 Hello, in this video I will present some basic information about antennas, and then we'll focus on antennas which can be used with STN32WB. The intent of this video is to provide a quick overview of antennas, especially for people who haven't worked with antennas before. If there is some topic that interests you more, for example how to use miss-charge for antenna matching, you can use it as a keyword to get more detailed information. The agenda has three main topics. A brief introduction to antennas, then we will focus on antennas for STN32WB, and as the last point we will show few practical information which is good to know when implementing the antenna. Let's discuss the basics of antennas. What is an antenna? It is a device which transforms conducted wave. It means electric current moving in metal conductor to radiated wave, which is propagated through space and vice versa. The antenna is reciprocal. The same antenna can be used for receiving or transmitting. We can see the antenna also as a kind of filter. Frequency filter. It works only in some frequency range. Directional filter. Some directions are radiated or received better. Some are attenuated. Polarization filter. In my filter, the signal according the wave polarization. There are many antenna parameters. The basic ones are for example, impedance. It means what impedance a transmitter or a receiver can see. Return loss. It means what portion of energy is reflected back from the antenna port. If the energy is not reflected, then it is radiated. Last parameters are operating frequency and bandwidth, radiation efficiency and power rating. It is important mainly for transmitter antennas how strong transmitter can be connected. Radiation pattern or receiving pattern in case of receiving antenna is a 3D graph that shows us radiation intensity in space. It can be also displayed as a 2G graph which shows one particle cut of the 3D pattern. The last parameters we will mention are antenna gain and directivity. The antenna gain shows us again relative to an isotropic antenna. The isotropic antenna is a hypothetical antenna that radiates equally all directions. The bigger gain, the bigger directivity the antenna have. It means it has very good gain in some direction but poor in others. There are several ways how to get parameters of the antenna. In case the antenna has a particular vendor, parameters can be obtained from our datasheet. Antenna parameters can be also calculated, but this is valid mainly for simple antennas. For some antennas, the calculation may be very complex. The next way is a simulation. RF simulator is a typical tool when designing or optimizing the antenna. Last option is measurement. This option can give us the most accurate results. Here is a short example of antenna simulation. At first the antenna must be modeled in the tool, then the material and environmental parameters must be set. Setting of the simulation, for example mesh, solver type, etc. have also impact to the simulation results. Some experience and skills are needed to get the best results. Results of the simulation can be as one-one or return loss, electromagnetic field distribution or radiation pattern. Measurement of antennas can be divided into two groups, measurement of electrical parameters like impedance, return loss, standing wave ratio, bandwidth or operating frequency band. In this case, the antenna is connected directly to the measurement instrument, like VNA. The next group is measurement of radiation parameters, like radiation pattern, directivity or gain. The antenna is measured in an anechoic chamber. Antenna application workflow is usually an iterative process, because parameters depend on target environment which is usually unique to the design. At first, we must define what antenna parameters we need, for example frequency band, bandwidth, radiation pattern, etc. Then we can select appropriate antenna type, which can fit our requirements. Then we must optimize the antenna to our design, for example fine-tune the antenna matching network. The last step is to verify that the parameters match our needs. If not, we have to optimize the antenna or select another type. Now let's focus on antennas for STN32WB. The RF part of STN32WB looks like this. RF pin, which is shared both for transmitter and receiver, is connected to the matching network and the low pass filter. These blocks are also implemented in IPD if used. The output of the filter is connected to the antenna through the matching network, which matches an impedance of the antenna to 50 ohms. The antenna for STN32WB should have the following parameters. This frequency range, which is the range of Bluetooth low energy band. To have good parameters, S11 or return loss should be lower than –10 dB within the band. Impedance with a matching network around 50 ohms. Other parameters depend on the particular design, for example radiation pattern, antenna dimensions, antenna type, PCB or chip, placement, working environment, etc. ST supports the STN32WB antenna to pick with two application nodes. AN-5434 and AN-5129. The AN-5434 describes several antenna types, for example, monopole T-shaped antenna, inverted F-antenna, chip antenna, etc. These antennas were simulated and measured. You can easily compare parameters of these antennas. The next application node, AN-5129, describes a low cost PCB meander-antenna, which is used for example STN32WB nuclear or dongle boards. In the next slides, an example of a design with this meander-antenna will be described. The antenna will be used on a test board. It will be simulated at first and then measured. Then an example of the antenna matching will be shown. The test board with the meander-antenna looks like this. Here we can see the simulation model and here the real sample. Antenna matching network is placed as close as possible to the antenna. 50 ohms Coplanar waveguide is used between the antenna matching network and the SMA connector. This is the ground plane. Another ground plane is also below all this area. The antenna has no ground plane below. At first, we can measure impedance of the antenna without the matching network. There are many variants how to do it. In the simulation, we place the board here. In case of measurement, we place the semi-rigid pigtail on the board. In this slide, we can see the results of the simulation and the measurement. We can see the return loss and the impedance. Results are placed at the beginning, middle and the end of the BLE band. The simulation and measurement results are quite close. From the Smith chart, we can see that the impedance can be improved. This can be done in the matching network. To match the impedance, we need to know the antenna impedance. From the previous simulation or measurement, it is around 29 plus J19 ohms at 2.44 GHz, which is the center of the BLE band. In the Smith chart, we can estimate the matching network structure and values which are needed to get impedance of 50 ohms. In this case, serial inductor 0.4 nanohenry and parallel capacitor 1.9 picofarad were used. Here is the calculation in the Smith chart, and here is the structure. The real values, which were finally used, are a bit different due to parasitics of the board and components, which were not included in the simple calculation. Instead of inductor, we used capacitor of 10 nanofarads, which is assured at this frequency. It has also some parasitic inductance, which was useful in this case. Here we can see the simulation and measurement results with the matching network as observed on the SMA connector. The results are very close. The antenna is matched well in the BLE band. Simulated 3D radiation pattern of the test board looks like this. The red color means higher radiation intensity. The 2D radiation diagram shows the gain in this blue plane. And finally, simulated antenna radiation of the E field. You can see how the energy is conducted from the SMA connector to the antenna and then radiate it into space. In this last chapter, we will cover some basic information that is good to know when implementing an antenna. Size of the ground plane has significant impact to the antenna parameters, for example return loss or impedance. For example, design with smaller ground plane has the impedance here. The design with bigger ground plane will have different impedance. Both boards will need different antenna matching network. Antenna parameters depend on the environment. Here we can see three examples of different working environments. Impedance, red curve and return loss, blue one, are shown in the measurement results. In the first case, the board is unplugged and 5 centimeters above the table. In the middle case, the board is plugged into the docking station and around 1.5 centimeters above the table. In the last case, the board is plugged into the USB hub and is about 0.5 centimeters above the table. In all cases, the measured impedance and return loss are different. The best parameters has the board in the middle case. This is the environment for which the board was optimized by the matching network. As we mentioned earlier, an antenna usually don't have impedance 50 ohms and the impedance changes with the environment. The matching network can help to tune the impedance close to 50 ohms. The antenna matching network is usually placed close to the antenna. If the antenna vendor recommends some matching network structure, use it. If you are not sure which antenna matching network will be needed, you can place this universal petropology on the PCB. In the design, usually 1.5 will be populated depending on the impedance of the antenna. Here is a short example about the antenna matching using the Smith chart. At first, the matching network is not populated. We need to measure the impedance of the antenna. The antenna must be placed in the target environment. Because impedance depends on frequency, use impedance in the middle of the band. For BLE band, it is 2.44 GHz. For example, we can measure this value which is shown in the Smith chart. If we know the impedance, we want to get to the center of the Smith chart. There are many tutorials and videos on the web. We recommend you to take a look at them. In this case, I know the fastest way to get to the center is by using a serial inductor and then parallel capacitor. The serial inductor with one nano Henry value will move the impedance to this important point. If serial capacitor with 1.3 picofarad value is connected, then the impedance is transformed to 50 ohms. In this case, we assumed ideal values. In real, we don't use ideal components, also there are parasitics on the board, so the real values of matching components may be a bit different. It must be fine tuned during the measurement. And that's all. I hope you have found something interesting in this video. Thank you for watching, bye!