Symmetry-breaking antenna opens up design options

June 02, 2016 // By Bill Schweber
Antenna plot
Bill Schweber discusses how some assumptions are "baked in" to design methods and tools and what happens when innovators are able to change things with a breakthrough.

One of the first lessons we learn about antennas is that they have reciprocity, meaning that their "transmit" field-radiation pattern is identical to their "receive" pattern. In most situations, this symmetry is a good thing, such as when a handset is linked to a base station, since you want the patterns and paths to be the same in both transmit and receive modes. Still, there are times when it might be nice to have different patterns for the two modes, as way of minimizing interference, masking an antenna's location, or implementing a clever mesh-network topology.

But the reciprocity situation may have a new development that is intriguing.

While not the first non-reciprocal RF device, a team at the University of Texas at Austin has developed what appears to be a more practical antenna which implements non-symmetry, Figure 1 . I won't summarize what they did and how they did it, as you can read your choice of the dense, hard-to-follow, jargon-laden academic abstract from the Proceedings of the National Academy of Sciences , " Breaking temporal symmetries for emission and absorption ," the well-written university press release " UT Austin Engineers Design Next-Generation Non-Reciprocal Antenna ," or the longer but very readable and clear article in Physics Today , " A nonreciprocal antenna speaks without listening " (the latter is well worth the few extra minutes).

The normalized transmission and reception patterns, as a function of direction, for (a) the unmodulated antenna and (b) the antenna with the 600-MHz modulation. Source: Physics Today.

Assuming what these researchers have done is viable (I am in no position to judge it), I was trying to think how that would affect design fundamentals and underlying assumptions. The reality is that every design begins with a set of assumptions – whether consciously articulated or not – that are then "built in" to the resultant topology as well as subsequent design decisions and tradeoffs.