been demonstrated tha t C P antennas can be real-

ised by cutting

a

cross-slot into a circular patch [l ,

21.

Further-

more, the size of the patch is reduced when compared with that

without the

ci-oss-slot.

In this CP microstrip antenna, flexible

impedance matching is provided by a proximity-coupled feed

[3] .

For the conventional single-element CP antenna, the impedance

bandwidth and the axial ratio ban dwidth are relatively narrow.

The use of sequential rotation

[4,

51 can alleviate these difficulties.

In this study, a 2 x 2 circularly polarised microstrip phased array

antenna was designed and m easured experimentally. Each array

element is a circular microstrip antenna with a cross-slot with a

proximity-coupled feed. With the cross-slot, each element size

is

reduced and therefore the array can be designed with smaller ele-

ment spacing. When comparing the experimental results for the

single element CP antenna with those for the array, it is

found

that the

ne\$

2 x 2 array configuration offers a wider impedance

bandwidth than the single element C P antenna. Similarly, the CP

array also improves the axial ratio bandwidth and the boresight

axial I-atio. Experimental results of retu rn

loss,

radiation pattern

and polarisation aspect ratio are also presented

in

this Letter.

line width

WL t

slot Width w

length

Lb

circular patch with cross

slot

microstrip

ground plane

a

element spacing

D=0 59h0 ~ ~

Fig.

1 Antennci

t o i ~ f i ~ i i r c i t i o n s

U Single element

W

= 2111m,

L , =

20mm.

L ,

= IO W

= 4. 68mm = 23mm,

h

=

1.57min

h

Array

0

-1

m

20

:

3

P 30

-40

50

I I

I I I

1.5

1.6

1.7

1.8 1.9

frequency GHz

3

169412

Fig. 2

R r f u r n

loss against frequency

~._array

single element

An~znznaconfigurmtiun: The configurations of the single-element

antenna and the CP antenna array are shown in Fig. 1. The rela-

tive phases for the array at four feed points are

0,

90, 180 and

270 , respectively. Th e substrate used f or the an tenn a has a dielec-

tric constant E = 2.33 and the substrate thickness h = 1.57mm, the

width of the 50Q microstrip feed W is 4.68 . Th e rad ius of the

circular patch

R is

66 The length of the longer slot

Lo is

2190

ELECTRONICS LETTERS 12th

November

1998

Vol

34 No. 23

8/10/2019 circularly polarized antenna

2/2

20mn, the length of the shorter slot

L

is 10inm and the width

W

of the slots is

2

The patch-line overlap length of a single ele-

me nt is 23. Bas ed on the design of the single-elemmt CP

anten na, the design of the 2

x

2

CP

antenna ar ray is shown in Fig.

lh. T he designed frequency of the antenna array is 1.61GIIzand

the element spacing of the array is 0.59

A

and the patch-line

overlap length is the same as the single element.

0

12

10

8 -

m

E 6 -

._

-

4 -

2

270

large phased arrays

- I

R.J. Mailloux

A

technique

is

presented which combines the subarraying qualities

of constrained dual transform beamforming sections and p artial

overlapping netw orks to produce arrays of contiguous subarrays.

This approa ch is shown t o facilitate wideband scanning or limited

Geld

of

view coverage with a minimum number of controls and

low sidelobes.

-

Intvoduction: Elements of large arra:ys are often grouped into sub-

arrays

for

the purpose of decreasing the array feed complexity or

that scan over

a

limited field of view (LFOV) and also in wide-

band scanning systems. In an LFOV system that scans to kO,,,,,

reducing the number of controls. SiibarrdyS are useful

in

systems

the use of only a single phase shifter per subarray results in signif-

icant cost savings since the maxim um subarray spacing

s

of the

-

I

225 \__ 35

180

antennas are shown in F ig. 3. It reveals that the directivity

of

the

CP antenna array is better than that of the single element due to

the sharper radiation pattern.

Also,

from experimental results, it

is

found that the single elenlent and the antenna array generate

RHCP

(right hand circular polarisation) when the microstrip line

excites the circular patch as showri in Fig. 1. The array indeed

provides a much better

RHCP

than does the single element. Fig. 4

shows the measured axial ratio

of

ihe single element and that of

the array antenna where the 3dB axial ratio bandwidth of the

antenna array is 4.1%1which is much wider than the single element

of

O S6/0

The best axial ratio of the array is 0SdB a t 1 .62GHz

which is also much better than

the

single element of 2.8dB

at

the

same frequency.

Aclcnowledgnient: This project is supported by the Research Gran t

Council of H ong K ong (Project number: 9040199 and 9040210).

EE

1998

Electronics Letters

Otzlincj No

19981573

W.K. Lo C.H.

Chan and

K.M. 1,uk

(Wireless

Communications

Luboratory, Department O Electronic Engineering, City

niversity

o j

Honfi Kong, 53 Tat Clzee Avenue, Kowloon, Hong Kong SA R, Peoples

Repuldic o f China)

16

Septeniber

1998