Indoor Antennas are usually simple half-wave dipole antennas for VHF or UHF loop antennas used for television (and VHF radio). These are often called ‘rabbit ears’ or ‘bunny aerials’ because of their shape. The length of the telescopic ‘ears’ can be self adjusted and should be about half of the wavelength of the signal for the desired channel.
These are not as efficient as an aerial rooftop antennas since they are less directional and rarely adjusted to the proper length for the desired channel. Dipole antennas are bi-directional (receive signals evenly forward and backwards) and also cover a broader band than antennas with more elements. This makes them less efficient than antennas designed to maximize the signal from a narrower angle in one direction.
Indoor antennas which are usually poorly placed, closer to the ground are worse than multi-element rooftop antennas at receiving signals which are not very strong. These simple antennas are called set-top antennas because they were often placed on top of the television set or receiver.
The actual length of the antenna ears is optimally about 91% of half the wavelength of the desired channel in free space. Quarter-wave television antennas are also used. These use a single element, and use the earth as a ground plane and therefore no ground is required in the feed line.
Soon after television broadcasting switched from analog to digital broadcasting, indoor antennas have evolved beyond the traditional ‘rabbit ears’ to more advanced antennas such as the flat antenna which are very lightweight, thin and square-shaped. They connect to televisions or to digital converter boxes with a single coax cable and may come with a signal amplifier. The amplifier needs to be plugged into a power source however the flat antenna itself does not require a power source to function.