A 90 degree hybrid splits a signal into two equal parts in phase quadrature, or combines two into one, which makes it the building block for balanced amplifier pairs, circular polarization feed networks and beamforming architectures where relative phase governs the design. Holding 3 dB coupling with better than 20 dB isolation and 0.3 dB insertion loss across 600 MHz at 26 GHz is a machining and characterisation problem as much as an electrical one. VSWR holds below 1.5:1 on a WR-34 waveguide interface. The design lineage runs to NASA's Solar Dynamics Observatory, a long-duration on-orbit record for a component of this type. Qualification follows NASA GEVS Table 2.4-3 with 14.1 GRMS overall random vibration, minimum resonant frequency verification, and 0.25 g low-level sine sweeps before and after vibration. Thermal cycling is to mission requirements. S-parameter testing runs from 1 to 40 GHz, with workmanship inspection and acceptance testing before shipment. Custom hybrid couplers from L-band through Ka-band in 90 or 180 degree configurations, coaxial or waveguide, are developed to mission-specific requirements.