On 30/09/2008, Andreas <awnd329@...
> --- In firstname.lastname@example.org, "Ian Woollard"
> <ian.woollard@...> wrote:
>> No, no. These are carefully worked estimates.
> Maybe carefully worked, but also very optimistic. None of the
> component efficiencies are worse than 88%.
> Klystrons currently available have around 60%, but are not
> phase-stable enough. TWT amplifiers are also very efficient, generally
> 60%. There are rumours of devices reaching up to 80%, but I have not
> found concrete examples.
You don't necessarily need high power, modern silicon is now up to gigahertz speeds anyway, this bit is if anything getting easier. Some designs just stick the transmitter on the back of the solar panels and uses low power phased array techniques. I think the main challenges are in the spectral purity.
I forget what the record link efficiency was. It was around 40-50%, and I don't think they were trying all that hard for maximum efficiency. It was only over a few miles, but the beam physics for longer distances is extremely well understood.
> And that is only one of the components. I am particularly intrigued
> about how they plan to capture 88% of the beam, what with side-lobes
> caused by imperfect phase or geometry which will send part of the
> power into empty space. A large part, if everything is not absolutely
> perfect. And the 88% also includes RF capture by the rectenna, which
> is equally hard. The rectenna must neither reflect nor transmit more
> than 12% of the power that hits it, much less if not all power hits
> it. That sounds hard to me.
Nah, not particularly. The wavelength is order centimetres, getting the waves lined up to that kind of accuracy is not difficult. There's also a concept of a pilot wave system where it transmits a beacon and you adjust your phase to aim for that. You essentially can't miss with those kinds of systems.
> There is not a Klystron or other microwave source currently available
> better than 50-60%, AFAIK.
Dunno, it's not an area of electronics I've looked at too hard. You have to credit the US DOE authors with some degree of technical skill though.
We live in an imperfectly imperfect world. Life in a perfectly imperfect world would be much better.