UK TV is transmitted in a UHF band between 21 and 68. TV aerials are designed to receive certain bands. The bands are:

Group A - Channels 21-37
Group B - Channels 35-53
Group C/D - Channels 48-68
Group E - Channels 35-68
Group K - Channels 21-48
Group W - Channels 21-68
A Wideband aerial is optimised to receive TV channels anywhere in the UK TV band. In areas of weak signal, a wideband aerial may not be as effective as a high-gain aerial designed for the specific band you’re trying to receive (a mast-head amplifier may be needed to help boost the signal). If you’re looking to upgrade aerial, getting a good quality wideband aerial is usually the thing to do, so that if additional services (such as Freeview) appear elsewhere in the band, you’ll be able to get them.

High gain aerials can be used to reduce certain types of problem - including weak signal, interference and ghosting. They do this by getting the most out of the signal. For best results, high gain aerials aren’t wideband, and should be pointed directly at the target transmitter.