This multi-frequency band receiver system has effectively compensated atmospheric phase fluctuation
using a unique phase referencing technique in mm-VLBI observations. However, because the original
optics system incorporated individual cryogenic receivers in separate cryostats, a rather bulky optical
bench of size about 2600 mm x 2300 mm x 60 mm was required. This paper proposes an integrated
quasi-Optical circuit incorporating a more compact triple-band receiver in single cryostat to circumvent
difficulties in installation and beam alignment. The recommended frequency bands of the improved
triple-band receiver are K(18–26 GHz) band, Q(35–50 GHz) band, and W(85–115 GHz) band. A
frequency-independent quasi-optical circuit for triple band is adopted to obtain constant aperture
efficiency as a function of the observed frequencies.