A design of Rectangular Waveguide TM11 to TE10 Mode Converter for S-band Applications
Subject Areas : ICTHamed noroozy 1 * , Hossein Chabok 2 , Samane Pakniyat 3
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Keywords: Mode converter, S-band applications, TM11 to TE10 mode conveter, high power microwave (HPM) applications,
Abstract :
A design of a compact, easy to fabricate and applicable structure rectangular waveguide TM11 to TE10 mode converter is presented in this paper. The design procedure of the proposed structure can be divided into two parts in sequence. The beginning one is dedicated to the transformation from TM11 to TEM mode using a central conductor, while the second part is the transformation from TEM to TE10 mode using a dielectric loaded waveguide carrying out 180o phase shift. The proposed structure has the advantage of high efficiency of above 90 %, which are demonstrated in simulation results
[1] A. Chittora, J. Mukherjee, S. Singh and A,Sharma, “Dielectric Loaded TM01 to TE11 Mode Converter for S-band Applications,” IEEE Trans. Dielectrics and Electrical insulation, vol. 22, pp. 2057-2063, August 2015.
[2] A. Tribak, J. Zbitou, A. Mediavilla, A,Sharma and NA. Touhami, “Ultra-broadband High Efficiency Mode Converter ,” Progress in Electromagnetics Research, vol. 36, pp. 145-158, January 2013.
[3] R. L. Eisenhart , “A Novel Wideband TM01-to-TE11 Mode Converter,” Microwave Symposiun Digest, vol. 1, 1998, pp. 249–252.
[4] K.S.S. Prasad, S.A. Singh, S.S. Shanmukha, R. Seshdri and M.V. Kartikeyan “Design of a TM01-TE11 Circular Bend Mode Converter Operating at 3GHz,” IEEE International Vacuum Electronics Conf., pp. 177-178, February 2011.
[5] S.H. Lee, B.M. Lee, J.Ahn, Y.J. Yoon and J.H. So “The Design of X-band Non-constant Serpentine TM01-TE11 Mode Converter with Short Length,” Asia-Pasific Microwave Conf., Vol. 1, pp. 4, 2005.
[6] B.M. Lee, W.S. Lee, Y.J. Yoon, J.H. So, “X-band TM01-TE11 Mode Converter with Short Length for High Power,” Electronics Letts, vol. 40, No. 18, pp. 1126-1127, 2004.
Iranian Journal of Information Technology & Communication | No.33-34, Vol.9, Fall & Winter 2018 |
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A design of Rectangular Waveguide TM11 to TE10 Mode Converter for S-band Applications
* Hamed Niroomand * Hossein Chabok * Samane Pakniyat
* Department of Electrical and Electronics Shiraz University of technology Shiraz, Iran
Abstract
A design of a compact, easy to fabricate and applicable structure rectangular waveguide TM11 to TE10 mode converter is presented in this paper. The design procedure of the proposed structure can be divided into two parts in sequence. The beginning one is dedicated to the transformation from TM11 to TEM mode using a central conductor, while the second part is the transformation from TEM to TE10 mode using a dielectric loaded waveguide carrying out 180o phase shift. The proposed structure has the advantage of high efficiency of above 90 %, which are demonstrated in simulation results.
Keywords: Mode converter; S-band applications; TM11 to TE10 mode conveter;high power microwave (HPM) applications
1. Introduction
High power microwave (HPM) systems have been much improved, recently, due to their trait of high power transmission. Mode converting should be considered in overmoded waveguides to achieve the desired mode. Rectangular waveguide has lower loss than circular waveguide and usually is the preferred structure in many applications. Therefore, efforts are made to achieve the dominant mode in rectangular waveguide, TE10. A TM01 to TE11 mode converter in circular waveguide has been presented in [1] using a tapered conductor and a Teflon dielectric. A TM01 to TE11 mode conversion procedure has been presented in [2] utilizing an octagonal shaped structure which could not simply be fabricated. Another TM01 to TE11 mode converter has been proposed in [3] using an indirect TM01-TEM-TE11 method. The expressed method is expensive, not easy to fabricate, and narrow band. In [4-6], some serpentine shaped mode converter structures have been presented which are commodious, not compact, and not easy to fabricate.
In this paper, we tried to design an applicable and easy to fabricate S-band TM11 to TE10 mode conversion procedure considering high conversion efficiency in rectangular waveguides. The desired simulations for aforesaid mode converter are performed in CST Microwave Studio computer program. The simulation results show that the proposed structure takes the advantage of high conversion efficiency, above 90%, and provides an appropriate mode conversion bandwidth. The paper is organized as follows. In Section II, the intended structure is defined, while the respective simulation results are presented in section III. The dielectric loss is presented in Section IV, and finally, the paper is concluded in Section V.
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2. Main structure
The design procedure of the expressed mode converter can be divided into two parts. First, it is tried to convert TM11 to TEM mode, as an intermediate mode, in rectangular waveguide structure. Therefore, the second part is the conversion of TEM to TE10 mode. To achieve the first demand, we have utilized a tapered conductor. To achieve the TE10 mode as the expected output mode, a proper 180o phase shift is needed, which is obtained using Teflon®/PTFE (Polytetrafluoroethylene). Figure 1 shows an overview of the main structure with all dimensions. It should be mentioned that section 2 in Fig. 1 has been considered to prevent abrupt changes in electric field pattern. The length of loaded dielectric can be achieved using [1]:
| (1) |
If 
, we have:
| (2) |
We can rewrite the above equation as
| (3) |
Cross-sectional views of the simulated electric field patterns in proposed structure are presented in Fig. 2 at operation frequency. Simulations are performed with a 10
5 rectangular waveguide. It is necessary to say that all units are in centimeters. Obviously, cutoff frequencies of TE10 and TM11 modes can be calculated analytically using:
| (4) |
Therefore, cutoff frequencies 
and 
are 1.5 and 3.35 GHz, respectively.
Fig. 1: An overview of the main structure
3. Simulation results
Figure 2 shows cross-sectional views of simulated electric field patterns at operating frequency, i.e. 3.6 GHz. It is clear that the incoming TM11 mode can be transformed into TEM using the centered conductor and then, the 180o phase shift is obtained using PTFE dielectric loaded. The choice of PTFE for dielectric part is based on its high efficiency according to the simulated results in Fig. 3. In this figure, the comparison between different materials is presented. Table 1 shows a detailed comparison of different materials. In the case where the compactness is intended, Mica could be considered; otherwise Teflon/PTFE is preferred. A proper coaxial cable is utilized as the feeder for the waveguide in order to excite TM11 mode. It should be mentioned the coaxial cable is located at the center of X-Y plate which is shown in Fig. 4.
4. Dielectric loss
As we mentioned previously, a loaded dielectric structure is needed to obtain 180o phase shift in the TEM to TE10 mode conversion procedure. According to the choice of lossy PTFE dielectric, a dielectric loss is encountered depending on the operation frequency, loss tangent of the dielectric, and the specifications of materials (e.g. dielectric constant, dielectric types) [1]. Figure 5 indicates the loss tangent for PTFE.
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Fig. 2: Cross-sectional views of electric wave patterns |
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Fig. 3: Mode conversion efficiency comparison between different materials
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Table 1: Comparison of different materials
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Table 1: Comparison of different materials
Table 1: Comparison of different materials
Fig. 4: A coaxial cable feed for TM11 mode excitation.
Figure 5. Loss tangent for PTFE
5. Conclusion
In this paper, a novel structure is presented which is able to convert TM11 mode to TE10 dominant mode in the rectangular waveguide. The proposed structure can be simply fabricated and provides sufficient bandwidth. Simulation results show that the presented structure has the advantage of more than 90% conversion efficiency.
References
[1] A. Chittora, J. Mukherjee, S. Singh and A,Sharma, “Dielectric Loaded TM01 to TE11 Mode Converter for S-band Applications,” IEEE Trans. Dielectrics and Electrical insulation, vol. 22, pp. 2057-2063, August 2015.
[2] A. Tribak, J. Zbitou, A. Mediavilla, A,Sharma and NA. Touhami, “Ultra-broadband High Efficiency Mode Converter ,” Progress in Electromagnetics Research, vol. 36, pp. 145-158, January 2013.
[3] R. L. Eisenhart , “A Novel Wideband TM01-to-TE11 Mode Converter,” Microwave Symposiun Digest, vol. 1, 1998, pp. 249–252.
[4] K.S.S. Prasad, S.A. Singh, S.S. Shanmukha, R. Seshdri and M.V. Kartikeyan “Design of a TM01-TE11 Circular Bend Mode Converter Operating at 3GHz,” IEEE International Vacuum Electronics Conf., pp. 177-178, February 2011.
[5] S.H. Lee, B.M. Lee, J.Ahn, Y.J. Yoon and J.H. So “The Design of X-band Non-constant Serpentine TM01-TE11 Mode Converter with Short Length,” Asia-Pasific Microwave Conf., Vol. 1, pp. 4, 2005.
[6] B.M. Lee, W.S. Lee, Y.J. Yoon, J.H. So, “X-band TM01-TE11 Mode Converter with Short Length for High Power,” Electronics Letts, vol. 40, No. 18, pp. 1126-1127, 2004.