Cisco Wireless :: 1230AG Is There A Good Antenna Which Will Do Both Floors

I have a small building which has two levels. I have a 1230 on the top floor and about 10 people. Below that floor is another office with 10 people. They don't all use wireless, infact its only used for guests and smartphones, tablets of which there aren't many.I was wondering instead of sticking another unit in the downstairs office, Can I either use two anntenna's, one on each floor connected to the one controller or is there a good antenna which will do both floors?The floor is concrete, I have one antenna attached to the right hand connector of the 1230 and can get 2 or 3 bars in the lower office. Thou as its a flat antenna this doesn't cover the part of the office directly beneath it.