The dipole T antenna is designed and manufactured by BETAFPV for a 2.4G/915MHz/868MHz receiver. This antenna is omnidirectional. RF balun circuit comes with this dipole antenna, just inside the injected rubber enclosure. Every piece of the antenna is tested with the frequency spectrograph to make sure it works in the correct status.
Which antenna should I choose? Are these antennas compatible with other receivers like Frsky or TBS receivers?
First, it is compatible with any receiver with an IPEX MHF connector. Note that do NOT use the antenna with the wrong frequency. Even they look almost the same outside, but different balun circuit inside. It will have totally different performance in the wrong frequency point. Second, the shorter 915MHz/868MHz antenna is just made for small whoop drones. If you expect full-range performance, highly recommend the longer version.
The BETAFPV dipole T antenna is omnidirectional. Below is the antenna 3D radiation pattern image.
What is a Balun and why should we use it in these dipole T antennas? In order for these balanced antennas to be fed by coaxial cable, an antenna balun is often included at the feed point. For more details, please check this article "What is a Balun: RF Antenna Balun".
For the dipole T antenna, the balun circuit is in the injected rubber enclosure. For the different antennas, there is a related balun circuit.