Table of Content

PROJECT TITLE: The LionSat Nanosatellite Transmitter Design Team

SUBMITTED TO: Dr. Timothy Wheeler

ADDRESS: Electrical Engineering Department

0319 ELEC ENGR EAST
UNIVERSITY PARK, PA 16802

CONTACT: CHARLES L CROSKEY

TELEPHONE NUMBER: 1 814-865-2357

FAX: 1 814-863-8457

EMAIL: CCroskey@psu.edu

SUBMITTED BY: Nhan Fong

Eli Modlin

Rhianna Rodgers

TEAM CONTACT: ELI MODLIN

ADDRESS: 0124 Mckee Hall

University Park, Pa. 16802

TELEPHONE NUMBER: 1 814-862-2163

EMAIL: emm191@psu.edu

DATE: April 15, 2003

EXECUTIVE SUMMARY:

The Local Ionosphere Measurement Satellite (LionSat) is a nanosatellite that will obtain ambient measurements of the plasma environment in the ionosphere. In order for these measurements to be of any use, their must be a two-way communication network between the satellite and the ground station. In order for the LionSat satellite to communicate properly with the ground station, the transmitted signal must have enough power to make it to the ground station from its position in earth’s ionosphere.

The goal of the LionSat Transmitter Team is to design and fabricate a power amplifier that will be able to add power to the transmitting signal that will eventually be radiated out of the transmitting antennas. This will be accomplished through the efforts and electrical engineering skills of the members of the Transmitter Team and their contributors.

The final modifications and deliverables will be completed by May 5, 2003 within the allotted budget of $600. The deliverables at projects end will include:

Professional schematic for all components of the final power amplifier design
A power amplifier that will receive a half watt of power and output approximately one watt of power
A link margin analysis of the communication of the system of the satellite
A project report detailing the project’s life cycle
A project web page summarizing the project
A project poster to be displayed at the showcase in May

TABLE OF CONTENTS:

Page

Introduction 4

Problem Statement 4

Objectives 4

Project Development 5

Technical Approach 6

Simulation/Optimization 10

Design 13

Fabrication 14

Value of Project 14

Deliverables 15

Work Schedule/Gantt Chart 16

Conclusion 17

References 18

Appendix 19

INTRODUCTION:

Our project is part of the telemetry system of a satellite. A typical telemetry system for a satellite consists of a ground station, receiving antenna, receiver, demodulation system, decoder, multiplexer, transmitter, output stage amplifier and a transmitting antenna. The area of importance for our telemetry system that we are designing is the output stage amplifier that amplifies the transmitted signal coming out of the transmitter.

The purpose of this amplifier is to provide enough power to the transmitted signal so the transmitting antenna can radiate the signal so the base station can receive. In order to do this, it is necessary for these power amplifiers to be designed to work at the frequency of the transmitted signal. Furthermore, they may also need a pre-amp buffer between the transmitter and itself in order to prevent accidental damage. Also important is the fact that they must be biased with a voltage that can be supplied by the satellite. If the amplifier or any other part of the communication system fails the entire satellite will be useless.

We know that there are several losses and margins for error in any telemetry system. In light of this fact, a link margin analysis must be done for the LionSat telemetry system.

PROBLEM STATEMENT:

The LionSat nanosatalitte needs an output stage power amplifier that operates at 2.365 GHz and can be biased by less than 12 Volts, to boost a ½W input into a 3W output, at order to power the output antenna.

PROJECT OBJECTIVES:

Complete research in the following areas:

Power Amplifier chips and transistor that operate in the L-band frequency range
Voltage regulator that can be used to bias the Power Amplifier chips
Proper sequence of powering the Antennas
Link margin analysis

Design a model of the power amplifier with the following specifications:

Operates at 2.365 GHz
Output 3W of power for an input of ½W
Can be powered by an 12V power supply or less

Construct a prototype of the power amplifier with these specifications:

It must be lightweight
It must fit into the allotted space, which is yet to be determined

Its output must be able to drive the input of the antenna at 3 W radiated power.

Prepare the following for the project showcase:

A final report for the project
An informative poster to complement the project at the show case

PROJECT DEVELOPMENT:

The following organizational pattern will govern our design process:

Planning

Consider the product and assess technologies
Identify production constraints, such as size, weight, and available DC power
Allocate project resources, such as funding and equipment
Establish team member qualifications and task

Concept Development

Identify primary use
Estimate production cost and feasibility

Detailed Design

Identify suppliers of key components
Identify specific tooling needed for fabrication of the model
Define a final Power Amplifier design
Generate and record a schematic for the Power Amplifier

Refinement

Seek approval of design from Dr. Croskey
Seek approval of design from Dr. Bilen

Production and Testing

Make final detailed Auto CAD drawings of the circuit board
Fabricate the prototype model
Test the prototype for reliability life and performance

Presentation Accessories

Construct project web page
Create project poster

Project Finalization

Final project report
Design showcase

TECHNICAL APPROACH:

In order to increase data rate of transmission on the Local Ionosphere Measurements Satellite (LionSat) project, we will be designing a power amplifier to amplify the out put of the transmitter. The power amplifier transistor that we have chosen to use is NEC’s NE6510179A. This amplifier is suppose to be capable of will have approximately a ½ Watt of power (from the transmitter) into it and will output 3 Watts to the antenna. This amplification should increase the data rate by a factor of six. All simulations of the power amplifier will be done in Microwave Office a software program that simulates RF circuits. In order to fabricate the power amplifier, we plan to design the board layout in AutoCAD and then use the fabrication facilities in EE East to etch out our board on copper. After fabrication, we will test our prototype amplifier.

In conjunction with the power amplifier design we will also be producing a link margin analysis of the satellite’s communication system. These values will be obtained from specific parameters and specifications that LionSat needs to comply with. The data that is unavailable to us at this time will be estimated until a more accurate value can be obtained later. This analysis will periodically need to be updated over the next two years as LionSat is developed.

In light of our combined experience and education, we expect to develop a working power amplifier by the end of the semester. Other deliverables include a detailed report of the project, schematics and descriptions of the various parts of the structure, a detailed web page describing the project, and a poster to be displayed at the project showcase.

Diagram (1) shows how the circuit will be implemented. The transmitter and the voltage regulator will receive 12 Volts from the LionSat power supply. The voltage regulator will then output 5 Volts into the charge pump as well as the switching/delay circuit. Negative 3 Volts will be coming out of the charge pump into the power amplifier. As the negative bias is reached the delay switch will then output positive 5 Volts into the power amplifier. At this time the charge pump will be adjusted down to -0.5 Volts by the use of a potentiometer. This will enable the power amplifier to function correctly, which in turn will output the desired 3 Watts of power. The following sections will detail each block:

TRANSMITTER

The transmitter we will be using is the T-155, FM Telementary Transmitter. It will be coming from Sandia Labs (See Picture 1). Arrival date is still unknown.

The transmitter has the following parameters:

Operating Frequency = 2.365 GHZ

Pout = 0.5 Watts

50 ohms output impedance

Operating voltage = 12 volts

AC coupling

Modulation Type: True FM

Unlimited Altitude

Picture (1)

T-155 transmitter.

VOLTAGE REGULATOR

There will be 12 Volts coming out of the transmitter and the power amplifier that we have chosen (NE6510179A) will be operating at 5 Volts. Because of this we need a voltage regulator, and have chosen the LP2954AIT from National Semiconductor. The high current along with the maximum allowable power dissipation forced us to choose the TO-220 3-Lead package rather than the SO-8 package with the built in shutdown. Also the tight line and load regulation as well as very low output temperature coefficient make the LP2954 well suited for a low power voltage regulator.

The LP2954 is a 5 Volt micro power voltage regulator. It has a very low quiescent current (typically 90 µamps at a 1mA load) and dropout voltage (typically 60 mV at light loads and 470mV at 250 mA load current). The 250mA output current is guaranteed. It is recommended that it be used as a high-efficiency linear regulator and that is exactly what we will be using it for.

CHARGE PUMP

The Charge-Pump will serve as a negative voltage generator for the biasing network of the power amplifier. It will provide the -0.5 Volts need by the gate to bias the transistor. The charge-Pump MAX840 offers an adjustable negative output voltage down to -9.4 V. The input voltage range for the device is 2.5V to 10V. The circuit can operate with small capacitors, as low as 0.22uF. The voltage ripple reduces to 1mVp-p.

DELAY/SWITCH

While the negative bias voltage comes up the +VDD of the power transistor will need to be delayed for an interval of time. The power MOSFET switch we will use is the IRLD014 from International Rectifier in series with the N-channel MOSFET switch driver MAX1614 from Maxim. These feature internal on/off latch, able to drive single or back to back MOSFETs, 5-26 Volt input range, has a controlled turn-on for low inrush current, and is capable of fast switching.

POWER AMPLIFIER TRANSISTOR

Amplification is one of the most basic and prevalent microwave circuit functions. A power amplifier is an active RF component used to increase the power of an RF signal. Amplifiers use three-terminal solid-state devices field effect transistors (FETs), silicon, silicon bipolar transistors, heterojunction bipolar transistor (HBTs) and high electron mobility transistors. NEC’s NE6510179A is a GaAs HJ-FET designed for medium power mobile communications. It is a good choice for the design, because of its capability of delivering an output of 3 watts at 5 volt with high linear gain, high efficiency and good linearity. Since our emphasis will be on circuit design using transistors, we will treat transistors primarily in terms of their terminal characteristic- either S parameter or equivalent circuit. Even though we will use S parameter method for our design work, it is good to consider the small-signal equivalent circuit model for this device.

SIMULATION/OPTIMIZATION:

We simulated our power amplifier in Microwave Office, which is a software package for simulating RF circuitry. With this software were able to tune our circuit and find the values that would give us an optimum power output. Below in Figure (4) is the circuit schematic from Microwave Office. In graphs (1a, 1b), we simulated the S-Parameters in order to maximize the power out of the transistor. The power is essentially maximized when S₁₁ is at its minimum and S₂₁ is at its maximum.

Text Box: Figure (4)
Microwave Office Simulation
Amplifier Circuit

Graphs (1a, 1b)

S-Parameter data from Microwave Office Simulation

(a) Phase of the S-Parameters (b) Magnitude of the S-Parameters

At the operating frequency of 2.365 GHz, our power amp has the following S-parameter values:

S-Parameters	Magnitude (dB or scalar)	Angle (Deg)
S₁₁	-4.875 dB or 0.3255	-41.38
S₁₂	-21.7 dB or 0.00676	40.7
S₂₁	10.6 dB or 11.48	-169.5
S₂₂	-17.45 dB or 0.01799	-166

Table (2)

Δ = S₁₁S₂₂– S₁₂S₂₁= 0.0434 + j0.0631

K = (1+׀Δ ׀²+ ׀S₁₁ ׀²+ ׀S₂₂ ׀²)/(2 ׀S₂₁ S₁₂׀) = 7.165

Since the magnitude of Δ < 1 and K > 1 our transistor is unconditionally stable at our operating frequency.

DESIGN:

We obtained this design form the simulation and tuning in Microwave Office. These capacitor values and microstrip line specs are the ones that found through simulation and tuning would maximize our gain in realizable way. The following is a schematic of our circuit which follows the test board layout recommended by California Eastern Laboratories (CEL). However, our design is tailored to work for our frequency of 2.365

GHz.

LN8

LN7

LN6

LN3

LN5

LN4

LN2

LN1

Figure (3)

Power Amplifier Test Board Layout Schematic

C5,C1	39 pF
C6,C7	2 pF
C4	4.4 pF
C14	1 pF
C12,C13	4.7 uF
C10,C11	0.1 uF
C8,C9	1000 pF
C2,C3	82 pF
L1,W1	248, 50 mils
L2,W2	0, 0 mils
L3,W3	60.5, 100 mils
L4,W4	973, 10 mils
L5,W5	875, 10 mils
L6,W6	30, 80 mils
L7,W7	97, 50 mils
L8,W8	185, 50 mils

Table (1)

Values from Simulation in Microwave Office

FABRICATION:

In order to fabricate, the power amplifier we are going to use a FR-4 fiber glass epoxy board that has the specs seen in Table (3). We chose this board because it close to the board used in the test board layout in the data sheet from CEL and that it allows our design to be small - about one square inch in size. This is due to the high dielectric constant of the board which is 4.1. The higher the dielectric constant of the substrate the smaller the circuit board can be made.

Figure (4)

AutoCAD layout of the power amplifier

We will fabricate our amplifier on a FR-4 fiber glass epoxy board.

FR-4 fiber glass epoxy board
Dielectric Constant	4.1
Copper	Double sided 1 ounce on each side
Dielectric thickness	31.25 mils
Copper thickness	1.35 mils

Table (3)

VALUE OF THE POWER AMPLIFIER

The value of this project has different meanings for the different aspects of the project. As far as LionSat is concerned its mission has been developed to address several research areas of interest to its sponsors (Air Force, NASA, and the Space Vehicles Directorate). The objective is to take measurements of the undisturbed local ionospheric plasma and compare it with the ram/wake structure it leaves behind. It will also be testing thrusting methods which maintain stability.

Because it is an extremely low power nanosatellite, the value of our individual project carries a different meaning. By amplifying the power coming out of the transmitter by a factor of six, we will be able to increase the data rate. Although the antenna system hasn’t been designed yet, there is talk of having two antennas with only one of them being turned on at a time. When the bit rate is increased the amount of time for the transfer of information will be lowered, enabling the satellite to be off longer which will in turn conserve power over all. Our solution is practical, achievable, and desirable: we are maximizing our power output and gain. Although we don’t know if LionSat will incorporate our amplifier in its final design, we are sure that what we have laid the foundation for future students to follow.

This project has also been a valuable experience to us. Having a small part in a big project shows how everything needs to come together. Although we won’t be here to see the end result it has been an experience to be part of something that will continue to grow and change over the course of the next two years. Even though it has been frustrating for us at times we feel that LionSat has been a very real experience on how projects are initiated and carried out in industry.

LionSat also has the value of education. Part of the mission is to provide a breadth of learning experiences to the undergraduate and graduate level students. The sponsors would like to encourage productive careers in technical and nontechnical fields relating to space systems. While building upon teamwork skills, LionSat wants to bring together students of diverse backgrounds and interests and introduce meaningful, realistic project examples.

DELIVERABLES:

The following is a list of deliverables that our team expects to complete by the end of the semester:

Professional schematics and descriptions for all components of the final power amplifier design
A power amplifier that will receive a half watt of power and output approximately three watts of power
A link margin analysis of the communication system of the satellite
A project report detailing the project’s life cycle
A project web page summarizing the project
A project poster to be displayed at the showcase in May

WORK SCHEDULE/GNANT CHART:

Project Management:

The following table shows the distribution of responsibility of specific areas. Because of the limited number of people in our group, most tasks will require all of us.