In this paper, we study and evaluate shorted path and CPW-feed square slot antennas, both of which are the most suitable for use in inter pico satellite communications in terms of gain, bandwidth and size. We have simulated both antennas in the High Frequency Structure Simulator (HFSS). Our results shows that the shorted path antenna achieves higher gain; e.g., 4.8 dBi, wider impedance bandwidth; e.g., 3.9-11.1 GHz with Voltage Standing Wave Ratio (VSWR) <= 2 at resonance frequencies of 4.4, 6.9 and 10.1 GHz. In addition, the Quasi Newton method is used to shift the shorted path antenna's operating frequency to 2.45 GHz (S-band). This thus enables its use in the unlicensed ISM band without critically affecting its radiation performance. The simulated results show an impedance bandwidth of 3650 MHz (2.05-5.7 GHz) with VSWR <= 2 at a resonance frequency of 2.45 GHz.