Ranatec Feedthrough Filters for Shielded Cabinets
The air is filled with noise and in this context we mean radio waves. The massive amount of wireless communication today makes for a frequency spectrum brimming with signals. To make the most out of this spectrum as a limited resource, radio devices have stringent requirements to enforce a reasonable coexistence. This includes for example the maximum transmit power, allowed frequency channel, out-of-band emissions and taking turns through control from a base station or by polite channel access.
The need of shielded cabinets for device development and verification
The requirements need to be tested during device development and verified in certification testing. Some of these tests can be performed through connections to the device and some need to be over-the-air so that the antennas are included in the system. For the latter and sometimes also for the former, the electromagnetic noise in the environment will disturb the measurements. The tests are then performed in a shielded cabinet, which could be a large chamber or a small box.
Understanding the shielding effectiveness of shielded cabinets
The level of shielding for such a cabinet is determined by the quality of its joints, by the sealing of the lids, by the dimensions of air vents and by the filtering quality of feedthroughs. Typically, the shielding effectiveness of a box needs to be 60, 80 or 100 dB, depending on the application and frequency range. It is measured as the difference in transmission between an interior and an exterior antenna, when the lid is opened and closed, respectively.
The role of a high-quality construction
Joints and lids need to be free from airgaps, have consistent contact pressure and conducting or absorbing gaskets. For air vents, it is the number of holes, the hole diameter and the thickness of the penetrated wall that determines the level of shielding. There is always a cutoff frequency, above which the honeycomb vent stops working.
How to get access to a shielded cabinet while maintaining shielding integrity
A feedthrough filter provides access into the shielded box for power or communication signals. It can be for 110/230 V AC power or low voltage feed. Signal interfaces can be ethernet, USB, HDMI or fiber. The feedthroughs need careful design if the shielding integrity shall remain.
The importance of careful design of feedthrough filters
If a cable is just inserted into the box through a hole, it will cause a huge leakage. The cable and hole will act together as a coaxial line that guides electromagnetic waves of any frequency in and out of the cabinet. Instead, a careful filtering design must be applied for the feedthroughs.
The Ranatec panel mount feedthrough filters
The Ranatec feedthrough filters have very careful designs and compromise between the level of leakage suppression and distortion of the wanted pass-through signal. They come in aluminum boxes of practical sizes. The panel mount versions are prepared with standard M-series screw mount holes and conducting gaskets. They can be mounted on either side of the cabinet wall, whichever fits best for the application. Ranatec also provides fabric mount feedthrough filters, please contact us for more information.
