Frequency Independent LO Injection in Quasi-Optical Heterodyne Systems

In quasi-optical heterodyne systems, such as those used in radio astronomy receivers, it is very typical to consider LO injection once the RF path has already been designed. In many cases, LO and RF optical paths share several optical components, and this imposes restrictions on the LO injection design. In this paper, this common situation has been carefully analyzed, and simple design equations have been derived in order to achieve frequency-independent designs. Due to the low power available at THz frequencies, frequency-independent LO power transmission gains importance in this band due to the need to get efficient LO injection at all frequencies. The presented quasi-optical analysis have been confirmed with physical optics simulations.