Virtual Antenna™ for easy design of IoT devices with embedded antennas

Virtual Antenna™ for easy design of IoT devices with embedded antennas

Technology News |
By J. Anguera, A. Andújar, C. Puente

Smart sensors, smart meters, smart tracking, smart factories, smart agriculture and all possible smart things you can imagine need to be connected. IoT enables connecting things with other things, in consequence a relevant player is needed which transmits and receives data to and from each thing: an IoT antenna.

Wireless engineers working on the development of the all the new bunch of IoT devices are looking for the best IoT antenna: the one covering all desired bands, with the smallest footprint and with the highest efficiency. On top of this, the antenna needs to be integrated in the design with other radiofrequency components such as modules, amplifiers, and filters, therefore, why not treat it as just another component?

Virtual Antenna™ technology enables one antenna component to cover all IoT frequency bands. The antenna called antenna booster is a very small chip antenna component able to be tuned to any frequency worldwide as needed. And because it is off the shelf, no customization on the antenna part will be needed so the IoT architecture becomes predictable from day one and is the ideal solution for mass production.

This paper presents the main features of Virtual Antenna™ technology and shows a simple design flow comprising only three simple steps on how wireless design engineers can embed Virtual Antenna™ in IoT devices.

Virtual Antenna™ features

Virtual Antenna™ technology is based on replacing a complex and usually customized antenna designs with an off-the-shelf, miniature and multiband component called an antenna booster (Figure 1). Being surface-mount and chip-like in nature, the antenna booster fits seamlessly in an electronic printed circuit board the same way any other electronic component (an amplifier, filter or switch, to name a few) does. Virtual Antenna™ gets this name from the fact that an antenna booster, when is strategically placed on a device’s PCB (Printed Circuit Board), can boost currents on the ground plane of the PCB to make it an effective radiator [1]-[6]. Consequently, the size of an antenna booster can be very small compared to other conventional multiband antennas (Figure 1). For example, the antenna booster shown in Figure 2 has a size of 12 mm x 3 mm x 2.4 mm which in terms of the wavelength, represents only λ/30 at 824 MHz referred to its longest dimension of 12 mm. This tiny and versatile component has been recently adopted, among other IoT devices, in the open-source hardware platform mangOH™ Yellow, a super sensor for cellular industrial IoT.

Figure 1: Antenna boosters are tiny SMD antenna components featuring small size about 100mm3 and able to operate at any band within the frequency range from 698 MHz to 6 GHz.

Besides its small size, Virtual Antenna™ features multiband operation in the frequency range from 0.698 GHz up to 6 GHz. To achieve either single or multiband operation, a matching network is combined with an antenna booster with a totally passive solution since the matching network comprises lumped components (inductors and capacitors). In some particular devices where the size of the device is small (∼50 mm), architectures using smart matching networks can be combined with Virtual Antenna™ as well [7]. A recent IoT platform adopting this technology is the Thingy:91 by Nordic Semiconductor which is a multi-sensor prototyping kit ideal for kick starting cellular IoT projects.

An antenna booster can be assembled with a conventional pick-and-place machine, making the manufacture and design of the new generation of IoT wireless devices simpler, faster and more cost effective (Figure 2).

Antenna booster RUN mXTEND embedded in the IoT platform mangOHTM yellow.
Figure 2: Antenna booster RUN mXTENDTM embedded in the IoT platform mangOHTM yellow. The antenna booster being an SMD component means it can be easily assembled with a conventional pick-and-place machine.

Easy design of IoT devices with embedded antennas in three steps

Virtual Antenna™ enables the integration of embedded antennas in IoT devices in three simple steps. Following these basic steps, wireless engineers designing IoT devices, can easily embed an antenna.

#Step 1: The first step is to place the antenna booster in the PCB of the device. As a recommended rule, the preferred positions are the corners of the ground plane of the device (Figure 3). In this situation, bandwidth and efficiency can be maximized which is especially attractive for multiband applications such as for example devices operating at 698 MHz – 960 MHz and 1710 – 2690 MHz for instance. However, in other situations, where bandwidth is not a constraint, such as in single band applications, for example ISM (BW∼3%), GNSS (BW∼3%), Bluetooth (BW∼3%), others positions different than the corners can be used as well.

Figure 3 Illustrations showing the preferred (marked with a green tick) and non-preferred locations (marked with a red X) for an antenna booster.

It is important to emphasize that antenna location should be determined at the very beginning of a device design project in order to optimize performance of the antenna within the device. Otherwise, performance can be poor and difficult to improve in more advanced phases of a project. This means that the antenna performance should not consider the antenna only: the performance depends on the antenna in combination with the device. Therefore, a correct selection of the antenna booster location will optimize radiofrequency performance in terms of transmitted and received power.

#Step 2: The next step, step 2, is to design a matching network. Since the input impedance of an antenna booster is mainly reactive across the frequency bands of operation, a matching network is needed to maximize the radiated power into space and maximize the received power from space (Figure 4). This design flow differs from the traditional antenna design where the antenna geometry is customized depending on the frequency bands of operation [8]. For Virtual Antenna™ instead, the only customization needed is for the matching network, resulting in a faster and easier design flow. In effect, the design of a matching network can be fully automatized by using network synthesis tools available in most of microwave circuit simulators used in the wireless industry such as the following synthesis network tools: the NI AWR software offered by National Instruments and the Optenni-Lab offered by Optenni [9]-[10].

Figure 4: A matching network is designed and located between a radiofrequency module (represented by the source Vs and impedance Zg) and the antenna booster.

Thanks to this design flow, an antenna booster can operate at any band and in any device by just designing a suitable matching network. For example, if we have an IoT device that needs operation at the NB-IoT 900 MHz band, a simple L-type matching network can work (Figure 5). However, if the device needs to operate at several LTE bands, the same antenna booster as previous case is used but with a different matching network (Figure 6).

Figure 5: (Top left) An antenna booster (12 mm x 3 mm x 2.4 mm) with a matching network comprising two lumped SMD components for operation at 900 MHz (Bottom). (Top right) Measured VSWR and total efficiency.
Figure 6: (Top left) An antenna booster with a multiband matching network comprising seven SMD lumped components for operation at 824 MHz – 960 MHz and 1710 MHz – 2690 MHz (Bottom). (Top right) Measured VSWR and total efficiency.

As seen from these two examples, the antenna booster is the same component for both cases, and the only part that changes is the matching network design for each case. Therefore, a new antenna design is not needed for each situation since the same antenna booster can be used for any band. Furthermore, if the PCB size changes, the same design flow applies, that is, the antenna booster can be the same and only the matching network is designed to operate at the desired number of bands [11]. Consequently, this is an advantage for wireless engineers that need to embed an antenna in their devices since the antenna booster remains the same and there is no need to choose a different antenna to integrate in all their different devices. Also, this represents an economy of scale advantage since same antenna booster can be integrated across different platforms.

#Step 3: The third step in the design flow is to test the device. Once the matching network has been implemented into the device’s PCB, VSWR and efficiency must be tested. VSWR can be tested with a vector network analyzer (VNA) providing information about VSWR (or S11). By measuring VSWR (see examples at Figure 5 and Figure 6), the wireless designer knows how well the matching network and the antenna booster behave. Usually the VSWR results of less than three are preferred across the frequency bands of operation. Compact VNA are available in the market for testing VSWR such as those offered by Rohde&Schwarz.

Once, the VSWR achieves a specified target, total efficiency must be tested which is carried out with the device inside an anechoic chamber (Figure 7). Total efficiency is the ratio between the power radiated into space (Prad) over the available power of the radiofrequency module (Pavs) – (Figure 4). Although VSWR measurement provides a good sense on how well then antenna system is behaving, total efficiency will inform on how much power from the module is radiated into space and how much is lost in nearby components, materials, and components of the matching network. Total efficiency is, therefore, a relevant figure of merit to be sure that the device will be competitive in the market. Moreover, when total efficiency is measured taking the full device parts (the PCB including the antenna booster, the matching network as well as battery, displays, casing, etc.) provides information about the TRP (Total Radiated Power) which is used in many wireless device certifications (eq. 1) such as PTCRB certification. TRP is linked to total efficiency as shown in eq.(1):

TRP(dBm) = Pout(dBm) + 10·log(total efficiency)       – eq(1)

where Pout is the nominal output power from the radiofrequency module.

For example, imagine we have a radiofrequency module with a nominal output power of 23 dBm and to certify the product, the TRP should be above 18 dBm, this means that the total efficiency must be above 31.6%.

Figure 7: Anechoic chamber for testing total efficiency – full 3D pattern is measured.

This reveals that total efficiency is a parameter of paramount relevance. In this sense, Virtual Antenna™ can easily control how to optimize total efficiency in a product certification since if any adjustment needs to be done, this can be addressed by adjusting the matching network. Adjusting the antenna design in this situation will put the project at risk since a new design takes weeks of works which is critical at this stage. On the contrary, Virtual Antenna™ has the flexibility to simply adjust the matching network, which is faster and easier and at the end, this is an efficient process which is very convenient for wireless design engineers developing IoT devices.



Virtual Antenna™ enables the wireless designer to easily embed a tiny antenna component in IoT devices. This tiny antenna component is called antenna booster being around 100 mm3, up to ten times smaller than traditional customized antennas. Besides being very small, an antenna booster can operate at any band in the range 0.698 GHz – 6 GHz by only designing a matching network.

A simple design process comprising three steps enables to embed antenna booster in IoT devices: antenna booster placement, design of the matching network, and testing the full device with the embedded antenna booster.

Antenna placement is an important decision that need to be taken at the very beginning of a device design in order to optimize performance. The performance of an embedded antenna should be considered along with the device and not by considering the antenna only; the behavior is at the end, determined by the antenna and the device together.

The design of a matching network is easily systematized with a microwave circuit simulator which makes the design flow the same procedure as a matching network for an amplifier. This facilitates wireless engineers to embed an antenna into an IoT device since it does not require antenna expertise but circuit design skills instead. This design flow is very flexible since if any mechanical change on the device affects the antenna performance, the antenna does not need to be redesigned but only the matching network must be tuned. This is a faster, easier and cheaper design flow.

Finally, an antenna booster is an off-the-shelf component ready to be used and being a SMD component is compatible with typical pick-and-place mounting machines.

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[6] A. Andújar and J. Anguera, “Integration of a Non-Resonant Antenna in a Smartphone for Multiband Operation,” European Conference on Antennas and Propagation, EUCAP 2018, London, UK, April 2018.
[7] J. Anguera, A. Andújar, J. L. Leiva, C. Schepens, R. Gaddi, and S. Kahng, “Multiband Antenna Operation with a Non-Resonant Element Using a Reconfigurable Matching Network,” European Conference on Antennas and Propagation, EUCAP 2018, London, UK, April 2018.
[8] J. Anguera, C. Picher, A. Bujalance, and A. Andújar, “Ground Plane Booster Antenna Technology for Smartphones and Tablets,” Microwave and Optical Technology Letters, vol.58, no. 6, pp.1289-1294, June 2016.
[9] D. Vye, “Network Synthesis Wizard Automates Interactive Matching-Circuit Design”, Microwave Journal, Nov. 2018, pp.96-102.
[10] J. Juntunen, J. Järveläinen, and D. Linden, “MIMO Dual-Band WiFi Antenna Using NI AWR Software, Optenni Lab, and Premix PREPERM Materials,” MMee, March-April 2019, pp.12-14.
[11] A. Andújar, J. Anguera, and R. Mª Mateo, “Multiband Non-Resonant Antenna System with Reduced Ground Clearance,” European Conference on Antennas and Propagation, EUCAP 2017, Paris, France, April 2017.

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