This is one rare information about the Samsung Galaxy A5 that you can search on Google. Information about it's internal antenna location is quite obsolete. Fortunately this site and the Russian Samsung manual guide has the information although not in English but it's pretty obvious where the internal antenna of the Samsung Galaxy A5 is. The article is found here in Russian Samsung Galaxy A5 antenna.
There are 3 types of Antenna
1. GPS Antenna - for GPS signal reception
2. NFC antenna - Near Field Communication antenna for short range communication with other electronic devices.
3. Main Antenna - This is the internal main antenna responsible for the GSM, WCDMA, and 4G LTE signal reception.