My iPhone 5 connects to wifi but shows one bar on wifi signal meter but my iPad2 and Macbook Air both show full wifi bars when all three are side by side next to my apple router. have an antenna problem with my iPhone 5

It appears that my iPhone 5 has a wifi signal reception issue. I only show one bar on the wifi signal meter even when I an next to the router.  Both my Macbook Air and my iPad2 show full wifi signals at the same time.  Rebooting the Apple router and each device results in the same meter readings.