Centre for Electromagnetic and Antenna Engineering, Department of Electronic Engineering No 1

Achieving high gain and large bandwidth using hybrid DR antennas

to feed short horns

Nasimuddin1 and Karu Esselle2

1Institute for Infocomm Research, Singapore2Centre for Electromagnetic and Antenna Engineering

Department of Electronic Engineering, Macquarie University Sydney, NSW 2109, Australia

Email: nasimuddin@i2r.a-star.edu.sg, karu@ieee.org

Centre for Electromagnetic and Antenna Engineering, Department of Electronic Engineering No 2

Outline

Introduction Gain-Enhancement using Surface Mounted Short Horns (SMSH) DRAs with SMSHs, designed for high gain Hybrid dilectric resonator on patch (DRoP) antennas with SMSHs, designed for high gain over wide bandwidth Conclusion

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Introduction

• DRA has the advantages of low cost, compactness, high efficiency and a low profile.

• Traditional microstrip antennas and dielectric resonator antennas have gains around 6 dBi to 8 dBi.

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To enhance the gain of DRAs, several methods have been employed:

offset dual-disk dielectric resonators (DR)

stacking parasitic DR with an air gap between radiating and parasitic DRs

Use of composite layered high permittivity DR

dielectric resonator loaded waveguide antenna with parasitic dielectric directors.

In most cases the gain enhancement is limited or the structure is complex. We propose to integrate DRAs and hybrid antennas with surface mount short horns to enhance gain significantly.

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Typical Structure of DRA integrated to a surface mounted short horn (SMSH)

Feed substrate

DRAMaterial

Material

H

Microstrip feed line Ground plane

D

Role of DRA:

Radiating Element

Feed to SMSH

  The SMSH is excited by the DRA.

Total Radiation is a combination of the radiation from DRA and the aperture of the SMSH.

Supporting Material of SMSH also effect the radiation properties.

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Design of SMSH for Maximum Gain

A SMSH, with an aperture coupled DRA, has been designed to give maximum gain at 6.0 GHz.

The distance (D) in the bottom of the SMSH from edge is less than or equal to o/4.

Select the shortest height of SMSH to achieve high gain, for a given taper angle of SMSH.

For this height, we investigate the gain variation with the taper angle of SMSH, to achieve highest gain.

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Gain vs frequency for various SMSH heights

4.5

5.5

6.5

7.5

8.5

9.5

10.5

5.8 5.85 5.9 5.95 6 6.05 6.1 6.15 6.2

Frequency (GHz)

Gain

(dB

i)

H = 0 H = 2 H = 3 H = 4H = 5 H = 6 H = 7 H = 8

H = 9 H = 10 H = 11 H = 12

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Gain variation with horn height around 6 GHz

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

0 2 4 6 8 10 12Horn Height (mm)

Gai

n (d

Bi)

f = 5.95 GHz

f = 6.0 GHz

f = 6.05 GHz

Maximum Gain for around 8.50 mm horn height

4

5

6

7

8

9

10

11

0 0.05 0.1 0.15 0.2

Horn height/wavelenght

Gai

n (d

Bi)

• The gain increases with increasing height up to 0.15 o and then starts to decrease.

• Smallest possible horn height with optimum gain is 0.15o at 6 GHz.

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Gain vs frequency for different taper angles of SMSH

1.5

2.5

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

5.8 5.9 6 6.1 6.2

Frequency (GHz)

Gain

(dB

i)

th = 0 th = 5 th = 10 th = 15

th = 20 th = 25 th = 30 th = 35

th = 40 th = 45 th = 50 th = 55

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Fabricated DRA with SMSH

SMSH aperture is 48.1 mm 43.1 mm, ground plane is 60 mm 60 mm.

The rectangular DRA is located symmetrically over a rectangular aperture-coupled slot in the ground, which excited by a 50- microstrip line feed.

The rectangular DRA dimensions are: length = 12.8 mm; width = 7.3 mm; height = 6.35 mm; dielectric constant = 9.8; and loss tangent = 0.002.

Aperture coupled feeding structure dimensions are: aperture length = 6.4 mm; aperture width = 1.24 mm; stub length (s) = 1.8 mm; microstrip width = 1.16 mm; substrate dielectric constant = 3.38; loss tangent = 0.0022 and thickness = 0.508 mm.

Other horn dimensions are: area at lower (substrate) level = 27 mm 32 mm; taper angle = 45o: and height (H) = 8.1 mm (0.15o).

The total height of structure is only 0.172 o i.e. 8.61 mm at 6.0 GHz.

SMSH fabricated using solid Copper block

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Return loss of DRA with SMSH

-16

-14

-12

-10

-8

-6

-4

-2

0

5.5 5.7 5.9 6.1 6.3 6.5

Frequency (GHz)

Ret

urn

loss

(dB

)

Expt.

CST

Measured return loss (RL) at 5.95 GHz is -13.5 dB and -10 dB RL bandwidth is 3.2 %.

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Gain Enhancement

0

1

2

3

4

5

6

7

8

9

10

5.8 5.9 6 6.1 6.2Frequency (GHz)

Gai

n (d

Bi)

TheoreticalMeasured DRA Measured

Gain at 5.95 GHz:

Theoretical gain : 8.8 dBiMeasured gain : 8.5 dBiMeasured gain of DRA

alone is 3.7 dBi

For SMSH fabricated from copper block

Gain enhancement due to SMSH is 4.8 dB

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E-Plane Radiation Pattern at 5.95 GHz

-25

-20

-15

-10

-5

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (degree)

Nor

mal

ized

Am

plit

ude

(dB

)

CST

Expt

-70

-60

-50

-40

-30

-20

-10

0

-180 -80 20 120observation angle (deg)

norm

alis

ed a

mpl

itud

e (d

B)

copol

crosspol

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H-Plane radiation pattern at 5.95 GHz

-25

-20

-15

-10

-5

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (degree)

norm

aliz

ed A

mpl

itude

(dB

)

CST

Expt.

-60

-50

-40

-30

-20

-10

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (deg)

norm

alis

ed a

mpl

itude

(dB

)

Copol

Crosspol

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E-Plane radiation pattern at 6 GHz

-25

-20

-15

-10

-5

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (deg)

norm

alis

ed a

mpl

itud

e (d

B)

.

CSTMeasured

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (deg)

norm

alis

ed a

mpl

itud

e (d

B)

Co_pol

Cross_pol

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H-Plane radiation pattern at 6 GHz

-25

-20

-15

-10

-5

0

-180 -140 -100 -60 -20 20 60 100 140 180observation angle (deg)

norm

alis

ed a

mpl

itude

(dB

)

.

CST

Measured

-60

-50

-40

-30

-20

-10

0

-180 -140 -100 -60 -20 20 60 100 140 180

observation angle (deg)

norm

alis

ed a

mpl

itude

(dB

) .

co-polarised

cross-polarised

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Another Prototype with DRA To verify the effect of

supporting material we fabricated another SMSH with foam as supporting material. It gives a further gain enhancement of around 1.5 dB.

-2

0

2

4

6

8

10

12

5.8 5.9 6 6.1 6.2Frequency (GHz)

Gai

n (d

Bi)

Metal

AirEr = 2.2

Er = 4.0Expt. (Metal)

Expt. (Air)

Gain of aperture coupled DRA with different horns (metal support and foam support)

Gain at 5.95 GHz:

MeasuredMetal gain is 8.50 dBi

Air gain is 9.84 dBi

TheoreticalMetal gain is 8.80 dBi

Air gain is 9.4 dBi

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Feed substrate

DRA

Material

Material

Horn

Microstrip feedline Ground plane

Patch Substrate

Upper slot

Patch Resonator

H

•Rectangular Dielectric Resonator on Patch with SMSH

Feed Microstrip Line :W = 1.16 mm, stub length = 2.6 mmh = 0.508 mm, r = 3.38, tan = 0.0022

Lower coupling aperture: 8.4 mm 0.9 mmUpper coupling aperture: 6.8 mm 0.7 mm Patch substrate: 12 mm 16 mmh = 0.762 mm, r = 2.45, tan = 0.001

Patch : 9.05 mm 8.1 mm DRA : 7.02 mm 12.0 mmh = 6.35 mm, r = 9.8, tan = 0.002

To increase the bandwidth, we replaced the DRA with a hybridDielectric Resonator on patch (DRoP) antenna

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Fabricated DRoP with SMSH

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Theoretical and Experimental results of the rectangular DRoP

antenna with SMSH

-35

-30

-25

-20

-15

-10

-5

0

6 6.5 7 7.5 8

Frequency (GHz)

Ret

urn

loss

(dB)

Measured CST

Measured Impedance bandwidth is 24.4%

2

3

4

5

6

7

8

9

10

11

6 6.5 7 7.5 8

Frequency (GHz)G

ain

(dB

i)

CST

Measured

Theoretical and measured Gain

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E & H-plane radiation patterns of the DRoP antenna with SMSH at 6.5

GHz

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

-135 -105 -75 -45 -15 15 45 75 105 135

observation angle (degree)

norm

aliz

ed a

mpl

itud

e (d

B)

Co-pol

Cross-pol

CST

-60

-50

-40

-30

-20

-10

0

-135 -105 -75 -45 -15 15 45 75 105 135

observation angle (degree)

norm

aliz

ed a

mpl

itud

e (d

B)

Co-pol

Cross-pol

CST

E-Plane H-Plane

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•A Cross-Shaped Dielectric Resonator on Patch with SMSH

Centre for Electromagnetic and Antenna Engineering, Department of Electronic Engineering No 23

0

1

2

3

4

5

6

7

8

5.5 6 6.5 7 7.5 8Frequency (GHz)

VSW

R

Rectangular DR on Patch

Cross DR on Patch

The measured 2:1VSWR impedance bandwidth of the rectangular DR on patch is 6.04 to 8.0 GHz (27.9%) and cross DR on patch is 23% (6.06GHz to 7.64GHz).

Comparison of rectangular and Cross-DR on patch: VSWR

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3

4

5

6

7

8

9

10

11

6 6.5 7 7.5 8

Frequency (GHz)

Gai

n (d

Bi)

Rectangular DR on Patch

Cross DR on Patch

Comparison of rectangular and Cross-DR on patch:Gain

The measured gain of both antennas is more than 9dBi within the 2:1 VSWR impedance bandwidth.

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CONCLUSIONS A theoretical and experimental study has been conducted on achieving high gain with wideband performance. Various DRAs and hybrid (DRoP) antennas coupled to SMSHs have been considered.

The measured results in general show good agreement with results obtained using CST Microwave Studio.

We demonstrated a 4.9 dB gain improvement at 5.95GHz with a SMSH fabricated from a copper block. The total height of the structure is only 8.6 mm, i.e. 0.172 o.

The SMSH supporting material affects both the gain and radiation patterns.

The DRoP antennas integrated to SMSHs have high gain, wide bandwidth and low profile. We achieved 28% 2:1 VSWR bandwidth, and gain over 9 dBi within this bandwidth, using a rectangular DRoP and SMSH.