  In this paper, we introduce the receiver architecture for the Black Hole
Explorer (BHEX) Mission, designed to reveal the photon ring of black holes. The
primary instrument is a dual-polarization receiver operating over the 240-320
GHz frequency range, utilizing a Superconductor-Insulator-Superconductor (SIS)
mixer. This Double-Side-Band (DSB) receiver has an intermediate frequency (IF)
range of 4-12 GHz and operates at a bath temperature of 4.5 K, for optimal
performance, which necessitates the integration of a cryocooler. Complementing
the primary receiver is a secondary unit covering the 80-106 GHz spectrum,
featuring a cryogenic low noise amplifier. This secondary receiver, affixed to
the 20 K stage of the cryocooler, serves to augment the SIS receiver
performance by employing the Frequency Phase Transfer technique to boost the
signal-to-noise ratio at the correlator output. Together, this sophisticated
receiver duo is engineered to achieve the quantum-limited sensitivity required
to detect the photon ring of black holes, marking a breakthrough in
astrophysical observation.
