Helical Antenna
A helical antenna is a quarter-wave structure physically shortened by winding the conductor into a coil. It provides the same electrical length in a much smaller volume, at the cost of low efficiency and narrow bandwidth. A hand, a body or a metal surface nearby easily shifts its tuning.
Shortening lowers the radiation resistance and increases the share of the loss resistance; the result is typically a few dB of disadvantage compared with a full-size wire antenna at the same frequency. Remembering the 6 dB rule, this is a difference that reflects directly on range.
- Narrow band: the resonance peak is sharp, and a small shift degrades the SWR noticeably.
- Near-field sensitivity: taking the antenna into the palm or leaning it against metal shifts its tuning.
- Its advantage is mechanical: short, durable, low risk of being snagged and broken; a practical choice for handheld remote controls.
That is why helical antennas are common in handheld remotes; the few dB lost are accepted in return for mechanical durability. On the receiver side, where there is no mechanical constraint, taking a full-size antenna to an open position is the better decision. The simplest improvement on the operator side is holding the remote control so that the antenna is not gripped.
Context where this term is used: 433 MHz or 2.4 GHz?