A summary of the state-of-the-art performance of terahertz mixers. SIS mixers are marked with filled circles, HEB mixers with squares and triangles, and the Schottky mixers are marked with diamonds.
HEB mixer DSB noise temperature : solid squares with a Mylar beam splitter, open squares with Mylar beam splitter and a signal path extended by ; solid triangles with Mylar beam splitter, open triangles with Mylar beam splitter and a signal path extended by .
(Left) A scanning electron microscope (SEM) image of a double slot antenna (DSA) with a HEB at the center (covered with a resist pad). The slots in the gold ground plane appear black. (Right) The HEB chip is glued to the back of an elliptical silicon lens, covered with an antireflection coating (see the text). Antenna dimensions are given in units of the wavelength in free space, .
(a) The impedance of a DSA (designed for , see the text) at the HEB terminals: real (triangles) and imaginary (squares) parts. (b) DSA normalized response, calculated using HFSS (squares), and measured with FTS (thin solid line). The thick solid line shows the calculated air transmission for the laboratory conditions ( spectral resolution).
(Left) A fully assembled band flight mixer unit. The silicon lens is seen on the front, and the dc connector is seen on the back of the mixer unit. (Middle) An inside view of the mixer unit. The IF board is seen with the HEB chip in the cutoff window at the center of the IF board. (Right) A large view of the HEB chip, glued to the back of the silicon lens and bonded to the IF board.
The HEB mixer test setup. FIR laser was used as a LO source. Both the and the room temperature loads were made of Eccosorb® AN-73 sheets.
DSB mixer noise temperature: band 6 (squares) at , and band 7 (triangles) at .
FTS response of (squares) and DSAs (circles). DSB mixer noise temperature for band 6 (filled squares) and band 7 (filled circles) mixers.
(a) Current-voltage characteristics of a HEB mixer with LO power levels around its optimal value. The optimal bias area is marked with a red ellipse. The nonpumped CVC over the pumped CVCs is shown in the inset. (b) The mixer noise temperature as a function of the bias voltage for the corresponding pumped CVCs.
DSB mixer noise temperature (corrected for the input loss) vs intermediate frequency for HEB mixers with a (triangles) and a (squares) lateral dimensions. The LO frequency was .
Output power variance vs integration time for devices: squares (HEB heated to the resistive state, i.e., no LO), triangles (, optimal LO power), filled circles (, optimal LO power). The solid line follows the radiometric equation (see the text). Open circles correspond to a size HEB mixer under the LO at the optimal bias point (the curve is shifted for clarity).
DSB receiver noise temperature (uncorrected for the input loss) and the optimal LO power for HEB mixers of different sizes at LO frequency.
The mixer output power and the Allan time for a HEB mixer driven by either the heater, or the LO, or the LO.
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