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ELCT564 Spring 2012

ELCT564 Spring 2012. Chapter 3: Waveguides and Transmission Lines. Waveguides. Metal Waveguides. Dielectric Waveguides. Comparison of Waveguides and Tlines. Transmission Line. Waveguide.

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ELCT564 Spring 2012

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  1. ELCT564 Spring 2012 Chapter 3: Waveguides and Transmission Lines ELCT564

  2. Waveguides Metal Waveguides Dielectric Waveguides ELCT564

  3. Comparison of Waveguides and Tlines Transmission Line Waveguide Metal waveguides are typically one enclosed conductor filled with an insulating medium while a dielectric waveguide consists of multiple dielectrics Two or more conductors separated by some insulating medium (two-wire, coaxial, microstrip, etc. Normal operating mode is the TEM or quasi-TEM mode (can support TE and TM modes but these modes are typically undesirable. Operating modes are TE or TM modes (can not support a TEM mode) No cutoff frequency for the TEM mode. Tline can transmit signals from DC up to high frequency Must operate the waveguide at a frequency above the respective TE or TM mode cutoff frequency for that mode to propogate Lower signal attenuation at high frequencies Significant signal attenuation at high frequencies Can transmit high power levels Small cross section line can transmit only low power levels Large cross section waveguides are impractical due to large size and high cost. Large cross section tlines can transmit high power leves. ELCT564

  4. General Solutions for TEM, TE and TM Waves ELCT564

  5. General Solutions for TEM, TE and TM Waves TEM Waves TE Waves TM Waves Attenuation due to Dielectric Loss ELCT564

  6. Parallel Plate Waveguide TEM Waves ELCT564

  7. Parallel Plate Waveguide TM Waves ELCT564

  8. Parallel Plate Waveguide TE Waves ELCT564

  9. Summary of Results for Parallel Plate Waveguide ELCT564

  10. Rectangular Waveguide TE Waves ELCT564

  11. Rectangular Waveguide TM Waves ELCT564

  12. Summary of Results for Rectangular Waveguide ELCT564

  13. Example I Consider a length of Teflon-filled (εr=2.08, tanδ=0.0004) copper K-band rectangular waveguide, having dimensions a=1.07 cm and b=0.43 cm. Find the cutoff frequencies of the first five propagating modes. If the operating frequency is 15 GHz, find the attenuation due to dielectric and conductor losses. ELCT564

  14. Example II ELCT564

  15. Circular Waveguide TE Waves ELCT564

  16. Circular Waveguide TM Waves ELCT564

  17. Summary of Results for Cirular Waveguide ELCT564

  18. Example I Find the cutoff frequencies of the first two propagating modes of a Teflon-filled (εr=2.08, tanδ=0.0004) circular waveguide with a=0.5cm. If the interior of the guide is gold plated, calculated the overall loss in dB for a 30cm length operating at 14GHz. ELCT564

  19. Example II ELCT564

  20. Attenuation of Waveguides ELCT564

  21. Coaxial Line Higher Order Modes ELCT564

  22. Coaxial Line: Example Consider a piece of RG-401U coaxial cable, with inner and outer conductor diameter of 0.0645’’ and 0.215’’, and a Teflon dielectric(εr=2.2). What is the highest usable frequency before the TE11 waveguide mode starts to porpagate? =563.4 m-1 =18.15GHz Field lines for TEM mode of a coaxial line Field lines for TE11 mode of a coaxial line ELCT564

  23. Coaxial Connectors ELCT564

  24. Strip Line ELCT564

  25. Strip Line: Example Find the width for a 50Ω copper stripline conductor, with b=0.32 cm and εr=2.2. If the dielectric loss tangent is 0.001 and the operating frequency is 10 GHz, calculate the attenuation in dB/λ. Assume a conductor thickness of t=0.1mm. ELCT564

  26. Microstrip Line ELCT564

  27. MicroStrip Line: Example Calculate the width and length of a 50Ω copper microstrip line, with a 90o phase shift at 2.5GHz. The substrate thickness is d=0.127 cm, with εr=2.2. ELCT564

  28. Wave Velocities and Dispersion Dispersion: If the phase velocity is different for different frequencies, then the individual frequency components will not maintain their original phase relationships as they propagate down the transmission line or waveguide, and signal distortion will occur. Group Velocity Calculate the group velocity for a waveguide mode propagating in an air-filled guide. Compare this velocity to the phase velocity and speed of light. ELCT564

  29. Summary of Transmission Lines and Waveguides ELCT564

  30. Other Lines and Guides ELCT564

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