NEARLY PERFECT RIGHT ANGLE BENDS Adam Abramowicz Abstract: The new geometry of right angle bends is developed. The concept can be applied to any type of a transmission line. Examples of bends in rectangular waveguides, strip lines and microstrip lines are presented. Waveguide bends have return loss better than 35 dB in full TE 10 mode operation range. Strip line bends have return loss better than 40 dB up to 25 GHz and microstrip line bends have return loss better than 25 dB up to 20 GHz. The optimization of bends has been performed in FDTD electromagnetic simulator. INTRODUCTION In many RF and microwave guided wave structures an application of bends is unavoidable. Unfortunately bends influence wave transmission. At the bend interface the reflections occur as well as waves passing through are attenuated. Additionally in open transmission lines like stripline or microstrip line and especially in dielectric waveguides bends are source of radiation which can be a severe problem in densely packed circuits. The most popular method to produce bends having low reflection is to cut the corner (miter) of the bend. Over the years a number of formulas for design of optimally mitered bends have been developed [1,2,3,4]. In this paper a new structure of optimal bend is proposed. Instead of cutting the bend corner along the straight line the corner is formed as a part of the circle. Such a change in the bend shape allows obtaining much better parameters in comparison with traditional mitered bends. PROPOSED BEND STRUCTURE A new right angle bend structure is presented in Fig.1. The radius of the rounded corner (R) is bigger than the width of the transmission line (w) thus the length of rounded corner is always shorter than a quarter of a circle. The ratio R/w completely describes the bend. Let us call the ration R/w as OBR. In a case of rectangular waveguides for a specified width and height there is only one optimal OBR value. For other transmission lines optimal OBR depends on relative permittivity of used dielectrics and impedance of the line. The proposed bend structure can be applied to any transmission line. It produces lower reflections and lower radiation thus the transmission is improved. The length of proposed bend is shorter than length of other bends. Due to its simplicity and good performance it can be called the nearly perfect bend. The optimization of bends has been performed in FTDT electromagnetic simulator QuickWave [5]. Fig.1. The new structure of the right angle bend. ______________________ The author is with Warsaw University of Technology, Institute of Electronics Fundamentals, Nowowiejska 15/19, 00-665 Warsaw, Poland, tel. 48 22 2347710, e-mail: aabr@ise.wp.edu.pl