Design of a hermetically-sealed ka-band LNA module with high reliability

This paper presents the design and test of a hermetically-sealed low noise amplifier (LNA) module at Ka-band, in which the reliability is fully considered for its application in critical environment. An overall design scheme is worked out for the project-oriented LNA module. It consists of two LNA MMICs, a waveguide-to-microstrip transition, three fixed value attenuator chips and an amplitude equalizer which is fabricated by using hybrid microwave integrated circuit (HMIC). A waveguide-to-microstrip transition with a hermetic coaxial bead is designed and applied to form the hermetic housing of the RF devices and circuits. The LNA module is fabricated, tested and measured. The robustness of the LNA chips, passive components as well as the effect of the assembling technique have been tested out under a temperature shock process with temperatures being -40 ^o°C to +70°C. The measured noise figure of the LNA is 2.4 ± 0.02dB including the insertion loss of 0.4dB of the waveguide-to-microstrip transition. Measured linear gain of is 37.8±0.3dB over the a testing bandwidth of 2GHz at room temperature. The recorded gain variation is within ±0.9dB over the temperature range of -40°C to +50°C.