Designing a Patch Antenna for Doppler antenna. They vary in shape, size, and construction •The...

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Transcript of Designing a Patch Antenna for Doppler antenna. They vary in shape, size, and construction •The...

  • DESIGNING A

    PATCH ANTENNA

    FOR DOPPLER SYSTEMS

  • 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

  • Antenna Miniaturization

    • Consumer Electronics

    • Light weight, low volume,

    thin profile

    • Low fabrication cost

    • Microwave ICs

  • Microstrip Antennas

    • Radiating Patch

    • Dielectric Insulator (εr ≤ 10)

    • Ground Plane

    • Size conducive to

    GHz frequencies

    • We require a simple,

    low range antenna

  • 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

  • Types of Microstrip Antennas

    microstrip dipoles microstrip patch antennas

    slot antennas Not antennae!

  • 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.

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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

  • Polarization

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

    0∠𝛼𝑥 and 𝐸𝑦 0∠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)

  • 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

  • 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

  • Circular Polarization

    • Two types of circular polarization:

    LHCP and RHCP

    LHCP: ( 𝛼𝑥 − 𝛼𝑦 = + 𝜋

    2 ) RHCP: ( 𝛼𝑥 − 𝛼𝑦 = −

    𝜋

    2 )

  • Feed Point

    Inset

    Probe

    Quarter-Wave

    Aperture

    Coupled

  • 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

  • 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

  • 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.

  • 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

  • Testing

  • Testing

    • Network Analyzer • Spectral distribution

    • Reflection coefficient

    measurement (Γ)

    • SWR ≤ 2

    • Smith chart

    • Input impedance

    ||1

    ||1

    

     SWR

    CL

    CL

    ZZ

    ZZ

     

  • Testing

    • Vector Voltmeter

    • Measures magnitude of

    voltages and their

    corresponding phase

    • Allows us to quickly

    determine gain using

    vector magnitudes

  • Anechoic Chambers

  • QUESTIONS?