Coax-waveguide transition design

Context

When designing slotted waveguide antenna, the most popular technique to feed the antenna is the use of a coax-waveguide transition.

Fig. 1 Slotted waveguide antenna: a) Waveguide antenna is known for its high gain, high power

b) Photo of a waveguide antenna

 

A transition structure is required due to:

  • Difference of guided modes: In the coaxial cable, the mode is TEM where both magnetic and electric fields are transverse (orthogonal to the propagation axe). Meanwhile in the waveguide, the mode is TE10.
  • Difference of characteristic impedances: impedance in the coaxial cable is 50 Ohm and that of waveguide can be several times higher (depending on the structure), in the range of 300 – 400 Ohms. What does it mean “characteristic impedance”? Well, long story short, the geometry and the material of a transmission line defines a factor between the electric field strength and the magnetic field strength. That factor is “characteristic impedance”. It tells how the structure favor electric field compared to magnetic field.

Read More

Magnetron, a cheap and simple way to create power microwave source

Context

Magnetrons are widely used as RF power sources because they offer high energy conversion efficiency (around 75%) at a low cost. The magnetron was invented during World War II, when its small size, high power and short wavelength made it ideal for use in radar, but with mass production and the development of automatic manufacturing techniques, magnetrons made the move into the home as the radiation source in microwave ovens.

a) a microwave oven making use of magnetron as electromagnetic source

b) what a magnetron looks like

b) what a magnetron looks like

Fig. 1

Read More