12 Difference Between Waveguide And Transmission Line

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What Is Waveguide?

A wave guide is a structure that guides waves such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction.  Typically, waveguides are hollow metal tubes (often rectangular or circular in cross section). They are capable of directing power precisely to where it is needed, can handle large amounts of power and function as a high-pass filter.

An electromagnetic field can propagate along a waveguide in various modes. The two common modes are Transverse-magnetic (TM) and Transverse-electric (TE). In TM mode, the magnetic lines of flux are perpendicular to the axis of the waveguide. In TE mode, the electric lines of flux are perpendicular to the axis of the waveguide. Any of these modes can provide low loss and high efficiency as long as the interior of the waveguide is kept clean and dry.

Waveguides acts as a high pass filter in that most of the energy above a certain frequency (the cutoff frequency) will pass through the waveguide whereas most of the energy that is below the cutoff frequency will be attenuated by the waveguide.  Waveguides are often used at microwave frequencies (greater than 300 MHz, with 8 GHz and above being more common. Waveguides are commonly used in microwave communications, broadcasting and radar installations.

Types of Waveguides

  • Rectangular waveguides
  • Circular waveguides
  • Elliptical waveguide
  • Single ridged waveguide
  • Double ridged waveguide

What You Need To know About Waveguide

  1. A waveguide is a hollow metallic pipe design to carry microwave energy from one place to another.
  2. Metal waveguides are typically one enclosed conductor filled with an insulating medium (rectangular, circular) while a dielectric waveguide consists of multiple dielectrics.
  3. Wave theory is considered in waveguide analysis.
  4. Power handling capacity is high.
  5. The operating frequency is 3 GHz to 100GHz in waveguide.
  6. Operating modes are TE or TM modes (cannot support a TEM mode).
  7. The large surface area of waveguide reduces copper losses.
  8. Dielectric losses are less in waveguide.
  9. Lower signal attenuation at high frequencies than transmission lines.
  10. It acts as a high pass filter.
  11. Wave impedance (characteristic impedance) is a function of frequency.
  12. In waveguide, the electromagnetic signal is transmitted.

What Is Transmission Line?

A transmission line is a pair of electrical conductors or wire which is designed for carrying an electrical signal from one place to another. Transmission line is made up of a conductor having a uniform cross-section along the line.

The performance of a transmission line depends on the parameters of the line. The transmission line has mainly four parameters that is, resistance, inductance, capacitance and shunt conductance. These parameters are uniformly distributed along the line. The capacitance and conductance form the shunt admittance whereas the inductance and resistance form series impedance.

Types Of Transmission Line

  • Short Transmission Line
  • Medium Transmission Line
  • Long Transmission Line

What You Need To Know About Transmission Line

  1. The transmission line is a conductor or wire which is designed to carry electrical energy below microwave range from one place to another.
  2. Transmission lines are two or more conductors separated by some insulating medium (two-wire, coaxial, microstrip, etc).
  3. Circuit theory is considered in transmission line.
  4. Power handling capacity is low.
  5. The operating frequency is up to 18 GHz.
  6. The normal operating mode is the TEM or Quasi-TEM mode (can support TE and TM modes but these modes are typically undesirable).  
  7. Two wire transmission line have large copper losses due to small surface area.
  8. Dielectric losses are more in two wire transmission line.
  9. Significant signal attenuation at high frequencies due to conductor and dielectric losses.
  10. All frequencies pass through.
  11. Characteristic impedance in transmission line depends on the physical parameters of transmission line.
  12. In transmission line, the electrical signal is transmitted.
BASIS OF COMPARISON WAVEGUIDE TRANSMISSION LINE
Description A waveguide is a hollow metallic pipe design to carry microwave energy from one place to another.   The transmission line is a conductor or wire which is designed to carry electrical energy below microwave range from one place to another.  
Structure Metal waveguides are typically one enclosed conductor filled with an insulating medium (rectangular, circular) while a dielectric waveguide consists of multiple dielectrics.   Transmission lines are two or more conductors separated by some insulating medium (two-wire, coaxial, microstrip, etc).  
Supporting Theory Wave theory is considered in waveguide analysis.   Circuit theory is considered in transmission line.  
Power Handling Capacity Power handling capacity is high.   Power handling capacity is low.  
Operating Frequency The operating frequency is 3 GHz to 100GHz in waveguide.   The operating frequency is up to 18 GHz.  
Operating Mode Operating modes are TE or TM modes (cannot support a TEM mode).   The normal operating mode is the TEM or Quasi-TEM mode (can support TE and TM modes but these modes are typically undesirable).   
Copper Losses The large surface area of waveguide reduces copper losses.   Two wire transmission line have large copper losses due to small surface area.  
Dielectric Losses Dielectric losses are less in waveguide.   Dielectric losses are more in two wire transmission line.  
Signal Attenuation Lower signal attenuation at high frequencies than transmission lines.   Significant signal attenuation at high frequencies due to conductor and dielectric losses.  
Filter Functionality It acts as a high pass filter.   All frequencies pass through.  
Impedance Wave impedance (characteristic impedance) is a function of frequency.   Characteristic impedance in transmission line depends on the physical parameters of transmission line.  
Type Of Signal Transmission In waveguide, the electromagnetic signal is transmitted.   In transmission line, the electrical signal is transmitted.  

Advantages of Waveguides

  • The microwave energy when travels through the waveguide, experiences lower losses than a coaxial cable.
  • Power loss is very negligible in waveguides
  • They can handle very large power (in kilowatts)
  • They are easy to manufacture
  • They offer very low loss (low value of alpha-attenuation).

Advantages Of Transmission Line

  • Maintenance of the line is easier
  • Long distance transmissions
  • Low installation and material cost