Antenna Arrays Could Replace Satellite TV Dishes 183
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 Those have since been replaced by today's compact dishes, but now it looks like even those might be on the road to obsolescence.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."
Re:No (Score:3, Interesting)
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)
Re:Phased Array antennas (Score:3, Interesting)
Array info (Score:5, Interesting)
A collection of links on antenna arrays at a ham radio antenna design site: http://www.dxzone.com/catalog/Antennas/Array/ [dxzone.com]
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 [wikipedia.org], 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.
Got an 802.11n receiver?Then you have this at home (Score:3, Interesting)
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.
Power spectral density (Score:3, Interesting)
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.
Re:No (Score:3, Interesting)
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.
Re:No (Score:3, Interesting)
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.
Re:Why? (Score:2, Interesting)
#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.
Re:No (Score:1, Interesting)
It's not just the LNAs. It's also that we are no longer using separate LNA and LNCs. Less parts means less signal losses.
I can remember having to choose a feedhorn, then the LNA, then the optimal LNC and worrying about terrifying coax losses trying to get the signal received and down converted and in the house. Sure it worked but it could be interesting when it didn't.
Now, all of that is handled right in the LNB and the whole part is $40 new, or less at flea markets. This is the unsung innovation of DBS. Stuff that used to be close to home brew or at least contain a good deal of magic is now off the shelf and stuck on the sides of millions of homes.