Anechoic Chamber Antenna Testing

Key Takeaways

• An anechoic chamber simulates antenna testing if the test is conducted in outer space.

• Anechoic chamber antenna testing conditions are more tightly controlled than in outdoor testing facilities. 

• The anechoic antenna testing setup consists of the antenna under test, RF transmitter system, reference antenna, receiver system, and positioning system. 

An anechoic chamber is the second-best antenna testing location next to outer space

An antenna is an electromagnetic signal sensing element in many applications such as radio, local area networks, and telecommunication systems. Antennas transmit and receive electromagnetic signals between multiple wireless points and convert radio frequency signals traveling on a conductor into electromagnetic signals propagating through free space. Depending on the application, the size, shape, and type of antenna changes. It is imperative to test antennas to understand their nature and other specifications. Anechoic chamber antenna testing is one such testing procedure employed in the electronics industry to test and measure antenna parameters such as radiation pattern, gain, and efficiency. We will discuss anechoic chamber antenna testing in this article. 

What Do Antennas Do?

Antennas are used for data transmission between two points. This data transmission is realized by the kinetic energy associated with electromagnetic waves. The kinetic energy of an electromagnetic signal is equal to the product of signal frequency and Planck’s constant. As the frequency increases, the kinetic energy also increases. The higher the frequency, the more powerful the wave is. 

The Importance of Understanding Antenna Characteristics

Like power, other signal frequency-dependent parameters play a significant role in antenna performance. Characteristics such as the antenna’s radiation pattern, gain, and efficiency are influenced by signal frequency. The signal frequency utilized for each application is different, which is why the fundamental parameters of the antenna vary.

It is highly risky to employ an antenna without understanding its nature, specification, and characteristics. To choose an antenna for a given application, engineers typically inspect the radiation pattern, gain, and efficiency of the antenna by conducting antenna testing. 

What Is the Purpose of Antenna Testing?

Antenna testing determines how the antenna performs and helps engineers understand whether the antenna possesses the desired characteristics. The location of antenna testing is also crucial, as the reflections from objects can lead to inaccurate antenna measurements. The outer space is the ideal location, but the next best testing location is an anechoic chamber.  

Anechoic Chambers

The anechoic chamber is an isolated room free of electromagnetic signals utilized for antenna testing. Anechoic chambers simulate antenna testing if the test is conducted in outer space. Anechoic chambers are free space ranges where signal reflections from neighboring objects are suppressed for accurate antenna test measurements. Anechoic chambers form screened rooms fully or partially covered with electromagnetic absorbers. They create an enclosure with high shielding attenuation against electromagnetic interference. Anechoic chambers absorb 100% of ambient emissions but reflect the minimum amount of internal radiation. 

Anechoic Chamber Antenna Testing

Anechoic chamber testing conditions are more tightly controlled compared to outdoor testing facilities. An anechoic chamber antenna testing setup is covered with jagged triangles that are effective in suppressing reflections. The antenna testing setup is made inside the anechoic chamber and consists of the following.

1. Antenna Under Test

An antenna whose characteristics are determined by antenna testing is called an antenna under test or test antenna. The antenna under test and an RF transmitter system are positioned at a known distance from a reference antenna. A receiver of known sensitivity is attached to the antenna under test. 

2. RF Power Transmitter

The RF power transmitter injects RF energy into the antenna under test and outputs a stable known power level. The energy at frequencies other than the desired frequency should be minimum in the antenna testing transmitter system. 

3. Reference Antenna

An antenna with known characteristics such as radiation pattern, gain, and efficiency is called a reference antenna. The reference antenna should radiate efficiently at the desired signal frequency. Typically, dual-polarized horn antennas are employed as reference antennas for measuring horizontal and vertical polarization simultaneously. The reference antenna is connected to a known receiver. 

4. Receiver System

The receiver system is used to measure the power received by the antenna under test. The receiving system simply needs to determine how much power is received from the test. Usually, a power meter that measures the RF power is connected to the test antenna terminals using a co-axial cable and connectors. The receiver system is designed as a 50 Ω system.

The gain of the antenna under test can be determined from the signal amplitude measured at the receiver of the test antenna. The ratio of the measurements from the receiver and transmitter of the antenna under test gives the efficiency of the antenna. Usually, a vector network analyzer (VNA) replaces the transmit or receive system in the antenna testing setup. 

5. Positioning System

The positioning system controls the orientation of the antenna under test. The positioning system rotates the antenna under test and helps measure the radiation pattern of the test antenna. To determine the radiation pattern as a function of the angle, the test antenna is rotated with respect to the source antenna.

Anechoic chamber antenna testing is one of the most popular free space antenna testing ranges that gives stable and predictable antenna measurements. Anechoic chamber antenna testing gives excellent antenna measurements, especially above 300MHz. Cadence Clarity 3D Transient Solver can simulate anechoic chamber antenna testing to find a suitable antenna type in the early stages of system design. 

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