In 2023. the Chinese company PIESAT launched the multi-static X-band SAR constellation Hongtu-1 (HT1). HT1 consists of the active monostatic SAR sensor HT1-A and the three additional passive SAR receivers HT1-B. HT1-C and HT1-D. https://www.petsafewirelessfence.com/product-category/cd/