Milestone 2

Project Plan

Roles and Responsibilities:

Hardware Developer: Ajay Thakkar 

Software Developer: Juan Jimenez

Embedded Engineer: Tomas Esson

Project Manager: Ajay Thakkar, Juan Jimenez, Tomas Esson

Hardware:

Using ORCad, we will create a schematic and layout for a transceiver PCB which takes of the transmitting (signal synthesis, amplification, propagation) and receiving (filtering, heterodyning). This is possible by the use of RF integrated circuits meant for dealing with high frequency signals. We will then print our board and solder the integrated circuits onto the PCB for a standalone transceiver board.

Embedded System:

In order to use the RF integrated circuits and process the data that the PCB receives, we plan on using either a microcontroller, FPGA, or Raspberry Pi to control the PCB. This will include programming in either VHDL or C and interfacing with peripherals such as a DAC, ADC, and GPIO breakout boards.

Networking:

We will use IoT frameworks such as Batman ADV, MongooseMQTT, or Modbus/TCP to allow our embedded system to communicate upstream to a user machine and amongst the other nodes in the network. This will require an interface written in C++ to handle our data and package it in the format necessary for the IoT framework, as well as setting up the IoT framework on the different nodes and user machine.

Task Breakdown

Concepts

The team has identified two alternative radar designs which fit our needs and requirements as defined in milestone 1. The first radar design which we are considering is a chirp radar design also known as frequency-modulated continuous wave (FMCW) radar. In FMCW radar frequency modulation is used to improve the performance over a traditional radar design. The second design which we are considering is a phased array radar design. The key component of the phased array design are various antennas whose signals are variated with different phases to create a beam and electronically steer that beam. Both of these concepts have distinct advantages that make them viable alternatives to our objective of sensing missiles. 


FMCW Radar:

As explained in the previous section frequency modulation provides several advantages that make it attractive for the purposes of this project:

Sample FMCW Radar design

Phased Array Radar:

Phased array radars use an array of antennas to steer the resulting radar beam electronically, without having to physically move the antennas. Traditional radars, including FMCW radars rely on mechanically rotated antennas to scan the surrounding space but phased array radar achieves beam steering by controlling the phase of the signals sent to each antenna element in the array. The key advantages of the phased array radar design are outlined below:

Phased Array Radar design showing electronic steering and the beamforming capabilities of phased array systems.

Controls for Radar

Besides the overall radar design there is also the question of what will control the radar in the case of the phase array as well as what will process the information that is received from the radar. The team has developed two controls concepts that we consider plausible for the controls aspect of our project:

Concept 1

Concept 2

Concept 1:

The main feature of concept 1 is that a microcontroller serves as the controls chip for our radar design. In this design the microcontroller is in charge of supplying the control voltage for the various chips on our radar PCB as well as the tuning voltage necessary to create an analog signal on the VCO and PLL components of the radar PCB. The microcontroller would also need to process the information gathered from the radar array, applying an FFT and determining the main frequency components of the signal. It would also need to keep track of timing in order to calculate things like velocity as well as deciding how to digitally steer the beam in the case of the phased array. Velocity and angle information would then be transferred to some networking interfaces which would then communicate with the various other radar nodes on the network and then eventually display the information on a main computer such as a Raspberry Pi. 


Concept 2:

The Raspberry Pi has the capability of doing everything that the microcontroller can with the added benefit of having a fully functional operating system on the controls interface. This allows us to both the real time processing, the controls, and the networking all on one device. The downsides of this concept is that the raspberry pi has a much higher cost when compared to a microcontroller and it adds additional power requirements that the microcontroller does not have.  

Concept selection

FMCW vs. Phased Array

The team decided to go with the phased array radar design for the main concept behind or radar project. Although FMCW meets several of our frequency and sensing requirements and would ultimately be easier to build, the group believes that phased arrays with their beamforming capabilities and electronic scanning hold the best potential for an effective missile tracking system. The ability to electronically scan their field of view makes it so that our distributed nodes will have greater range and will not require expensive mechanical components to rotate our radar in the field. This will in turn reduce the power requirement of each of our nodes as we will remove the need of having to use electrical energy to physically rotate our entire radar. Both phased array radar and FMCW radar are similar in their design and electrical components, the major difference is that instead of modulating a frequency signal we will be changing the phase of the signal that goes to each of the transmitting antennas which requires the additional electrical component of a phase shifter as seen on the right.

Controller Concept Selection

The two controller schemes as shown in the previous controller section each have their pros and cons but for the purposes of our project we intend to utilize both concepts. Mass production of Raspberry Pi's for the final version of our product is neither feasible nor desired as it would incur heavy costs and the Raspberry Pi's have much higher capabilities and overhead than is needed for the purposes of this project. However, Raspberry Pi's are an excellent prototyping and testing platform that will allow our group to quickly setup and test various nodes without having to go through the trouble of designing a PCB which has all the connections for the pins of the microcontroller as well as the connections necessary to provide a networking interfaces to allow the nodes to transfer information between each other. For these reasons we will adopt concept 2 as our control scheme for our electrical  components and our radar design. 

Sample phased array design featuring phase shifters and antennas.

Concept 2

Design

High Level System Diagram of Singular Node

Low Level System Diagram of Singular Node

Process Flowchart

Analysis

Hardware Specifications:

Transmitter:

VCO- The Voltage Controlled Oscillator is a chip which can synthesize high frequency signals via a tuning voltage, which the user can create to dictate the frequency of the signal it outputs. For our project, we want to transmit in a band between 1-2 GHz, and for this reason we chose the CVCO55BE-1530-2700 which has a band of 1530-2700 MHz. The tuning voltage ranges from .5V-10V, and it needs a supply voltage of 4.75 volts. At the moment, it has a price of $25.96 on Digikey.

Phase Shifter IC- In order to beamform, the different antennas on the node must be transmitting at different phases to constructively and destructively interfere in certain places. To change the phase of our VCO output, we need a phase shifter rated for high frequencies. For this reason, we chose the PE44820B-X which has a band of 1700-2200 MHz. It has an 8 bit resolution for shifting phase and takes in 8 bit words through an SPI interface that we will control using the microcontroller. At the moment it has a price of $13.09 on Digikey.

RF Power Amplifier- Now that our different signals have been phase shifted, they must be amplified before being fed out of the antenna to increase the distance the signal can go without dissipating. Since this is a radar application, we care more about a higher gain from our power amplifier rather than distortion of the signal. For this reason, we chose the GRF5112.

SMA Connectors and Antennas- Finally, RF signals usually need an SMA connector and antenna for propagation. For this reason, we chose the RF2-04A-T-00-50-G as the connector and ANT-5GWWS6-SMA as the antenna since they cover a wide band including our target frequency range. Together, they cost $6.90 on Digikey.

Receiver:

RF Low Noise Amplifier- The low noise amplifier will be used to amplify the signals which the antennas pick up, and it is imperative to retain signal integrity here since the return signal might be very weak. This is why we chose the HMC618ALP3E. At the moment, it has a price of $8.86 on Arrow.

RF Mixer- A technique called heterodyning is a way to mix a high frequency signal with a slightly different high frequency signal to create what it is called an intermediate frequency which is much lower and cheaper to sample while still retaining the information we want. To heterodyne, we must use an RF mixer which mixes two RF signals together, and so we selected the HMC400MS8ETR which has a frequency band of 1700-2200 MHz. It is currently $6.70 on Arrow.

Controls/Processing:

Microprocessor- To control our VCO, phase shifters, and sample the return data we need a microcontroller which has a good number of GPIO ports, as well as a high clock speed for sampling. It should also have DSP instructions in its ISA and compatibility with communication protocols like SPI, I2C, and UART. This is why we chose the STM32F412RGT6TR which has a clock speed of 100 MHz, 50 GPIO ports, and compatibility with the communication protocols listed above. For testing, a development board costs $15.04, and the standalone microcontroller costs $10.71 on Digikey.

Raspberry Pi- For higher level processing like making visualizations and networking, we have chosen to use a Raspberry Pi upstream in our workflow. We plan to use a Raspberry Pi 3B+ which costs $35.

PCB:

Printing- For RF PCBs, certain materials need to be used to retain signal integrity. For this reason, we will be printing from OSH Parks with their four layer service. They use a FR408-HR substrate which has a dielectric constant of 3.61 at 1GHz, which is acceptable for our purposes. They charge $10/square inch and provide three copies of the board at this rate, which is perfect for our nodal needs. 

Budget:

For one node, we would need 1 VCO, 4 phase shifters, 4 amplifiers, 4 SMA connectors, 4 antennas, 4 low noise amplifiers, and 4 mixers. As well as this, we would need one STM development board and one Raspberry Pi 3B+. While we do not know the exact specifications of our PCB, we believe it will come out to be around 10 square inches. This comes out to $303.8 for one complete node, and two extra PCBs, not considering any extra cost for testing and errors.

Software Specifications:

PCB Design:

We plan to use ORCad to make our schematics and layouts for the PCB. ORCad can interface with Digikey via the UltraLibrarian plugin which helps with getting schematics and footprints for the hardware we want to use. We can then make a Gerber file for printing the PCB.

Microcontroller:

The majority of the controls will be coded in C. Since we plan to use the STM32, we will be able to use STMCubeMX which is STM's development toolchain as well as the hardware abstraction layer (HAL) provided by STM for processor specific programming. This will allow us to interface with the ADC in the chip, write logic for the phase shifters, compute the FFT on the return signal, etc.

Some of the programming such as computing FFT can be very complex. For this reason, we plan to use MATLAB's Embedded Coder for writing blocks of code for computations like the FFT which we can then implement into the microcontroller.

Raspberry Pi:

To visualize our incoming signals and provide metrics like distance, angle, and vector of motion of an object, we plan to use Python for creating a UI which allows the user to visualize what the radar is seeing. As well as this, we will use the IoT framework BatmanADV to form a mesh network amongst nodes. Then, we will use C++ to form both server and client side functionality in terms of accepting and decoding information and packaging and sending information via the Batman protocol.

Test Plan

Our test plan is intended to serve as a guide to accelerate production by preemptively deciding and designing testing procedures. This is with the aims of setting safety precautions as well as necessary test bench implementations. 

The objectives for testing include testing for correct phase modulation, signal coherence and clarity, reflected power, as well as the natural harmonics of the system. Additionally safety is a paramount concern when working with microwave systems. 

Phase modulation testing aims to verify the accuracy and efficiency of our phase modulation system. Without an accurate distribution of phase amongst, a phased array would not positively construct. The testing of which requires the use of signal generators and phase meters. 

Signal coherence an Clarity shall be ensured to guarantee proper operation without scattering. The testing of which includes the evaluation of SNR ( Signal to Noise Ration) and the BER (Bit Error Rate). The necessary hardware for this segment includes spectrum analyzers and oscilloscopes. 

Reflected Power is a particularly difficult issue to solve when dealing with UHF (Ultra High Frequencies). Fortunately the testing shall include a very sophisticated technology, a network analyzer, which greatly simplifies testing. Using this test device, we will be able to accurately measure and correct any reflected power. 

Finally natural harmonics shall be tested to identify any unintended frequency emissions and distortions. These unintended products of wave generation can impact the detection and recording of signals and shall be eliminated completely. These harmonics can be found using an S-Parameter device which will allow the tuning of the internal resistance to better situate signal propagation. 

Safety is a very important concern for our team. The proper precautions regarding microwave safety shall be taken at every instance. Proper test zoning shall be strictly enforced. 

By systematically addressing all of the aforementioned issues, out plan not only assures the quality and performance of the phased array system, but also ensures the safety of all involved.