project1 presentation

8/8/2019 Project1 Presentation

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ISM Band Transmitter/Receiver Bob SosackBob Sosack

Chris LettowChris Lettow

Justin QuekJustin Quek

TA: Julio UrbinaTA: Julio Urbina

July 27, 2001July 27, 2001


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Introduction Project created for Aerial Robotics ClubProject created for Aerial Robotics Club

Develop main communication link betweenDevelop main communication link between

airplane and ground base stationairplane and ground base station

Design system to work in ISM Band (902Design system to work in ISM Band (902--928928MHz)MHz)

RF system consists of microcontrollerRF system consists of microcontroller--drivendriventransceiver chip, a power amplifier, and transmittransceiver chip, a power amplifier, and transmitand receive antennasand receive antennas


3/30

Project Features and Goals Transmit and receive ISM Band signalsTransmit and receive ISM Band signals

High power transmission with low powerHigh power transmission with low power

consumptionconsumption

Obtain at least 11.6 dB gain in the powerObtain at least 11.6 dB gain in the power

amplifieramplifier

Antennas have 2:1 VSWR Bandwidth inAntennas have 2:1 VSWR Bandwidth inentire ISM Band (902entire ISM Band (902--928 MHz)928 MHz)


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General Design Schematic


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Signal Generation and Modulation

The Transceiver Chip Texas Instruments TRF6900A transceiver chipTexas Instruments TRF6900A transceiver chip

Modulator on chip takes digital binary signalModulator on chip takes digital binary signal

generated from microcontrollergenerated from microcontroller

Digital word input into Direct Digital SynthesizerDigital word input into Direct Digital Synthesizer(DDS) which outputs an analog sine wave(DDS) which outputs an analog sine wave


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Transmitter/Receiver Block Diagram


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MSP430 Microcontroller


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Programming the Microcontroller Started with sample code from TI:Started with sample code from TI:

Transmit at 869 MHz and receive at 859 MHzTransmit at 869 MHz and receive at 859 MHz

Provides checksums, RS232 communicationProvides checksums, RS232 communication

Adapted for our own use:Adapted for our own use:

Transmit or receive at 915 MHzTransmit or receive at 915 MHz

Sets the TRF6900 mode appropriatelySets the TRF6900 mode appropriately


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Power Amplifier Maxim power amplifier chip usedMaxim power amplifier chip used

Goal: obtain 11.6 dB Gain (typical value obtainedGoal: obtain 11.6 dB Gain (typical value obtainedfrom data sheets)from data sheets)

Transceiver outputs 4.5 dBm signal (2.8 mW).Transceiver outputs 4.5 dBm signal (2.8 mW).

Goal is to obtain about 40.47 mW output powerGoal is to obtain about 40.47 mW output power

11.6 = 10log(Pout/Pin)


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Power Amplifier Chip

with Biasing and RF Matching Network


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Power Amplifier Impedance

Matching Goal: Match 50Goal: Match 50 output impedance of transceiveroutput impedance of transceiver

board and 50board and 50 antenna feed impedance to internalantenna feed impedance to internal

source and load impedances of amplifier chipsource and load impedances of amplifier chip Zs = (5.025+j2.173)Zs = (5.025+j2.173) at 915 MHzat 915 MHz

Zl = (5.939 + j1.629)Zl = (5.939 + j1.629) at 915 MHzat 915 MHz

Impedance Match especially critical on input sideImpedance Match especially critical on input sidebecause of very low power inputbecause of very low power input Must haveMust haveVERY little reflection lossVERY little reflection loss


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AmplifierInput Impedance Matching Network


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840 860 880 900 920 940 960

freq, MHz

-45

-40

-35

-30

-25

-20

-15

-10

dB(S(2,2

))

Reflection Loss for input impedance matching network

840 860 880 900 920 940 960

freq, MHz

-60

-50

-40

-30

-20

-10

dB(S(2,2

))

Ideal values C2= 7.3 pF,

C1 = 5.37 pF

Actual used values C2=7 pF

C1 = 5 pF


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840 860 880 900 920 940 960

freq, MHz

-20

-18

-16

-14

-12

dB(S(2,2

))

Reflection Loss for output impedance matching

network. C1 = 1000 pF, C2 = 8.2 pF


15/30


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Solution #1: Surface Mount

Capacitors

Smaller size, reduced parasitic inductanceSmaller size, reduced parasitic inductance

from lumped element capacitor wiresfrom lumped element capacitor wires

Capacitor values changed slightly due toCapacitor values changed slightly due to

part availability, but still acceptablepart availability, but still acceptable

impedances matches obtainedimpedances matches obtained


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840 860 880 900 920 940 960

freq, MHz

-20

-18

-16

-14

-12

dB(S(2,2

))

Reflection Loss of impedance matching networks

using surface mount capacitors

840 860 880 900 920 940 960

freq, MHz

-35

-30

-25

-20

-15

-10

dB(

S(2,2

))

Output matching network

C1 = 1200 pF, C2 = 8.2 pF

Input matching network

C2 = 6.8 pF, C1 = 5 pF


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Solution #2: SMA Connectors Much more reliable for RF applicationsMuch more reliable for RF applications

than BNC: conductor directly fromthan BNC: conductor directly from

connector housing to copper feedlineconnector housing to copper feedline

Test results after these improvementsTest results after these improvements

showed very little change, gain still onlyshowed very little change, gain still onlyaround 1dBaround 1dB


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Solution #3: Change Capacitor

Values Trial and error process: Capacitor values on inputTrial and error process: Capacitor values on input

and output matching network loweredand output matching network lowered

Testing showed gain of 12.2 dB at 915 MHzTesting showed gain of 12.2 dB at 915 MHz

Amplifier Conclusions:Amplifier Conclusions:

Gain surpassed design goalGain surpassed design goal

RF parasitic effects most likely causedRF parasitic effects most likely causedtheoretical values to be ineffectivetheoretical values to be ineffective


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Microstrip Patch Antennas Used for two reasons:Used for two reasons:

Flat surface makes them ideal forFlat surface makes them ideal for

mounting on airplanemounting on airplane

Impedance matching fairly simpleImpedance matching fairly simple

"009.32

!!

r

oPL

I

P

Calculating Patch Length:


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Impedance Matching Inset

Feeds Patch edge has impedancePatch edge has impedance 150150 ..

Matching to 50Matching to 50 would require a long, thinwould require a long, thin

/4 feedline/4 feedline Alternative: Inset feedAlternative: Inset feed Obtain 50Obtain 50

impedance at patch edgeimpedance at patch edge

No need for impedance transformerNo need for impedance transformerThicker feed line should limit inductanceThicker feed line should limit inductance

)(cos50150 4

L

xo

T

!


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Antenna Testing

Problems/Solutions Problem #1: First design did not resonate atProblem #1: First design did not resonate at

correct frequency (correct frequency ( 950 MHz)950 MHz)

Increase patch sizeIncrease patch size increaseincrease /2/2

decrease resonant frequencydecrease resonant frequency


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Antenna Testing

Problems/Solutions Problem #2: Patch edge impedance not lowProblem #2: Patch edge impedance not low

enoughenough 69.2769.27

Increase insetIncrease inset Impedance drop more gradualImpedance drop more gradualas it tends to 50as it tends to 50

Problem #3: High Reactive Capacitance degradesProblem #3: High Reactive Capacitance degrades

impedance match, Bandwidthimpedance match, Bandwidth Replace BNC connectors with SMAReplace BNC connectors with SMA

ConnectorsConnectors


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-80.00

-60.00

-40.00

-20.00

0.00

20.00

40.00

60.00

80.00

8.5000

E+08

8.5638

E+08

8.6275

E+08

8.6913E+08

8.7550

E+08

8.8188

E+08

8.8825

E+08

8.9463E+08

9.0100

E+08

9.0738

E+08

9.1375

E+08

9.2013E+08

9.2650

E+08

9.3288

E+08

9.3925

E+08

9.4563E+08

9.5200

E+08

9.5838

E+08

9.6475

E+08

9.7113E+08

9.7750

E+08

9.8388

E+08

9.9025

E+08

9.9663E+08

Re(Z)

Im(Z)

Antenna Design #2 Resonant at 918 MHz with

Z = (69.27-j32.06)


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SW

R

00.5 1

1.5 2

2.5 3

3.5 4

4.5

8.9969E+08

9.0081E+08

9.0194E+08

9.0306E+08

9.0419E+08

9.0531E+08

9.0644E+08

9.0756E+08

9.0869E+08

9.0981E+08

9.1094E+08

9.1206E+08

9.1319E+08

9.1431E+08

9.1544E+08

9.1656E+08

9.1769E+08

9.1881E+08

9.1994E+08

9.2106E+08

9.2219E+08

9.2331E+08

Frequency

SWR

AntennaDesign#22:1V

SWRBandwidth(13


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Antenna Testing

Problems/Solutions Problem #4: New design showed high reactiveProblem #4: New design showed high reactive

inductanceinductance

Decrease inset gap spacing to add capacitanceDecrease inset gap spacing to add capacitance negligible effectnegligible effect

Antenna ConclusionsAntenna Conclusions::

Resonates at the correct frequencyResonates at the correct frequency

Achieved 50Achieved 50 at patch edgeat patch edge Over half desired bandwidth obtainedOver half desired bandwidth obtained

More bandwidth could be achieved byMore bandwidth could be achieved byneutralizing the inductive effectsneutralizing the inductive effects


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-20.00

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

8.50

00E+0

8

8.56

38E+0

8

8.6275

E+0

8

8.69

13E+0

8

8.75

50E+0

8

8.81

88E+0

8

8.8825

E+0

8

8.94

63E+0

8

9.01

00E+0

8

9.07

38E+0

8

9.1375

E+0

8

9.20

13E+0

8

9.26

50E+0

8

9.32

88E+0

8

9.3925

E+0

8

9.45

63E+0

8

9.52

00E+0

8

9.58

38E+0

8

9.6475

E+0

8

9.71

13E+0

8

9.77

50E+0

8

9.83

88E+0

8

9.9025

E+0

8

9.96

63E+0

8

Re(Z)

Im(Z)

Final Antenna Design Resonant at 916 MHz with

Z = (49.77+j13.80)


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SWR

00.5 1

1.5 2

2.5 3

3.5 4

4.5

9.0250E+08

9.0400E+08

9.0550E+08

9.0700E+08

9.0850E+08

9.1000E+08

9.1150E+08

9.1300E+08

9.1450E+08

9.1600E+08

9.1750E+08

9.1900E+08

9.2050E+08

9.2200E+08

9.2350E+08

9.2500E+08

9.2650E+08

9.2800E+08

9.2950E+08

9.3100E+08

9.3250E+08

Frequenc

y

SWR

FinalAntennaDesignVSWRBandwidth(15.7


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Final Conclusions and

Recommendations Antennas: Use higher quality substrate,Antennas: Use higher quality substrate,

higher dielectric to decrease size, find wayhigher dielectric to decrease size, find way

to increase antenna gainto increase antenna gain

Amplifier: Determine exact cause ofAmplifier: Determine exact cause of

mismatch from theoretical values, cascademismatch from theoretical values, cascadetogether to increase overall gaintogether to increase overall gain


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Final Conclusions and

Recommendations Transceiver:Transceiver:

Determine the cause of frequency driftDetermine the cause of frequency drift

(PLL)(PLL)

Update board layout for better sizeUpdate board layout for better size

matchingmatching

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