Microstrip Antenna Designs for Sensor and Communications Applications

David Pozar

Electrical and Computer Engineering

University of Massachusetts at Amherst

Amherst MA 01003

email: pozar@ecs.umass.edu

slides: http://www.ecs.umass.edu/ece/pozar/AntResRev2005.ppt

Outline

Near field focused microstrip arrayKu band fan beam microstrip arrayImproved bandwidth microstrip reflectarray

One of the main goals of the Center for Advanced Sensor and Communications Antennas at the University of Massachusetts is to

identify and develop antenna technologies with improved performance and/or reduced cost for future applications.

Near Field Focused Microstrip Array

• Application to low-cost radiometric temperature sensor• Food industry, chemical processing, materials manufacturing• Radiometric technique works through smoke, dust, or steam• Developed by ProSensing Inc (Amherst), and K. Stephan (Texas State U)• 12.5 GHz, focus to a spot size of 2.6” at 12” from aperture• Two array versions were designed, fabricated, and tested• Near field testing done at Hanscom AFB• Resulting antenna is substantially smaller and cheaper than original horn

Original dielectric loaded horn antenna

Radiometric Temperature Sensor Antennas – Before and After

Near field focused microstrip arrays

Calculated Near Field Contours of Microstrip Array

-36

-24-30

-36-36

-36

-36

-36

-30

-30-30

-24

-24

-30

-30

-36

-36

-24

-24

-24

-18 -18

-18

-18

-18

-36

-36

-12

-12

-12

-12

-30

-30

-30

-30

-30 -30

-30

-30

-6

-6-6

-24

-24

-24

-24

-24

-30

-30

-24

-24

-24

-30

-30

-30

-30

-30

-36

-36

-36

-30

-30

-12

-36

-36

-36

-36

-36

-18-30

-36

-36

-24

-24

-30

-36

-36-30

-30

-24

X axis (inches)

-5 -4 -3 -2 -1 0 1 2 3 4 5

Y a

xis

(inch

es)

-5

-4

-3

-2

-1

0

1

2

3

4

5

Near Field Measurement of Microstrip Array at Hanscom AFB

Measured Near Field 3D Pattern of Microstrip Array

Measured Near Field E-plane Patterns of Microstrip Arrays

f = 12.45 GHz. Red curve for array using non-symmetric feed network, green curve for array with reversed patches in E-plane. Note: main beam peaks are

off center due to mechanical misalignment of test fixture.

Ku Band Fan Beam Microstrip Array

• Application to short range ocean surface topography mapping• Two arrays used for differential phase shift measurement of backscatter• 45” long aperture at 16.15 GHz, 2 degree beamwidth• 20 dB sidelobe level• Short pulse duration requires time delay feeding across aperture• Loss and space considerations require subarraying (2x4 and 2x6)• Design completed, subarrays tested, final array being fabricated

Ku Band Array

176 patch elements, 2x4 and 2x6 subarrays

Improved Bandwidth Microstrip Reflectarray

• Microstrip reflectarray uses a flat aperture of microstrip patches with individual phase shifts to form a coherent beam

• Reflectarrays typically use variable-length patches, patches with tuning stubs, or CP patches with rotations to achieve required reflection phases

• Bandwidth (gain) is generally limited to 2-4% with these methods• A new technique using aperture coupled patches with stub tuners provides

much better bandwidth properties,

see “Microstrip Reflectarrays: Myths and Realities”, JINA 2004, at http://www.ecs.umass.edu/ece/pozar/jina.ppt for more discussion of

microstrip reflectarrays

Microstrip Reflectarray

This reflectarray uses variable length microstrip patches to provide a shaped beam pattern.

Aperture Coupled Stub Tuned Microstrip Reflectarray

ground plane with apertures

microstrip patches

variable length tuning stubs

unit cellcross section

Patches and apertures are identical for all elements; stubs vary in length to control reflection phase.

Reflection Phase vs. Patch / Stub Length

Stub Length (cm)

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Ref

lect

ion

Pha

se (d

egre

es)

-360

-270

-180

-90

0

90

180

270

360

f = 5.0 GHzf = 5.2 GHzf = 5.4 GHz

Patch Length (cm)

1.2 1.4 1.6 1.8 2.0 2.2 2.4

Ref

lect

ion

Pha

se (d

egre

es)

0

50

100

150

200

250

300

350

400

f = 5.0 GHzf = 5.2 GHzf = 5.4 GHz

variable-length microstrip patches

stub-tuned aperture coupled patches

Comparison of Gain Bandwidth

Frequency (GHz)

1.8 1.9 2.0 2.1 2.2

Gai

n (d

B)

20

22

24

26

28

30

Variable Size PatchesAperture Coupled Patches w/ Stubs

1 dB gain bandwidth is improved from 3.5% to 9%