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A project log for 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.

luke-westonLuke Weston 07/01/2014 at 08:020 Comments

I've just ordered some new PCBs for the RF stage, with some very minor artwork revisions from the previous iteration.
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.


Prototype IF amp/filter/ADC and ramp generator module. This PCB was sent to the fab house last week. For experimental prototype purposes, one of TI's USB audio codec chips is used to provide ADC / DAC capability from the PC, as a sound-card device.

Here are some earlier prototypes of the RF board.

I've fixed up the RF layout a bit to make it neater and more compact, changed the gain blocks to HMC476s, moved the IF output to a shielded SMA connector instead of one pin on the Molex header, changed the Mini-Circuits MCA/MAC-series mixers to a Hittite part for easier/cheaper availability, used quarter-wave high-impedance chokes on the PCB for the MMIC DC bias, changed most of the resistors and small capacitors to 0402 package for improved SRF / high-frequency performance, and replaced the Mini-Circuits GP2X splitter with a Wilkinson on the board - this means reduced cost, and also means the entire BOM for the board is available at Digi-Key.

Mini-Circuits makes some very fine hardware, but I wanted this design to be easily, cheaply reproducible by anyone throughout the world at minimal cost, using components that can be ordered internationally in small hobby-scale quantities (i.e. just a couple of chips at a time) without high shipping or handling costs. To be honest, despite their fantastic engineering, Mini-Circuits devices are just not available in this way through cheap, small-order "hobby-friendly" distributors without high shipping prices and/or larger minimum order quantities. This is especially true for international customers outside the USA. "I need to order 20x $20 VCOs at a time" instead of being able to just order one at a time is potentially prohibitive for non-commercial hobbyists with constrained cash flow.

However, moving over to certain RF components from Hittite means that these components are available from the major distributors such as Digi-Key at relatively low cost, in one-off or any small quantity, without excessive shipping costs, for anyone in the world. (Well, OK, if you live in North Korea or something I'm not sure that they'll export to you.) The recent announcement of Hittite's acquisition by Analog Devices is also likely to improve wider distribution. 

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