SIM300D provide RF antenna interface . And customer’s antenna should be located in the customer’s mainboard and connect to module’s antenna pad through microstrip line or other type RF trace but the impendence must be controlled in 50?. To help you to ground the antenna, SIM300D comes with a grounding plane located close to the antenna pad. The antenna pad of SIM300D is shown as figure 25(right):
А мне так вообще нужно чтобы два модуля на одну антенну работали - можно на плате извратиться... Зато корпус удобнее.