I grew up with the fundamental axiom that if you needed a better antenna, you had to put more metal into the air. The performance of recently announced super-small antennas upsets my intuitive sense of the entire electromagnetic (EM) field and its The recent news item about a tiny 2.4 GHz antenna, just 3.7 x 2 mm, from Fractus S.A. (“Startup makes antenna the size of a rice grain”, click here) got my attention.
I've always been interested in antennas, and grew up with the fundamental axiom that if you needed a better antenna, you had to put more metal into the air, it was that simple The extremely small antennas, such as the Fractus unit, really throw my long-hold belief out the window, so to speak.
I am not new to small antennas; I wrote a technical article on them for EETimes (“Small antennas, big gains”, October 23, 2006, click here). Nor do I doubt the Fractus claims, for two reasons. First, they are an established supplier with a solid track record and they have delivered units in large volume. Second, an antenna's basic performance is relatively easy to assess, and if their unit falls short, we'll hear about it very soon. It's not like benchmarking a processor, where you can have complicated and legitimate arguments about the benchmark test suites used, coding efficiency, and other variable factors.
Still, the performance of these super-small antennas upsets my intuitive sense of the entire electromagnetic (EM) field and its interaction with the antenna. I always viewed an antenna in a receiver as a sort of lens, designed to intercept, capture, and focus as much of the EM field energy as possible to the receiver's front end. When transmitting, the antenna also acts as a dispersing lens, by directing the output energy with a desired propagation pattern.
I can intuitively and internally understand how a tiny antenna can work in transmit mode, since the RF amplifier's output will be focused and broadcast by the small device, assuming it is a properly designed as a EM launcher. But I still can't “feel”, in my gut, how a tiny antenna can intercept enough RF energy to be effective. At the same time, the antenna reciprocity principle (click here) that is a key to antenna design must certainly apply, right?
So I'm perplexed. On one hand, these tiny antennas apparently do provide reasonably good performance despite their diminutive size. On the other hand, I just can't see how they can possibly work well at all for receiving mode. And on that proverbial third hand, there's that reciprocity principle which is a well-established key to antenna design. Oh, how my head does hurt!