How do I design a wideband power amplifier for an electronic attack system covering 2-18 GHz?

Designing a wideband power amplifier for an electronic attack (EA) system covering 2-18 GHz (a 9:1 bandwidth ratio, or 3 octaves) requires addressing the fundamental challenges of achieving flat gain, adequate output power, and stable operation across this extremely wide frequency range. The design approach involves: selecting the semiconductor technology (GaN HEMT is the preferred technology for modern EA amplifiers due to its high power density (5-10 W/mm), high breakdown voltage (> 100 V), and good performance to 18 GHz and beyond; GaAs was used in earlier generations but has lower power density), choosing the circuit topology (distributed (traveling-wave) amplifier: the most common topology for multi-octave bandwidth; the transistor capacitances are absorbed into artificial transmission lines, providing flat gain from DC to a cutoff frequency determined by the line's unit cell length; typical: 5-15 dB gain per stage, 2-5 stages cascaded for 20-40 dB total gain; reactive matching amplifier: provides higher power and efficiency than distributed but over narrower bandwidth; used in sub-octave designs or as the final stage of a wideband amplifier chain), designing the bias network (the bias network must present low impedance to the DC supply and high impedance to the RF signal across the entire 2-18 GHz band; this requires multiple bypass capacitors in parallel and bias line lengths that avoid resonances in the operating band), and thermal management (GaN amplifiers at 2-18 GHz with 10-100 W output generate significant heat; the die must be mounted on a high-thermal-conductivity substrate such as SiC or diamond, with heat sink temperatures maintained below 80-100 degrees C).