What happens when the resonant frequency of an antenna is increased?

When the resonant frequency of an antenna is increased, the antenna must become shorter. This relationship stems from the fundamental principle that the length of an antenna is inversely related to its resonant frequency. Specifically, the resonant frequency of an antenna is determined by its physical dimensions; longer antennas resonate at lower frequencies, while shorter antennas resonate at higher frequencies.

As the frequency increases, the wavelength of the radio waves that the antenna is designed to transmit or receive decreases. To effectively couple with these higher frequencies, the antenna must therefore be shortened to match this new wavelength. This shortening is key to achieving resonance, which allows the antenna to efficiently radiate and receive signals at the designated frequency.

The other choices touch upon aspects of antenna behavior, but they do not correctly address the relationship between resonant frequency and antenna size. For instance, although an increase in frequency might affect the radiation pattern and gain, it does not directly lead to the antenna becoming larger or cause a reduction in gain when the antenna is properly tuned to the new resonant frequency.