This article presents a T-Shaped Tri-Band (TSTB) antenna based on the Characteristic Mode Analysis (CMA) for satellite applications. Tri-band characteristics are achieved by exciting two orthogonal radiating modes for the L5-band and L1-bands, and one higher order radiating mode for the S-band. Initially, cavity model theory is applied to a rectangular antenna to calculate orthogonal modes (T M z 010 & T M z 001 ) at L5-band and S-bands, and these modes are validated using the CMA method. With the help of surface current study and modification of a rectangular antenna, the one higher order radiating mode and orthogonal modes are excited by using the CMA method. All desirable radiating modes are excited by a single coaxial feed line in full-wave simulation, which is based on FIT (Finite Integration Technique). The proposed antenna's measured operating frequencies are 1575 MHz (L1-band) for GPS (Global Positioning System) system, 1174 MHz (L5-band), and 2495 MHz (S-band) for IRNSS (Indian Regional Navigation Satellite System