ASTM D 4935 Flanged Coaxial Fixture

This is a common method for far field Shielding Effectiveness (SE) measurements and is well standardized in ASTM D 4935. The test fixture shown below is an enlarged coaxial transmission line which has flanges for inserting the test sample. The flanges provide capacitive coupling, but the flange size limits the lower frequency bound due to decreasing coupling at lower frequencies.

Dual TEM Cell

A TEM Cell is a section of expanded rectangular coaxial transmission line tapered at each end to match standard 50 ohm coaxial connectors. In the Dual TEM Cell (DTC), two of these cells are connected with an aperture in the shared wall to form coupled transmission lines. The test material is placed over this aperture for SE measurements. The DTC is unique from most other measurement techniques in that it has two output ports. The aperture couples power to the two output ports asymmetrically which permits separate examination of the couplings of the electric and magnetic fields.

HVS can design custom microwave fixture for your specific application. These fixtures can be used to make microwave measurements, such as shielding effectiveness measurements, at frequencies below 2 GHz. HVS also has expertise in Resonant Cavities, Surface/Volume Resistivity measurements, and other probes.