Direct-Path Antenna Backscatter Antenna C-Band Receiver ADC Signal Generator (a) (b) Digital Log S1 Aux, Antenna, LNA, Filter Amplitude Demodulation S2 Dynamic Compression (c) CH1 LNA z TerraSAR-X Six-Channels Receiver System τstart R5 RT(τend) RT(τstart) R0 R1 R2 RRn(τ) Y Signal Detection PRF X Synchronization FPGA Module (d) Timing Data Recording Mixing A/D Band-Pass Filter Local Oscillator Mixing A/D Band-Pass Filter τend LNA CH2 S3 Comparator S4 Phase-Locked Loop (DPLL) DPLL S5 (e) FIGURE 4. (a) An SABRINA prototype deployed on the roof of a building at the Universitat Politècnica de Catalunya campus during an acquisition [41]. (b) A PAMIR antenna front end with three rows, each composed of three subapertures and an antenna configuration on top of the aircraft's fuselage [15]. (c) Phase synchronization using the direct satellite signal [15]. (d) Imaging geometry in a spaceborne/stationary bistatic DBF BiSAR configuration [18]. (e) One synchronization receiver and one echo receiver system [51]. ADC: analog-to-digital converter; Aux: auxiliary; LNA: low-noise amplifier; CH1: channel 1; CH2: channel 2; A/D: analog-to-digital; PRF: pulse-repetition frequency; FPGA: field-programmable gate array. 158 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE SEPTEMBER 2022 Velocity 270 m Ground Range