Antennas are literally everywhere. It is a common piece of equipment that it has become a natural part of our environment so that we have stopped noticing them. They might be invisible to us but a great part of our wireless communication depends on their presence. Antennas act as core parts of modern devices, cars, phones, notebooks or even smart home devices developed by FIBARO. Not having them would keep our lives back just as it was in early 20th century. We took a deep insight to the world of antennas and ask some questions during a thorough conversation with one of our experts – Robert Giżycki, the Senior Hardware Engineer FIBARO.
Przemysław Kaczorowski: Robert, tell us more about the antennas, what is their role in IoT devices, including those developed by FIBARO?
Robert Giżycki: The antenna is usually made of metal of a certain shape and size. Physical features of its structure define its properties and performance — including the range. Antenna is the final part of the radio system, which is designed to effectively convert the electrical power supplied to its input into an electromagnetic wave (EM) that spreads freely in space reaching distant devices — it carries information. The nature of the antennas is that they work simultaneously in both directions, the thing is that they are simultaneously a transmitter and a receiver of an EM wave. A pair of antennas distant from each other is connected by an “invisible cable” connecting devices and letting them communicate. The main difference is that an ordinary wire (usually connects two devices, and the antennas radiate in all directions allowing to connect multiple devices at different locations and at the same time. Of course, there are directional antennas, however, in IoT devices, including FIBARO smart devices, a uniform radiation in all directions is what we are exactly aiming at. Wired connection is stable and has virtually identical attenuation as a function of time or position change. In the case of antennas it is completely different, the attenuation between the two antennas is not constant. It strongly depends on the mutual location of the devices relative to each other, on the material to which they are attached, the structure of the building, and also, interestingly, on the location of the people in the building. Of no small importance is the phenomenon of reflection and summation of the wave, which locally can manifest itself as a large disappearance of the signal. Our research conducted in FIBARO R&D department showed that attenuation fluctuations between antennas can be up to 20-30dB (differences 100-1000 times). This means that the range between the same devices in a certain building can equal 30 meters while in another one it will be only 15 meters and all this is caused by a set of external factors.
PK: What do FIBARO smart home users need to remember to make their devices range stable? What are the rules the installer should keep in mind when installing the system??
RG: FIBARO devices are designed in a way the user does not have to worry about losing range. However, in some cases it is good to remember certain rules. For example, devices with an external antenna have a better range performance if the antenna is straghtened and separated (straightened and stand-off) from the device. The more curled and hidden is the antenna, the worse range we have. Remember not to close the devices in metal boxes or close to any metal surface as this greatly reduces the efficiency of the antenna.
PK: What is the process of designing antennas in FIBARO and what kind of antennas are used in our smart devices?
RG: We approach the radio track design process comprehensively. At the very beginning it is to place the antenna in the best part of the device. Basically, it can’t be covered by large metal elements that can affect the shape of radiation characteristics. It should not be too close to the housing as it is prone to detuning due to inaccuracy of the housing assembly. If there is a lot of space in the housing, we use antennas printed on the PCB – they are the most advantageous from an economical and functional point of view. A perfect example is the 433MHz antenna in Home Center 3. If there is not much space to work on, the chip or external antenna make a perfect alternative, as in FIBARO The Heat Controller. Our engineers use an electromagnetic simulator to modelling and verifying PCB antenna resonance frequency. Rest of the parameters are tested on a prototype in the FIBARO R&D department. Another step is to determine the efficiency of the antenna, its maximum amplification (gain) and design the matching circuit, which usually consists of several coils and capacitors. If any of the parameters is unsatisfactory, another revised version is designed. Throughout the entire process, we do not forget about impulse voltage regulators which are the source of interference entering the antenna (integrated circuit) that turn the higher voltage into a lower one these are the most popular elements in any electronic device. The team tries to locate the loudest tracks in the regulator circuit and next modify it to obtain the lowest antenna noise floor. Monopole antenna is the most popular type used across our devices.
PK: Speaking of design, can you specify the conditions and what tests are carried out on FIBARO devices?
RG: It is our aim to make the antenna band and its impedance optimal for the nominal operating conditions. Each product undergoes efficiency tests including the antenna radiation characteristics performance test. If the parameters obtained with the first prototype are poor, we design a new one. Sometimes it takes four or five different antenna designs to develop a proper product. Vector network analyzer helps us measure impedance and separation between antennas. On the other hand, the efficiency and characteristics of radiation are examined in the GTEM chamber (equipped with) automatic manipulator. The idea of measurements in the GTEM chamber has been developed earlier. Our team have developed a measurement system from scratch and had personalized it to improve FIBARO smart home devices examination.
PK: What parameters are most important for you and what problems do you encounter most often during your daily work?
RG: The main thing is to develop omni-directional radiation characteristics. This will provide a proper range in every direction. Secondly, the antenna efficiency. Our goal is to exceed 50% which is quite realistic for antennas working in the 2.4GHz and 5GHz bands. A lot more challenging are antennas designed for small devices operating at 433MHz or 868MHz frequencies (e.g. 868MHz frequency of FIBARO Keyfob). Size of the device determines the efficiency of the antenna where for smaller devices lower values are accepted. It is desirable that the antenna has a wide bandwidth and is not particularly prone to detuning. Antenna polarization is no longer so important because in the real system the devices are mounted in different ways and the transmission inside the building causes additional changes in this area. Therefore, it is very difficult to define the requirements in this area. The antenna itself is not everything, its surroundings are also crucial. As a sensitive receiver of the electromagnetic field, FIBARO devices record everything that happens around. This happens quite often: the spectrum of the output signal contains noise hills generated by DC/DC converters and also discrete peaks being harmonics of digital signals. Problems occur even if the electromagnetic emission of the device is low and meets all the required standards. The thing is that the sensitivity of the current radio systems is very high, and if antenna receive unwanted system noise, ability to the lowest signals reception disappears. Now comes the interesting part of the engineer’s work. Every single recovered decibel of sensitivity is a great success to an engineer. End user gets a strong and stable network within all smart devices.
PK: How did you manage to hide the antenna in Home Center 3 device? What was the goal of having such design and features?
RG: Home Center 3 has more than one antenna. Initially, there were seven of them, because we considered the use of the LTE interface. Finally, there are six antennas that support Z-Wave, ZigBee, WiFi 802.11abgn, BLE and Nice interfaces. We gave up the LTE interface and added an antenna that supports the 433MHz band, which is responsible for working with the Nice group products. The integration of so many antennas is a rather complicated process. Including the optimization, the whole process took us around two months. At first, we defined the size of the device which would be acceptable in terms of design and price. Engineering team wanted to maintain large device size to achieve better antenna performance in the lower frequency range (433-870MHz). Large size of the PCB gave us some flexibility when it comes to optimizing antennas separation, what allowed us to keep low intermodulation distortion. After that, we have focused on measuring radiation characteristics and optimizing antenna impedance. High efficiency and relatively uniform radiation characteristics were our priority.
PK: Do you remember the case of 2010 iPhone 4 losing their GSM range? Is it probable it will happen again?
RG: Yeah, I am familiar with the subject. It’s an issue of today’s engineer. Engineers are the ones who need to define what typical use really means to a certain product and conduct research to fit the requirements. It may happen that someone does not capture a certain property of the antenna and, as a result, the user will be struggling with a range problem. Smartphones are a good example of what can exactly go wrong. Users handle phones in a different manner by holding them in their hands or by making a call – current position of the device makes a huge difference to the antenna performance. Our researchers say it is impossible to examine all possible scenarios, especially when they are getting short on research time. Customer’s demand made us push hard on every single product launch and they are expecting one every 6 months. Combined design teams with experienced testers are essential. If they can figure out the worst case scenario, the team is able to develop a solution to it. If not, it will surely be pointed out by the users. Of course, it is not guaranteed that there will be no problems at all. If someone decides to place the active part of the antenna outside the housing, they must reckon with the fact that its impedance can take extreme values and, as a result, the efficiency of the solution may vary.
PK: FIBARO devices operate in the so-called mesh network – can you explain how does it work? What does it consist of and what are the benefits?
RG: The point is that devices that are not in direct range with the smart home gateway (e.g. Home Center Lite, Home Center 2 or Home Center 3) are connecting via other devices using the same network. Method of this kind builds a strong Z-Wave network range which is reliable even in big apartments or houses. It is also worth remembering that the retransmitted information block (exploits) the radio channel a little longer than the direct communication, so the better range is achieved at the expense of retransmission and lowering of the radio channel bandwidth.
PK: Is Home Center Lite enough for a 40m2 apartment? Can it handle the range? How would you assess the need for individual FIBARO smart home gateways depending on the home size?
RG:Home Center Lite will easily manage the range in an apartment with an area of 40m2. However, it should be remembered that each case is different, as I mentioned earlier. When it comes to range, both the Home Center 2 and Home Center Lite have similar range, however, Home Center 2 provides more system configuration capabilities. Home Center 3 smart home gateway has an additional power amplifier module and LNA and its range performance is second to none. I’m pretty sure it provides a two time better range coverage from the previous gateways versions.
There is no doubt that technological development and users increasing requirements force more advanced solutions. To be able to fully enjoy the possibilities offered by the FIBARO smart home you should observe some important issues and entrust the installation to a professional installer. This connection guarantees reliability, and in case of any doubts – almost immediate help.