In contrary to WLAN with Mobile networks it's more difficult. Let's do it step by step:

1. In which country do you use OWL? And which provider do you use? - Depending on country and provider the frequency range(s) might differ.
2. Which OWL do/will you use? OWL-3G demands UMTS antenna(s). OWL-LTE - obviously - might use LTE antennas depending on your demand.
   Usually antennas support one or more frequency range(s). The frequency range your provider offers must fit to your antenna. In case you use 2 different providers be aware that they might use different ranges.
   Keep in mind that using OWL-LTE it offers a fall-back to UMTS or even 2G in case of LTE is down. The UMTS frequency range might be different than the LTE frequency range. If you need this fall-back, then the antenna need to support both ranges.

The rest is comparable to WLAN antenna:

1. Where do you use the antenna? Indoor or outdoor with demand for a specific IP protection and temperature range?
2. Which radiation characteristic do you want? Omnidirectional or directional?

What else to care for?

1. Antenna connection is SMA. This is different to WLAN/BAT. Make sure you select the right connector or you need an adapter.
2. How shall the antenna be mounted?

With all these answers you now can buy the right antenna.
Does Hirschmann offers antennas or recommends an antenna manufacturer? - Currently neither of both. We recommend to buy the antenna at the next electronics shop available or at the Hirschmann partner you trust according to your demands.