please suggest some ideas for mounting tv on plywood . I need to do clamp the lcd tv on the window. So i think it's better to cover the window using plywood first. After mount the tv on plywood . Is that good ? is there any suggestion, is there any other designs ?
Why don't you consider a free-standing TV stand, similar to this? This would easily handle a large LED TV up to at least 50", is easy to move and doesn't require covering your window.
Covering the entire window with plywood then mounting an LED TV on it, and having it look good, will take some doing. I would think that you'd want to screw 3/4" plywood into the window frame (the studs/cripple studs, ledger and header under the drywall), sand it well, put some kind of attractive edging or molding around it and paint it. If you're going to hang a TV of any size on it, I wouldn't go thinner than 3/4". Or if you do go thinner (like 1/2"), I'd probably put a cripple stud centered in the window to brace it. To secure that, I'd put a block on the bottom and top sill, screwed into the window frame, then I'd screw the cripple stud sideways into the blocks. Then I'd screw the plywood to the cripple stud as well as all around the window frame.
Use screws for everything you attach, don't use nails anywhere.
If you do all that, then you should have a solid base, and you would just use a standard LED TV mounting bracket screwed straight into the plywood with substantial screws (here again, using 3/4" instead of 1/2" plywood helps you).
Something along these lines:
I presume you're doing this to mount a larger LED TV. Most of the articulating-arm style of mounts are for smaller TV's and monitors, although there are some that are designed for larger panels, similar to the pictures below. Of the two, I'd probably prefer the first example. But do note that the second example has a deceptively large mounting plate, with holes in a much bigger pattern than the standard 75mm and 100mm pattern you see on smaller mounts.
Also keep in mind, though, that with these types of mounts, all the weight of the panel is concentrated on a much smaller mounting surface and it has to be mounted very securely to a strong surface. The top screw(s) in the base, in particular, will be bearing the lion's share of the weight, and if you pull the TV out from the wall the force on that top screw(s) will be magnified. So if you do this, center the mount directly on the cripple stud that you positioned inside the window frame, and using nice long screws (2.5" to 3") to secure the mount.
I would strongly advise against trying to make an ad hoc mounting for a TV. Its a lot harder than you might think. Use a production mounting arm of some type. A typical example shown below:
If you screw it into the window frame it will probably hold.