Slashdot Mirror
Antenna Arrays Could Replace Satellite TV Dishes
Zothecula writes "There was a time not so very long ago when people who wanted satellite TV or radio required dishes several feet across. Those have since been replaced by today's compact dishes, but now it looks like even those might be on the road to obsolescence. A recent PhD graduate from The Netherlands' University of Twente has designed a microchip that allows for a grid array of almost-flat antennae to receive satellite signals."
This does appear to be a solution in search of a problem. Today's dishes are already tiny enough to easily mount on an RV. Although, someone needs to tell Allstate insurance, because their commercial seems to indicate they believe a 25 pound dish can obliterate a carport.
Gamingmuseum.com: Give your 3D accelerator a rest.
if you connect it with Monster cables.
Eloi are stupid, throw morlocks at them!
Raw size does matter here. A larger receptor is better.
Which explains why the small dishes now do similar things that the old big ones did?
I suspect it *is* the software that can filter out/account for that interference on a slightly less quality signal that makes the smaller dishes do just fine.
Bigger is better at the extreme end of a broadcast range; i.e. listening for something from outside the solar system or something incredibly weak compared to background noise.
I would also bet that the satellites being used now are more powerful than the original communications sats. So higher signal means, smaller dishes are workable.
If a flat antenna can pickup the signal, I'm sure it will be a bit different than a parabolic concentrating dish. That's exactly was software is made to do. (aren't most internal cell phone antennas these days flat by design? thought I something a while back on fractals in antenna design towards that effect)
People in cars cause accidents....accidents in cars cause people
Phased-array antennas really do work but they are not new. The nice thing about them is that they have electronic steering, so they can steer really fast while a conventional antenna of equivalent size would take much more time to move.
The problem with articles like this (and their Slashdot introductions) is that they always come off as student makes big scientific break-through rather than student applies well-known science.
Bruce Perens.
Its probably a phased array antenna http://en.wikipedia.org/wiki/Phased_array. The big thing here isn't the fact that its been done, but that the chip makes it easy, cheap, and fast to manufacture one. The actual size wouldn't be very different, since the size is based on the required gain, and the physics don't change for a parabolic antenna or a phased array.
The big advantage I see to this is two-fold: 1. Mounts flat so it is much less of an eyesore. Also you could conceivably hide it behind something that is radio transparent. 2. Can be pointed via software, so that the physical installation only needs to be pointed in the rough direction of the satellite.
does it snow a lot where you live ? If it does, can you please tell me the model of your small dish ?
Jehovah be praised, Oracle was not selected
A collection of links on antenna arrays at a ham radio antenna design site: http://www.dxzone.com/catalog/Antennas/Array/
It's not all about signal strength. Sensitivity these days is rarely an issue; the electronics in the receiver are excellent. Of greater relevance are polarization, rejection of off-axis noise, directivity, and the ability to reject signals from adjacent bands. There are also issues of setup difficulty, and this is what the primary focus of the design in question is.
Aiming a dish antenna is a chore, and high winds which shake a parabolic dish can cause signal strength to fluctuate dramatically. An electronically controlled phased array can, by introducing delays to various antenna elements, "steer" itself and lock onto a satellite with great accuracy (within a few degrees of the direction the array is aimed). A small antenna, perfectly aimed, will outperform a larger antenna poorly aimed, and if the antenna's controller can aim itself without physical adjustments many thousands of times per second, wind and a... coarse job of aiming the antenna are non-factors.
A military example: PAVE-PAWS, a 435Mhz missile detection array used by the US Air Force. The antennas in question are made of thousands of smaller elements (a single dipole element at 435MHz is about 35cm long), do not move, but the transmitted radar beam and the reception-aiming can be extremely precise. The more elements you have, the narrower the beam but the higher the gain.
L-band, commonly used by companies like satellite TV providers, is 1 to 2 GHz. An array of 16 log-periodic (wideband) antenna elements would therefore be 60cm square. A 4-element array would be 30cm square. Pretty compact, and if it gets rid of the most common cause of poor signal strength (a poorly-aimed dish), it's a win.
Everybody gets what the majority deserves.
802.11n directionality is achieved by phase summing the signals from 2 or more dipoles.
Yawn.
Oh yeah the patent for 2 or more phase locked receivers on one chips is pretty old. So even getting it onto one chip is not new.
http://www.freepatentsonline.com/7636554.html
A MIMO radio transceiver to support processing of multiple signals for simultaneous transmission via corresponding ones of a plurality of antennas and to support receive processing of multiple signals detected by corresponding ones of the plurality of antennas. The radio transceiver provides, on a single semiconductor integrated circuit, a receiver circuit or path for each of a plurality of antennas and a transmit circuit or path for each of the plurality of antennas. Each receiver circuit downconverts the RF signal detected by its associated antenna to a baseband signal. Similarly, each transmit path upconverts a baseband signal to be transmitted by an assigned antenna.
Antenna elements in an array are usually about 1/2 wavelength apart. L-band, 1ghz to 2ghz, has a wavelength of 20 to 30cm. So... half that, assuming 1/2 wave separation.
Everybody gets what the majority deserves.
Forget about snow. A friend used to lose his TV signal about 45 minutes before it rained.
Lost at C:>. Found at C.
GP is correct - the dish size has all to do with the gain of the antenna, not the resonant frequency. The actual antenna is at the focal point of the dish and it's length IS frequency-critical. The surface area of the dish directly corresponds to its gain.
The reason we no longer use giant 6' dishes is twofold - because they are using 24 GHz instead of 5 GHz means the antenna at the focal point is much smaller, and the area of the dish is relatively the same size - with relationship to the wavelength - which is also much smaller.
The other reason is the peak power of, say the DirecTV sats, is as high as 150W for some transponders, whereas the older C-Band stuff was about 10W peak.
Dishes typically are designed to produce somewhere around 30dB of gain, which is 1000x magnification of the signal over a straight dipole with no reflector.
-- You are in a maze of little, twisty passages, all different... --
The amount of spectrum bandwidth required to transmit a few hundred audio channels is a fraction of what is needed to transmit a few hundred TV channels.
So given a constant amount of power available, the power spectral density when transmitting audio only is significantly higher than when transmitting television.
Also, Sirius uses satellites in Tundra or Molniya orbits (I don't remember which), which are geosynchronous, but not geostationary.
retrorocket.o not found, launch anyway?
Raw size does matter here. A larger receptor is better.
If you RTFA (yes I know it is Slashdot but hope springs eternal) you'll see that the system uses a GRID of flat antenna which it combines to simulate a larger antenna. By altering how the signals are combined i.e. the delays between them you can "point" the antenna at different sources. Hence you not only have a large detector from combining several smaller one but you can also point the thing without having to mechanically move it. It's brilliant idea and one that radio astronomers have been using for quite a while.
Your attribution of this effect is wrong.
The old 2m-3m satellite dishes were for receiving analogue signals. By going digital, it is far easier to detect and sufficiently correct for using a very weak signal. That gets the dish size down to about 1m. The other 50cm difference in size is due to the newer satellites using a higher power output.
www.wavefront-av.com
Have the wavelengths of the sat broadcasts changed?This about using a new type of antenna to handle an existing broadcast, not trying to receive a different signal, no? I suppose the old sats might use a different wavelength than say DirecTV sats I guess.
Yes, the old C-band has a much greater wavelength than the present Ku-band.
"The likes of Facebook and WhatsApp are free to those whose privacy is of zero value."
GP and YOU are mildly incorrect. WaveLength of the signal is impotant to the gain of the dish. a 5ghz signal has less gain on a 5 foot dish than a 20ghz signal does.
a 3 meter dish at 5 ghz has 21.704db of gain.
the same dish at 20 ghz has 54.415db of gain....
massively more gain on the same size of dish simply because of the frequency of the signal.
you also ignore that the LNA's used today are 20 times better than the ones from only 5 year ago.
The article states that this work is being done by a recent graduate in a PhD program. That doesn't make him a student. A young Ph.D. has developed a low power controller for a phased array radio receiver. This is a nice piece of kit with a range of applications in mobile devices. It builds upon technologies that have in the past been dominated by defense contractors. Our young Ph.D. is helping to make this technology more accessible to the 99% of the world who are not spooks. This is all good, even if it is not groundbreaking.
Think global, act loco
How long ago was that? Up until I got U-Verse I had been a Dish customer and I never lost signal even during hurricane Ike (I live in Houston). Well at least I didn't until the power went out. My next door neighbor lost her comcast cable about an hour after the storm hit and it was out for six weeks.
"A person is smart. People are dumb, panicky dangerous animals and you know it." - K
#2 is even bigger than huge, because it removes the need for geosync satellites, meaning someone could orbit some satellites at a much lower orbit and the phased array could track them in real time. That means much cheaper costs put your birds into low-earth orbit, much lower power the satellite has to put out and much higher frequencies available for signal density, and much lower latency. Screw TV, we're talking viable satellite telephone and low-latency satellite Internet access. Hell, you could launch a bunch of high-altitude drones powered by solar arrays and a phased array antenna would have no problems picking up the nearest dozen of them simultaneously.
Phased arrays are currently available, you can buy one today. They've been available to the consumer market for years. They do, however, draw some significant power and start in the thousand-dollar range. I suspect this is more about making them cheaper and less power-hungry. The beauty of cheap, low-power phased array is that you can orbit the cheaper satellites and still have affordable no-moving-parts antennas that can use them. Cell companies don't need to install hundreds of towers to blanket a state with signal, they can orbit some drones or put up a half-dozen LEO satellites and get the whole country at once.
"This post contains words, known to the State of California to cause thought. Wash brain thoroughly after reading."
"The actual antenna is at the focal point of the dish and it's length IS frequency-critical."
The dish is a simple parabola, it's focal point is not frequency dependent. Its gain IS frequency dependent however. Achieving the same gain at half the frequency requires double the dish size (or, double the frequency and you can halve the dish size for the same gain).
As long as the dish is smooth enough its focal point is not frequency dependent. At the extreme low end things fall apart (i.e. the dish becomes on the order of a wavelength in size).
No. An analog receiver could work with way worse signals. The image wouldn't be good but there would be an image, while the digital receiver would state something like: "no signal". Many a farmer in my area was appalled by that. As many educated people have stated: the frequency is the change that caused the dishes to be smaller.
Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
Yeah, I should be a well paid politician :)
"The likes of Facebook and WhatsApp are free to those whose privacy is of zero value."