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 Those have since been replaced by today's compact dishes, but now it looks like even those might be on the road to obsolescence.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."

Comments

Where's the problem?

[operagost]

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.

Re:Where's the problem?

[natehoy]

The problem is that the dish weighs 25 pounds, offers significant wind resistance, cannot be used while the vehicle is in motion, needs to be aimed at a satellite each time the RV is moved, and depends on geosynchronous satellites or continuous aiming with a servomotor. It's also ugly, but that's an aesthetic problem, not a practical one.

The advantage of phased array systems like this would be that you don't need to deploy and aim the dish once you reach your destination. You simply turn the system on, and the handful of flat metal pads glued directly to the roof of your RV (plus possibly a couple or three on each side if you're in high latitudes) can pick up the signal without moving anything around. The pads can be utterly unobtrusive, installed permanently, and offer no wind resistance at all.

There are no moving parts because the array is "aimed" only in a virtual sense by software. You'll still need a good bit of surface area to pick up a useful signal, but that surface area can be flat and spread over a larger area in smaller bits (you don't need one big contiguous dish, just a few squares or rectangles of surface area). It can even track a moving satellite and keep it in view (or track a moving or geosync sat while you are driving down the road).

No wind resistance when driving, no moving parts to wear out or replace. Just a few metal bits glued flat to the roof, wired to a computer that compensates for the time difference between the various signals. You could get signal from multiple satellites in different parts of the sky simultaneously, or based on which one happens to be in the clearest view at the moment, without carrying around a sky chart and signal meter or depending on a complex array of servos to do it for you.

Phased arrays are not new. It just takes a lot of number-crunching and a lot of power, which up until now has been accomplished more cheaply by hammering out a parabolic dish and aiming at a stationary target, saving all that number-crunching.

This guy's algorithm and chip design may (or may not) make it cheap enough to be practical for routine use.

It will still work

[GungaDan]

if you connect it with Monster cables.

Phased Array antennas

[Bruce Perens]

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.

Re:Why?

[Nyeerrmm]

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.

Array info

[Caerdwyn]

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.

Re:No

[Mister Transistor]

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.

Re:No

[Anonymous Coward]

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.