For my senior design project, we had originally intended to develop a noncontact vital signs monitor, and we decided to do this using a radar we would develop. With coronavirus happening and campus shutting down, that full goal wasn’t as achievable with less resources and equipment to test and develop, and inability for group members to meet up. For that, we descoped the project to just developing our own CW radar and using it to measure speed. Additional credit on the project goes to my group members: Ryan Printup, Jean De Dieu Niyomugabo, Christian Proctor, and Shawn Lazik.

The design was a typical continuous-wave radar at 2.0 GHz. This was chosen to make design easier, and have parts for it be cheaper and more available, while not being at 2.4ghz where noise could come from Wifi or other signals.

A CW radar is very basic, it transmits a continuous sine wave, and uses a mixer to output a wave with a frequency that is the difference between the transmitted wave and the recieved wave, where the recieved wave is shifted due to the doppler effect. This lets us measure speed toward/away from the radar but not direction or distance. Filling in the components for each of these blocks in the diagram brings us the following schematic.

The schematic has voltage regulators and DC input in the power section. In the transmit, we have our VCO and power splitter, going to the transmit antenna. The transmitted power is approximately +3dBm. On the recieve side is our bandpass filter, the RF amplifier, mixer, and output amplifier. The frequency response of the output amplifier acts as a lowpass filter. the output amp is an opamp in a differential amplifier configuration.

On the PCB layout, the traces and pads on this drawing are color coded to identify purple for RF, orange for LF, blue for power, and red for GND/other.

The antenna was designed by my group member, Shawn, I laid it out onto a board and ordered them with the radar PCB. We designed the antennas on 1mm thick FR-4, and the radar circuit, while being mostly 1 layer, was put on JLCPCB’s 4-layer impedance controlled stackup.

For the ADC, we used a Teensy 4.0 board, and wrote the software in arduino. The Teensy just read the ADC pin, and printed its value to the serial port, all other processing for our main software for our project was done in python on the recieving computer, doing a fourier transform to find the measured doppler frequency. For an alternate software and simple demo video, I made teensy code to do the data processing on the teensy and have it output direct speed values, calculated by measuring the period of the signal, which is shown in the video further down the page.

Code for this project can be found here: https://github.com/RyanPrintup/CW-Radar-DAQ-Driver

The video above shows the radar (located near the camera) measuring speed in real-time. Noise reduction filters could be used to make the calculated signal less rough-looking and having fewer spikes in the measurement. I am holding a piece of sheet metal to maximize reflected signal, as if it were measuring a car. The range tested here is 75 feet. Apologies for the low quality video, it was a WiFi camera input in my yard, so had a bad connection. The data graph should be accurate to real-time.

The radar worked as designed, and was a fun design project for school. While it certainly isn’t any new technology or high-end accuracy, it was a good demonstrator of some RF design and application. Thanks to all my group members listed above in help with this project.