Flat Panel Antenna for C-band TVRO?

Anonymous Coward asks: "Does Slashdot know of any anyone who makes a flat panel antenna for C-band Satellite TV? The only makers of commercial flat panel antennas that I'm aware of is this one, but it's only KU-band."

Comments

Huge?

[BigZaphod]

Wouldn't a flat panel for C-Band need to be rather huge? I'm not that familiar with how that stuff works, but it seems there had to be a reason why the BUDs where, well, big.

Re:Huge?

[JCMay]

Yep. It'd be in the realm of the same size of a C-band dish, about ten feet across. I've seen Ku-band fixed beam arrays like the one mentioned, but I've not seen a C-band array like that.

hmm

[sn0wman3030]

I can tell this is going to be a popular thread.

Suggestion

[Anonymous Coward]

Have you tried contacting KU and the Sunshine C-Band?

One site

[Hungus]

One site shows pics and says they have at least prototyped a flat panel c-band antenna:
http://www.skygate.bg/skygate/Acivities/SampleProd ucts.htm They are a Bulgarian company with Dutch backing partnering with AlcaTel I might be a bit difficultto buy one from them however.

Re:One site

[khanyisa]

Another company to try would be OmniPless

Re:One site

[Isao]

FYI, that's not a C-Band antenna, that is a C-Band feedhorn (the part that goes at the focal point of a parabolic or spherical dish).

Build your own

[unitron]

About 20 years ago Radio-Electronics magazine had an article on building your own out of plywood. Really. It used concentric rectangles that worked as a sort of lens at those frequencies. Like microwave waveguides that somehow use empty spaces as antenna elements, the physics involved was way over my head.

Re:Build your own

[Anonymous Coward]

I think I remember reading about that. After cutting the plywood and painting it with aluminum paint, it would act as a giant microwave/radio fresnel lens. This lens would focus the signal on the feed horn placed behind the plywood, instead of in front, like with the big dishes.

This antenna with the lens and feed horn together aren't exactly flat and still take up the same or more space as a dish. I'm still looking for a true flat panel C-band antenna, mostly for watching NASA and TechTV.

Re:Build your own

[JCMay]

I saw something similar to this a few weeks ago at an Engineers' Week presentation. One company was showing their planar "parabolic" reflectors. It was basically a fixed-beam rectangular reflectarray that duplicated the funcionality of a parabolic dish. It would still need a feed at the focus of the reflectarray.

Re:Build your own

[Technician]

If you study microwave waveguides, they are not just empty space. They resemble twin lead transmission wire. How they get an insulator to seperate the two conductors is the hardest part for most people to understand, but in reality most waveguide is twinlead.

Here is how it works. The simplest model is square and the easiest to describe. The same rules apply to eliptical and circurlar. The center of two sides are the conductors. Believe me on that one. Now to insulate them from each other.. Take the conductors and mount them on a pair of 1/4 wave stand off's to ground. The stand off's are conductive. They have a voltage gradient from zero at ground up to the voltage at the conductor they support. A pair of conductors supported by back to back 1/4 wave stubs extended the length of the conductors becomes a waveguide. Two conductors oposite each other made of flat wire seperated by 1/2 wave (the two quarter wave) stubs that extend the entire length of the conductor. This closes the waveguide into it's rectangular shape. Due the skin effect and the influence of the magnatism from currents, the voltage is only on the inside of the waveguide. the outside can be grounded on all 4 sides. This provides 100% shielding of the twin lead transmission line (waveguide).

Knowing the theory doesn't explain the concentric rectangles working as a lens. Hmm I'm going to have to look that up.

Flat antenna's work by having lots of elements, then adding in a sum network all of the elements. Signals in phase add. Those out of phase cancel. Two types of antennas are popular at microwave frequencies. One is a slot antenna where slots are put in a waveguide so the openings are a wavelength apart. This antenna works well with high gain parallel to the face. The drawback is this is a strip antenna with a wide x and narrow y pattern. It is not a narrow beam antenna. To get a beam, many of these would havet to be placed side by side and phased to each other.

The other type of flat antenna is the phased array. This antenna is a flat antenna with lots of dipoles above the face of the array and summing network, or if made in a Printed Circuit Board, (common in pleasure boat radar's) in the plane of the summing network. With active components and more than one face, the phased array antenna is electricaly steerable. Nice if you need an antenna that can be pointed quickly without moving anything. Due to complexity, this type antenna is very expensive. Use may be military for instance to radar track a missle in real time.

Your best bet for a true C'band flat antenna would be to design a printed circuit board antenna. A good place to get ideas would be a service manual for a Ratheon Marine radar for small vessles. Design the phased array from a strip long and narrow (for radar) to a very large square array for C-band. Good luck.

Re:Build your own

[unitron]

If I hadn't already commented I'd mod you up, but then if I hadn't commented neither would you have and at this point my eyes are starting to glaze over all over again :-)

ok

[Monkelectric]

This sounds really cool but WTF does any of it mean? :) Please drop some knowledge on me

Re:ok

[brendan_orr]

Wiki-pedia: C-Band and KU-band.

Re:ok

[Monkelectric]

ok thats a start. What can you do with it? why do you want it? who uses it? Whats on these sat channels?

Re:ok

[Anonymous Coward]

I think what he means is:

C-Band, what's it all about, is it whack?

Re:ok

[N3Bruce]

C-Band operates in the 4.7 Ghz range, and predates current DSS systems, such as Direct TV et.al. It operates primarily in analog mode, with most of the channels of the newer systems, though sadly most commercial signals are scrambled these days. Most of the free stuff is things like religious broadcasters, HSN, QVC and their clones, public affairs stuff, and so on. Programming meant for other countries is sometimes not scrambled, and you sometimes find some interesting stuff. No it is not nearly as interesting as the days unscrambled wild feeds or even chipped videocipher units, but there is an occasional nugget out there for the C-band surfers.

C-Band signals with a good antenna look better than DSS because the signals are analog and operate on lower frequencies than the DSS Stuff. They suffer less from rain fade than the higher frequencies, and compression artifacts from the digital modes. My parents have a big dish I helped install in the late 80's. They retired to a rural area beyond the reach of cable and the nearest TV station was 75 miles away, so the big dish was really their only option then. It still looks great today, though if they had to start over from scratch they would opt for the small dish. They use a small dish for their motorhome when they travel, and a small dish for broadband internet.

That being said, the big dish's main drawbacks are its size, with 6 footers being the minimum to get a decent signal, and the fact that there are only 24 transponders on each satellite. This means that unless you want to install multiple dishes like the cable companies, you need a way to steer the dish, which adds a layer of complexity to the operation and maintenance of the dish.

Re:ok

[Anonymous Coward]

Nick is deadfly, forgot my password.

C Band is now mostly digital also. A couple of different formats which are really just variations of the same thing. DVB MPEG2 which comforms to the MPEG standard, and digicypher which is a variation on MPEG2 by Motorola.

There continue to be some analog feeds also which are either unscrambled or available by subscription with videocipher II. Most of the digicipher channels can be subscribed to, some of the DVB channels can also be subscribed to. You need a different receiver for DVB than for digicipher. Many DVB channels are not encrypted and free to view, some digicipher channels are not encrypted. The nice thing about C Band subscriptions has always been the packaging. If you only want HBO, that is all you have to buy.

C Band continues to be the state of the art as far as signal quality is concerned. Small dish systems generally compress their streams 2 to 3 times more than C Band feeds. This results in a picture that looks blurry. This also means less channels per satellite for C Band and the need to be able to rotate the dish. This kind of makes me wonder why anyone would want to build a flat C Band dish.

Re:ok

[N3Bruce]

Since I posted I can't moderate, but perhaps someone else can. Thanks for the updated information, I have an old C-band dish here that I was going to listen in on AO-40 with, but since it went Silent Key, perhaps I can find an alternate use for it.

Re:ok

[michael_cain]

The most interesting flat-panel antennas -- where the structure is literally a thin, flat panel rather than depending on a parabolic dish -- are phased-array designs. I always thought that phased arrays were a really neat concept. Explained badly, they consist of a collection of small individual antennas and the signal from each runs through a very precise time-delay element. By adjusting the delay elements, it is possible to use constructive interference to "point" the antenna in a particular direction. The result is a steerable antenna that has no moving parts. If I remember correctly, much of the original work in making them practical was paid for by the US Air Force -- because radar antennas with moving parts tended to freeze up badly in the Arctic. I believe that the big application in consumer electronics is going to be with Ka-band satellites. The FCC is going to allow those birds to be spaced much closer together than the older Ku-band satellites, and the stamped-metal dishes are not selective enough.

Real experts should chime in here and correct my errors.

Build your own-Baby got back.

[Anonymous Coward]

There's a type of antenna that allows you to put the feedhorn in the back of the antenna. Flat panels are great for mounting on roofs, or attics.

ok-Can you view me now? Good!

[Anonymous Coward]

"C-Band signals with a good antenna look better than DSS because the signals are analog and operate on lower frequencies than the DSS Stuff."

Agreed I have stuff that I taped from way back when and it still looks better than what cable delivers.

"This means that unless you want to install multiple dishes like the cable companies, you need a way to steer the dish, which adds a layer of complexity to the operation and maintenance of the dish."

A "complexity" that's been there from the get go. It's not as bad as you make it out to be. BTW Flat panels can be steered.

Re:Don't overlook Radio

[Technician]

Many of the offerings on C-band are not TV. They are many radio signals spaced through the 6 meg band of a transponder. The best way to get to these is to pick off the IF and tune it with a good scanner. Some signals are FM and some are single sideband. Look for weather fax and other non-TV signals. There is a bunch of scrambled narrow band stuff mixed in there also so don't worry if you don't understand why some things just don't tune in.

Another manufacturer to try for flat-panel C-Band

[fuzzy's_world]

Another place to try contacting for a *potential* flat-panel C-Band satellite panel is here. The Alien Works, Ltd. website is at Alien Works, Ltd. but it only has a PDF file that's been there for several years. I don't know if they'll ever have a commercial product, but it's worth a try. Also, for C-Band/TVRO satellite newbies, try reading the TVRO FAQ.

Re:Wiki-pedia

[fuzzy's_world]

Thanks for the props, brendan_orr! I wrote both of those articles (really).

Wikipedia is a good resource for all types of information, even on C-Band/TVRO.