The Built-In Self-Test for Simultaneous Transmit and Receive (BIST for STAR) will be able to solve the challenges of transmitting and receiving at the same time at the same frequency. One of the major components is the STAR antenna which transmits and receives along the same pathway. The main problem with doing both on the same path is that the transmit signal is usually much stronger in power compared to the received signal. The transmit signal has echoes and leakages that cause self-interference, preventing the received signal from being properly obtained. The solution developed in this project is the BIST component, which will help calculate the functional gain and phase offset of the interference signal and subtract it from the pathway so that the received signal remains. The functions of the proposed circuit board can be modeled in Matlab, where an emulation code generates a random, realistic functional gain and delay for the interference. From the generated values, the BIST for STAR was simulated to output what the measurements would be given the strength of the input signal and a controlled delay. The original Matlab code models an ideal environment directly recalculating the functional gain and phase from the given measurements in a second Matlab script. The actual product will not be ideal; a possible source of error to be considered is the effect of thermal noise. To observe the effect of noise on the BIST for STAR's performance, the Matlab code was expanded upon to include a component for thermal noise, and a method of analyzing the results of the board.