The xaVNA is a two port VNA with a typical frequency range of 137MHz to 3.5GHz, and a guaranteed frequency range of 140MHz to 2.5GHz. It plugs directly into USB and requires no additional power supply. All measurements are done using an intuitive and easy to use UI on a computer.
It is both open source hardware and open source software, with a GitHub repository containing all schematics, PCB layouts, FPGA VHDL, and software that will be kept updated during development:
Stretch goal: C$25,000
We will introduce a 10MHz to 2.5GHz version if budget permits.
What can you do with the xaVNA?
A VNA (Vector Network Analyzer) allows you to measure the impedance of an arbitrary device (such as an antenna) across a wide range of frequencies, as well as the transmission coefficient (gain/loss and phase) of a two port device (such as an amplifier, filter, or isolator).
It can do everything an antenna analyzer can do, but 10x better: it gives you phase information as well, and lets you see the exact complex impedance of an antenna, allowing you to easily design matching networks without tedious trial and error tuning.
What makes the xaVNA superior?
Less trace noise than other low cost VNAs on the market (see graphs below)
No warm-up needed: achieves spot-on measurements within 1 minute of power up
Entirely powered from USB; no power adapter needed
- Open source hardware & software
- Lower cost
How accurate is it? What are the specs?
- Frequency range (guaranteed): 140MHz to 2.5GHz
- Frequency range (typical): 137MHz to 3.5GHz (achieved in iteration 1 prototype)
- Signal level: -20dBm to 10dBm (achieved in iteration 1 prototype)
- S11 trace noise: <<0.1dB (achieved in iteration 1 prototype)
- S11 dynamic range: >50dB (achieved in iteration 1 prototype)
- S21 dynamic range: target >=70dB (achieved 50dB in iteration 1 prototype)
- Dimensions of the VNA board: 10cm x 10cm
- Weight: <200g
- Interface: Micro USB
- RF ports: SMA Female
- Current draw: ~500mA @ 5V
- Windows, Linux, and Mac OS will be supported
Accuracy comparison (measured vs simulated):
Comparison to other low cost VNAs on the market:
See last page of http://www.gsm-modem.de/M2M/wp-content/uploads/2014/04/IoT-M2M-Cookbook-Harald_excerpt.pdf
What is the current status of the project?
We have a fully functional prototype on a 2-layer PCB, as shown in the demo. For iteration 2 all the wiring (including the coaxial cables) will be eliminated and everything will be on one board, to prepare for mass production. The iteration 2 PCB has already been designed and is now undergoing DFM verification.
What will the final product look like?
The T/R version next prototype and final product will be a single 10cm x 10cm 4-layer PCB; Here is a top view rendering of the current design:
The full two-port version will be a similar but slightly larger PCB (estimated 10cm x 15cm).
If time and budget permits, we may include an acrylic case.
Software and interfacing
Software will be provided for Windows, Linux, and Mac OS. An API (in C/C++) will be provided to control and read data from the VNA from your application. All code will be licensed under the GPLv2 and will be available on GitHub.
A screenshot of the software in development:
(Measuring a 900MHz power amplifier)
- SOL calibration
- Smith chart
- Impedance, admittance, and series/parallel equivalent value display
- S parameter export (s1p and s2p)
- S11, S21, S22, S12 magnitude/phase plots
- Distance to fault graph
- Persistence plot
The provided calibration kit will consist of 3 SMA female connectors (for short/open/load), one SMA-f to SMA-f adapter (for through), and 2x 100ohm precision resistors. The references need to be soldered like so:
If you would like the calibration references pre-soldered (at no charge), leave a remark with your pledge.
What is the difference between the T/R version and the full two port version?
A T/R VNA allows you to measure S11 and S21, that is reflection coefficient on port 1 and transmission from port 1 to 2. To measure S22 and S21 you will need to physically reverse the DUT. The full two port version has a directional coupler and signal source on both ports, allowing you to measure S11, S21, S12, and S22 as well as calibrate with an unknown length through reference.
Risks and challenges
The T/R version iteration 1 prototype is fully working and achieves almost all of the target specs, and iteration 2 DFM (design for manufacturability) is close to completion. A quotation has been received for all parts and PCB assembly. This is our first time designing something for manufacture in volume, but we are confident in being able to deliver given the above.
The full two port version will require more R&D.
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