8/11/2019 00900136

1/4

On Reducing the Patch Size of U-Slot and L-Probe Wideband Patch Antennas

Aaron Shackelford, Kai-Fong Lee, Deb Chatterjee*

Department of Electrical Engineering, University of Missouri-Columbia

Columbia, MO

6521

1

*Coordinated Engineering Program in Kansas City

1. Introduction

The coaxially-fed U-slot rectangular patch antenna (Figure 1 and the L-probe fed rectangular

patch antenna (Figure

2)

are two recently developed single-layer single-patch wideband

microstrip patch antennas

[1 2].

In both cases, a second resonance is introduced near the main

patch resonance, either by the U-slot or by the L-probe. The U-slot or the L-probe also introduce

a capacitance which counteracts the inductance of the coaxial feed, allowing for the use of thick

substrates 0.08

-

O.lh,) where h is the free space wavelength. Using foam substrates (with E =

l), the impedance bandwidths of these antennas operating in the fundamental mode are in the 30-

40

range, with stable pattern and gain characteristics. These bandwidths are more than

sufficient for most wireless communication applications. The resonant length of the fundamental

mode is about half of the free space wavelength.

For many applications, it is desirable to reduce the size of the patch to conserve real estate

space. For this reason, there have been extensive investigations on patch size reduction

techniques. One method uses microwave substrates with values of E, > 1. Use of microwave

substrates also allow the fabrication of electronic circuits. Another method uses a shorting wall

at the location of zero electric field

so

that the resonant length is halved, resulting in the quarter-

wave patch. Yet another method uses a shorting pin near the feed. This introduces capacitive

coupling to the patch resonance, tbereby increasing the effective E and reducing the frequency,

which means that, for a given resonant frequency, the patch size becomes smaller.

In this paper, results of some of these investigations are presented.

2.

U-Slot Patches on Microwave Substrate

We have obtained simulation results using

Ansoft

ENSEMBLE 6 0 to design U-slot patch

antennas at various center frequencies and for several microwave substrates. n example, for

900 MHz center frequency, is shown in Table 1. The details of the patch and U-slot dimensions

and the feed positions are not shown for brevity. It is seen that, taking the area of the

E

= (air or

foam) as the reference area of the patch, the patch area is reduced to

41

when E

2.33

is used

and to 8.7 when E 9.8 is used. The impedance bandwidth changes from

42

when

E

1 to

26.5

when

E

2.33,

to

22.1

when

E

4.0

and

to

14.4

when

E

=9.8.

The VSWR versus

frequency curve for the case of E 4.0 is shown in Figure 3 as an example.

5

8/11/2019 00900136

2/4

Table 1 Wideband U-Slot Patches for 900 MHz Center Frequency

E Patch Dimensions Thickness Normalized Probe BW

Area Diameter

cm) (cm>

O 21.97x12.45 2.69(0.08h0)

1

3.0

mm

42%

2.33

12.40x8.96

2.76(0.08h0) 0.41

3.4 mm 26.5%

9.8 5.74x4.14 2.01(0.06h0)

0.087

0.08

mm

14.4%

4.0 9.29x6.71 2.40(0.07h0) 0.23 1.7 22.1%

h free space wavelength at center frequency

When a shorting wall is placed in the location where the electric field is approximately zero,

the resonant length is shortened by half, leading to about four times reduction in patch area. It is

found that the bandwidth

of

such small-size quarter wave patches are still substantial. Detailed

results will be presented in the meeting. At the time of writing, the use of shorting pins to reduce

U-slot patch sizes are in progress.

3. Two-Layer L-Probe Patches

It is difficult to implement the L-probe design if a single layer microwave substrate is used

because the horizontal rmof the L-probe would have to lie inside the solid substrate. To reduce

this difficulty, a two-layer configuration is conceived, consisting of one layer of microwave

substrate and another layer of foam

or

air. The horizontal

rm

of the L-probe can then lie in the

air or foam layer. This is shown in Figure

4.

Table 2shows the simulation results obtained for

four values

of

E

when the rectangular patch has dimensions a=3.0 cm and b 2.5 cm and the

patch and L-probe dimensions are fixed (not shown). It is found that the center frequency is

4.75 GHz when

E

=l . It decreases to 3.65 GHz when E 2.32 and to

2.80

GHz when

E

4.2

The bandwidths for the three cases are 36%,

40

and 37% respectively.

Table

2

Two-layer L-probe wideband patch antennas

1 o

-

6.6 (O.lh,)

4.75

1

o

36%

2.32

3.1 6.7 9.8(0. 12h,) 3.65 0.77 40%

4.2

5.3 6.7 12.0(0.1 h,)

2.80

0.59 37%

~ ~~

h free space wavelength at the center frequency f

6

8/11/2019 00900136

3/4

4. Concluding Remarks

This paper presents some recent work on reducing the patch size of U-slot and L-probe

wideband patch antennas. Encouraging simulation results using ENSEMBLE 6.0 have been

obtained. More extensive simulation results and some measured results will be presented in the

meeting.

5 References

[11 T.

Huynh and

K. F.

Lee, Single-layer single-patch wideband microstrip antenna,

[2] K.

M. Luk,

C.

L. Mak, Y. L. Chow and

K .

F. Lee, Broadband microstrip patch antenna,

Electronics Letters, Vol.

32

9, p.

418-420, 1996.

Electronics Letters, Vol.

34 15), pp 1442-1443, 1998.

6.

Acknowledgement

The authors would like to acknowledge he support of Honeywell International, Inc.

t I--L

of p r o b e

TOPView

atch

Side View

L-probe

Ground

Plane

coaxia l

feed

Figure Geometry of the wideband coaxially-

Figure 2 Geometry of the wideband

L-probe fed patch antenna

ed U-slot patch antenna

7

8/11/2019 00900136

4/4

I t?

Frequency

GHz)

Figure 3 VSWR versus frequency for a U-slot patch antenna

on

~ = 4 . 0ubstrate

SIDE

VIEW

PatchDimensions a

s b

r

t

r

L probe t 2

ir or

Foam

Ground Plane

Coaxial line

Figure 4 Geometry of the two-layer L-probe patch antenna

8