In this article, effects of negative capacitor loading on the bandwidth (BW) and efficiency of a rectangular microstrip antenna (RMSA) have been investigated. The active negative capacitor is made of a field-effect transistor that exhibits negative resistance as well as capacitance. It can, therefore, compensate the loss of an inductor having antenna. A single negative-capacitor-loaded RMSA gives broadband frequency operation with broadband radiation. A nucrostrip patch operating at 10.5 GHz having 12.22% BW has been utilized as a reference antenna. Theoretical results for the impedance and the radiation patterns have been presented. It is also shown that the impedance BW of the antenna has been enhanced by using active negative capacitance networks front 12.22% to 16.96%, respectively. In addition, it has been shown that active compensation significantly improves the radiation pattern.