Vivaldi antenna is a main candidate for phased array antenna. This paper presents the design, testing and measurement of tapered slot antenna with strip line feed which works at X-band frequency. Methods/Statistical analysis: The design of Vivaldi Tapered Slot Antenna (VTSA) and the results of radiation patterns and return loss are obtained through the use of electromagnetic simulation software HFSS. Further, testing and measurement of fabricated Vivaldi antenna using Vector Network Analyzer and radiation patterns are observed in Anechoic Chamber. Findings: The designed VTSA satisfies the requirements on the maximum reflection coefficient which is less than -10dB. The half power beam width of 120o in H-plane and 110o in E-plane with gain of 3-dB for single element is obtained, and satisfies the requirements of Voltage Standing Wave Ratio < 2 for X-band frequency. The S-parameter, radiation characteristics, and gain simulations for the VTSA are given to verify the design concepts. The measured beam width around 90o is achieved in vertical polarization at X-band frequency. Design of linear array of 7-elements is presented and simulated return loss for center element is achieved less than -10dB including mutual coupling effects. The good radiation characteristics are obtained with gain 9.2 dB for linear array. In this work a Vivaldi notch antenna element is fed by Stripline and may be coupled electromagnetically by tapered transitions. The simulated and fabricated results are in good agreement. Application/ Improvements: The results established that the designed Vivaldi Tapered Slot Antenna is a suitable candidate for X-band active phased array for airborne radar applications.