How do I design a power amplifier for a high duty cycle military radar application?

Designing a power amplifier (PA) for a high duty cycle military radar application addresses the unique thermal and electrical challenges of operating the PA at high average power for extended periods, which is fundamentally different from the low-duty-cycle pulsed operation typical of legacy radar transmitters. High duty cycle radars include: AESA (Active Electronically Scanned Array) radars that operate near-continuously (50-100% duty cycle) compared to legacy mechanically scanned radars (approximately 1-10% duty cycle), and CW (Continuous Wave) radars used for missile guidance and illumination. The key PA design challenges are: thermal management (at 50% duty cycle: the PA average power dissipation is approximately 10x higher than at 5% duty cycle for the same peak power; this dramatically increases the junction temperature and demands aggressive cooling; example: a GaN PA producing 50 W peak at 10 GHz with 40% PAE: at 5% duty: P_avg = 2.5 W, P_diss = 3.75 W. At 50% duty: P_avg = 25 W, P_diss = 37.5 W. The thermal solution must handle 10x the heat dissipation), bias network design (at high duty cycle: the bias network must deliver sustained DC current to the PA, not just short current pulses; the bypass capacitors must have low ESR to handle continuous current without excessive heating; the bias inductors must not saturate under the sustained current; the power supply must deliver the average current without voltage droop), linearity (AESA radars use complex waveforms (FMCW, OFDM-like, coded pulses) that require linear amplification; the PA must maintain acceptable EVM or spectral regrowth levels across the waveform bandwidth; high duty cycle operation increases the PA's average temperature, which affects the linearity (gain compression, AM/PM distortion shift with temperature)), and device selection (GaN HEMT is the dominant technology for high-duty-cycle radar PAs because: GaN's high power density (5-10 W/mm) reduces the die size, GaN's high breakdown voltage (100-400 V) allows high-impedance matching (easier broadband design), and GaN's thermal conductivity on SiC substrates (4.9 W/cm-K) enables efficient heat extraction).