How is your antenna doing?

Do you know the answer? How should the antenna be doing? Just well enough for needed communications? Could antenna be too good? Maybe it should perform like it is designed to perform? In many cases, this is not the situation at all.

Antenna size, place and type should be designed to meet target performance. Antenna performance sets many quality prerequisites to the whole wireless system, not just with communication issues. We need to consider very carefully how and when we should perform R&D measurements to ensure final prototype performance. Measurement aspects against R&D specification need to be considered from the beginning of the project. Do you have antenna specification; and can antenna design fulfil it?

Wireless product + best antenna = wireless product with superior wireless performance

Is this simple equation true? In quite many cases, even the best antenna might perform poorly if there is some error in implementation. The antenna might be slightly tuned to the wrong frequency or impedance is not matched correctly. The antenna might be in a wrong place, or there are some coupling issues with surrounding mechanics or electronics. These are aspects that should be considered already in the design phase and checked in the testing phase.

An antenna is not a component that works every time like the data sheet says. Usually, the antenna should be tuned to certain environment and materials. The antenna should also see enough free space to radiate well. If some of these things are altered from original measurement environment, the performance is different. Antenna performance needs to be checked, and fine-tuning and optimization are always needed. Antenna performance is not the same in a free space than in a place filled with metals. A handheld device should be tested in hand and wearable device according to its use.

How is antenna performance measured?

Radientum’s anechoic chamber

Antenna measurements need proper measurement equipment, but also knowledge of antennas’ usage. Many times, measurements need some verification of test methods. Antenna and mechanics size brings own challenges. If a device is small compared to the wavelength of used frequency, then testing is done differently than with a bigger device. Measurement cables change the behaviour of the antenna and the cable could play a too big part in the device performance if this is not taken account during the testing phase.

An antenna is connected to RF with a transmission line, which could be for example a stripline, coaxial cable or waveguide. Transmission line impedance needs to match the antenna and system impedance. This is quite many times 50 ohm. Impedance mismatch could be measured with a network analyzer. The equipment measure transmitted and reflected power, and then calculates S11. We call it usually matching. A mismatch causes power reflection back to the RF and less power is connected to the antenna.

Radiated performance is measured in an anechoic chamber. The system is working in far-field and measurement result is 3D radiation pattern. With one measurement, it is possible to see antenna gain values to a different direction and calculate antenna efficiency. These are usually most important values that are needed to evaluate the antenna performance. An antenna is possible to measure in passive mode, which means that we feed signal to the antenna through cable, and then radiated signal is measured. A more accurate method sends signals from the device and measures power with a power meter. This needs usually some special software features from the device.

Mobile phone testing is done with communication tester, which acts like base station and sets certain power level to the transmitter. Transmitted power is only part of the measurement because there is two-way communication. Device sensitivity describes lowest possible received signal level with some BER (Bit Error Rate) level. Sensitivity is usually different with different data speed and used cases. The devices are often tested with phantom hand and head models to see more realistic results.

Benefits from superior antenna performance

Communication coverage expands with a better antenna. 6 dB improvement is double area coverage. Radiation direction is important in many cases, and it could be omnidirectional or directed to one sharp beam. In both cases, communication distance comes from antenna gain to used direction. Communication should not be very uncertain and some margins should always be set.

Energy savings are very important in battery powered devices. If the antenna is for example 3 dB better, the power amplifier needs only half the power to perform with the same wireless performance. This is huge save on energy consumption.

Antenna size and type have a huge effect on devices’ industrial design. An external antenna might not be needed if almost the same performance is achievable with an integrated antenna.

When antenna testing is needed

Successful antenna project always starts simultaneously with the mechanic considerations. This makes antenna testing very simple. Tuning is checked within all possible environments and small changes might be needed. Problems can be solved without massive redesign.

What if antenna works poorly and it is noticed in the late phase? This is not a catastrophe. The modification needs are possible to find in antenna laboratory with qualified engineers. Radientum has the best possible knowledge to test your product and solve any antenna and RF problems.

By | 2018-08-23T14:02:22+00:00 March 5th, 2018|Blog|

About the Author:

Janne is a senior antenna engineer. He has 8 years of RF design and 10 years of antenna design experience. His knowledge of base-station and terminal antennas can help you with the most challenging antenna projects.