How is Your Antenna Doing? An Overview of Antenna Testing

As technology advances, diving into the highly technical world of RF can be a challenge to anyone – even those with an engineering degree! We want to bridge this gap by giving insight into our world of antenna testing. Antenna testing involves a lot of different steps and complicated methods, but we have done our best to summarize all of the major steps.

Let’s start with the main purpose of our work. Day by day, our society is becoming increasingly streamlined. Our work life has embraced a newfound flexibility, our devices are becoming more powerful and compact, and even the world itself is more agile than ever. This societal development relies on the advancement of wireless connectivity: the modern world has an increasing demand for a reliable, secure and high-speed connection. But how do we make sure that this integral connection stays reliable?

The answer is, of course, as simple as it has always been: by planning ahead. You can achieve reliability only by doing quality design work and rigorous testing. And since you’re reading our blog, you probably already know how this all relates to Radientum. This quick, comprehensive guide is here to help you understand how we do our antenna design and antenna testing work! Hopefully this should shed some light on the integral parts of a typical antenna project.

When beginning a new product of any size, scope or subject, focus is usually on the big picture. Unfortunately, that sometimes comes with a cost: it’s often the smaller things, that we forget to take fully into account – and with advanced technology, the devil is truly in the details. When it comes to electronics, if the key components aren’t designed and tested comprehensibly, even the most elegantly designed device underperforms severely. There’s a reason for the saying “measure twice, cut once.” This is where Radientum, and our extensive knowledge of antennas comes in.

With us, every project starts from the same place: defining the actual needs of the customer. Devices are different, and the end use of a device also defines which antenna is best suited for it. Antenna design also involves careful consideration of the size, placement, and type of antenna, to align to your specific needs – as well as to provide superior performance. The desired performance of the antenna also sets prerequisites to the whole wireless system. It is crucial to plan when and how to conduct R&D measurements, in order to ensure optimal performance with the final prototype. One also needs to take the measurement aspects against the R&D specifications into account, from the beginning of the project. Do you have antenna specifications, and can your antenna design meet them?

It’s easy to think that a simple and straightforward equation like “wireless product + best antenna = wireless product with superior wireless performance” might be true. In reality however, even the strongest and most precise antennas can underperform severely due to poor implementation. Errors in the implementation stage can lead to, for example, tuning discrepancies, impedance mismatches, improper placement or coupling issues with the antenna. If your antenna engineer does their job right, potential problems such as these are considered already in the design phase – and assessed rigorously during testing.

An antenna is also not a component that always performs as stated in the datasheet. Antennas often need to be tailored to specific environments and materials, and they need adequate space around them. Also remember, that any deviations from the measurement environment can – and will – affect the performance. Therefore engineers need to check, fine-tune and optimize antenna performance periodically. Every detail has to be taken into account, such as the difference between free space and metal-rich environments. For handheld and wearable devices, testing also needs to reflect real-world usage scenarios. Simply put, a handheld device is tested while holding the device. After all, you wouldn’t want a phone that is unable to connect to a smartwatch, when the phone is held in a human hand!

After getting all the requirements from the client and creating a device to fit them, we finally move into antenna testing. But how do we actually measure the prototype’s antenna performance? Testing antenna performance requires appropriate equipment and a deep understanding of the antenna’s usage. Often the measurements require some verification of test methods, and the physical size of the antenna brings its own challenges. For example, if the device is small compared to the frequency wavelength, tests are done differently than with a larger device.

In the testing process itself, an antenna connects to RF with a transmission line, which could be a stripline, a coaxial cable or a waveguide. It’s vital to ensure, that the impedance of the transmission line matches the antenna and system impedance (which is often 50 ohm). You then measure the impedance mismatch with a network analyzer, which measures both the transmitted and reflected power, and calculates S11 – commonly known as matching. If there’s a mismatch, power is reflected back to the RF system, which in turn decreases antenna’s performance.

We also measure radiated performance in a sophisticated anechoic chamber. The system operates in the far-field, providing the measurement result as a 3D radiation pattern. This process provides us with both antenna gain values in different directions, as well as calculations concerning antenna efficiency. All in just one measurement. These are also often the most important values when evaluating antenna’s performance. In addition, we can also test antennas in passive mode. This works by feeding a signal to the antenna through a cable and measuring the radiated signal. A more precise method involves sending signals from the device, and measuring power with a power meter. This often requires specialized software.

The type of the device will naturally affect the testing procedure. To illustrate the point, let’s take a closer look into mobile phone testing. Testing mobile phones involves a communication tester, which functions as a base station whilst setting a power level to the transmitter. Because of the two-way communication capabilities of the mobile device, transmitted power is only a part of the measurement. Device sensitivity describes the lowest possible received signal level, with some Bit Error Rate (BER) level. The level varies, depending on data speeds and use cases. These kinds of tests are often done with a phantom hand and head models to achieve more realistic results. It’s just like before: you wouldn’t want to buy a phone that underperforms when held against a human head!

So, is all of this really necessary? Simply put: absolutely yes! A tested antenna performs better, and a better performance means better coverage. An improvement of just 6 dB already doubles the area covered. You can achieve similar improvements in energy efficiency, since a better antenna is also more cost-efficient. It’s good to keep in mind, that the importance of energy-saving choices  increases year by year. If an antenna is improved just by 3 dB, you can halve the energy consumption of the power amplifier – with zero negative effects on the wireless performance. These kinds of energy-savings can be remarkable.

On top of the larger coverage and energy savings, industrial design offers great benefits. The size and type of the antenna can significantly affect the device’s industrial design. An integrated antenna can often offer nearly identical performance to an external one, eliminating the need for any additional hardware. An untested or hastily designed antenna is an unnecessary, easily avoidable risk, especially when dealing in a highly competitive market where performance is a key selling point.

A successful antenna project always starts simultaneously with the mechanic considerations, in order to streamline the process.  Regular tuning assessments in various environments identifies the need for minor adjustments. This in turn helps to avoid any major – and costly – redesigns. So in layman’s terms: the best time start the antenna testing process is before any testing is needed yet.

But what if you fail to take some of these steps into consideration and the antenna ends up working poorly? Or what if you also fail to notice the problem until a later stage? No need to panic! If you don’t have your own antenna testing facilities, our qualified engineers at Radientum can resolve your antenna problems in our state-of-the-art laboratory. You can find more details about our services here on our site. Or you can contact our team directly and ask for their assistance!

This blog post is a revised version of an older blog post by Janne Heiskanen, principal engineer at Radientum. Revision written by Matias Puro.