Frequency Behavior of a Resonant Shielded Loop With a Variable Gap Position

Size and bandwidth are among the most common tradeoffs in antenna design. Electrically small antennas (ESAs) suffer from low radiation resistance, high reactance, and typically narrow bandwidths. Resonant antennas offer a higher radiation resistance lower and input reactance than ESAs at the cost of a larger footprint. Shielded loops offer a compromise between bandwidth and size. We observed that S<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> is minimum when the electrical length between the gap and the short from inner to outer conductor is λ/4. The frequency behavior depends on this gap position rather than the overall loop radius.