Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and...

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DESIGNING A PATCH ANTENNA FOR DOPPLER SYSTEMS

Transcript of Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and...

Page 1: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

DESIGNING A

PATCH ANTENNA

FOR DOPPLER SYSTEMS

Page 2: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Doppler Requirements for Antennas

• Range

• Determines power consumption

• Defines frequency band

• Narrow Bandwidth

• Tolerance range for reflected signals

is relatively low for Doppler systems

𝑅𝑚𝑎𝑥 = 𝑃𝑡𝐺𝜎𝐴𝑒

4π2𝑆𝑚𝑖𝑛

4

𝑓𝑐 ≫ ∆𝑓 𝐷𝑜𝑝𝑝𝑙𝑒𝑟

Page 3: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Antenna Miniaturization

• Consumer Electronics

• Light weight, low volume,

thin profile

• Low fabrication cost

• Microwave ICs

Page 4: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Microstrip Antennas

• Radiating Patch

• Dielectric Insulator (εr ≤ 10)

• Ground Plane

• Size conducive to

GHz frequencies

• We require a simple,

low range antenna

Page 5: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Types of Microstrip Antennas

• There are many types of microstrip

antenna. They vary in shape, size, and

construction

• The four main categories of microstrip

antenna are microstrip patch antennas,

microstrip dipoles, slot antennas, and

microstrip travelling-wave antennas

• We will discuss the most commonly used

type: the rectangular microstrip patch

antenna

Page 6: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Types of Microstrip Antennas

microstrip dipoles microstrip patch antennas

slot antennas Not antennae!

Page 7: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Rectangular Patch Antenna

• Like a normal patch antenna but rectangular!

• Most common microstrip form factor due to streamlined design and manufacturing.

• Easy to control various factors such as input impedance, center frequency and bandwidth.

• Often used in phased arrays to produce small beam width, high directive gain antennas.

Page 8: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Design Parameters

• Construction

• Conductive strip for transmission

• Dielectric substrate

• Conductive ground plane

• Shape

• Effects the antenna gain efficiency

• Size

• Varies based on desired frequency

• Substrate type

• Permittivity and thickness of substrate affect impedance and

efficiency

Page 9: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Substrate

• A dielectric material

• Typically PCB or alumina are used

• PCB for cost reasons, alumina for dielectric constant

control

• Parameters in selection of substrate

• Thickness

• Dielectric constant

• The thickness and dielectric constant affect the

characteristic impedance and the radiation efficiency of

the antenna

Page 10: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Antenna Dimensions

• Shape of patch antennas have an important effect on many attributes of the antenna, including: o Resonant Frequency

o Radiation Pattern

o Input Resistance

o Bandwidth

• Length: o determines resonant frequency

• Width: o has a minor effect on resonant frequency and radiation pattern

o affects input resistance and bandwidth

𝑓𝑐 =𝑐

2𝐿 ε𝑟

Page 11: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Radiation Pattern

• Radiation pattern refers to the direction dependence of radiation from the antenna

• Important in determining radiation characteristics such as beam width and gain

Page 12: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Radiation Pattern

• There are many design choices which change how a radiation pattern appears. For a patch antenna, the main effectors are:

• The length of the patch

• The shape of the patch

• The ground plane cutting off radiation behind the antenna

• This picture shows a typical radiation pattern for a square patch antenna

Page 13: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Radiation Characteristics

Radiated Power: Total power emanating from the antenna. Measurement of radio frequency energy in watts.

Directive Gain: Measures the directional properties of the antenna versus an omni-directional antenna

Directivity: The maximum directive gain

Beamwidth: The angle between the half-power (-3 dB) points. It’s the direction dependence of the antenna

As Beamwidth increases, directive gain decreases

Page 14: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Polarization

• defined as the phase correlation between the orthogonal components of a traveling electromagnetic wave, with plane phasors 𝐸𝑥

0∠𝛼𝑥 and 𝐸𝑦0∠𝛼𝑦

• three types of polarization:

linear, cylindrical, elliptical

• determines the amount of power received by an antenna • Matched Polarization

→ Max Power

(Plane Wave Solution for Electric Field)

Page 15: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Linear Polarization

• Linearly polarized waves and antennas have in-phase orthogonal electric field components ( 𝛼𝑥 − 𝛼𝑦 = 0 𝑜𝑟 ± 𝜋 )

• Common design

• Single feed point

• Less design

overhead

• Very effective for

fixed polarization systems

• Example:

• TV transmissions are horizontally polarized

• AM/FM transmissions are vertically polarized

Page 16: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Circular Polarization

• Circularly polarized waves and antennas

have out-of-phase orthogonal electric field

components ( 𝛼𝑥 − 𝛼𝑦 = ± 𝜋

2 )

• Can handle polarization diversity

• 2+ feedpoints

• High complexity

• Can be used to

receive any linearly

polarized signal

Page 17: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Circular Polarization

• Two types of circular polarization:

LHCP and RHCP

LHCP: ( 𝛼𝑥 − 𝛼𝑦 = + 𝜋

2 ) RHCP: ( 𝛼𝑥 − 𝛼𝑦 = −

𝜋

2 )

Page 18: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Feed Point

Inset

Probe

Quarter-Wave

Aperture

Coupled

Page 19: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Dielectric Cover

Advantages: • Protection from

environmental conditions

• Superstrates can increase the gain of an antenna

• Often used for handset receivers

Disadvantages: • Radiation efficiency is

decreased

• Effects must be taken into account in the overall design

Page 20: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Dielectric Cover

Other Effects:

• Increase in dielectric constant causes

• Decreases in

• Resonance frequency

• Impedance of patch

• Characteristic impedance of feed lines

• Increase in antenna gain

Page 21: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Microfabrication

• Design is put into a CAD program to develop a mask for fabrication

• Polymer pellets are melted and compressed to form a substrate layer

• Metal (usually Cu) is evenly coated onto the substrate

• Photoresist is then coated onto the surface and exposed to UV light after mask image is applied to surface

• PCB is then dipped in a acidic solution to etch out the wanted pattern for the metal layer

• Lastly, the substrate is rinsed and baked to anneal the conduction metal.

Page 22: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Fabrication

No-chemical milling process (used at MSU)

• FR4 laminate with width of .06” and 1oz. of copper on both sides

• Design put into CAD software

• CAD files are used to define the layout and the unwanted copper is physically milled out by a prototyping machine

Page 23: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Testing

Page 24: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Testing

• Network Analyzer • Spectral distribution

• Reflection coefficient

measurement (Γ)

• SWR ≤ 2

• Smith chart

• Input impedance

||1

||1

SWR

CL

CL

ZZ

ZZ

Page 25: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Testing

• Vector Voltmeter

• Measures magnitude of

voltages and their

corresponding phase

• Allows us to quickly

determine gain using

vector magnitudes

Page 26: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

Anechoic Chambers

Page 27: Designing a Patch Antenna for Doppler Systems · antenna. They vary in shape, size, and construction •The four main categories of microstrip antenna are microstrip patch antennas,

QUESTIONS?