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Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers

Consumer Electronics product design and development has come a long way from traditional product development. Earlier, product development involved a semi-conductor company building a reference design around a brought out silicon/processor and promoting it in the targeted market segment. Some examples include semiconductor companies like Texas Instruments and Analog Devices, who are/were building reference designs around their flagship processors for a variety of Lifestyle Electronics and Consumer Electronics product development like cell phones and automotive infotainment applications. The OEM would then invest heavily on both Hardware and Software engineering resources to customize the hardware to fit the form factor of the Consumer Electronics product design they envisioned.

 

Today, we have seen a radical change in the process of designing. Most fabless semi-conductor companies and ODMs operate in the heavily commoditized consumer electronics market space. Except for some big companies like Apple and Samsung, most OEMs are involved in only defining the specifications and functionality of products. The new age fabless semiconductor companies that dominate the consumer electronics or lifestyle electronics market today do not just stop at creating a reference design, but are also involved in the Consumer electronics product design which are nearly 80-90% completed. Not only do they define the components that go into the product, they also bring together the entire eco-system of component makers required to for a Consumer Electronics product development.

 

Wireless communication is increasing, more and more devices are being connected to the Internet of Things (IoT) or use 5G networks.  More and more devices are incorporating wireless connectivity as the Internet of Things (IoT) continues to grow around the world. We are using these kinds of devices every day, such as mobile phones, IoT (Internet of Things) devices and different wearables, such as smartwatches.

 

The design of Wireless consumer products needs to consider trade-offs to solve your SWaP-C equation (size, weight, power, and cost). A large part of this will depend on understanding the differences between wireless technologies and which is right for your product. For more complex products, choosing the right wireless technology is rarely a simple one-to-one affair. In other words, a combination of variously configured LoRa, Wi-Fi, Bluetooth, and cellular technologies is often needed.

 

Wireless devices require RF design that spans the gamut from implementing active wireless communication technologies (transmit and receive) like satellite, cellular, Wi-Fi and Bluetooth, to passive RFID tagging used in applications such as NFC payment systems or tagging of retail items like clothing. RF system design also includes UL- and FCC-related issues, robust circuit design, and good PCB layout to minimize unintentional radiated emissions and low susceptibility to outside interference.

 

The wireless product design process requires an awareness of and attention to a host of matters that ordinary product design doesn’t demand of teams, from the idea and prototype stage through the manufacturing of a finished product. One of the unique aspects of wireless product design is the certification process. During the design process, you’ll need to work with a variety of regulatory bodies to help create product requirements for your product, including the FCC, PTRCB and UL.

 

The certifications required will vary based on your product’s intended use as well as where and which country it will be used in. For example, for devices intended for pharmaceutical and medical applications, certification from the FDA is important.

 

For cellular radios, PTCRB and FCC certification helps ensure that they will work with a specific carrier, such as AT&T as well as testing the limits for radiated power and spurious emissions. SAR testing is required for any wearable device, to test absorption of energy into the skin.

 

 

LoRa, Wi-Fi, Bluetooth, and cellular technologies all enable wireless communication between devices.

LoRa

LoRa is a long range, low power, proprietary wireless platform with geolocation capabilities that is an integral part of IoT networks worldwide. LoRa devices and the open LoRaWAN® protocol support smart IoT applications across use-cases that include smart cities, smart buildings, smart agriculture, smart metering, smart supply chains, and more.

Wi-Fi

Wi-Fi is a wireless networking technology that enables multiple devices and equipment to connect to the Internet without the use of physical cables or connections. For Wi-Fi to function, it needs an ethernet connection to an internet service provider, a modem, or mobile phone with an Internet data package.

The range of Wi-Fi networks is limited by their frequency, transmission power, antenna type, location, and environment. A typical indoor wireless router in a point-to-multipoint arrangement comes with a range of about 60 feet or less. Using directional antennas, outdoor point-to-point arrangements can be extended for many miles between stations. While Wi-Fi is well established, Wi-Fi 6 is the next generation of this technology and holds game-change possibilities for new product development.

 

Bluetooth

Bluetooth is a wireless technology designed to communicate with other devices over short distances. Bluetooth does not require a Wi-Fi or cellular connection to function. Depending on conditions, connectivity extends about 30 feet and delivers a maximum data transfer speed of up to 24 Mbps.

Power usage is an overarching concern in solving the SWaP-C challenge. (The higher the power usage, the faster the battery life of a device is drained.) Bluetooth has a surprisingly small power requirement, meaning that its effect on a device’s battery life is much less than using Wi-Fi or an ethernet connection. Bluetooth and other wireless technologies featured prominently in creating the Zibrio Smart Scale, a CES Innovation Award-winner that our teams at Pivot helped develop.

 

Cellular

Cellular networks (often called mobile networks) are wireless technologies that depend on signals sent by clusters of land-based cellular towers. Like Wi-Fi, access to the cellular network requires purchasing an internet data package through a cellular provider.

Cellular services can reliably be accessed in any well-populated area. In more remote areas, signal connection often becomes spotty or non-existent. A typical mobile device has enough power to connect with a cell tower up to 45 miles away. However, as with Wi-Fi and Bluetooth, the actual range of connectivity can vary widely depending on conditions and the number of towers in a given area. The speed of connectivity depends on the speed of network connection. The better the network connection, the faster data, download, and upload speeds a device is capable of.

 

One of the unique aspects of wireless product design is the certification process. During the design process, you’ll need to work with a variety of regulatory bodies to help create product requirements for your product, including the FCC, PTRCB and UL.

 

Antennas

An antenna is a length of wire, or some structure, to which RF energy is applied and this energy then radiates out into space. With so many diverse applications and form factors, antennas must be tailored to optimize performance within tight size, weight, and power constraints.

 

Antennas are the critical link to transmit and receive information using Wi-Fi, Bluetooth, Zigbee, and Cellular (LTE, UTMS) protocols.  Bluetooth Classic, Bluetooth Low-Energy, WiFi, and ZigBee all operate at a carrier frequency of 2.4GHz. The FCC designation for this frequency band is the Industrial, Scientific and Medical (ISM) band.  Almost any antenna designed to work in the 2.4GHz ISM band will work for any of the wireless standards such as BLE, WiFi or Zigbee.

 

First of all, in order to have a good wireless device you need a good antenna. If your antenna is not designed efficiently then the transmitter has to deliver higher power to the antenna terminals to achieve the range and distance for the application. Driving the transmitter at higher power means more draw on the system power supply which in turn increases heating of components and reduces the battery life for portable devices.

 

Several factors can influence antenna performance, such as:

  • Antenna pattern change
  • Impedance mismatch loss
  • Antenna detuning
  • Self-interference

 

Most antennas are designed to have an impedance of 50 ohms.  This means that the PCB layout should match the impedance of the RF transceiver (module or chip) to the antenna. You need to design your PCB so that the impedance between the antenna feedline and nearby ground planes is 50 ohms. By matching the impedance the maximum signal power is transferred between the antenna and the transceiver. Without proper impedance matching much of the signal will be lost along the antenna feedline.

 

Most designs incorporate a pi-matching network (made of inductors and capacitors) to allow adjustment of this impedance for optimum tuning. For maximum performance tuning will need to be done inside the final product enclosure.

 

For short-range wireless protocols such as Bluetooth, WiFi, ZigBee, and Z-wave having a less than perfect antenna design is usually acceptable. The operating range and data rate may be somewhat reduced but everything will still work. On the other hand, the antenna design for something like a Global Positioning System (GPS) is extremely critical. You are after all trying to receive incredibly weak signals from multiple satellites in space.

 

PCB trace vs. chip antenna

When it comes to small on-board antennas there are usually two ways to go: a PCB trace antenna, or a chip antenna. Chip antennas are more compact than PCB trace antennas and they are easier to tune accurately. On modules with a built-in antenna the complex RF design details have already been addressed by the module manufacturer. The real concern for the designer is placing the module so that the antenna is kept away from metal objects, like other traces, ground planes or a battery. Most modules will specify a ground clearance area around the antenna

 

PCB trace antennas have various names that sometimes describe their shape. For example, an inverted F antenna looks like the letter F and a microstrip patch antenna looks like a square or rectangular patch. The primary advantage of a PCB trace antenna is they are essentially free since they are made entirely from a trace on the PCB, however, they will increase the board size.

 

If you plan to use a PCB trace antenna then the PCB insulating material becomes more critical. FR-4 is the most common PCB material but the dielectric constant of the material is not well controlled and may even vary significantly from lot to lot. The result is the antenna may no longer be properly tuned on some boards

 

Rogers Corporation makes a PCB material called RO4350B, which is a suitable low cost replacement for FR-4 when building RF circuits. RO4350B provides tight control of the dielectric constant and is low loss, two things that generic FR-4 does not have.

 

Wireless Device Testing

The traditional method of testing wireless devices has been through directly wired cables. Wired cables are (galvanic connections) connected to the devices’ temporary antenna connectors, which are ports used for conformance testing. This approach of testing is suitable for the most existing wireless performance tests. Since not only is it conveniently accessible, it is not vulnerable to radiated noise or interference in the test environment.

 

At the same time, there are some disadvantages in conducted testing. It does not take into account the wireless performance of the device’s antennas. Also, it overlooks problems that might appear in the antenna due to poor design or faulty construction. With the birth and advancement of multiband devices using multiple antennas and MIMO (Multiple Input Multiple Output) technologies, conducted measurements that bypass the antennas are no longer a good indicator of radiated OTA performance. That is why it is necessary to use other methods to assess antenna performance. Compared to conducted testing, OTA testing has the advantage of not needing to break down or alter the test device to conduct testing.

 

Optimal location for antenna placement,  whether for an off-the-shelf or custom-designed antenna is based on product needs, product application, and performance requirements. For a custom antenna solution- electromagnetic (EM) modeling and simulation capability is desirable.  With careful EM simulation analysis, rapid feedback on antenna placement strategy, electromagnetic behavior, s-parameter data, antenna efficiency and gain data can be determined. Providing evidence-based predictions of antenna performance early in the design cycle helps OEM’s make critical design decisions quicker with no unwanted surprises during product launch.

 

Over-the-Air, OTA testing

Over-the-Air, OTA testing, is a method to test the wireless performance and reliability of wireless devices that include embedded antennas.  To perform an OTA test, the device under test (DUT) is placed in a test environment inside a test chamber. The test chamber is isolated from any outside signals.

 

During the development process of any IoT (Internet of things) or M2M (machine to machine) device, the design and configuration of selected antennas need to be tested. This is done to ensure that the device performs as intended, for example with battery-powered IoT devices that the power consumption remains reasonable. With the help of emerging new technologies, these devices are becoming more and more compact. As a result, antennas are placed near other antennas, displays, computer processors, high-speed memory, etc. All these can interfere and degrade the devices’ wireless performance. A good wireless connectivity is an important criterion for customers when choosing a device. Having a well-functioning device ensures customer value and builds trust in the brand.

 

The goal of the OTA testing process is to ensure that the device has a good wireless performance at every situation. Many factors can affect the performance of a wireless device, for example choice of materials, placing of components and purpose of use. Typically, devices also need to be tested in different situations depending on their purpose of use. For example, a smartwatch must be tested in both hands, left and right, to ensure its wireless performance.

 

A wireless device’s receiver relies on the antenna to capture very weak RF radiated signals then convert them into voltages at the receiver front end. Improperly placing the antenna in a manner that couples noise to the receiver will dampen the receiver sensitivity and negatively impact wireless communications.

 

The aim of the Over-the-Air testing method is to simulate realistic radio wave propagation conditions that match real life as closely as possible. These tests are usually carried out in an anechoic chamber that is covered within with absorber material to reduce the signal reflections. Anechoic means without echoes, as in no RF waves are reflected back from the sides of the chamber. This absorber material commonly takes the shape of small pyramids, consisting of rubberized insulating foam that is saturated with conductible metals. Radio waves are absorbed by dissipating their energy when colliding with these pyramids. Anechoic chambers also function as faraday cages to shield them from external interfering signals. The benefit of conducting measurements in a controlled laboratory environment compared to doing them in-field is that any noise that might interfere with testing is eliminated.

 

When a transmitted radio wave collides with an object, parts of it are diffracted, reflected, or absorbed. In an anechoic chamber, a radio channel emulator and multiple antennas placed at various angles are used to simulate these conditions, replicating real-life scenarios, such as urban and indoor surroundings within a controlled lab environment. These conditions include e.g. multipath propagation, noise, and interference.

 

The OTA chamber provides the tools to optimize the placement of the antenna relative to the enclosure and the supporting digital circuitry to maximize the receiver’s sensitivity. Highly sensitive receivers extend the transmission ranges, enable higher data throughput, and provide greater communication reliability. With the new OTA chamber, engineers can easily visualize the antenna radiation in 3D then design antenna elements and placement within the end product to achieve optimal performance.

 

The OTA chamber is also used to evaluate Total Radiated Power (TRP), Total Isotropic Sensitivity (TIS), and Relative Sensitivity on Intermediate Channels (RSIC). These measurements are key performance metrics for the cellular industry network operators such as ATT, T-Mobile, Sprint, and Verizon. With this new fully-anechoic antenna chamber, our clients integrating cellular radios can save time and cost through testing their devices in advance of formal compliance at a certified CATL Lab.

 

In October 2001 CTIA published the first SISO (Single input single output) OTA test specifications, defining two metrics for the device: Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS). Total Radiated Power measures the total overall antenna power radiated by the antenna and is defined as the integral of the power transmitted in different directions over the entire radiation sphere. Later, within the 3GPP OTA specifications, Total Isotropic Sensitivity used by the CTIA was renamed Total radiated sensitivity (TRS), and the two terms are now used interchangeably. Total radiated sensitivity (TRS) is a measurement that signifies the reference sensitivity of the DUT averaged over all the directions.

 

RF shielded antenna test chambers for wireless Over-The-Air (OTA) testing are built as full anechoic
chambers. Typical equipment under test is mobile & telecom products as well as other electronic products using wireless communication techniques. Typical validation procedures for full anechoic chambers used for wireless (OTA) testing are Free Space VSWR (ANSI/IEEE-149), CTIA OTA Rev. 2.2.1 Jan 2008 and ETSI TR102 273.

 

OTA Testing in 5G

In comparison to 4G, the fifth-generation (5G) mobile network is designed to deliver three primary use cases: the capacity to transmit/receive more data, improve responsiveness, and connect millions of devices at once. More specifically, this includes enhanced mobile broadband (eMBB), ultra-reliable, low-latency communications (URLLC), and increased connectivity to allow billions of devices and applications to come online seamlessly and communicate simultaneously.

 

To test mobile devices in situations similar to what users actually experience, the tests must be executed wirelessly or over the air. As a result, designers can see what truly happens as the radio waves propagate over the air from the user equipment to the base station and from the base station to the user equipment.

 

OTA testing of wireless devices is required by numerous regulatory agencies, standards organizations, industrial bodies, and carriers. To have global access and interoperability of mobile systems, certification tests have been developed so that manufacturers around the world provide the same level of quality in all new mobile devices. The CTIA (Cellular Telephone Industries Association) has set standards for OTA testing of 3G and 4G LTE devices and has certification labs all around the world.

 

When OTA testing is done in an early phase, costly design errors can be avoided. If a product is launched and the manufacturer notices that the wireless performance of the device is not good, it can seriously harm the reputation of a company, not to mention the recall costs. Great OTA test result can also help with bench-marking.  In addition, most of the biggest network operators have specific OTA requirements and to meet them, the product must be OTA tested. Overall, OTA testing ensures that the wireless device is ready to be sold on the market.

 

As 5G mobile technology evolves to millimeter-wave (mmWave) frequencies of 28 GHz, 39 GHz, and beyond, several drivers will necessitate OTA testing. At mmWave frequencies, signal-absorption rates are much higher, requiring the need for directional transmissions/reception (beam focusing or beamsteering) to boost the gain. Beamsteering will be a key feature in the context of 5G. It’s a significant challenge to test the beamsteering capabilities of base stations and user equipment in every phase from research and development through production.

 

Only test systems that can handle 3D center-of-beam and off-center-of-beam measurements in a radiated environment with extremely accurate positioning systems can properly characterize a 5G device. This includes measuring EIRP/EIS, beam-transmit signal quality, beam-receive performance, beam-acquisition timing, and beam-tracking performance. It also involves side-lobe measurements that affect total radiated power, including in-band and out-of-band spectrum-emissions-related performance.

 

As the technology advances toward 5G systems, finding the proper setup and positioning for the 3D antennas to test the moving beams, while accounting for interference and scattering, will be difficult.

 

One factor that the devices must account for is the blocking effect of the human body on the radiation pattern by using phantoms during OTA tests. OTA tests that measure the 3D antenna pattern can be performed in either near field or far field. Measurements in near field allow for smaller anechoic chambers. However, they require setups capable of measuring both phase and amplitude with high location precision and additional post-processing for the near-field to far-field transformation.

 

MIMO OTA

MIMO (Multiple Input Multiple Output) is a technology that lets radio signals to be sent and received using multiple antennas located in the device. The system uses multipath propagation to achieve a more efficient way to transmit RF signals. In this method by using different coding, the complex, high-power signal is split to multiple low-power signals and transmitted to the receiving device’s antennas from multiple different paths. When both the transmitting and receiving devices have multiple antenna ports and antennas, and multiple data streams are transmitted simultaneously to the receiving device using the same time/frequency resources, the peak throughput of a single user can double (2×2 MIMO), or quadruple (4×4 MIMO), and so on.

 

When testing MIMO devices over-the-air, the SISO OTA test methods and TRP and TRS metrics do not scale up to SIMO (Single Input Multiple Output) and MIMO conditions. When testing a DUT with receive diversity, the anechoic chamber test method of using a single angle of arrival (AoA) and single polarization presents the DUT with an unrealistic signal. The solution to this problem by the CTIA entails testing each receiving antenna in the DUT individually. While this approach is practical and thorough, it does not fully reflect the device’s performance in real-life conditions, where multiple simultaneous angles of arrival and polarizations exist.

 

 

References and Resources also include:

https://verkotan.com/2021/what-is-ota-testing-everything-you-need-to-know-about-the-process/

https://www.hackster.io/news/introduction-to-developing-a-new-wireless-product-bf0a6c5b51a4

https://www.designworldonline.com/wireless-product-design-from-prototype-to-product/

 

 

Cite This Article

 
International Defense Security & Technology (January 31, 2023) Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers. Retrieved from https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/.
"Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers." International Defense Security & Technology - January 31, 2023, https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/
International Defense Security & Technology December 28, 2022 Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers., viewed January 31, 2023,<https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/>
International Defense Security & Technology - Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers. [Internet]. [Accessed January 31, 2023]. Available from: https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/
"Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers." International Defense Security & Technology - Accessed January 31, 2023. https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/
"Wireless consumer Electronics product design and testing RF/ Over The Air (OTA) measurement systems/chambers." International Defense Security & Technology [Online]. Available: https://idstch.com/technology/electronics/wireless-consumer-electronics-product-design-and-testing-rf-over-the-air-ota-measurement-systems-chambers/. [Accessed: January 31, 2023]

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