25 th NATIONAL RADIO SCIENCE CONFERENCE (NRSC 2008) D12 1 March 18‐20, 2008, Faculty of Engineering, Tanta Univ., Egypt ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ــــــــــــــــــــــــــــــــــــــــــ DESIGN AND ANALYSIS OF MULTIMODE X-BAND WRAPAROUND MODE CONVERTER AND EXTRACTOR FOR PULSE COMPRESSION SYSTEMS Yasser M. Madany * and Ahmed F. Miligy * Member, IEEE, Alexandria University, Egypt, ymadany@ieee.org Abstract The characteristics of multimode x-band wraparound mode converter and extractor for RF pulse compression systems have been analyzed using a full 3D electromagnetic field inside a structure based on the finite element method (FEM). The converter performance is sensitive to the number of guide feeding and the feed of the WR90 rectangular waveguide while the extractor at two and seven guide feeding is sensitive to the feed of the WR90 rectangular waveguide and the circular output waveguide radius, which allow small reflection near 0.2 occurring at the input. The two output ports have transmission equal to unity at most x-band frequencies for the useful circular TE 01 mode. For the specific circular mode extractor, the transmission is large or is equal to 0.5 at most x-band frequencies. The converter and extractor characteristics at the first five modes TE 11 , TE 21 , TE 01 , TE 12 and TE 22 such as reflection coefficient, transmission coefficient and the magnitude of electric field are obtained using numerical simulations. Keywords: RF pulse compression systems, MDLDS, Mode converter, Mode extractor. I. Introduction High power radio frequency RF pulse compression systems provide a method for enhancing the peak power capability of high power RF sources. Pulse compression matches the source capabilities to the input requirements by exchanging pulse width for peak power. There are different systems for RF pulse compression such; Slack Linear Energy Doublers (SLED) [1], Slack Linear Energy Doublers II (SLED II) [2] and Binary Pulse Compression (BPC) systems [3-4]. However the Delay Line Distribution Systems (DLDS) and Multi- moded Delay Line Distribution Systems (MDLDS) are RF Pulse compression equivalent systems based on the different operation principles from ordinary Pulse compression systems. The DLDS [5] utilizes the time of flight of the beam in the accelerator to reduce the length of the over-moded waveguide assembly [6-7]. To make the DLDS even more attractive, the concept of multi-moding was introduced [8] for the Next Linear Collider (NLC) [9-10]. The resulting system reduces the length of the waveguide system by multiplexing several low-loss RF modes in the same waveguide [11]. The system has an intrinsic efficiency of 100%, and the total over-moded waveguide length is less than that required by the compact SLED II system. The component developments have to achieve two major goals: high efficiency and reliable high power handling capabilities. The DLDS is an alternative to conventional pulse compression which enhances the peak power of an RF source while matching the long pulse of that source to the shorter filling time of the accelerator structure. The Multi- mode DLDS scheme works as follows. Instead of the several delay lines, one delay line is set to have several mode extractor that are inserted on the one delay line to give the delay time as required by the DLDS operation [12]. Each mode extractor is designed as to extract only a specific mode and at the same time to transport the other modes completely. The one end of the delay line where RF sources are located, the mode launcher is attached. Primary RF pulse from the klystron is divided into the short RF bins and each RF bin is converted into the different mode through the mode launcher and lead into the delay line. Thus, each RF bin is extracted, in other words, distributed to the necessary location just as an ordinary DLDS. This multi-mode DLDS requires several new RF devices such as a mode launcher, mode extractor, mode converter, special waveguides and other devices [13-15]. The advantages of Multi-Moded DLDS are; high energy efficiency and its intrinsic efficiency equal to 100%, which is better than that of SLED family systems by about 20%, over-moded waveguides are widely used to increase the power handling capacity. Losses in the system are minimized by transporting power in circular waveguides in azimuthally symmetric modes such as the TE 01 mode. In many instances the RF power is easier to manipulate in rectangular waveguides than in circular waveguides [16]. Therefore, the power is often manipulated in rectangular waveguides and transported in circular wave-guides. In order to transport power between a rectangular waveguide and a circular waveguide, the two waveguides should be connected through a