Yes you can leave out a connector and will just act as a regular 2 antenna 2x2 card without issues. Some general info, hopefully I'm not too confusing: Each connection for an antenna is for a single stream. 2x2 (2 in x 2 out) cards generally only have 2 connectors. 3x3 cards like your new one will have 3, it's just a rebranded Broadcom card. There are some weird ones like 2x3, 3x2 where you have 3 antennas but less active streams in one direction either uplink or downlink. A great example is the 2nd gen or 3rd gen Chromecast which is a MiSo WiFi device 2x1, 2 physical antennas but only 1 upstream connection. Its upstream switches to the best antenna depending on positioning for upstream. Also 1x1 cards like Intel's 3165 and other have 2 connectors as the single up and down streams can switch between either antenna for optimal connectivity. So basically the extra antenna is still useful for antenna diversity. Another great example of less streams and more antennas is the Linksys WRT1900AC series routers. They are 3x3 units but have 4 antennas basically any antenna can be used but only 3 used at any time. This allows the 3 streams to optimally use any combination antennas to better connect to clients at various angles.