Spaceborne Synthetic Aperture Radar (SAR) represents the core aerospace payload with all-time and all-weather Earth observation capabilities, widely applied in land resource survey, marine environmental monitoring, disaster emergency response, military reconnaissance and other fields. It has become the standard key payload for low-orbit remote sensing satellites and high-orbit Earth observation satellites. The high-voltage modulation power supply acts as the critical power component of spaceborne SAR systems, providing high-amplitude, narrow-pulse and high-stability high-voltage pulse output for microwave power devices such as Traveling Wave Tubes (TWT) and klystron amplifiers. It directly determines the transmitting power, pulse waveform quality, range resolution and imaging clarity of SAR systems, serving as the energy core of the entire SAR platform. Spaceborne SAR imposes extremely stringent technical requirements distinct from conventional aerospace power supplies: 1.Narrow-pulse & high-amplitude output: Thousands to tens of kilovolts of high-voltage pulses with pulse width ranging from hundreds of nanoseconds to several microseconds; rising/falling edges controlled within tens of nanoseconds and pulse top droop lower than 1%. Traditional pulse power supplies fail to achieve nanosecond edge control and ultra-low droop due to topological limitations and parasitic parameters. 2.High repetition frequency & wide duty-cycle adjustability: Pulse repetition frequency continuously adjustable from hundreds of Hertz to tens of kilohertz with a 0.1%–10% duty-cycle range, maintaining consistent pulse waveform across full operating conditions; conventional designs suffer waveform distortion and uneven heat generation under wide duty cycles. 3.Aerospace-grade miniaturization, lightweight design & high reliability: Strict volume and weight constraints with power density ≥200 W/in³; capable of adapting to extreme space environments including high vacuum, wide temperature ranges and high-energy particle radiation; on-orbit design life reaches 5–8 years. 4.Ultra-low electromagnetic interference: As a highly sensitive microwave receiving system, SAR is vulnerable to switching noise and electromagnetic radiation from power supplies, which degrade signal-to-noise ratio and imaging quality; excellent EMC performance and ultra-low noise output are mandatory. This methodology establishes a full-process universal technical framework covering topological design, narrow-pulse waveform optimization, high-stability control, aerospace environmental adaptability and EMC enhancement, fully matching the high-voltage power demands of various spaceborne SAR systems and providing standardized design criteria for domestic localization and performance upgrading of core SAR payloads. Targeting the core challenges of narrow pulses, high amplitude, fast edges and low droop, the all-solid-state Marx generator is adopted as the main topology, combined with nanosecond synchronous drive control and low-parasitic layout, breaking the bottlenecks of traditional linear modulators and rigid switch modulators. The Marx topology eliminates high-voltage pulse transformers; high-amplitude pulses are generated by series charging and parallel discharging of multi-stage low-voltage energy storage capacitors, removing waveform distortion caused by transformer leakage inductance and distributed capacitance. It supports nanosecond edge regulation and flexible pulse parameter tuning for SAR narrow-pulse wide-range operation. Five core design principles are specified: 1.Gallium Nitride (GaN) HEMT wide-bandgap semiconductor power switches replace traditional Si/SiC MOSFETs, featuring faster switching speed, lower loss and smaller parasitic capacitance with rise time within 10 ns. Multi-series architecture reduces voltage stress of each stage to 1/N of total output voltage. 2.High-frequency thin-film capacitors with ultra-low ESR and parasitic inductance are adopted for energy storage; self-resonant frequency far exceeds pulse spectrum limits to suppress voltage droop during nanosecond discharge. Symmetrical circuit layout ensures consistent switching and discharging characteristics across all stages. 3.Constant-current charging topology with isolated DC-DC converters guarantees uniform charging voltage for each capacitor under variable repetition frequencies and duty cycles; closed-loop voltage control compensates temperature drift and component aging. 4.Low-impedance stacked busbar design restricts total discharge loop parasitic inductance within 1 nH, optimizing edge steepness and eliminating overshoot/ringing. Impedance matching at high-voltage terminals suppresses pulse reflection. 5.Modular architecture enables flexible amplitude adjustment via stage number configuration and power expansion through parallel connection, adapting to multi-band multi-power SAR systems while improving manufacturability and maintainability for aerospace projects. Narrow-pulse waveform optimization is the core of this methodology: Nanosecond synchronous drive control adopts FPGA-based fully digital control with ≥100 MHz high-precision crystal oscillators and timing synchronization accuracy ≤5 ns. Isolated optical/magnetic drive eliminates high-low voltage crosstalk; gate resistance optimization balances switching speed and surge suppression. Low-parasitic loop design utilizes 3D stacked busbars with reverse current cancellation to minimize inductance; symmetrical component layout ensures uniform discharge impedance; terminal impedance matching eliminates waveform reflection. Active waveform compensation integrates real-time droop correction via FPGA dynamic timing adjustment and auxiliary compensation current, limiting pulse top droop within 0.5%. Active clamping restricts overshoot below 0.5%; fast discharge circuits eliminate pulse tailing to prevent SAR spectrum broadening. High-stability wide-range control adapts to multi-mode SAR observation: Fully digital closed-loop control with ≥1 GHz high-speed ADC sampling realizes per-cycle pulse calibration, achieving amplitude stability better than ±0.2% and pulse width accuracy within ±10 ns across all working conditions. Flexible parameter configuration supports rapid mode switching within 1 ms. Built-in temperature and aging compensation algorithms maintain long-term on-orbit parameter consistency throughout the service life. Aerospace extreme environment reliability design includes three dimensions: Radiation hardening adopts a three-level protection system: radiation-tolerant aerospace-grade devices (total dose ≥50 krad(Si), single-event LET ≥60 MeV·cm²/mg), triple modular redundancy for control circuits, redundant power loops and aluminum alloy shielding structures. Thermal design implements full conduction cooling with auxiliary radiation heat dissipation; high-thermal-conductivity substrates connect directly to satellite heat sinks; uniform component layout avoids hotspots; high-emissivity thermal coatings enhance radiation heat exchange, ensuring stable operation within -40 ℃~+85 ℃. Mechanical vibration resistance adopts integrated milled aluminum alloy housings, epoxy potting for heavy components, multi-point PCB fixation and aerospace anti-loose connectors to withstand launch vibration and impact. Full-link EMC & low-noise design: Double-layer fully sealed shielding integrates magnetic and electric shielding to suppress radiation emission; multi-stage EMI filters eliminate conducted interference; soft-switching optimization reduces dv/dt and di/dt to lower original noise; complete physical isolation between power and control loops with single-point grounding avoids ground loop interference. On-orbit monitoring and multi-level protection: Real-time telemetry collects voltage, current, pulse parameters, junction temperature and shell temperature via 1553B/CAN buses; on-orbit pulse waveform storage supports fault traceability. Comprehensive hardware-software dual protection including overvoltage, overcurrent, short circuit, overtemperature and arc protection responds within 100 ns; automatic single-stage fault isolation ensures continuous SAR observation without system shutdown. In summary, this integrated methodology solves the inherent defects of conventional power supplies in nanosecond narrow pulses, fast edges, low droop and high stability. The all-solid-state Marx topology with GaN devices realizes nanosecond edge control; fully digital closed-loop control ensures ±0.2% amplitude stability; full aerospace-grade reliability meets 5–8 years of on-orbit service. It provides core technical support for domestic substitution and performance improvement of all low/high-orbit spaceborne SAR payloads.