Is it possible to improve the antenna on a 5s?

I travel, widely in remote areas, in Australia in a truck. Telephone signal is often border-line or non-existent, and I frequently drive some distance to get a connection. Earlier iPhones had the capacity to be hard-wired into a high gain, external antenna, via their USB to iPhone connector. This would usually result in a gain of one, sometimes two, extra ‘bars’. To my dismay, though, the new Lightning connector does not allow this, and using the cradle with an external antenna (Bury System 8 car kit which employs a useless, passive connection), actually leads to a drop in performance. In short, I upgraded my phone, and my car-kit, and a marked drop in performance was the result.

I am hoping, that there will eventually be a solution, as I do not want to interrupt my long term association with Apple products but as it stands there is a better option available to me.

Bury have informed me that the metal bands surrounding the iPhone constitute the antenna in the current models, and the phone switches from upper to lower antenna depending on whether it senses a lightning connector. I’m hoping that somebody will come up with a method of physically connecting an external antenna to it but so far there doesn't seem to be an option. The passive connection is worse than uselss because the car kit is mounted up under the roof restricting the signal further.

Thanks in anticipation.