What type of antenna does the transponder use to transmit a coded reply?

The transponder uses an omnidirectional antenna to transmit a coded reply, which allows it to send signals in all directions equally. This type of antenna is particularly advantageous for transponder systems, as it ensures that the coded replies can be received by a variety of receiving stations located in different orientations and distances from the transponder.

Omnidirectional antennas are essential in applications where the direction of the incoming signal cannot be predicted, thereby increasing the chances of successful communication. It enhances the versatility of the transponder, making it effective in dynamic environments where the position of communication devices may change.

In contrast, unidirectional and directional antennas focus their signal in a specific direction, which would limit the range of the signal and potentially cause issues with reception if the receiving devices are not positioned correctly. A specific type called a coded reply antenna does not exist as defined; thus, it does not apply in this context. The nature of the transponder's operation aligns perfectly with the characteristics of omnidirectional antennas for effective and reliable communication.