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What is an Electromagnetic Reverberation Chamber?

What is an Electromagnetic reverberation chamber? Reverberation chamber construction and working principle, key benefits, limitations, and applications?

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Editorial Team - EMC Directory

Apr 5, 2024

Like an anechoic chamber, semi-anechoic chamber, TEM cells, and GTEM cells, the Electromagnetic reverberation chamber is another EMC test site/environment for conducting Electromagnetic compatibility (EMC) testing and other electromagnetic investigations. 

 A reverberation chamber (RC) is a screened room or shielded enclosure formed by highly conductive walls, often equipped with tuners (stirrers). It is designed to provide high field strength (V/m) with statically uniform electromagnetic field distribution within the chamber for EMC testing. This chamber can be used for both radiated immunity and emission measurement testing. But, particularly, the reverberation chamber is suitable for use in EMC radiated immunity testing to create a uniform field with very high field strength (V/m) using moderate input power. Some standards, such as DO-160 (200 V/m), called out high field strength for EMC testing. The chamber can create high field strength up to several hundred or thousands of V/m (e.g., 200V/m - 7000V/m or higher) while radiated immunity testing. 

Figure 1: Inside look of a reverberation chamber. The walls are highly conductive. The vertical mode stirrer (tuner) changes electromagnetic boundaries to ensure a (statistically) homogeneous field distribution.

The electromagnetic reverberation chamber is ideal for performing EMC testing for all electrical & electronic products according to EMC standards, such as RTCA DO 160 and MIL STD 461, IEC61000-4-21, ISO 11452-11, etc. This chamber can also be used to evaluate the shielding effectiveness of materials and cables, determine the total radiated power of a DUT, and be used in antenna measurement, the channel modelling of mobile communication, the omnidirectional sensitivity test for mobile devices & the base stations, and more. 

The application areas of this chamber include defense, automotive, and aeronautics fields. In recent years, this chamber has been used in biological, communication, and other.  

What is EMC testing?

An electrical and electronic product/device can be sold in a market of a country when it meets the requirements of relevant EMC emission and immunity standards. 

EMC testing is the process of checking whether the product meets the requirements of EMC standards. When a product meets/complies with the requirements of the EMC standards, the product is said to be an EMC-compatible/EMC-certified product. An EMC-certified product can operate satisfactorily in its intended electromagnetic environment without emitting harmful electromagnetic emissions that could disturb/interfere with other nearby devices. 

Typically, two types of tests are involved in the EMC testing. They are the emissions measurement testing and the immunity testing. The EMC testing is conducted according to EMC standards, usually in a laboratory environment using EMC testing tools such as an antenna, signal generator, anechoic chamber/reverberation chamber, and other required tools. The EMC standards define various aspects such as electromagnetic emissions limits, immunity test levels, EMC testing procedures, testing setup, and so on.

Various EMC standards, including MIL-STD 461E, RTCA DO 160D, IEC 61000-21, and ISO 11452-11, allow the use of reverberation chambers for EMC certification testing. 

Construction and working principle of Electromagnetic reverberation chamber:

The reverberation chamber (RC) is an enclosure constructed with perfectly conducting walls (Figure 1). Also, the chamber often features mode stirrers (tuners). Additionally, other auxiliary equipment such as a drive motor, signal generator, power amplifier, transmitting and receiving antenna, receiving device, and a computer are used for performing EMC testing.

The reverberation chamber (RC) walls are typically formed by using highly conductive materials, such as aluminum or galvanized steel. The highly conductive walls create a highly reflective environment within the chamber, where electromagnetic waves bounce off all surfaces with minimal energy loss. Due to the low energy loss during reflection, the chamber can create very high field strength (V/m) inside the chamber with moderate input power for performing radiated immunity testing. 

Inside the chamber, because of electromagnetic wave reflection from the walls, the electromagnetic field distribution is strongly inhomogeneous (standing waves). This inhomogeneity can be reduced by changing the electromagnetic boundary of the chamber. Changing the electromagnetic boundary of the chamber will change the standing wave pattern (i.e., will change electromagnetic field distribution inside the chamber), thereby creating a statistically uniform field environment inside the chamber for EMC testing. 

The following techniques are applied to reduce inhomogeneity (i.e., to change the boundary of the chamber to create statistically uniform field distribution).   

  • Generating a uniform field environment by using one or more tuners (stirrers) inside the chamber. This reverberation chamber is called a mode-stirred chamber (MSC). The mode stir technique is mostly used in the reverberation chamber (Figure 1&2). 
  • Generating a uniform field environment by vibrating the walls of a shielded tent instead of using stirrers (tuners). This chamber is called the vibrating intrinsic reverberation chamber (VIRC).

In this way, the reverberation chamber can create a uniform field with high field strength inside the chamber. This chamber can be used to conduct both EMC emission and immunity testing.

Basic concept of the mode-stirred chamber (MSC): 

Figure 2: A mode-stirred chamber (MSC) with a horizontal and vertical stirrer, used in EMC emission testing

A mode-stirred chamber (MSC) is an enclosure constructed with perfectly conducting walls fitted with tuners (stirrers). A tuner (stirrer) is a rotating paddle with large metallic reflectors that can be moved to various orientations to change the boundary of the chamber to achieve a uniform electromagnetic field environment inside the chamber. To efficiently stir the field patterns, usually, the chamber construction can use two stirrers (horizontal and vertical) inside the chamber (Figure 2). The material of the tuner (stirrer) is the same as that of the chamber wall, such as aluminum or galvanized steel. The Lowest Usable Frequency (LUF) of the mode-stirred chamber depends on chamber size and the tuner design. Small chambers have a higher LUF compared to large chambers. 

The stirrer system is driven by a stepper motor. The motor is controlled by the computer through a motor control unit to ensure the efficient performance of the chamber. The computer is loaded with software that automatically tunes the stirrers and controls the instruments to collect the measurement data of DUT (device under test) and analyze the measured results (Figure 2). 

Basic concept of vibrating intrinsic reverberation chamber (VIRC).

Figure 3: Vibrating intrinsic reverberation chamber (VIRC)

The VIRC is a tent made from conductive fabric. In this chamber, instead of using the conventional paddle wheel (i.e., stirrers), the walls of the tent are vibrated/shaken (typically between 5 and 20 Hz), see Figure 3.  The walls’ vibration alters the chamber's boundary and effectively changes the standing wave pattern, resulting in a more uniform electromagnetic field distribution inside the chamber. The VIRC is the most affordable version of the reverberation chamber (RC). This chamber is easy to mount and can be assembled and disassembled quickly at the customer's location within a matter of hours.  

Key benefits of reverberation chamber (RC) over the traditional EMC test sites such as anechoic chamber and semi-anechoic chamber: 

  • RC provides a more realistic test environment and can generate a uniform field with very high field strength (V/m) using moderate input power. 
  • RC can illuminate equipment under test (EUT) from all angles while radiated immunity test. 
  • Low construction and repair costs since NO RF absorbers in the reverberation chamber. This chamber is a low-cost alternative to semianechoic chambers for EMC testing. 
  • This chamber has good test repeatability in the radiated immunity test.
  • RC has lower testing times 
  • Also, compared to TEM Cell methods, the reverberation chamber has benefits such as a more realistic test environment, good test repeatability, and an easy-to-achieve high-field strength environment.

Limitation of RC: 

At low frequencies, a large size is required for the reverberation chamber to function properly. Hence, the RC may not replace traditional test sites in the lower frequency bands.

Key features of Reverberation chambers:

  • Screened environment, meaning- no ambient signals
  • The Electromagnetic reverberation chambers are available wide frequency range with customization features
  • This chamber can Illuminate with all directions and polarisations (immunity test)
  • Avail with a large working volume 
  • Reverberation Tents are available with flexible and modular designs, and they can be easy to set and disassemble quickly 
  • Available as a Turnkey Package – chamber, turntables, Antenna & mast, instrumentation and software
  • Provide convenient solutions at a low cost.

Click here to view the Reverberation Chambers on EMC Directory.


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