UHF Amplifier Project Tasks
Test of Existing Amplifier
In order to become familiar with RF testing and equipment, set up Test equipment as shown in Figure One and test the existing AMISR prototype power amplifier.
UHF Amplifier
A UHF power amplifier will be implemented that takes a nominal +10 dBm peak input power and delivers a +60 dBm peak output signal. The amplifier will operate at any one of three frequencies (440.0, 440.2 and 440.4 MHz ) with a maximum 10% duty cycle and standard 50 ohm input and output
UHF Amplifier Specifications
Power Output +60.0 -0.0/+0.2 dBm Peak
Frequency of Operation 440.0, 440.2 and 440.4 MHz
Maximum Duty Cycle 10%
Maximum Pulse Width 2 milliseconds
RF Pulse Rise/Fall Times Typ 200 nS/ 500 nS maximum
Input/Output Impedance 50 ohms
Operating Temperature -10° to 65° C
Maximum Amplitude overshoot 10 %
Maximum Amplitude droop 10 %
Phase stability over pulse duration less than ± 5 %
Harmonics less than -40 dBc at 1 Kw Peak output
Input Signal Return loss less than -17.7 dBm (VSWR of 1.30 max)
Overdrive Sensing of Greater than +13.5 dBm
Temperature over sensing
Greater than Max Pulse Width Sensing
Design
Electrical
• Design an overall architecture for the power amplifier. Selection should be based on which amplifier class of operation is optimal. Whether using a single ended, push-pull or balanced amplifier design is appropriate. Will a single or multiple channel design best meet the specifications.
• Select the type of and specific model number of the transistor to be used. Availability and cost need to be considered.
• Using Eagleware design software create an amplifier model in sections. Sections will include the amplifier stages , impedance transformations, matching circuits, DC biasing and RF combining or dividing. Some components within these sections may best be implemented with RF transmission line techniques.
• Simulate the performance of individual sections and in combination to evaluate the overall gain, output power, input VSWR, harmonics, and phase characteristics of the amplifier.
• Vary components and techniques within individual sections and in combination to evaluate the effect on overall performance with the goal of optimizing the design
Thermal
• When considering the overall architecture and individual sections in the above electrical design thermal considerations must be taken into account.
• Determine the thermal characteristics of the transistor selected.
• Using the thermal characteristics of the transistor selected and the operating characteristics of the amplifier determine the heat dissipation of the amplifier. Be sure the transistor does not exceed maximum operating temperature. Design in the appropriate temperature sensor for measuring temperature(s) where needed.
• With the amount of heat dissipation known check various heat sinks and cooling methods to dissipate the heat. This unit needs to operate in an environment of -10° to 65° C. Comsol software may be utilized to simulate thermal designs.
Mechanical
• The layout of the unit will be such that it will mount into a standard 19 inch rack.
Fabrication
• Finalize electrical and thermal design, check lead times, and order parts.
• Implement the basic amplifier PCB layout using Altium PCB design software. Get the design to pass all rule checking and DFM steps.
• Design review of PCB layout and final amplifier design
• Send PCB for fabrication, organize parts for assembly.
• Hand assemble one unit while others are built externally. Learn soldering techniques.
Integration and Test
• Test assembled PCB with heat sink and evaluate its performance such as output power,input VSWR, operation vs frequencies and operation with various pulse widths and duty cycles.
• Evaluate the ability of the unit to operate over temperature.
Design Notes
• Primary electrical design will focus on meeting the general requirements of the RF output power at the required frequencies and pulse widths within the duty cycles given.
• Included in this primary design focus is proper thermal operation. For the Integration and Test phase the proper operation of the PCB boards with a heat sink is acceptable.
• Secondary requirements such as sensing overdrive input power, extra wide pulse inputs, high output VSWR's and responding to over temperatures will be performed by external control electronics. The external control electronics is not considered a task in this project. Only over temperature sensors must be included in the initial design and be made available externally for control purposes.
• If time allows integrating the final design into a complete mechanical design is to be performed.