The proposal presents a low space, weight and power (SWaP) and low cost chirped linear frequency-modulated continuous-wave (LFMCW) radar based UAS collision avoidance system. A novel radar structure is applied to make the system having enough working range and at the same time having high enough range and angle estimation accuracy. The smart antenna technique is applied, so one transmit can be used to search all interested angles with a gated range. The software defined radio (SDR) concept is applied to make the system having the plug and play capability. The system integrates a mixture of state-of-the-art modeling and algorithms, such as range gated chirp radar receiver, and a lot of mature techniques, such as smart antenna angle estimation, Fast Fourier transform (FFT) for target detection, Commercial off-the-shelf (COTS) parts, etc. This combination of the state-of-the-art techniques and mature techniques/devices greatly reduces the system implementation risk.