Improved electrically small antenna

Efficient, broadband ESAs capable of exceeding the gain-bandwidth performance restriction dictated by the Chu Limit

Communications Electronics

We are surrounded by tiny devices radiating or receiving RF signals with electrically small antennas (ESAs). Such devices are monitoring the environment, health, security, and other critical domains which impact our lives. But there are limitations to how small these devices can go and one such limitation is driven by the decreases in radiating efficiency and bandwidth as antennas get smaller. Antenna miniaturization is challenging.

Navy engineers have worked this problem and developed a novel ESA which exceeds the Chu Limit – a fundamental principle of electromagnetics which dictates that the bandwidth an antenna can function in has a maximum level proportional to the physical size of the antenna—the smaller the antenna, the smaller the bandwidth and the slower and less capable the communications link.

Measured bandwidth performance comparison of non-Foster integrated antenna vs. passive (conventional) antenna of the same physical size. Credit: Space and Naval Warfare Systems Center


The novel design comprises a driven element, an input feed, and a non-Foster circuit (in this case, a circuit with negative impedance). The input feed is coupled to the driven element and is configured to be connected to a receiver. Combining a non-Foster circuit with the antenna is the key to achieving the broader bandwidth without the prior loss of efficiency. While traditional passive impedance matching methods are limited by the Bode-Fano limit, non-Foster matching allows for the possibility of implementing negative reactances that are not bound by this limit.

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