Design and implementation of ultra-wideband receivers are critical in Electronic Warfare (EW) systems. In this work, we propose a new multi-resolution, multi-rate, direct RF sub-Nyquist sampling ultra-wideband Electronic Support Measures (ESM) receiver architecture. Multiple ADCs operating at different sampling rates are used for unambiguously resolving 9 GHz bandwidth. Multiple time and frequency resolutions are achieved by computing multiple FFTs with different lengths. The receiver is based on direct RF signal sampling, hence it has a simple hardware implementation. The proposed receiver has 9 GHz instantaneous bandwidth, and its instantaneous dynamic range is over 50 dB along this band. The total data rate is only 4.77 GHz, which is around one quarter of the theoretical 18 GHz Nyquist limit. Collected measurements from the implemented receiver hardware are presented in detail.