Accurate embedding circuit model for terahertz HEB receivers

Slot antennas coupled to coplanar waveguides (CPW) are being developed for quasioptical single-pixel detectors for atmospheric and astronomical instruments in the submillimeter-wave/terahertz frequency range. We present a procedure that characterizes the strong reactive contributions associated with bolometer-to-CPW transition and with the RF band stop filter that connects the mixer to the DC/lF systems of the receiver. First, we briefly describe the geometry of the overall mixer embedding circuit. Then, the CPW parameters (characteristic impedance and propagation constant) are derived. These are both complex due to the fact that there is power leakage associated with the propagating mode. Utilizing these parameters, the phase shift caused by the imaginary part of the RF band stop filter is taken into account. Then the lumped reactances associated with the bolometer-to-CPW transition are included in the equivalent network model. Comparisons between predictions and measurements of submillimeter wave bolometric receivers show very good agreement for frequencies up to 2.5 THz.