Design and Building of

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• Design and Building of
• 20 MGHz 2.5 Ghz SP4T RF Switches
• Soumo Ghosal
• BTech Final Year
• Institute of Radiophysics and Electronics
• University of Calcutta
• Under the Guidance of -
• Mr. A Praveen Kumar
• Engineer F
• GMRT, Khodad

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RF/ Microwave Switches

• Switching is one of the most important function
  in control of microwave signals
• Microwave switch is a microwave circuit made up
  of high speed microwave devices.
• PIN diodes , GaAsFET MMIC are used extensively.
• The GMRT Receiver System also puts to use
  microwave switches at various stages such as
• (1) Band Selection
• (2) Swicthing Filter Banks
• (3) Attenuator Selection
• (4) Injection of various levels of noise for
  calibrating the
• receiver system

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Switch Design Configurations

• Series
• Series SPST

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• (2) Shunt

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• (3)Series Shunt

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Switching Parameters

• Insertion Loss

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• Isolation

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• VSWR

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• Switching Speed
• Trise
• Tfall
• Ton
• Toff

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• Switching Transients
• The transients are due to the DC shifts which
  occur internally in the switch during switching.
• RF Handling
• PIN diode switches are usually considered to
  be small signal devices and generally handle RF
  power levels upto 20dbm (100mW) with optimum
  performance below 5dBm.

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GaAsFET used as a RF Switch

• nanosecond order switching.
• minimal power consumption.
• minimal area occupied on the circuit.

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• Based on Metal Semiconductor Field Effect
  Transistors (MESFET) as the active elements.
• MESFETS are arranged in two mirror-image
  series-shunt configurations originating from a
  common RF node.
• The series MESFET provides a through path for the
  ON arm while the shunt MESFET provides an
  isolation for the OFF arm.

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MMIC Performance

• With less than 1dB insertion loss and about 30dB
  isolation at 1.5GHz the SW239 demonstrates
  impressive RF performance in a small package.
• High switching speeds of Trise/fall 2ns typical
  
• Input power for 1dB compression is 25dBm for
  standard 0/-5V DC control. Second and Third order
  Intermodulation Intercept points are 66 dBm and
  41 dBm typical, respectively.

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• PIN Configurations

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Controlling SW 239 using LM339 Comparator
Current WILL flow through the open collector when
the voltage at the PLUS input is lower than the
voltage at the MINUS input.
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The SP4T Design Layout
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Truth Table for Operation
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RF Microstrip Line Calculation for PCB
imlementation

• For lowest cost, microstrip devices may be built
  on an ordinary FR4 (standard PCB) substrate.

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Measurements made using Network Analyser

• BSATR SP6T switch is operated over the frequency
  range 10 MHz-1 GHz and its VSWR,return loss and
  gain studied.
• The calibration
• has to be done.

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• The S11 and S21 are obtained and the VSWR, return
  loss and gain are obtained.
• We did it by choosing frequency paths 233MHz and
  610MHz were chosen.

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• Return loss plot (233MHz)
• VSWR (233MHz)
• Gain (in dB)

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Conclusion and Future Scope for improvement

• SP4T PCB layout and logic circuitry successfully
  made on genesys software.
• Due to shortage of time the final PCB could not
  be made for the footprints in the design were too
  fine to be made at GMRT PCB Machine.
• Vector Network Analyser put to test BSATR module.

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• Thank You