22 nd International Symposium on Space Terahertz Technology, Tokyo, April 2-4, 2012 Abstract— The losses of ~1.2 m long WR10 (2.54x1.27 mm²) rectangular waveguides were measured at room temperature across the 70-116 GHz band. Ten different waveguide modules were machined in two different materials (Aluminum alloy and Brass) using different surface roughness (Ra) and different split- block waveguide geometries (E-plane and b-edge) as to establish the dependency of the losses on the various parameters. The measurements of the various units were performed with the IRAM mm-wave Vector Network Analyzer (MVNA) across the 70-116 GHz single-mode band of the WR10 waveguide. Index terms---WR10 waveguides, losses, machining, surface roughness, gold plating. I. WR10 WAVEGUIDE MECHANICAL BLOCKS Ten modules with ~1.2m long WR10 rectangular waveguide were fabricated at IRAM: five in Brass (CuZn39Pb3) and five in 6060 Aluminum AlMgSi. Each module consists of two split blocks in which the waveguide was machined in a meandering pattern that fits on a surface of 140x71 mm 2 . Fig. 1 shows photos of some of the assembled units together with the internal details of one of the two module halves. Fig. 1. Top: six assembled WR10 waveguide modules (three in Brass on the left, three in Aluminium on the right). Bottom: one disassembled split-block half showing the ~1.2 m long WR10 waveguide long cut. The authors are with IRAM (Institut de Radio Astronomie Millimétrique), Saint Martin d’Hères, 38406 FRANCE (contact author: A. Navarrini, e-mail: navarrin@iram.fr , phone: +33476824941). A. Different split-block geometries: Two different WR10 split-block geometries, the E-plane split and the b-edge split, were adopted for the modules, as illustrated in Fig. 2. Fig. 2. Photo of WR10 waveguide cut adopted on the two split block geometries. Geometry 1: along the E-plane (left). Geometry 2: along the b- edge (right). B. Different surface roughness: The waveguide cuts in each module were fabricated using a numerically controlled milling machine (using machining parameters =9000 rpm and V=45 mm/min). A conventional carbide drill as well as a diamond drill were used. A better surface finish is obtained using the diamond tool. Photos of the WR10 waveguide cuts fabricated with the two drill types are shown in Fig. 3. Fig. 3. Left: WR10 waveguide machined with carbide tool. Right: WR10 waveguide machined with diamond tool showing the specular effect at the waveguide bottom. The achieved surface roughness (Ra) was measured at the bottom of the waveguide cut (narrow side) using a non- contacting optical laser equipment. The roughness along the waveguide walls (wide side) was not measured. The losses are expected to be lower in a smooth waveguide with surface irregularities which are small in comparison to the skin depth. Assuming an electrical conductivity of 1.38x10 7 S/m and of 3.24 x10 7 S/m for, respectively Brass and Aluminium, the corresponding skin depths at 100 GHz are δ Brass =0.40 μm and δ Alu =0.28 μm. The measured surface roughness at the bottom of the waveguides machined with carbide tool were about Ra~0.34 μm for the Brass modules and about Ra~0.15 μm for Loss of WR10 Waveguide across 70-116 GHz I. Stil, A.L. Fontana, B. Lefranc, A. Navarrini, P. Serres, K.F. Schuster