The XM from FrSky is a single 2.4GHz antenna chip in their new line of micro receivers. Supporting 16 channels over S-Bus compatible with D16 mode. This product is perfect for those micro-builds weighing in at just 1g and measuring 15 x 10 mm. Even with that compact size the operating range still comes in at >600m.
Also see the XM+ which is slightly larger but includes a diversity antenna setup for full range.