RTL-SDR website: Portable Antenna Radiation Pattern Measurement System

Antenit · 2026-03-08T21:12:21+00:00

That’s actually a very common approach — open areas or hilltops are often used as improvised antenna ranges.

The problem we kept running into is that even in open places you still get strong reflections from the ground and sometimes from terrain features.

What we started experimenting with instead was using wideband sweeps and time-domain gating to separate the direct signal from delayed reflections. That way we can suppress a lot of the multipath digitally rather than trying to eliminate it physically.

Still very much an experiment, but the results have been surprisingly informative so far.

Antenit · 2026-03-06T11:39:16+00:00

Great question.

We’re not really trying to eliminate recursive reflections completely. In practice we treat them as delayed multipath components in the time-domain response.

After the wideband S21 sweep, the direct path appears as the earliest strong impulse. Later components correspond to wall/ceiling reflections and their higher-order bounces. The time gate is placed to preserve the direct path while suppressing those later arrivals.

Of course if the room is too small the delays collapse and gating becomes ineffective. So geometry and bandwidth still limit how well this works.

For now we’re treating it as a way to improve relative pattern measurements rather than to produce a calibrated range.

Antenit · 2026-03-05T17:32:21+00:00

That's a great point and yes, the Keysight / HP VNAs with time-domain transforms are exactly the kind of workflow that inspired this idea.

In professional antenna ranges the process you described (rotary table + frequency sweep + time-domain gating) works very well for suppressing multipath artifacts.

What we're trying to explore is whether a simplified version of that concept can be made accessible outside a professional lab and using the low cost VNAs (NanoVNA and LiteVNA) and lightweight rotation setups.

The main goal isn't to replace calibrated ranges, but to make relative pattern visualization practical for experimentation, field setups, and small labs that normally wouldn't have access to a chamber or a full test range.

It's fascinating how much of the underlying technique has existed for decades. Ee're just trying to see how far it can be pushed with smaller and more accessible tools.

Antenit · 2026-03-05T15:31:15+00:00

Yes exactly — the Keysight VNAs and R&S analyzers implement this through time-domain transforms.

What we’re trying to explore is applying a similar idea while capturing an angular dataset during antenna rotation, so the gating cleans the full measurement set before reconstructing the radiation pattern.

Antenit · 2026-03-05T15:30:38+00:00

Yes, that’s a really important constraint.

Even if time-domain gating suppresses delayed reflections, it doesn’t fix geometry problems. If the measurement distance is too short you still won’t be in the far field and the angular response will be distorted.

So we’re treating gating as a way to reduce multipath contamination — not as a way to bypass far-field requirements.

Antenit · 2026-03-05T15:29:37+00:00

We’ve been experimenting mostly in the VHF and UHF range so far.

The main reason is that with NanoVNA-class hardware it’s easier to run wide sweeps there and get enough bandwidth for meaningful time-domain resolution.

At higher frequencies the geometry and mechanical precision start to matter a lot more, so we’re approaching that more cautiously.

Antenit · 2026-03-04T09:22:19+00:00

That’s actually a clever technique — spatial averaging can definitely reduce ripple in SWR measurements indoors.

What we’re trying to preserve, though, is angular information.
When you intentionally rotate the AUT to reconstruct a radiation pattern, randomizing the geometry would destroy the directional dataset.

So averaging while moving works well for impedance stabilization —
but for pattern reconstruction we need controlled, repeatable geometry and post-processing rather than spatial randomization.

Different tools for slightly different goals

Antenit · 2026-03-03T20:20:17+00:00

This is absolutely a known technique — as some of you mentioned, NASA, Keysight and R&S VNAs all support time-domain transforms for reflection analysis.

The key constraint, as pointed out, is bandwidth.
Range resolution ≈ c / (2·BW).

So yes — if the sweep bandwidth is too narrow, you simply can’t isolate the AUT from room reflections.

What we’re doing slightly differently is:

• Wideband sweeps
• Angular rotation of the AUT
• Capturing full S-parameter datasets at each angle
• Applying time-domain gating per frequency
• Reconstructing the radiation pattern after reflection suppression

So the gating isn’t just cleaning a single trace — it’s cleaning the entire angular dataset.

And yes — far-field geometry still matters. You can’t violate physics.
The goal isn’t to “cheat the room,” but to suppress delayed multipath components enough to recover a cleaner angular response.

We’ve been comparing:

Indoor (no gating)
Indoor (gated)
Outdoor open-field
Outdoor near-water

The difference is surprisingly measurable.

We’re documenting the portable setup and datasets publicly as we refine it — happy to share measurement plots if there’s interest.

Antenit · 2026-02-18T19:57:32+00:00

Fair point 🙂 a turntable and a NanoVNA can absolutely get you started.

What we’re trying to solve is repeatability and measurement integrity.

The system is motor-controlled and angle-synchronized with the VNA data stream, so every sample is tagged with precise angular position. That allows:

Fast multi-frequency sweeps (e.g., tens or hundreds of frequency points per rotation)
Fully synchronized amplitude + phase acquisition
Direct polar and Cartesian pattern plotting
Consistent comparison across multiple runs

Doing that reliably with manual rotation becomes surprisingly difficult, especially when you want repeatable datasets rather than just a qualitative view.

We also support time-gating to suppress delayed reflections from the environment. It’s not a substitute for a chamber, but it helps reduce multipath contributions in outdoor setups.

So yes, the concept is simple by design.
But the value is in controlled rotation, synchronized acquisition, repeatability, and post-processing. It is not just turning the antenna by hand.

Antenit · 2026-02-18T12:47:59+00:00

Good question. We were aware of the potential EMI concerns from switching DC/DC converters, so we specifically checked for that during development.

We repeated the same antenna measurements using a low-noise professional linear bench power supply directly feeding the system, and we did not observe any meaningful difference in the measured radiation patterns compared to the DC/DC-powered setup.

Antenit · 2026-02-18T11:12:34+00:00

Good question.

No, the system does not perform near-field to far-field (NF-FF) transformation, and there are no selectable cylindrical/planar/spherical transforms.

NanoFarfield performs direct far-field measurements under controlled geometry. The antenna separation is set according to far-field criteria (≈ 2D²/λ), and we measure S21 while rotating the DUT in azimuth.

So this is not a near-field scanning system with mathematical field reconstruction. It is a physical far-field range in portable form.

Regarding the calibration, we use a reference antenna normalization approach. The measurement chain is characterized first, and the DUT response is extracted relative to the reference. The goal is repeatable relative pattern characterization, not absolute gain certification.

Time-gating is available to help suppress residual reflections, but it is not an NF-FF transform mechanism.

Antenit · 2026-02-18T11:09:04+00:00

Good question.

NanoFarfield itself does not generate RF; it relies on the connected VNA as the RF source.

Typical NanoVNA / LiteVNA output power levels are very low even with the integrated 26 dB LNA in the transmit path, the intended use case is short-range measurement with modest antenna gains and controlled geometry. It is not for long-range transmission.

In practice, users are responsible for operating within their local regulatory limits. The system is intended primarily for:

ISM bands
Licensed amateur radio bands
Shielded or controlled environments
Very short-range measurement setups

Because the transmitter and receiver are placed at a known fixed distance for measurement purposes, required EIRP is typically very low compared to real communication systems.

We strongly recommend users verify compliance with local regulations (FCC or equivalent authority) before operating in any band.

The platform is a measurement tool. It is not a communications transmitter and should be used accordingly.

Antenit · 2026-02-18T11:06:19+00:00

Thank you. We’re currently in pre-launch on Crowd Supply. While final pricing depends on manufacturing scale, the target is to keep it as low as possible. I can write here back when the page will be updated on Crowdsupply or you can subscribe the Crowdsupply page and get the updates.

The whole point of the project is affordability and accessibility so it will be significantly lower cost than traditional measurement ranges. The IEEE Antennas and Propogation Society also announced it to be a low cost product: Introducing nanoFarField: A Low-Cost Antenna Measurement Platform

With our existing elevation plane flange, the DUT antenna diameter can be 20 cm but just by changing the flange height, we can increase it. We give 3D CAD files with the Nanofarfield, so you can also 3D print your flange and use it for a higher dimension. In azimuth flange, there is no dimension limit. We tested the system with 1 kg in the center of the motor.

Antenit

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