In Filters/Diplexers

Several times per month we are asked about the feasibility of using Marki Microwave products at cryogenic temperatures for various research applications. Many customers have purchased various products (bias tees, diplexers, filters, couplers, power dividers, etc) for cryogenic applications, and so far none have complained about the products failing. Now for the first time we have actual data to show that our products function at cryogenic temperatures. As we acquire more data about the performance of our products we will post it here. If you are interested in a product that you don’t see listed here and you are willing to perform the test and share the results for this tech note, please contact [email protected]. We will send you a part to keep.


Cryogenic testing of our first product (the FLP-0750) comes courtesy of Patrick Harrington and Prof. Kater Murch of Washington University in St. Louis, who were the first customers to take us up on the offer. See their complete report here.  Read some fascinating work on quantum mechanics here.

This measurement shows the insertion loss of the FLP-0750 in a room temperature and cryogenic (50 mK) environment. The loss in the cryogenic chamber is de-embedded from fixturing with significant loss and ripple, so it is unknown how much of the ripple comes from the degradation of the filter and how much comes from the measurement system. It seems likely that the filter still successfully eliminates rejection band signals.

Bias Tees and Diplexers

Marki bias tees and diplexers have a relatively similar construction. These products have been used by numerous customers successfully at cryogenic temperatures. Most recently, Nathan Holman from the University of Wisconsin-Madison Department of Physics, has taken scattering parameter data of the BT-0024SMG as well as time domain data of the settling time of the DC input at 1.6K. It was shown that Marki Microwave bias tees (and by similarity, diplexers) will operate close to the datasheet specifications at cryogenic temperatures.

The plots above show that at 1.6K, the insertion loss was less than 3dB for frequencies above 8MHz and the DC port isolation is ~40dB which is within the datasheet specifications. Settling time was <100 μs for the DC input and it was shown that this bias tee was tolerant to repeated fast thermal cycling. For a more detailed look at the cryogenic performance of the BT-0024SMG, you can read the full report here.


Marki triplate stripline couplers are expected to work, based on the construction and performance over smaller temperature swings, as well as the feedback we have received from customers.

However, the high directivity bridge couplers (CBR series) is NOT expected to work at cryogenic temperatures. The directivity degrades due to construction shifts across temperature, and some of the components may become superconducting.

Power Dividers

The PD, PD3, and PD4 series of Wilkinson power dividers are expected to work, though possibly with degraded isolation, down to very low temperatures. These products do use surface mount resistors that could become superconducting at very low temperatures, however. We have not received meaningful customer feedback about these products.

The PBR series of high isolation bridge combiners is NOT expected to function at cryogenic temperatures for the same reasons as the CBR bridge couplers, listed above.


Our higher frequency, banded, capacitively coupled baluns (including the BAL-0106, BAL-0212, BAL-0520, BAL-0208SMG, BAL-0416SMG, BAL-0620SMG, and all MBAL products) are expected to operate well at cryogenic frequencies, as they consist exclusively of coupled transmission lines.

The rest of the balun product line uses magnetic cores. It is not clear whether these units will operate at cryogenic temperatures or not. We have not received meaningful customer feedback about these products.

Mixers, Amplifiers, Multipliers, and other Nonlinear Products

We have not received any feedback from customers about these products, but they are not expected to operate at cryogenic temperatures due to the degradation of the semiconductor devices.

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