This paper proposes a multiband microstrip antenna with modified pi-shape slot cut on the ground plane for wireless applications. Complete modal analysis and design process of the proposed antenna is demonstrated explaining the modes contributing to achieve the bands. By placing the modified pi-slot in the appropriate position on the ground plane, it tunes TM10, TM12, TM02 and TM20 and TM22 mode frequencies with respect to the fundamental mode frequency and thus realizes four band response which includes one broadband response having 164 MHz (6.5%) bandwidth. The bandwidth in the other bands are in the range of 6 MHz - 30 MHz. The surface currents at these modes are also altered to yield broadside radiation pattern. Suspended version of this antenna is also proposed that offers triple bands and improved broadside gain of around 4 dBi at the broadband besides 2.5 dBi and 1 dBi gain at other two modes. The proposed antenna saves 56% area with respect to the equivalent un-slotted microstrip antenna.