International Journal on Electrical Engineering and Informatics ‐ Volume 6, Number 1, March 2014 Rectangular to Parallel Plate Waveguide Transition and Its Tapering Effect for Microwave Devices Characterization Achmad Munir 1 , Ananto Eka Prasetiadi 1,2 , Levy Olivia Nur 1,3 , Sugihartono 1 , and Adit Kurniawan 1 1 Radio Telecommunication and Microwave Laboratory School of Electrical Engineering and Informatics Institut Teknologi Bandung, Indonesia, Jalan Ganesha 10, Bandung 40132, Indonesia 2 Institut für Mikrowellentechnik und Photonik Technische Universität Darmstadt, Merckstr. 25, 64283 Darmstadt, Germany 3 Telkom Engineering School Telkom University, Jalan Telekomunikasi, Dayeuh Kolot, Bandung 40257, Indonesia munir@ieee.org Abstract: The experimental characterization in exploiting the property of microwave devices is an essential complement to theoretical and/or simulation works. Thus, the need of instrument for the characterization is becoming unavoidable thing to be established. This paper reports the development of test-fixture in form of a parallel plate waveguide (PPW) to characterize the reflectivity and/or transmittivity of microwave device whereby the property of reflection and/or transmission can be achieved under normal incidence. Since the PPW is excited using a rectangular waveguide, a transition section which connects the rectangular waveguide and the PPW needs to be investigated to have an optimum performance required for microwave devices characterization. The tapering effect of transition section is examined and analyzed numerically in yielding the influences to the test-fixture performance. Here, a WR248 type rectangular waveguide which has working frequency of 2.60GHz to 3.95GHz for TE 10 mode is used as coaxial-to-waveguide transducer for exciting the PPW. The result shows that the linear-tapered transition has better performance in term of bandwidth compared to the step-tapered one. In addition, the discussions of taper length and number of step-tapered transition related to the performance of test-fixture as well as the experimental characterization for linear-tapered transition are also presented. Keywords: coax-to-waveguide transducer, linear-tapered transition section, microwave devices, parallel plate waveguide, rectangular waveguide, step-tapered transition section. 1. Introduction One of the important things in the design of microwave devices is the experimental characterization to compare and verify the characteristic of realized devices to comply with the design or specification. Unfortunately, for some devices with infinite number of structures or unit cell such as frequency selective surfaces (FSS), there is often impossible to directly measure their characteristics, i.e. reflectivity or transmittivity, especially at microwave frequency or the higher one. Some methods by using close-sided waveguide simulators have been applied to obtain the properties of array elements and FSS [1]-[4]. However, due to the nature of these simulators they suffer from the problem that the device under test (DUT) could be characterized only for certain angle of incidence which is positioned away from the path of normal incidence. To cope with this problem, a parallel plate waveguide (PPW) method was implemented as an alternative technique [5]-[6]. By using this method, the characterization of infinite number of structures can be carried out using a finite one since the walls of PPW behave as pairs of image planes. Received: October 31 st , 2013. Accepted: February 23 rd , 2014 181