I don't know what the "x-wing" antenna is, but here is the most common UHF antenna for aviation comms in the US military:
Valcom Manufacturing Group Inc - Guelph - AS-390/SRC
For most people a Discone is probably the best choice since they are cheap. plentiful and work well, especially the AT-197.
A collinear as pictured above is only going to cover a small part of the 225-400MHz mil air band and there are not many sections in the one shown so the gain is not going to be much.
Hello everyone, I would like some advice about the UHF antennas for aircraft, you think it is better to use the x-wing or a collinear antenna ?
Most of the antennas these guys are telling you about are very expensive! You do not need to spend a lot of money on antennas for aircraft monitoring. In fact Radio Shack's Cat. No. 20-176, outdoor VHF-Hi/UHF antenna works great. It's only $28.99. Try it before you waste hundreds of dollars on anything else.
20-176
Outdoor VHF-Hi/UHF Scanner Antenna - RadioShack.com
Most of the antennas these guys are telling you about are very expensive! You do not need to spend a lot of money on antennas for aircraft monitoring. In fact Radio Shack's Cat. No. 20-176, outdoor VHF-Hi/UHF antenna works great. It's only $28.99. Try it before you waste hundreds of dollars on anything else.
20-176
Outdoor VHF-Hi/UHF Scanner Antenna - RadioShack.com