A Power Amplifier Design for 440MHz

Robert MoffattMIT Haystack Observatory

REU 2008

Mentors:Jim Marchese and Frank Lind

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Project Description & Goals:• Replace driver klystron amplifier with solid-state

amplifier.• Advantages of solid-state amplifier:

• Wider Bandwidth (~10MHz vs. 50kHz)• Smaller size• Lower cost• Greater stability

• Specifications:• 440MHz• 1000W peak• 10% duty cycle• 50dB gain

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Amplifier Block Diagram:

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Impedance Matching:

Scattering Parameters:

S11 = Reflection from 1 to 1S21 = Transmission from 1 to 2S12 = Transmission from 2 to 1S22 = Reflection from 2 to 2

1 2

Impedance Matching:

S1 matches the transistor to input impedance.S2 matches the transistor to output impedance.

Impedance Matching Example:

Input matching network

The input matching network cancels the reflection at 440MHz.

Impedance Matching Example:

Matching network layout in Genesys.

Impedance Matching Example:

Matching network PCB.

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Input Board:

Input Board:

Phase Shifter

Input

To Board 2

Intermediate Board:

Intermediate Board:

From Board 1

To Board 3

Output Board:

Output Board:From

Board 2

Output

Output

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Mechanical Design:

Typical package for a high-power UHF MOSFET.

Mechanical Design:

Power MOSFET mounting technique.

Mechanical Design:Prototype Design:Aluminum project enclosure.

Provides RF shielding, and isolation between Gate & Drain.

Heatsink attached to aluminum plate under transistor(s).

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Construction and Testing:… In progress …

Outline:• Project Description & Goals• Block Diagram• Impedance Matching• PCB Design• Mechanical Design• Construction & Testing• Acknowledgements

Acknowledgements:Jim Marchese

Frank LindWill Rogers

Steve Holmberg

also:AgilentAltium