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A Multi Unsymmetrical Beam Tapered Slot Ya-gi Antenna with λ/4 for PMMW Imaging

Presenter: Ya Chung Yu

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Out Line Introduction Specification Antenna design Multi unsymmetrical beam antenna design Summary

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Introduction

Passive millimeter wave imaging (76~110GHz)Effective detection

Reveals any material: metal, liquids and gels, contraband, sheet and bulk explosives

Several millimeter resolutionEfficient, easy to carry and image

Small size and portable Single scan without changing position (multiple views with one scan) Primary and/or secondary screening

Respects Privacy Imaging system shows 3-D black and white silhouette, which is not

stored Options for privacy blurring, remote viewing and gender specific viewing Automatic detection option to support or replace analyst review of image

Harmless NOT X-ray technology Only receive heat radiation

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Key components of PMMW imaging system- High efficiency lens antenna- low noise amplifier (LNA)- Low bias power detector

Critical performance- Temperature resolution

- Where

k: Boltzmann constant

T: Absolute temperature

T0: Ambient temperature

F: Noise Figure

B: RF bandwidth

: Integration time

- Spatial resolution depends on Lens size and feed antenna design

B

FTB

FTTM1

21

2 02

0

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SpecificationITRI Passive Imaging System Specifications

Detection distance 1~3 m

Spatial resolution 2 cm x 2 cm

Lens Diameter 20 cm

Focal plane distance 14 cmSide-lobe Level -10 dB

Feed Antenna 3 dB Beam-width 70°

Feed Antenna array spacing 3.74 mm

Field of View 22 cm x 22 cm

Pixel (receiver array) 11 x 11 channels

Temperature resolution 0.5 K

System Bandwidth 20 GHz (75-95 GHz, W-band)

System Noise Figure below 10 dB

System Gain 30 dB

Integration Time 20 ms

Power Detector Responsivity 9.3 V/mW

ADC bit number 10 bits

ADC Sampling Frequency 100 MHz

Imaging Video Frame Rate Up to 30 fps

Integration Time 20 ms

Digital Signal Processing Time 10 ms

Detection distance: 1~3 mSpatial resolution: 2 cm @ 1 m detection distanceTemperature resolution: 0.5 KField of View: 22 cm × 22 cm (pixel: 11 × 11)

Detection distance: 1~3 mSpatial resolution: 2 cm @ 1 m detection distanceTemperature resolution: 0.5 KField of View: 22 cm × 22 cm (pixel: 11 × 11)

x

Y

x

Y

f(x,y) g(x,y)

數位信號處理函式示意圖

h(x,y)

70度15cm 100cm

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Antenna design Antipodal tapered slot antenna

- PCB layout (duroid 5880), low cost, low losstangent

- endfire radiation pattern, a pixel corresponds to an antenna Bandwidth 20GHz (78~98GHz)

- satisfy the requirement of the temperature resolution

3 dB beamwidth 70 degree

- satisfy the lens specifications (focal length of 15cm & lens diameter of 20cm)

Challenge problem:

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Multi unsymmetrical beam antenna design

Original symmetrical tapered slot ya-gi antenna form

Return Loss (dB

)C

o-pole pattern (dB)

Symmetrical pattern

3dB beamwidth 70°

90°

• antipodal tapered slot

• ya-gi directors

• λ/4 fan rejections

• at focal point of lens

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Unsymmetrical beam form (perturbation method) • λ/4 fan rejections (broadband structure)

• control traveling current phase (perturb current directions)

• reduced coupling interference

• at off axis focal plane

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Left unsymmetrical tapered slot ya-gi antenna

• current phase of right arm is slower than left one

• Left part of pattern is smoother than right part

• Main beam shift 10° to right

• 3dB beamwidth is also 70°

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Right unsymmetrical tapered slot ya-gi antenna

• current phase of left arm is slower than right one

• right part of pattern is smoother than left part

• Main beam shift 10° to left

• 3dB beamwidth is also 70°

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Comparison

Sym

Left

Right

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Feed antenna arrayLens

W-band Antenna

DC bias

DC output

W-band chip (LNA & PD)

λ/4 fan rejections

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Summary

Multi beam unsymmetrical tapered slot ya-gi antenna is useful for near field focusing lens, especially in the condition of the wider imaging range

It is easy to change radiation pattern with quarter-wavelength fan rejection structure without rotating physical angle

Reduce the area of layout and loss

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Thanks for Listening