PT Journal AU Cherednichenko, S Drakinskiy, V Berg, T Kollberg, EL Angelov, I TI The direct detection effect in the hot-electron bolometer mixer sensitivity calibration SO IEEE Trans. Microw. Theory Techn. PY 2007 BP 504 EP 510 VL 55 IS 3 DI 10.1109/TMTT.2007.891470 DE HEB; mixer; direct detection effect ER