6-4 1 Abstract—Last year, the design and implementation details of a new modular sideband-separating mixer block, intended as an upgrade for the current single-ended ALMA Band 9 mixers, were presented at this conference. In high-frequency observation bands like ALMA Band 9 (600—720 GHz), which is strongly influenced by atmospheric noise, employment of sideband-separating mixers can reduce, by roughly a factor of two, the integration time needed to reach a certain signal-to-noise ratio for spectral line observations. Alternatively, in the same integration time, a sufficiently larger selection of sources can be accessed. Two prototype mixer blocks were produced on a micro milling machine, and equipped with production Band 9 SIS mixer devices that have independently been tested in double-sideband mode. Here, we present the results of the first measurements, notably, the noise temperature, image rejection, LO pumping balance and IF response. We also present in detail a procedure of the image rejection ratio measurement, which is fast and can be used for single sideband mixers, so that a second IF chain is not required. Index Terms—Image rejection ratio, sideband separating mixers, submillimeter mixers, superconductor-insulator- superconductor junction I. INTRODUCTION HE possibility of reducing the atmospheric noise by a factor of two and increase as result a signal to noise ratio of about 1.4 times is the motivation for ALMA Band 9 mixers upgrade form dual sideband (DSB) to single sideband (SSB) mode. Manuscript received August 1, 2011. This work was supported.in part: by the ESO Band9 Upgrade Study PO-037021; European Community Framework Program 7, Advanced Radio Astronomy in Europe, AMSTAR+, grant agreement no. 227290; Dutch NWO/STW VENI Grant 08119, "Advanced Heterodyne Mixers for THz Applications", Dutch research school for astronomy (NOVA) NOVAIII Grant; Center of Excellence in Astrophysics and Associated Technologies (PBF 06), Chilie. A. Khudchenko and A. Baryshev are with Netherlands Institute for Space Research SRON, Landleven 12, 9747 AD Groningen, The Netherlands, (+31 50 363 4018, A.Khudchenko@sron.nl). R. Hesper, A. Baryshev, G. Gerlofma and M. Spaans with Kapteyn Astronomical Institute, Landleven 12, 9747 AD Groningen, The Netherlands P Mena with Electrical Engineering Department, Universidad de Chile, Av. Tupper 2007, Santiago, Chile Tony Zijlstra, Teun M. Klapwijk are with Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft The Netherlands J.W. Kooi with California Institute of Technology, MS 320-47 Pasadena, CA 91125, USA is with the National Institute of Standards and Technology, Boulder, CO 80305 USA. Because the ALMA correlator can only handle 8 GHz of intermediate frequency (IF) bandwidth per polarization, an SSB configuration with 4-12 GHz IF has been chosen [1], rather than a full two sideband (2SB) one, split over two 4 GHz bands. Also, in this way the existing DSB IF chain does not have to be modified for the upgrade, i.e., all the IF components can be reused. The only IF component to be added is one IF hybrid per polarization. The mechanical design of the SSB receiver was presented in [1]. The manufactured modular block is shown in Fig. 1. There are a few key features in this design. First of all, it is as modular as reasonably possible. Especially the holders containing the junctions are easily separable from the RF hybrid block. The standard single-ended Band 9 junction holders (“back pieces”) are used, so that junctions can be tested individually and easily matched. It means that no development of a new junction design is required. The SIS mixers are made in Nb/AlN/Nb technology. The mixer block is also compact: 45x21x53 mm 3 (see Fig. 1), so the upgrade mixers can be retrofitted into the existing optics blocks with minimal reworking. In this paper, we present the results of the first measurements performed to characterize this mixer. The properties of the RF hybrid and LO splitter were studied in a direct way, by measuring the balance of pumping levels, both through the LO port and the RF port. Moreover, the frequency response, noise temperature and sideband rejection ratio were also measured. Finally, we describe in detail a new procedure First Results of the Sideband-Separating Mixer for ALMA Band 9 Upgrade Andrey Khudchenko, Ronald Hesper, Andrey Baryshev, F. Patricio Mena, Gerrit Gerlofma, Tony Zijlstra, Teun M. Klapwijk, Jacob W. Kooi and Marco Spaans T Fig. 1. Photograph of the first SSB mixer. The corrugated RF input horn is on the right, the LO horn is on the back site opposite to it (not visible). One of the standard band 9 mixer back pieces is visible near the center.