The Integra has what amounts to two internal antennas... one for GPS reception and one for 406Mhz transmission.
Note the internal 406 antenna is a BACKUP antenna ONLY. An external antenna must be installed in order to comply with the TSO approval of the unit. That external antenna must be one of the antennas listed in the Integra installation manual - no other substitutes are acceptable as they will invalidate the TSO approval.
The internal "backup" antenna is there for two reasons. Firstly, if your installation is compromised during the crash sequence causing loss of connection to the external antenna, the unit will sense this loss of connection and revert to using its internal antenna. Secondly, if one were to remove the ELT from the aircraft for some reason post-crash, the unit would be able to transmit using its internal antenna. This might come in handy in a situation where the aircraft is sinking in water or perhaps about to slide off a mountain precipice. Again, note the ELT will transmit on its internal antenna ONLY if no external antenna is detected.
As for its internal GPS, it uses a flat patch antenna mounted in the top surface of the unit under the manufacturer's label. Ideally this surface of the antenna would point upward and have clear visibility of the sky through an RF-transparent surface like a fiberglass fuselage or a polycarbonate canopy. Again, like any GPS, a view of the sky is necessary. The GPS only powers up AFTER the ELT is activated and is powered by the ELT's internal battery, not ship's power.
I hope this explanation provides a better understanding of how the unit works. I've installed an Integra in my own aircraft as well as Compact AF models in my other aircraft as well as those of several other owners. They have all been rock solid.