Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicapable.

Attenuation in plated-dielectric waveguides results from copper losses (αmcu), and dielectric losses (αd). Copper losses are also a function of the presence of the dielectric.

The equations for attenuation losses are:

where,

a = wide dimension of guide;

b = narrow dimension of guide;

tanδ = loss tangent; and

λ = propagation wavelength in the dielectric.

If a material other than copper is used for plating, αtotal is found by multiplying the value for copper plating by the square root of the ratio of resistivities.

Insertion loss measurements on two test pieces of copper-plated waveguide using Eccofoam PS (4 lb), are as follows:

Frequency

Length of test piece (ft)

Theoretical attenuation (dB)

Measured

3.5

6

0.54

0.56

3.1

3

0.23

0.24

Joining waveguide and fitting flanges

Plating baths and grinding tables are limited in size. Therefore, when long lengths of waveguide were required, joining methods had to be found to eliminate unnecessary flange joints.

Joining methods that were developed are shown in Fig. 2. “Mortise” and “Dowell-pin” joints, similar to those used in carpentry, are shown. With these joining methods, several problems are:

  • Waveguide alignment. If a misalignment of 0.03 in. exists in the narrow dimension of the waveguide, a VSWR of 1.25 results.
  • Small gaps may occur between the two matting pieces. This is not considered critical because of the low dielectric constants of the substrates (ϵ = 1.08 to 1.15).
  • Resistivity difference between “gluing agent” (silver epoxy) when mating pieces are jointed. If the joints are well made, and the two pieces of waveguide are well mated, this difference of resistivity is of little consequence.
  • Rigid joint and excellent electrical characteristics. The assembled joints are shown in Fig. 3. VSWR over the frequency range from 7.2 to 8.2 MHz for the assembled joints is given in Fig. 4.