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Simple, low-cost FMCW radar

A basic radar system makes radar accessible at low cost for experiments with rangefinding & navigation of autonomous aircraft or spacecraft.

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This project was created on 06/30/2014 and last updated a month ago.

Description
This relatively compact, cheap, simple FMCW radar operates in the spectrum around 5.8-6.0 GHz and is aimed at lowering the barrier to entry for experiments with radar and general education around RF/microwave electronics. It is capable of speed measurement, rangefinding and SAR imaging (with appropriate moving antennas or a moving vehicle.) It is potentially applicable to experiments with autonomous aircraft (or spacecraft) altitude-finding, SAR imaging/mapping or navigation as an alternative to (or in addition to) other sensing techniques such as GPS, ultrasonics, LIDAR or barometry, without some of the limitations applicable to those technologies.
Details

Frequency-modulated RF is generated by the Hittite HMC431 VCO at top left, at about 5.8-6.0 GHz, amplified by the HMC476 MMIC gain block at top left, and split in half by the Wilkinson divider at top center. Half the RF output from the divider is amplified again and sent to the transmit antenna connector at top right.


The local oscillator, from the other side of the splitter, is amplified again and applied to the LO port of the Hittite HMC219 mixer at bottom center. The reflected RF from the receive antenna comes in at bottom right, where it is amplified by the Hittite HMC717 6 GHz LNA and the amplified output is applied to the mixer.

A couple of pi attenuators are used, after the VCO, before the mixer LO port and after the mixer's IF output, to "tune" optimal mixer LO level and overall performance, although I haven't fixed certain values for these attenuators yet, space for them is left on the board.

IF filtering, amplification and signal processing, along with generation of the 0-10V modulation signal for the VCO, are done on a separate board. More details to come, as design, fabrication, revision and testing progresses.

Components
  • 1 × Hittite HMC431LP4E 5.5-6.1 GHz GaAs/InGaP HBT MMIC VCO (voltage-controlled oscillator) with internal output buffer
  • 1 × Hittite HMC717LP3E 4.8-6.0 GHz GaAs PHEMT MMIC LNA (Low-Noise Amplifier)
  • 1 × Hittite HMC219AMS8 4.5-9.0 GHz GaAs MMIC double-balanced mixer
  • 3 × Hittite HMC476MP86 0-6.0 GHz SiGe HBT MMIC gain block (amplifier)
  • 3 × Molex 0732511150 50 ohm SMA socket, board edge end-launch style to suit 1.6mm PCB, specified up to 18 GHz.
  • 3 × Susumu PAT1220-C-3DB-T5 Susumu 0805 PAT series 50-ohm pi attenuators, specified up to 10 GHz. I will tweak actual values later.
  • 30 × Assorted capacitors, resistors, a couple of LEDs, 3.0V LDO and a couple small FETs.

Project logs
  • Where's the software?

    a month ago • 0 comments

    If you're interested in software, you might be wondering how much software I have for this project, or where you can check it out. I've just put some code up on GitHub, you can check it out by following the sidebar link.

    Truth be told, there isn't much software right now.
    Part of the reason for this is that I'm focussing on the relatively tricky microwave electronics first, and getting the RF hardware platform working. Another reason is that some people (Greg Charvat, for example) have already created some fantastic signal processing software tools and shared their contributions with the world.

    I've put up my quick SPI test code, using an Arduino to drive a Microchip SPI DAC to generate a triange-wave modulation signal (this is amplified, as previously discussed, into an 0-10V signal.) However, this was just a quick experiment and it is unlikely that the finished product will use an ATmega328 microcontroller or Arduino-compatible bootloader. I'll continue to share any quick little software tests, tools or scripts as they come along.

    Another thing I'm currently working on is to take the MATLAB signal processing and visualisation scripts provided by Greg Charvat and the MIT/Lincoln Lab folks, and to tweak these for the best match to my hardware characteristics - and to replace the use of MATLAB with free software tools, since MATLAB isn't really the cheapest, most accessible choice. As work progresses, I'll continue to share these changes and new code that is written.

  • Bits and pieces

    a month ago • 1 comment

    Here are a few little components I've been working on lately - reusable, modular, general-purpose building blocks for various RF experiments and R&D.

    - HMC431 VCO module with shielded can (top of can not shown)

    - A simple breakout board for SOT86/Micro-X RF gain blocks. (Top centre) This could be used with various MMIC devices in that package, from RFMD, Hittite, Mini-Circuits or various other manufacturers, they're all pretty similar. This board provides coupling capacitors, bias tee, power indicator LED, current limiting resistor in the MMIC supply rail, and a few decoupling capacitors. The passive values can easily be changed to suit different devices, so it's a generally usable module. An input attenuator is provided on this board so that the output power can be kept within the amplifier's linear region if the input power is too large.

    - HMC717 LNA breakout board (bottom centre).

    - Two different Wilkinson dividers, one of which uses a coplanar waveguide architecture (with top groundplane) and one of which uses more a microstrip approach (no top copper pour, fatter tracks compared to CPWG for the same given impedance.) We'll see if they exhibit any performance difference.

    - 20-DIP chip provided for scale reference.

    I made these boards with no solder mask at all - for a few reasons.

    (a) Because the thin dielectric layer of solder mask between the metal and the air introduces a slight error (admittedly it is small) into the physics (for impedance and width calculations etc) because it is not accounted for in the model. 

    (b) To see if the board fab would have any issues with it. (No.)

    (c) Because it makes it easy to see where all the signal traces are, makes it easy to shunt extra components between the signal tracks and the groundplane (eg. to add extra bypass capacitors), to cut the tracks and hack the boards in other ways, eg. adding extra attenuation, if the need arises.

    (d) Because it looks good. OOH SHINY. The slight disadvantage is that the solder looks slightly "messy" (although there aren't any shorts) where it spills across the ENIG groundplane.

    I did put a small region of solder mask underneath the 16-pin LNA, because with the 16-pin 0.5mm pitch QFN device I wanted to ensure it soldered successfully without any shorts or problems. (I haven't tested it yet, but to visual inspection it's good.)

    Mixer boards are coming, but they haven't arrived yet.

  • System block diagram

    a month ago • 0 comments

    So, you like block diagrams? Here, have a quick sketch of a diagram. :)

    (Note: the attenuator before the mixer LO port doesn't need to be there; that's a mistake.)

View all 18 project logs

Discussions

Jasmine wrote a month ago null point

Hello Luke, I think you have most of what we are requiring for the next round of The Hackaday Prize. The only thing I can't see is links to code repositories or software libraries. And remember to mention any licenses or permissions needed for your project. Best to document that information in the project details. Thanks for entering and good luck!

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Luke Weston wrote a month ago null point

Hi Jasmine, I will put an update up and some code online this weekend. :)

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rafael.menezes wrote 2 months ago null point

If you need help with the algorithms, I have some background.

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J Groff wrote 2 months ago null point

I wonder if the ultrasonic processing firmware would function with tweaks to constants?

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pfeffer.marius wrote 2 months ago null point

Have you thought about the legislations over the world ? Would be realy nice if this could be used worldwide.

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Adam Fabio wrote 2 months ago null point

Nice work Luke! I love those Hittite chips - though they can get pricey! Thanks for entering The Hackaday Prize - with 10 project logs, you're doing a great job keeping the updates coming in! Don't forget about the video, and good luck on your way to Space!

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Luke Weston wrote 3 months ago null point

I will probably start with some PC-based experiments building on the prior similar work of Greg Charvat and Tony Long, but I would also like to eventually have the ability for a lightweight, cheap embedded microcontroller system to digitize the signal and extract basic information such as speed or altitude for use in autonomous navigation of a vehicle such as a quadcopter or other UAV, autonomous altitude control etc. But this kind of software is one of the least mature, least developed parts of the project at this time. Thanks for your support :)

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zakqwy wrote 3 months ago null point

Sounds like a great plan. There are a number of industrial products out there that use FMCW radar systems for level monitoring in liquid/solid applications; while the firmware is always locked down and proprietary, the manufacturers often share some details of the echo processing system. Worth a bit of research to get you started I'm sure.

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pfeffer.marius wrote 2 months ago null point

Sounds great ! Currently it's not easy (and cheap) to measure the distance to the ground from UAVs which is realy helpful for autonomous landing or collision prevention.

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zakqwy wrote 3 months ago null point

Great project! I'd love to learn more about your plans for echo processing. Any algorithm details?

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