We present an analysis of the bandwidth of an asymmetric 8-beam Fourier grating as the beam multiplexer for a 4.7 THz local oscillator used in a heterodyne receiver. We take the grating designed for NASA GUSTO balloon observatory as an example to address the bandwidth question although it does not need to operate over a wide frequency range. By illuminating the grating at different frequencies from 4.445 to 5.045 THz, we simulated the changes of its performance in three aspects using COMSOL Multiphysics: diffraction efficiency, power uniformity, and the angular distribution of the output beams. These parameters can affect the coupling efficiency between the output beams of the grating and the beams of a mixer array. The bandwidth of the grating is found to be 230 GHz, corresponding to 4.9% of the operating frequency, which is sufficient for many applications.

We present an analysis of the bandwidth of a preliminary designed asymmetric 8-pixel Fourier grating as the beam multiplexer for the 4.7 THz local oscillator of the GUSTO mission. We take the GUSTO grating as an example to address the bandwidth question although GUSTO itself does not need to operate over a wide frequency range. By illuminating single beams with different frequencies from 4.445 THz to 5.045 THz to the grating, we simulated the changes in the grating’s performance in three aspects using COMSOL Multiphysics: diffraction efficiency, power distribution, and the angular distribution of the output beams. These parameters can reduce the coupling efficiency between the output beams of the grating and the beams of the mixer array of GUSTO. The grating’s bandwidth is calculated to be 250 GHz, which is sufficient for many applications.