The S band limits from 2 to 4 GHz, is part of the electromagnetic spectrum’s microwave band. It is used by radars, satellites and some communications. This paper is concerned with the theory and design of 3 GHz feedback type and negative resistance oscillators by using Aiglent ADS software simulator with GaAs ED02AH 0.2-μm technology, and comparison of their results. A lumped element resonator has used in the design of feedback type oscillator and a negative resistance oscillator has utilized a microstrip resonator. The negative resistance oscillator operates at 3.072 GHz with phase noise levels at -99.49 dBc/Hz and -119.6 dBc/Hz at 100KHz and 1 MHz offset frequencies respectively. The phase noise levels of feedback type oscillator are -83.30 dBc/Hz and -103.3 dBc/Hz at 100KHz and 1 MHz offset at oscillation frequency of 3 GHz. Furthermore, we compared the output power of these oscillators and negative resistance oscillator showed 7.124 dBm, and feedback type oscillator presented -10.707dBm.