We propose a compact and multi-band reconfigurable antenna based  on the coplanar waveguide (CPW)-fed slot loop topology with two additional pairs of slot stubs close to the main slot in order to enable frequency reconfigurable as well as to achieve better bandwidth and  to reduce the antenna size. Among different slot stub pair designs, the horizontal one on the ground plane helps to reduce antenna size by 10%-26%, while conserving wide bandwidth. The slot stub pairs are short-circuited on the antenna, and a set of PIN diode switches is put on them. With two slot stub pairs on both the ground plane and the patch plane, the antenna can be configured to work individually at four bands GSM1900/UMTS/LTE/4G from 1.8GHz to 2.7GHz with the gain from 3.6dBi to 4.2dBi and the efficiency from 80% to 89%.              A good agreement between simulation and measurement is presented.

frequency reconfigurable antenna, slot loop antenna.