Radar Technology for Level Gauging - Krohne

A negative value for r means that the polarity of the reflected pulse reverses.
Fig. 18 shows the value of r at the junction between a (standard) 50 W line and a line with
natural impedance Z 2:
In waveguide structures, when the waveguide is filled with materials having different dielectric
constants er, the challenge is to implement a junction that has the least possible reflections.
By combining different materials with matched ε r and using special geometries 15 an approximately
reflection-free junction can be obtained which effects “impedance transformation”
of the waves (Fig. 19).
ε ε ε
0
1
λ λ
4 4
2
ε ε ε
4.4.9 Plug connectors
Plug connectors are required to provide quick-connection facilities between coaxial cables
or between such cables and circuit modules. So-called SMA connectors are the most
commonly used for the maximum-frequency range up to 26 GHz. They exhibit low throughput
losses and good active return losses.
15 Mostly dielectric bodies with gradually or abruptly changing cross-section or filling of the waveguide, the geometry
being in a certain proportion to the wavelength in the dielectric.
Fig. 19:
Examples of
impedance
transformers in
waveguides
Radar handbook 23
0
λ
1
2
4
Fig. 18:
Voltage reflection
factor at the junction
of a 50 Ω line