Made this simple Vivaldi antenna. It's designed to work from 5.5 to 6.0 GHz and matching looks good at that band.

This is getting quite expensive for a hobby project.

New blog post: Synthetic aperture radar autofocus and calibration.

Synthetic aperture radar vs Gopro.

Wrote code for SAR image antenna pattern normalization and polarimetric calibration (channel imbalance and crosstalk). Image looks very nice now.

I implemented a new SAR autofocus algorithm and now the image generation is both better and faster. It's about as well focused as it can be now.

Fixed some bugs in my SAR processing code and now fast factorized backprojection generates a visually identical picture to the normal backprojection, but over 10 times faster. That's huge because normal backprojection was already extremely quick and there's still room for optimization with FFBP.

Found motivation to write some SAR processing code. Fast factorized backprojection generates several small polar format images and then interpolates them to one big image. It's faster, but has slightly worse image quality due to all the interpolations.

I made this new dual directional bridge coupler using 1 mm diameter coaxial cable. It's a little bit better than the previous one I made using 2 mm coaxial cable and much more annoying to solder.

Bought this thru with 3.5mm RF connectors. It's air filled with just a thin see-thru membrane holding the center pin in place.

Some new RF connector test PCBs. Nameless low-cost solderless 3.5 mm connector on the left and CONSMA003.062 clone on the right. Both work okay.

Bought this VNA calibration kit with 3.5 mm connectors. Looks good considering the 60€ price tag.

New blog post: "Designing a low-cost high-performance 10 MHz - 15 GHz vector network analyzer". hforsten.com/designing-a-...

Just found an annoying flaw with this cheap bias-T. The connector is threaded in the case and if the cable is tightened with a torque wrench, it can unscrew also the SMA connector when removing the cable.

There's a tiny gap between the case and SMA connector that radiates a little if not sealed. Putting some solder wick in the gap seals it nicely but there has to be some more elegant method.

CNC machined case for the VNA just arrived. Machining quality is good and it looks stylish (very important). The cost was $140 including shipping and taxes, much cheaper than I initially feared.

VNA also works as a temperature sensor and strain gauge.

This turned out to be slightly more difficult than I first thought. Foil tears easily and even a small tear will affect the isolation. It might require multiple layers to get a tear free lining. Foil also needs to be glued down so that it doesn't move around or it will increase drift of the VNA.

Got the VNA software working and made some first measurements. With shorts at both ports the isolation is excellent >100 dB and the VNA works well at least up to 10 GHz with slight dynamic range reduction at higher frequencies.

Managed to design RF enclosure for the VNA in FreeCad. It's 3D printed and lined with aluminium foil. I'll get it CNC machined if everything works out but this is good enough for now.

Assembled PCB for my newest project just arrived. This should be 10 MHz to at least 8 GHz VNA. Next is powering it on and testing if it works.

JLCPCB sent me an X-ray image of the FPGA on my PCB they assembled. Soldering looks good. Internal routing of the BGA package is also visible.

I added a sideways looking GoPro camera to my radar drone. Just tested it the first time and it looks very nice.

I added some example synthetic aperture radar processing code and data from my drone for anyone wanting to experiment with SAR image processing: github.com/Ttl/torchbp/...

+37 USD for 0.4 mm diameter vias. I'm pretty sure that this wasn't required when I previously ordered similar PCB last year.

Just sent my next project for manufacturing.

Suspiciously high amount of referrals from domains that include ".gov" lately.

New blog post: "Homemade polarimetric synthetic aperture radar drone". hforsten.com/homemade-pol...

2-port VNA can be used to measure full N-port network S-parameters even with non-ideal terminations. It's very useful but I haven't seen it used much by others. I guess one reason is that it isn't implemented in VNA built-in software? scikit-rf.readthedocs.io/en/v1.3.0/ex...

I made some dual directional bridge coupler test PCBs. It works very well and sharing the balun between two couplers doesn't seem to cause any issues. I also tested replacing the coaxial cable and ferrites with a transformer but it doesn't work very well.

I bought this cheap Bias-T from China. It claims to function from 10 MHz to 10 GHz. Looks very nice from both outside and inside. Enclosure is machined from aluminium and PCB is not FR4. Measured with VNA it seems to work fine up to 6 GHz, but there's a small 1 dB dip in S21 around 1.1 GHz.

I measured JLCPCB 4 layer stackup loss by extracting the transmission line propagation constant from TRL calibration. As far as I know JLCPCB doesn't specify tand anywhere? In the microstrip model I need to set tand to 0.014 to fit the measurements. That's better than the usual 0.02 assumed for FR4.

3D printed RF enclosure lined with aluminium foil. It probably isn't as good as if it was machined from metal, but it has excellent performance to price ratio.

Got superglue on my thumb and now I can't unlock my phone with fingerprint anymore.

Just as designed (Incorrectly).

Some new RF test PCBs. Only the pro RF designers can tell what the circuit on the bottom right does from the layout.

Trying out Qucs-S layout export to Kicad with Qucs-RFlayout. Looks very promising.

Power amplifier running too hot? Bolt on aluminium PCB under the PCB. Works great and this custom aluminium PCB only cost $4 for 5 pieces from China.

Family picture of my homemade radars, 2014 - 2024.

Hello Bluesky! Follow for homemade radars, RF electronics, FPGAs, programming, and other electronics related things.