RF Performance of a 600 - 720 GHz Sideband- Separating Mixer with All-Copper Micromachined Waveguide Mixer Block F.P. Mena 1,2,†,* , J. Kooi 3 , A.M. Baryshev 1,2 , C.F.J. Lodewijk 4 , T.M. Klapwijk 4 , W. Wild 1,2 , V. Desmaris 5 , D. Meledin 5 , A. Pavolotsky 5 , and V. Belitsky 5 1 SRON Netherlands Institute for Space Research, Groningen, the Netherlands 2 Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands 3 California Institute of Technology, MS 320-47 Pasadena, CA 91125, USA 4 Kavli Institute of Nanoscience, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, the Netherlands 5 Chalmers University of Technology, Group for Advanced Receiver Development, Department of Radio and Space Science with Onsala Space Observatory, SE 412 96, Gothenburg, Sweden †Current address: Department of Electrical Engineering, Universidad de Chile, Santiago, Chile * Contact: pmena@ing.uchile.cl, phone +56-2-978 4888 Abstract— Here we report on the RF performance of a 2SB mixer (600-720 GHz) fabricated in a new method that combines traditional micromachining with waveguide components fabricated by photolithography and electroplating. The latter allows reaching, in a reproducible way, the stringent accuracies necessary for the critical RF components at these high frequencies. I. INTRODUCTION A sideband-separating (2SB) mixer has several advantages over its double sideband (DSB) counterpart. Despite those advantages, its implementation at high frequencies is rather challenging as a more complex design is needed. In fact, the required waveguide circuitry becomes extremely difficult to fabricate employing traditional machining. Previously, we have demonstrated state-of-art performance of a 2SB mixer for 600–720 GHz band constructed exclusively by traditional micromachining [1]. In order to build such mixer one needs to produce a waveguide hybrid with a minimum branch width of 71 µm made with an accuracy better than 5 µm. However, traditional mechanical milling fails to deliver the required accuracy of the dimensions in a reproducible way. Here we report the first results on the RF performance of a 2SB mixer suitable for, e.g., ALMA Band 9 and fabricated using our cutting-edge microfabrication technique [2]. This technique meets the requirements for the dimension accuracy along with surface quality. It, moreover, allows the fabrication of the waveguide components with high yield and repeatability. This approach combines lithographical copper micromachining [3] for making the very fine waveguide structures while allowing regular milling of the remaining not critical mixer parts. II. DESIGN AND FABRICATION A. Design The mixer we describe here is based in a design we have presented in detail previously [1] and is intended to cover the 600-720 GHz range. The design, summarized in Fig. , uses waveguide components and it is planned for construction using the split-block technique. The critical RF waveguide component are a 90° hybrid, a LO splitter, two LO injectors, and two waveguide-to-microstrip transitions. B. Fabrication To fabricate the split-block we have followed a new approach which combines two different techniques. We first produce the critical waveguide RF components using a combination of lithography and electroplating. The result of this process is a single copper plate containing all the (small) RF components as shown in Fig.. Gold is finally sputtered on the plate to improve conductivity. Accuracies of less than Fig. 1 Proposed realization of the critical RF components. They are designed in waveguide and, therefore, represent the channels to be patterned. The transversal dimensions of the waveguide are 310×145 μm. 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April 2008 90