Mode Patterns, S-parameters and Dispersion Analysis of a Circular Waveguide

Abstract

A circular waveguide is a metallic hollow tubular structure that transmits high-frequency electromagnetic waves with negligible losses. This paper presents the design, simulation, and analysis of a circular waveguide in CST Studio’s waveguide template using frequency domain solver. The study focuses on mode patterns (focusing TE??, TE??, TE??), S-parameters (reflection and transmission), group delay, phase variation, and phase constant. In this paper, the waveguide is designed to operate in the X-band, functioning as a high-pass filter (HPF) that allows wave propagation above certain threshold frequency. Simulations reveal the field distributions for different modes, highlighting the dominant propagation characteristics. The S-parameter analysis indicates reflectionand transmission characteristics. Additionally, the group delay and phase constant analysis provide insights into dispersion and integrity of signal. These findings contribute to a better understanding of wave propagation in circular waveguides, aiding in their effective implementation in microwave and RF applications.

Introduction

Waveguides are essential in microwave and RF systems for efficiently transmitting high-frequency electromagnetic waves. Circular waveguides are favored due to their ability to support multiple modes, higher power handling, and lower dispersion than rectangular waveguides. Each mode in a waveguide has a specific cut-off frequency, above which signals propagate efficiently without attenuation.

The two main modes in circular waveguides are Transverse Electric (TE) and Transverse Magnetic (TM), characterized by electric or magnetic fields being transverse to the direction of propagation. The TE?? mode is dominant, preferred for its low cut-off frequency and low loss, while TM modes like TM?? are less desirable.

S-parameters (reflection S?? and transmission S?? coefficients) describe wave behavior at waveguide ports, revealing impedance matching and signal transmission efficiency. Below cut-off frequency, transmission is minimal and reflection low, while above it, transmission stabilizes near 0 dB with improved impedance matching.

The study involves designing a circular waveguide as a high-pass filter operating in the X-band, with dimensions optimized in terms of the cut-off wavelength. Using CST Studio Suite simulations, mode patterns (TE??, TE??, TE??) and S-parameters were analyzed, confirming theoretical behaviors and their practical relevance for applications like radar and satellite communications.

Further analysis of group delay, phase variation, and phase constant showed significant signal dispersion near the cut-off frequency but stable, low-distortion propagation above it. These parameters are critical for understanding signal integrity and phase synchronization in advanced RF and microwave systems.

Overall, the research demonstrates effective circular waveguide design and simulation, highlighting its suitability for efficient high-frequency communication, radar, and high-power microwave applications.

Conclusion

The analysis of mode patterns, S-parameters, and wave propagation characteristics in a circular waveguide is essential for practical applications in satellite communication, radar, and high-frequency microwave systems. The mode pattern study reveals how different modes propagate, influencing system efficiency in applications requiring low-loss and high-power transmission. The dominant TE?? mode ensures stable propagation, making it ideal for satellite feeds and deep-space communication, while higher-order modes like TE?? and TE?? play a role in advanced signal processing and high-power applications. The S-parameter analysis confirms the waveguide’s high-pass filtering behaviour, where S?? shows effective power transmission beyond the cut-off frequency, ensuring minimal loss in practical microwave and RF applications. Meanwhile, the S?? response highlights impedance mismatches that can be optimized to improve antenna performance and minimize signal reflection. The group delay analysis demonstrates that after the cut-off frequency, signal distortion stabilizes, which is critical for maintaining data integrity in high-speed communication systems. The phase variation and phase constant results ensure predictable signal behaviour, essential for phased-array antennas and precise frequency control in radar and satellite links. Overall, these analyses validate the circular waveguide’s efficiency in supporting multiple propagation modes while maintaining stable transmission, making it a vital component in modern high-frequency communication systems.

References

[1] Samuel Y. Liao, Microwave Devices and Circuits, 3rd ed., Prentice Hall, Englewood Cliffs, NJ, USA, 1990. [2] Allan W Scott, Understanding Microwaves, A Wiley-Interscience publication, Third Avenue, New York, USA, 1993. [3] James Benford, John A Swegle, Edl Schamiloglu, High Power Microwaves, 3rd ed, CRC Press, New York, USA, 2016. [4] Dr. Paul Chorney, “Group Delay in Rectangular Waveguides”, RF/Microwaves/ Millimeter Waves, 1191E. Versailles Dr. Tucson, AZ 85737-5844, 2001. [5] Seyed Mohammadreza Razavizadeh, “Modes and Dispersion Analysis of a Rect. Waveguide Using CST Microwave Studio”, Islamic Republic of Iran Broadcasting University, March 2016. [6] V. Prakasam and P. Sandeep, \"Mode Patterns in Rectangular Waveguide\", IJTRD, Hyderabad, Andhra Pradesh, India, 2017.

Copyright

Copyright © 2025 Sinchana M G, Prakruthi V, Amrutha B T, Manasa H S, Deepika K C, Prakruthi H L, Shivabhagya M S, D Senthil Kumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.