(semi) Anechoic chambers (EMC)



An anechoic chamber is simulating an Open Area Test Site (OATS), without interference from environmental electromagnetic field pollution. Its origins can be traced to efforts to build aircrafts which absorbed or scattered radar signals during the Second World War. Recent innovations such as the use of ferrite tiles, have greatly enhanced the performance of these anechoic chambers.

The anechoic chamber is typically used to house the equipment for performing measurements of antenna radiation patterns, electromagnetic compatibility (EMC) and radar cross section (RCS) measurements. Testing can be conducted on full-scale objects including various electronic devices, vehicles, aircraft or spacecraft. The internal appearance of anechoic chambers is sometimes similar to that of an acoustic anechoic chamber, however, the interior surfaces of the RF anechoic chamber are covered with radiation absorbent material (RAM)* instead of acoustically absorbent material.
 

*The more common name for RAM is microwave absorbers.
 

To satisfy each unique customer requirement Comtest Engineering can provide turnkey solutions for the following anechoic test chambers:

•    Compact full anechoic chamber
•    Semi anechoic chamber, test distance 3m, 5m, 10m.
•    Anechoic chamber for automotive testing (components / full vehicle)
•    Anechoic chamber for Mil-STD / DO-160 testing
•    Antenna pattern measurement room
•    (compact) Antenna test range


Applicable standards / test methods for semi / full anechoic chambers:

 
Radiated emissions

EN 61000-6-3
EN 61000-6-4
CISPR 11 / EN55011
CISPR 12 / EN55012
CISPR 13 / EN55013
CISPR 14 / EN55014
CISPR 15 / EN55015
CISPR 16-1-14
CISPR 22 / EN55022
CISPR 25
FCC part 15
Mil-Std 461-F (re section)
RTCA DO-160-G
Various ETSI standards
ANSI C63.4
SAE J551
Radiated immunity

IEC/EN 61000-4-3
EN 61000-6-1
EN 61000-6-2
CISPR 12 / EN55012
CISPR 20 / EN 55020
CISPR 24 / EN 55024
Mil-Std 461-F (RS section)
RTCA DO-160-G
ISO 11451
ISO 11452
SAE J551

 

Microwave chambers

 

Microwave chambers are full anechoic chambers used for testing in microwave frequencies. Typical equipment under test is mobile & telecom products as well as electronic products using wireless communication techniques. Larger microwave chambers (antenna test ranges) are built to test radars, satellites and a wide range of antennas and antenna applications. Comtest can provide (full) anechoic chamber solutions for OTA chambers and antenna test ranges to perform near field and far field measurements. Each microwave chamber is tailored to the specific requirements of the customer and its equipment under test.

OTA chambers
RF shielded antenna test chambers for wireless Over-The-Air (OTA) testing are built as full anechoic
chambers. Typical equipment under test is mobile & telecom products as well as other electronic products using wireless communication techniques. Typical validation procedures for full anechoic chambers used for wireless (OTA) testing are Free Space VSWR (ANSI/IEEE-149), CTIA OTA Rev. 2.2.1 Jan 2008 and ETSI TR102 273.

Antenna test chambers
Large antenna test chambers (antenna test ranges) are built to test radar systems (or RCS measurements), Aerospace equipment (such as satellites) and a wide range of antennas and antenna applications. These full anechoic chamber solutions can be used to perform near field and far field measurements. Validation of the RF characteristics in the quiet zone (QZ) of an antenna test range is done using the Free Space VSWR test procedure.

Framed antenna test chambers
For most microwave test applications our high performance polystyrene absorbers provide a sufficient degree of transfer attenuation making a RF shielded room superfluous. Comtest high performance, broad band, carbon loaded polystyrene absorbers have a modular design that consist of a separate base plate and tapers. Other benefits are that the product is light weight, rigid and has a superior tensile strength. These last features make the absorbers perfectly suitable to use as a self supporting structural product. The framed antenna test chamber is constructed using just the polystyrene absorbers as building blocks and a simple, light weight metal construction supporting these microwave absorbers. The modular design of the absorbers makes it possible to first build a room using the base plates and insert the tapers in the final stage of the installation. The result is a high performance antenna test chamber for an attractive price that fits even the smallest budgets.
 

Reverberation chambers



A reverberation chamber is a specialized EMC test chamber generating very high field strength using modest amplifier power. The reflections between the RF shielded walls are optimized to add up to maximum of as many standing waves as practically possible. The chamber is mainly used for testing electrical immunity of test objects. The RF shielding is established by constructing the reverberation chamber from a 2 mm pan-type galvanized or 3mm aluminum panel system.  RF shielded doors and cabling access to the reverberation chamber are specially shielded for RF signals. This ensures that unwanted electrical noise from the outside world does not affect the test results and electrical immunity testing can be made without disturbing the surroundings.

 

EMC testing in a reverberation chamber

When performing EMC testing the reverberation chamber is mode-stirred or mode-tuned by means of a stirrer. A stirrer system is a (large) structure of aluminum plates that is stepwise turned during testing. The objective is to maximize the standing wave pattern in the usable test volume. These EMC tests are statistically evaluated and the “worst case” data are used for the final evaluation of the test result. In addition to immunity testing electrical emission tests or specialized EMC testing in accordance to military, aerospace or automotive EMC test standards can be performed in the reverberation chamber.
 

Multi functional EMC test chamber

The reverberation chamber creates a multi functional EMC test chamber for commercial, military and automotive EMC testing. Comtest reverberation rooms comply with the IEC 61000-4-21prt 4-21, EUROCAE/ED-14F, MIL-STD 461F, RTCA/DO-160F stabdard as well as various automotive standards. The reverberation chamber can also be used for immunity and shielding effectiveness tests as well as for measuring total radiated power. Another application for the reverberation chamber is simulating complex multipath environments like computer rooms and other electrically congested areas.
 

Advantage of a reverberation chamber

The main advantage of EMC testing in a reverberation chamber over the traditional semi anechoic chamber tests is that less power input is required to achieve the same field levels which make expensive amplifier systems obsolete.


Reverberation chamber solutions

Comtest Engineering can supply the following reverberation chamber solutions:
 

- Reverberation chamber model 1716-0080 (LUF 80MHz)
- Reverberation chamber model 1716-0100 (LUF100MHz)

- Reverberation chamber model 1716-0200 (LUF 200MHz)
- Reverberation chamber model 1716-0400 (LUF 400MHz)
- Reverberation chamber model 1716-1000 (LUF 1000MHz)

RF shielded rooms & doors


 

RF shielded rooms

Since sophisticated electronics permeate modern life controlled electromagnetic environments such as RF shielded rooms become essential. RF shielded rooms and RF shielded doors are an integral component in modern EMC test facilities. Communication and data centers, calibration and EMC test laboratories as well as many other related test facilities all require electromagnetic shielding.


RF shielded doors

The Comtest RF shielded doors are designed for high performance shielded enclosures. The shielding characteristics are achieved using a double knife edge, matching quadruple beryllium copper finger contact strip. Comtest RF shielded doors are equipped with a unique parallel closing mechanism and patented locking and latching system. All Comtest shielded doors are available in manual, semi- and full automatic operation. Our standard range of swing and sliding doors consists of many different models and can be designed with a 50mm low threshold. In EMC applications both ferrites and absorbers can be affixed to the standard door leaf.