This blog post contains answers to questions asked during the "Embedded Antennas for IoT" webinar hosted by Nordic Semiconductor 17.10.2019.
You can watch a recording of the webinar here. You can download the slides at the bottom of this post.
We have tried to answer the questions as best as we can, but some are difficult to answer without being able to ask follow-up questions. Redundant questions were discarded. If anything is still unclear please do not comment here, but instead ask your question in the DevZone Q&A section here.
Q1: Can you tell me the time frame or packet size of NB-IoT and IoT cat M1? And How much time required to send one packet or its time to send.
This is dependent on so many parameters that we must recommend that you post a more detailed question to technical support on our developer zone.
Q2: Will the distance/range be different from the conventional separated antenna?
As a rule, the further distance between the cellular and GPS antennas helps to achieve a good isolation. However, for the TRIO mXTEND chip antenna used in Thingy:91, cellular and GPS signals are decoupled thanks to the switching mechanism enabling that the same antenna component can be used for cellular and GPS without the need of using two separate antennas.
Q3: we designing our tags using nRF52. Will be glad if we get assistance in antenna design for the same. some assistance. we will use the Wireless Fast Track tool. but any documents for the same to start with
Please find your device at www.nordicsemi.com and see reference circuitry (for package variant and DK) under the documentation for that device. Additional questions on minor assistance with antenna design can be filed on devzone.nordicsemi.com, where there are also many existing posts that relate to antenna design for the nRF52 Series devices.
Q4: My nrf52840 dongle prototype is encapsulated in platinum cure silicone. Will this affect the range?
Every type of casing will affect range, some more than others. Depending on layout, silicone rubber could affect sensitivity negatively by a few dBm.
Q5: As you have mentioned embedded antenna, it means can we place a metalic cover over the antenna? or I have to Keep free over the antenna?
Metal covers around the antenna will degrade performance so it is recommended to keep the are over the antenna free of any metallic component.
Q6: What is patented on this board/antenna? Are there any pending patents?
The nRF9160 SiP, the nRF52840 SoC are, and other components used on the board may or may not be patented. But nothing regarding the layout of the PCB is patented. From the antenna part, the TRIO mXTENDTM chip antenna component based on its proprietary Virtual AntennaTM technology are protected by one or more of the following Fractus Antennas patents and patent applications: https://www.fractusantennas.com/wp-content/uploads/2018/02/Patent-list-TRIO.pdf
Q7: I have seen the placement of the antenne on a retangular print. But where to place on a round print?
In a point that maximizes ground clearance. For further help, try the Wireless Fast-Track tool and you’ll get a ready-to-test antenna design for your Mobile/IoT device in 24h. Free of Charge* (subject to T&Cs). https://www.fractusantennas.com/fast-track-project/
Also for more information about antenna placement, see this video at:
Q8: I saw you also have a small cube antenna, can it be used successfully with the nRF9160 for both LTE-M and GPS?
Yes. The small cube is CUBE mXTEND antenna booster (https://www.fractusantennas.com/chip-antenna/).
There is also another low-profile antenna booster for GPS, such as DUO mXTEND with a small size (7 mm x 3 mm x 2 mm) with no ground clearance beyond its footprint. Furthermore, this DUO is a dual-port: one port can be used for GPS and the other port for Bluetooth. This avoids the need of using two separate antennas. See more information about Duo mXTEND antenna booster at https://www.fractusantennas.com/duo-mxtend-mobile-iot-antenna/
Q9: Where we place the antenna if the PCB is small (diam. 35mm) and round ?
In a point that maximizes ground clearance. For further help, try our Wireless Fast-Track tool and you’ll get a ready-to-test antenna design for your Mobile/IoT device. Free of Charge. https://www.fractusantennas.com/fast-track-project/
Q10: We want to put LTE and GPS in sleep and restart in interval to save battery. How much time it will take to settle again after wakeup
When the LTE link is awoken from PSM mode the settling time is carrier and signal connection specific. GPS is very variable. This is dependent on so many parameters (hot vs cold start of GPS, PSM and network settings, signal strength etc.) that we must recommend that you post a more detailed question to technical support on our developer zone.
Q11: For the tuning network, where is the best position for contacting the shield of the SMA cable? Is it better to use the Exposed Pad from the Nordic (because thats the central RF point) or somewhere at the Ground Plane?
The shield (outer conductor) of the SMA cable should be grounded at least at three points on the RF ground of the PCB (Printed Circuit Board): One close to the testing point, another in the middle of the cable (transmission line), and other at the SMA connector point. Also, ferrites should be used in order to minimize currents flowing through the outer conductor of the external transmission line after the SMA.
Please, have a look at the video: https://www.fractusantennas.com/videos/step-3/
Q12: If the Qorvo switches are not used, how is the Fractus antenna matched with only passive components? Roughly how many components would there be?
For this small platform, it is difficult to cover the whole bands with a good S11. In case you cannot use switches, there is a performance trade-off between different bands. If you have any project where you need to test the antenna without switches with only passive components just contact us via our Wireless Fast-Track tool at https://www.fractusantennas.com/fast-track-project/
Q13: Does the feed line of the Antenna inside the exclusion zone also need to be a 50 ohm transmission line?
The conductive trace from the antenna to the PCB can have any reasonable width between 1 mm and 2 mm. 1mm is recommended.
Q14: Can you provide a list of alternatives to Quora RF parts since it's hard to get hands on samples for prototyping?
QM12038 for instance is now available to purchase online https://www.qorvo.com/products/p/QM12038 We must recommend that you post a question to technical support on our developer zone for suggestions on alternative parts.
Q15: Is there a Bluetooth Low Energy (BLE) interface on Thingy91?
Yes, but it’s currently not used by the default FW. But this can be enabled by a FW update.
Q16: Is the Fractus Antenna can be used also for BLE?
Yes. The TRIO mXTEND in the Nordic Thinigy:91 has available another port which can be used for BLE. And in general, Fractus Antennas Virtual Antenna products can be used for any band and any device by only adjusting the matching network. In case you need assistance on your new project, try our Wireless Fast-Track tool and you’ll get a ready-to-test antenna design for your Mobile/IoT device. Free of Charge. https://www.fractusantennas.com/fast-track-project/
Q17: The GNSS part of the nRF9160 is it capable to receive all satellites like Glonass, GPS, Galileo etc.
No, this is GPS only. We refer to the nRF9160 product specification.
Q18: How is it that the transmission efficiency at a particular frequency can be so dramatically changed with matching circuitry in your Antennas? Matching other antennas usually only has a small influence on the efficiencies.
Our antenna products based on Virtual Antenna can operate at any band and in any device by just changing the matching network. This avoids the need of using a different antenna for each situation. Designing a matching network with Virtual Antenna is fast and easy, therefore this technology speeds up the design of IoT devices. The matching helps to optimize return loss and therefore, total efficiency can be optimized. If an antenna without a matching network is not matched but the radiation efficiency is high, then matching the antenna will result in a high antenna efficiency.
Q19: tiny antenna need also two switch ?
It depends on the bandwidth you need and the size of the ground plane of the device. For small platforms (ex. 50 mm x 50 mm) it is more difficult to get more bandwidth that in larger platforms (100 mm x 50 mm). This is the reason why in small platforms if the number of bands is large including low LTE bands (700MHz-960MHz), matching network with switches is a good option to optimize performance.
Q20: The efficiency of the lower frequency bands is around 15 .. 20%. Is this an acceptable figure or what efficiency should a design aim for?
At least you should achieve an efficiency to fulfill the certification in case you need to certify the radioelectric performance of the device. For example, imagine the minimum required TRP is 10dBm and the output power of the module is 23dBm; then, the minimum efficiency we should get is 5%.
For a small form factor (device less than 107 mm in the longest direction), minimum free-space TRP requirement (class 3) for a given operator is 12dBm at band 2, and 4 and 10dBm for band 12. These numbers translate into 7.9% and 5%, respectively, which are below the efficiencies obtained in Thingy:91.
Q21: Are slides available?
Yes, the pdf is available in this post.
For reference, the recorded webinar is at https://www.youtube.com/watch?v=rjPd0sFuAyU
Q22: Is it Kind of Travelling antenna?
This is a non-resonant antenna element that thanks to a matching network can be tuned at any band across the frequency range of 0.698GHz-6GHz.
If you want to get more information of that, please visit https://www.microwavejournal.com/articles/29138-antenna-less-wireless-a-marriage-between-antenna-and-microwave-engineering
Q23: Could you please explain why you have chosen to use Qorvo radio components on nRF91-DK and Thingy:91? Not a single distributor has them in stock.
Q24: why should we avoid the feeding of the antenna from the center of the PCB ?
Feeding the multiband antenna at the corner maximizes performance. This does not mean that we cannot feed an antenna at the center of the edge of the ground plane. The issue is that, usually, we get less bandwidth, but this bandwidth may be enough for narrow band applications such as Bluetooth, GPS, ISM, etc.
Q25: Why don't you use two different feed lines for GPS and LTE?
The TRIO mXTEND chip antenna component, thanks to its multiport nature, can do what you propose, that is, one feed for LTE (close to the corner of the device) and another feed for GPS. Please, have a look at Fractus Antenna application note at: https://www.fractusantennas.com/files/AN_FR01-S4-210_Mobile_GNSS.pdf
However, in the present case, the Qorvo switch has enough number of outputs to host the GPS and cellular on the same port, and thus keeping high isolation between LTE and GPS.
Q26: Is the performance in all bands the same when you adjust only the matching network? Normally when you change to a high frequency, there needs to be a shorter trace in the antenna that serves that frequency. This actually means that the antenna should be made ready to work together with the matching network?
TRIO mXTEND chip antenna component is optimized to balance efficiency at the low (f<0.96GHz) and the high frequency bands (f>1.71GHz). The matching network helps to optimize the return loss at the frequency bands of operation. In fact, the antenna can work at another frequency bands thanks to different matching network designs. For instance, TRIO mXTEND chip antenna component can also work at 4G and 5G: see application note at https://www.fractusantennas.com/files/AN_FR01-S4-210_Mobile_5G.pdf
Q27: What's the insertion loss of TRIO and the QM12038 (if any)? 2. If antenna signal is switched, how can you use the GPS and LTE at the same time?
Insertion loss of the QM12038 is 0.5dB.
GPS and LTE are not working at the same time since the signals are connected to a switch. Recommendation for switching time between LTE and GPS can be found in the following answers (see next one).
Q28: What are the recommendations for switching between cellular and GPS bands? How fast should it be done? We need to be registered in cellular network and at the same time we need to recieve GPS signal to have valid positioning.
This switching should be invisible from the application side and is part of the modem FW. So the application needs to send a command to the modem, and GPS positioning will then be done while the LTE link is in PSM. For more information please restate questions like this on devzone.
Q29: Does this Antenna require a big ground plane like PIFA?
As in any antenna technology, ground plane plays an important role. The advantage of Virtual Antenna is that the antenna geometry does not need to be customized depending on the platform (ground plane) size; only the matching network need to be adjusted which is faster and easier than to design a new antenna. See application note of TRIO mXTEND for different ground plane sized at: https://www.fractusantennas.com/files/AN_FR01-S4-210_EB_size.pdf
Q30: Can a good efficiency be reached if the ground plane is so small? How about passing PTCRB certification where max 5dB attentuation is allowed?
Efficiency depends on the ground plane size of the device. As a rule of thumb: the smaller the ground plane size, the lesser the antenna efficiency. However, for a small form factor (device less than 107 mm in the longest direction), minimum free-space TRP requirement (class 3) for a given operator is 12dBm at band 2, and 4 and 10dBm for band 12. These numbers translate into 7.9% and 5%, respectively which are below the efficiencies obtained in Thingy:91.
Q31: I would like to see the Radiation pattern for different band
Radiation patterns are almost omnidirectional. Please have a look at Fractus Antennas Application Note where it shows radiation patterns for the TRIO mXTEND chip antenna used in Thingy:91 on the same platform size. https://www.fractusantennas.com/files/AN_FR01-S4-210_EB_size.pdf
Q32: How fast can you switch between the matching networks? Regarding IOT, wake up time is short to save power and now you first have to wait for GPS get a fix, switch NW , connect (cold fix?) and transmit.
This is controlled by the modem FW. The switches themselves state switching speed 2 µs.
Q33: In many datasheets and integration manuals, I find that cellular and gps antennas should have as much space as possible between them to avoid one influencing the other. Does this type of antenna (GPS+cellular multiport) require special driving where only one can be used at the same time?
It is right that a further distance between the cellular and GPS antennas helps to achieve a good isolation. However, for the TRIO mXTEND chip antenna used in Thingy:91, cellular and GPS signals are decoupled thanks to the switching mechanism. This enables that the same antenna component can be used for cellular and GPS without the need of using two separate antennas, which save space and final costs.
Q34: Anout the Thingy:91 : Is the software interface (api, etc.) between nRF91 and nRF52 ready now? It seemed not to be a few months ago.
Currently the nRF52840 on the Thingy:91 is used as a UART-USB bridge.
Q35: Interested in WiFI, BLE and RFID Antenna
You can use Virtual Antenna to cover any frequency band from 698MHz to 6GHz. Please if you have an upcoming project use our WFT Service and we will recommend the best solution for your case.
Q36: If this is battery powered, how low is the power consumption of the circuitry? In terms of battery life, how long will the battery life will last if combined with other IOT sensors?
This is a bit hard to say, it depends a lot on the use case and how often you have to send data to the cloud. We refer to the documentation that is available on the nRF9160 where there are some numbers provided for different scenarios. For example the product brief located here: https://www.nordicsemi.com/Products/Low-power-cellular-IoT/nRF9160
Q37: What is the smallest size of the embedded antenna that it can embed. 2. Can the antenna be designed for multiple frequencies like for NB-IOT or BLE at the same time?
Virtual Antenna technology is available with different sizes and form factor to easily fit into your device. For example, other possibilities are RUN mXTEND antenna booster (12 mm x 3 mm x 2.4mm), BAR mXTEND antenna booster (10 mm x 3.2 mm x 3.2 mm), and CUBE mXTEND (5 mm x 5 mm x 5mm). All these antenna boosters can operate at NB-IoT or BLE at the same time. For a more detailed analysis, please use our Wireless Fast-Track tool and you’ll get a ready-to-test antenna design for your Mobile/IoT device. Free of Charge* (subject to T&Cs). https://www.fractusantennas.com/fast-track-project/
Q38: I have been burned by cell providers not supporting IoT connectivity. Example ATT dropping 2G and now Verizon planning to drop 2G. What is the outlook long term for thingy 91 cell provider support?
We don’t have any reason to believe the support won’t be extensive, and we certainly hope it will stick around for a long time.
Q39: Hi, What are the best practices while designing a custom board different from the GND plane dimensions given in the Antenna datasheet?
Please, have a look at the webinar at slides 21-25. Also, with Virtual Antenna, it is easy to embed the antenna in your device following 3 basic steps: 1) place the antenna component, usually at the corner of your PCB (see https://www.fractusantennas.com/videos/step-1/); 2) design your matching network - https://www.fractusantennas.com/videos/step-2/; 3)https://www.fractusantennas.com/videos/step-3/
Also if you have a new project, you receive our support using the Wireless Fast-Track tool and you’ll get a ready-to-test antenna design for your Mobile/IoT device. Free of Charge. https://www.fractusantennas.com/fast-track-project/
Q40: How close to the human body can the antenna be, and what are the best practical tips and suggestions for antennas in wearable devices?
The more space you can keep, the better. The advantage of Virtual Antenna based products is that the performance can be optimized according to each scenario without the need of changing the antenna design. We have a service to test the human body https://www.fractusantennas.com/consultancy-on-antenna-integration/
Again, if anything is still unclear please do not comment here, but instead ask your question in the DevZone Q&A section here.