Homemade 6 GHz pulse compression radar
A hobbyist-built 6 GHz pulse-compression radar, complete with custom high-speed PCB design and FPGA-based signal processing, impresses commentators as an unusually deep one-person RF project achieved with modest tools and open-source software. Readers explore potential applications such as low-cost 4D automotive sensing as an alternative to lidar, phased-array and SAR imaging, and even heartbeat detection, while noting the complexity and antenna counts needed to reach lidar-like resolution. The thread also touches on regulatory limits (FCC power rules, ITAR controls), safety of RF exposure, and the practical challenges of test equipment and component sourcing for GHz‑range hardware.
Overall reaction
- Strong enthusiasm for the technical depth: RF, high‑speed digital, FPGA, and signal processing all in one project.
- Several readers call it unusually sophisticated for a single hobbyist and compare it favorably to professional radar work.
- Some note the relatively low out‑of‑pocket cost (~$570 including VAT and shipping) versus the enormous time and expertise implied.
Cost, tools, and test equipment
- Itemized cost from the author: ~$330 for PCB fab/assembly of two boards, ~$240 for components.
- Readers assume expensive RF test gear is required; author reports using only an oscilloscope, multimeter, and open‑source tools.
- This prompts discussion that a lot of GHz‑class hobby RF is now being done with modest equipment, although others emphasize that debugging without analyzers can be hard.
PCB design and high‑speed layout
- Multiple questions on layer stack: why ground planes on inner layers, why not top/bottom.
- Explanations: components need very short ground access; continuous planes on inner layers give controlled impedance for high‑speed traces on outer layers.
- Discussion of DDR3 length‑matching: “squiggly” routes are to match delays within ~±10 ps; internal FPGA package delays can be exported and manually compensated in layout.
- Some note that FPGAs can correct timing in logic, but less so for hard IP like DDR controllers.
Applications and extensions (phased arrays, automotive, SAR)
- Curiosity about adapting such radar to 3D voxel mapping or LiDAR‑like use; replies say this needs large MIMO arrays (hundreds–thousands of channels) and heavy processing.
- Automotive 4D radars at ~80 GHz with compact phased arrays are cited as an existence proof and potential LiDAR competitor.
- Some want follow‑on projects: phased arrays, synthetic aperture radar, rotating/tilting mounts for volumetric mapping.
Legal, safety, and ITAR concerns
- Discussion of 6 GHz rules in the US: unlicensed, but with very low allowed EIRP; the demonstrated 1 W PA plus high‑gain antenna would exceed that.
- Consensus that regulators (e.g., spectrum authorities) would react before the military, though military aircraft may still see unknown radar emissions on warning systems.
- Multiple references to ITAR: passive radar code removed from some open projects; sharing restricted code may be a crime; others complain ITAR blocks useful civilian tech (e.g., advanced GPS antennas).
- RF safety: generally considered similar to Wi‑Fi/cellular (non‑ionizing), but high power can heat tissue; anecdotes about radar overexposure and debate about cancer risk vs pure thermal effects.
Miscellaneous
- Side discussions on cheap doppler and presence‑sensor radars, ultra‑cheap repurposed “PIR” radar chips, and the reliability and sourcing (including scrap) of low‑cost Chinese electronics and FPGAs.