Practical%20Radio%20design

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Practical Radio design

• Practical Antennas
• PCB-layout for optimum performance
• UART-extentions Pairing Radiocrafts modules with
  other equipment

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Practical Antennas
Quarterwave copper on FR-4 laminate
Quarterwave whip coated with plastic
Helical
Yagi Increased directivity
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Practical Antennas

• The most easy way to reduce range is by thinking
  about antenna as any piece of wire
• EM-waves are travelling along the antenna
  conductor and we want to radiate as much as
  possible of the power (when we transmit) or
  receive as much as possible (when we receive)
• To achieve this, the wire should be as long as
  possible while maintaining resonance to the
  centre frequency.
• Radiation is prevented by Nearby grounding,
  metal obstacles (like metal enclosures).
• Shorted antennas always reduces range but
  sometimes is required due to available space

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Practical Antennas
? c / f x 0.95
Feeding point
It is important that the antenna has correct
length which is a multiple of a quarter wave.
When so, the impedance will be purely resistive
in the feeding point, and we will get max power
transfer from a resistive source (usually 50 ohm)
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Antenna classes

• Monopole Usually ?/4 or 5/8?. Electric field
  dominates
• Dipole Usually ?/2 (can also be 5/8?). El. field
  dominates
• Loop (magnetic field dominates). Not covered.
• Helical (combination of electric and magnetic)
• Antennas containing elements of the above
• 5/8 ? Can be either monopole or dipole (Note
  serial inductor is needed for impedance match).
• Yagi Extra Directive antennas (lobe in one
  direction). Has one Dipole antenna element and
  directors reflectors

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Monopole vs. dipole
Monopole quarterwave Dipole
halfwave
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Radiation patterns
Gain0 dBi 5.15 dBi5/8? 8.2 dBi 2.15
dBi5/8? 5.2 dBi 5-10 dBi(or more)
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Practical Antenna guidelines

• Use quarter-wave stubs with sufficient ground
  plane extensionSufficient ground Preferably the
  longest length the same as the antenna length
• Can be considered as a wire, either in the shape
  of a whip antenna or a PCB-trace.
• Length should be L(c/f) / 4 x 0.95, i.e2.9 cm
  (2.4 GHz), 8.2cm (910MHz), 7.8cm (868MHz) or
  16.4cm (434MHz).
• Coated whip antennas www.procom-dk.com,
  www.badland.co.uk, www.elcard.fi

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Radiocrafts Range measurement setup
Antenna quarterwave, from RC1240DK, approximately
17cm
Cu-side FR4 board size 24x24 cm or at least
15x15cm, antenna placed in center
Coax-cable with conducting SMA-connector fastened
tightly to adaptor and connecting to Cu-plane
SMA-SMA adaptor in drilled hole in PCB
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Shortened antennas

• If not available space, shorter antennas can be
  used but an inductor (or more complex matching)
  must be added at the base to achieve better
  impedance match. Radiates less! Measure
  impedance!
• Dielectric antennas Ceramic material where ?
  gets shorter. Maintains resonance (see datasheet
  for req. match) but radiates less. Available for
  all frequencies 433-2400 MHz (www.fractus.com,
  www.johansontechnology.com, www.yageo.com )
• PCB-antennas Can be made more area-efficient by
  folding the antenna, which also is good for
  receiving different polarizations. Width 3mm
  is OK (the broader the width, the lower the
  resistive loss)

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PCB antenna example, 2 layer PCB, ?/4-monopole
Note There is NO gnd in layer 2 under
antenna-trace!!
Free space inside, both layers. Total length of
antenna 16.4 cm
Do NOT route antenna close to ground or metallic
parts
Large groundplane
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Helical antenna at 433/868 MHz

• Radiates in the direction normal to the axis
• Can be seen as monopole antenna shorted by
  coiling up the whip
• Resonance can be achieved for a much shorter
  construction
• Higher gain than with a non-helical structure of
  the same size
• www.stecom.com

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Helical antenna at 433/868 MHz
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PIFA-Planar Inverted F-antenna (2.4 GHz)
Feeding point, 50ohm line
Ground, GND
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Practical Antennas cont.

• Usually, FR-4 laminate is used Thickness and
  material does not affect length (as the antenna
  is a wire, not a transmission line)
• If orientation varies (equipment is used both
  vertical and horizontal), make a 90 degrees bend
  at the middle
• If there is any length from RF pin of module, use
  50ohm trace in PCB until antenna launches
  (connector or solder joint).

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Routing guidelines
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RF Basics

• The higher the frequency, the higher the loss in
  the air, the lower the range
• The higher the data rate, the lower the range
  (bandwidth is highwider internal filterreceiver
  receives more natural electromagnetic noise,
  masking a weak signal)
• The higher the frequency, the more straight line
  the EM signal is following
• Reflections All EM-signals are reflected, giving
  local field minimums or maximums. As frequency
  increases, these min/max occur more frequently

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UART extentions
www.wiznet.co.kr
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UART extentions II
www.oxsemi.com
www.ftdichip.com
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UART extentions III
www.informasic.com