3-01
Netty Honingh, U. Graf, K. Jacobs, M. Schultz, S. Wulff, I. Barrueto, M. Justen, S. Fathi, B. Schmidt, H. Krüger, L. Weikert, A. Mahmood, K. Vynokurova
Universität zu Köln
Compact Heterodyne Focal Plane Array Receiver Front Ends
On an expensive observation platform like SOFIA, simultaneous observation of as many pixels as
possible is an important way to make efficient use of the available observation time.
The upGREAT receiver (e.g. Risacher et al, https://doi.org/10.1142/S2251171718400147) has shown, at 1.9 THz and 4.7 THz, that focal plane array heterodyne receivers can be successfully operated on SOFIA. Focal plane array observation modes are well established by now thanks to this development.
The upGREAT receiver, however, still consists of separate mixer pixel units, combined in a rather complex optics. The local oscillator (LO) is distributed via a Fourier grating, and combined with the signal beam via a 300K beam splitter. In addition, although the upGREAT receiver has a large cryostat and is approaching the maximum weight limit for SOFIA receivers, the number of pixels is still considerably less than the maximum number of pixels that would fit the SOFIA telescope optics.
Further integration of pixels would be a way to fit more pixels in a practical and manageable receiver. Also a more efficient use of the available local oscillator power is very desirable for a receiver with more pixels. As a possible way forward to that goal we will present our present developments, at 460 GHz, to achieve a denser and more integrated focal plane array as it is developed for the FYST telescope of the CCAT-p observatory in the CCAT Heterodyne Array Instrument (CHAI). The CHAI receiver will have 2x64 pixels, in 2 frequency channels 460-495GHz and 800-820GHz.
Here we use balanced mixers, which supply us with a separate port for the LO, making the beamsplitter no longer necessary, and in addition suppressing possible the LO AM noise. We integrate some of the more critical RF circuitry on one membrane substrate with the mixers to make the pixels more compact, and to create repeatable and affordable similar pixels, that are relatively flexible to adapt. In general, we use on-chip circuitry to acquire compact and adaptable designs, also for the local oscillator distribution and for the IF combining.
As to the possibility to use these concepts also at higher frequencies: a second channel of the CHAI receiver, with 64 pixels at 800 GHz is planned. In addition, some preliminary developments of balanced on-chip mixers for 1.9 THz will be presented.
