Five Antenna Measurements Methods to Consider

Key Takeaways

• Antenna measurements can be regarded as the experimental validation of the parameter values given in an antenna datasheet. 

• The test setup uses source antennas or transmitting antennas with known characteristics so that field incidents on the antenna under test are approximately plane waves.

• The necessary condition for any antenna measurement method is to reduce the error in measured parameters to acceptable levels.

Antenna measurements are performed to determine various parameters such as radiation pattern, gain, directivity, input impedance, and polarization

Antennas are the lifeline of wireless communication systems, and faulty antennas can cause major connection issues in wireless networks. That is why it is critical to make antenna measurements before installing them in wireless systems.

Antenna measurements are performed to determine various parameters such as radiation pattern, gain, directivity, input impedance, and polarization. The antenna measurements ensure that the antenna under test meets all specifications. There are various antenna measurement methods available to characterize antennas, and we will explore these methods as well as antenna parameters in this article.  

Antenna Measurements

Antenna measurement is a fundamental task performed in antennas before placing them in a wireless system. It is possible to characterize the performance of an antenna through antenna measurements. There are several performance indices that can qualify how effectively and efficiently the antenna under test is working.

Before connecting an antenna into a wireless system, the engineer looks for the specifications and characteristics of the antenna, such as radiation pattern, efficiency, directivity, polarization, and beamwidth, that are suitable for the given application. The antenna measurements are then conducted to confirm the antenna under test meets the parameters as specified in the datasheet. Antenna measurements can be regarded as the experimental validation of the parameter values given in an antenna’s datasheet.

Parameters commonly measured using antenna measurements include:

• Radiation pattern
• Polarization
• Input impedance
• Voltage standing wave ratio (VSWR)
• Directivity
• Gain
• Efficiency
• Effective isotropically radiated power (EIRP)
• Antenna noise temperature

For any of these antenna parameter measurements, a proper test setup is required. The influence of the test setup is very important, as it can create error measurements. 

Antenna Measurement Setup

Typically, an antenna measurement utilizes plane waves for testing the antenna under test. The test setup uses source antennas or transmitting antennas with known characteristics so that field incidents on the antenna under test are approximately plane waves. The antenna measurement setup includes the following systems:

Antenna under test - The antenna whose characteristics are to be measured. 

Source antenna and transmitter - A source antenna with a known radiation pattern and transmitter system is used to send plane waves to the antenna.  The source antenna radiates fields that can be approximated to plane waves at the desired frequency. The polarization and beamwidth of the source antenna need to be in a range that is suitable for the antenna under test. Horn antennas are an example of a source antenna in the antenna measurement setup. 

Receiver system - The receiver system is used to measure the power received by the antenna under test. The receiving system must determine how much power is received from the test.

Positioning system - The positioning system controls the orientation of the antenna under test. The positioning system rotates the antenna under test and helps in measuring the radiation pattern of the test antenna. For determining the radiation pattern as a function of angle, the test antenna is rotated with respect to the source antenna. 

Antenna Measurement Methods 

Generally, most antenna measurement methods require the aforementioned subsystems. Here are a few methods that can be used to carry out antenna measurements:

1. Antenna Measurements With a Spectrum Analyzer

A spectrum analyzer can be used to measure antenna characteristics. This method requires a signal generator and an antenna with known characteristics. 

2. Antenna Measurements With a Vector Network Analyzer

A vector network analyzer is used to measure the impedance and radiation of an antenna under test in the presence of a reference antenna. For polarization measurements, this method requires two measurements: one for vertical polarization and another for horizontal polarization.

3. Antenna Measurements With the Field or Walker Method

In this method, the transmitter side system is fixed at a place and position. The receiver side system is carried around the fixed transmitter system to determine the reliable range of the antenna under test. 

4. Antenna Measurements in Normal Space

Antenna measurements can be obtained from the test setup in normal space. However, the reflections from the walls, ceilings, floor, surrounding objects, and atmospheric conditions influence the antenna measurements made.

5. Antenna Measurements in Anechoic Chambers

The influence of atmospheric conditions and surrounding objects are non-ideal for accurate antenna measurements. An anechoic chamber offers a non-reflective, no-echo room for performing the antenna measurements. The anechoic chamber can simulate outer space, which is the most ideal location for antenna measurements.

A necessary condition for any antenna measurement method is to reduce the error in measured parameters to acceptable levels. Antenna measurements performed in the anechoic chamber provide fairly good and accurate measurements when compared to other antenna measurement methods exposed to the reflective environment.

Cadence Clarity 3D Transient Solver can simulate antenna measurements in the anechoic chamber. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts.