Rotman Lens

https://en.wikipedia.org/wiki/Rotman_lens

by thomasjb • 22 days ago

140 47 22 days ago

en.wikipedia.org

d4ng• 21 days ago

If I understand correctly, is the application of this to quickly switch the direction of sending/receiving? Are there any other applications?

macnetic• 21 days ago

Not just switching, you can use all of the beams simultaneously.

colechristensen3• 16 days ago

No, this is to concentrate the radio waves into a desired shape. Stronger in this direction, weaker than that.

Think of it very vaguely like a parabolic mirror on a flashlight directing the light vs a naked light bulb putting light out in all directions. (this is a bad metaphor for what's going on but it's the basic idea of the goal)

To change the direction you have to physically move the antenna OR have an active phased array antenna with an electronic component which has a variable phase change to be able to move the beam around while leaving the antenna fixed.

Intralexical3• 16 days ago

It does do directional steering. No active array components or physical movement are needed.

If the output ports are connected to individual antennas in an antenna array, this allows shaping the beam in different directions by switching which input port the signal is sent to.

From TFA.

Presumably the geometrical shape of the lens is dictated by solving for useful phase shifts for different input points. Otherwise you could just use a bunch of delay lines.

I wonder if anybody's ever designed a 3D version of this. You might get a wider range of inputs, or more precise steering, by shaping the delays on a non-Euclidean (curved) surface (like a sphere or a saddle).

ErroneousBosh• 16 days ago

That's kind of it, yes.

You can aim an aerial by physically rotating it. You've probably done this, gone up on the roof to adjust the aim of your TV aerial or satellite dish. It makes sense, right? A Yagi aerial - a reflector, a driven element, and a bunch of directors - focuses the beam in a kind of aubergine-shaped blob in the direction of the pointy end.

But you can also aim aerials by having two of them, and varying the phase that you send a signal into them. This sounds a bit mental but consider how direction finding equipment like LoJack works - you have a transmitter in an unknown location and you have a cluster of aerials connected to one receiver. By comparing the phase of the incoming signal between two aerials you can work out which one it's nearer to! This trick works well enough if you make two dipoles spaced a half wavelength apart that you can easily homebrew something where by switching in a 180° phase shift at an audio rate, the difference in phase can be heard as a tone.

In this case you've got a bunch of aerials attached to the ports along the bottom and the phase of the signal reaching them depends on how long it's taken to cross the microstrip. If you fire it in at the top in the centre it'll be equal (notice the middle "legs" have kinks in them to keep the path length the same?), if you fire it in at the side then one of the ports at the side will get the signal sooner and its phase will appear advanced compared to the other one - and the beam will bend that way.

summa_tech• 16 days ago

Imagine a power splitter + phase shifter that produces a correct phase shift for each element in a phased array to produce a directional beam from one radio transceiver.

Now this clever arrangement, instead of having only one radio transceiver port, has multiple. And each of those ports corresponds to a different set of phase shifts, producing a directional beam at a different azimuth angle.

And because this is an entirely passive device, it's linear, and all ports can be active at the same time (principle of superposition essentially). So you can use a single phased antenna array to serve multiple directional beams at the same time.

amirhirsch3• 16 days ago

It creates pancake beams so you would usually use a separate Rx and Tx orthogonal to each-other to do imaging.

CamperBob2• 16 days ago

Basically, it lets you steer a beam very precisely in an arbitrary direction, as if you were physically rotating the transmitting antenna.

Usually you'd need to rotate the antenna or else use a large number of controllable phase-shifting elements to send an output beam in the desired direction. But a Rotman lens lets you use a small number of phase shifting elements to merge a small number of source beams (still > 1, though) into a single precisely-steered output beam.

Intralexical3• 16 days ago

If you monitored all the inputs simultaneously instead of switching, you could make a low-tech radio-wavelength camera. Presumably with less SNR per "pixel" than you'd get from monitoring just one input though.

grahamburger2• 16 days ago

It's a way to create constructive interference in an RF signal in a certain direction (the signal gets stronger in one direction and weaker in others without changing the hardware). It's commonly used in LTE and Wi-Fi as a way to increase SNR directionally for clients.

https://en.wikipedia.org/wiki/Beamforming

bt1a• 16 days ago

I was expecting some sort of fungal network with measurable compute on initial glance. Then the article image couldn't help but look quite like the outline of an Earthbound entity.

mooshx• 16 days ago

Looks ripe for a KiCad/Altium footprint.

brcmthrowaway2• 16 days ago

The type of old school black magick engineering Claude could never.

amirhirsch3• 16 days ago

Oh I dunno. I made a mm-wave radar with a Rotman lens using a generative loop between Python, Rhino, and EM simulation. Pretty sure AI could cook that up.

brcmthrowaway2• 16 days ago

How was it generative, generative AI?

varjag• 16 days ago

What did you use for the simulation part?

ano-ther• 16 days ago

Looks deceptively simple. Is there a good source to learn more about how it works?

actionfromafar2• 16 days ago

This looks like an optical Rotman lens:

https://academy.lucedaphotonics.com/modules/awg/guide/compon...

plasmatorch• 15 days ago

Used to work in photonics. The star coupler portion is a Rotman lens, the whole thing is different (an AWG). It's used to spectrally separate an input (or in this case, inputs) across different outputs.

Y_Y• 16 days ago

The principle was first published by Walter Rotman and R. F. Turner in 1963

Astonishing nominative determinism there

goodmythical• 16 days ago

Tito Beveridge creator of Tito Vodka, Ed Currie creator of the Carolina Reaper and Pepper X, Keith Weed the president of Britain’s Royal Horticultural Society, Usain Bolt one of the quickest people in the world, Thomas Crapper - commonly but incorrectly attributed with the invention of the modern toilet - founder of Crapper & Co plumbing company, meteorologist Sarah Blizzard, LEO Rob Banks, Donna/Mike/Bobbie Singer all singers with no relation.

I myself have a CTO of a plumbing company in my family from Flushing MI, but that's ever so slightly different.

ragebol• 16 days ago

These are called aptonyms: https://en.wikipedia.org/wiki/Aptronym?useskin=vector

Tade0• 16 days ago

I think nominative determinism has it backwards: people are actually nudged into careers which fit their names as whoever is on the receiving end of their services automatically has a more positive sentiment if they notice the name fits.

I experienced this myself as my first name was rare in my generation and normally found in history books or literary classics so I was perceived through that lens.

bbminner• 16 days ago

How difficult it is to get a perfect beam in practice? Can one manufacture a flat rotman lense like that to introduce sinc phase shifts - this should yield a well behaved very directed beam? What are the practical challenges in doing so?

RossBencina• 16 days ago

Suppose this is connected to a multiple-output RF transmitter (amplifier), what are the advantages/applications of shifting the phases of the signals passively with a Rotman Lens versus shifting the phases of the signals prior to feeding them to the transmitter (i.e. in the generator)? is the main purpose to compensate for different antennae geometry without having to change the signal generator? I guess things are very different when you can't commute everything into your SDR algorithms.

go_artemis• 16 days ago

Rotmans are elegant, but these days you can get full-duplex all digital phased arrays for cheap: https://www.crowdsupply.com/scale-rf/quadrf#

totetsu• 16 days ago

I wonder if you could do this with sea walls and gates and make beamformeable surf breaks.

SiempreViernes• 16 days ago

The precondition is a controlled input, if you can provide that in the context of sea walls I think you have solved a much bigger problem.

IAmBroom2• 15 days ago

Control is needed in directionality, which is pretty much solved - few tsunamis originate inland.

amelius2• 16 days ago

It would be nice to see an EM simulation of this.

Any open source packages that could do it?

Skwid• 16 days ago

You can do something similar in 3D with Luneberg lenses, as used on the AN/SPG-59[1]. A truly wild piece of engineering, as is the following SCANFAR system if you're into that sort of thing. I can only assume someone in the top brass had a skim of Arthur C Clarke's Superiority and forwarded it straight on to engineering with a big green approved stamp.

1. https://secwww.jhuapl.edu/techdigest/content/techdigest/pdf/...

po1nt• 16 days ago

This is the closest we can get to magical runes.

amarant• 16 days ago

R.F Turner is a pretty nice example of nominative determinism. Parents up and named him "radio frequency dial", so of course he works in antenna technology

FiatLuxDave• 15 days ago

Similar to the plasma physicist R.F. Heeter

summarybot2• 16 days ago

Hey if anyone else is wondering what the heck this thing actually does, there's a beautiful visualization made by Lukas Henkel on his LinkedIn: https://www.linkedin.com/posts/lukas-henkel-ovt_simulation-e...

summarybot2• 16 days ago

It's like a Tesla Valve for spreading butter evenly

Rotman Lens

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