Batboard

http://campustechnology.com/articles/20 ... garea=news

http://ieeexplore.ieee.org/xpl/login.js ... er=6887369

Summary:
Researchers have found a way to make a component that will allow RF to pass in one direction unchanged, but cause RF passing the other direction to be shifted in frequency. Thus, a system can transmit on one frequency while being able to listen on the same frequency over-the-air, by having the incoming frequency mixed to a new frequency in the device.

So, in theory you could transmit on 146.52 while somebody else is also transmitting on 146.52, and hear them by tuning to 10.7MHz.

Interesting concept. It's difficult to conceive how a very low level signal on the same freq could pass without being swamped by the much stronger transmitter. But, apparently that is the promise of TVTL (time variable transmission line). Here is a link to Mr. Qin's paper where he states he achieved 13db of isolation between tx and rx with less than 5db insertion loss on the rx path.

How could such a device differentiate between the inevitable reflected signal, not only internal to the antenna but also reflections of the transmitted signal from other nearby objects which are many tens of db higher than the desired signal?

It looks to me like a more compact version of a circulator, but the shifting to a different frequency seemed to be accomplished by a mixer after the fact, which you could also do with a circulator.

I suspect that it is an over-enthusiastic appraisal of the device's capability, but a compact ciculator certainly has promise as well....

Apparently, it's a race to the market with innovative ways to reduce the size of circulators. The brain trust at University of Texas Austin have developed a tunable circulator.