Feature: IIoT
Embedded antennas One of the most challenging antenna types to design is embedded antennas. For example, take any embedded antenna mounted on four different evaluation boards of various lengths. When you measure the efficiency of each of the boards in an anechoic chamber - if the board is too short for the antenna, the efficiency at low and high frequencies can drop drastically. Tis highlights that the size of the ground plane plays an integral role in antenna performance, and this is true for every embedded antenna, no matter the manufacturer, technology or frequency. Tis is the reason why there are several embedded antenna
types, and depending on the PCB size, some will work better than others. Te five most common embedded antenna types are ceramic/helical monopole, ceramic magnetic loop, ceramic/ FR4 PIFA multiband, stamped metal PIFA and patch. Tese off- the-shelf antennas are available from TTI’s suppliers, including Abracon, Amphenol, Pulse, AVX, Taoglas, and TE Connectivity. When deciding which type of embedded antenna to select, it’s probably easier to compare the two extremes – the monopole and loop antennas.
Ceramic monopole antennas Ceramic monopole antennas are the most accessible embedded antennas to design in, and are placed in the corner of the PCB. Tey operate similarly to a standard monopole, producing a dipolar radiation pattern. Typically, you need a series component and one parallel component for impedance matching, which is quite straightforward if you follow the Smith Chart. However, the drawback of using this kind of antenna is that the ground clearance, which is the area surrounding the antenna, is relatively big for maximum radiation efficiency. If you do not have much space on the PCB, then a good solution might be a helical monopole antenna.
Ceramic loop antennas Te third antenna type is the ceramic loop antenna. Out of the embedded antenna types, in the best-case scenario, it gives the highest radiation efficiency and greatest RF gain. It is also more resilient to hand-loading effects – so they are best suited for handheld applications. One of the biggest drawbacks of ceramic loop antennas is that because they are dipole antennas, they need a larger ground plane area than a monopole antenna. Te ground clearance is especially important for a loop antenna
because of the way it is connected to the board (Figure 2) with one feed and a grounded element on one side and a second grounded element on the other, which makes the return surface current flow around the ground clearance making a loop – hence the name. You can influence how the current flows by changing the ground clearance – tuning the impedance and frequency up and down. Te second factor to consider is the electromagnetic field and its appearance on the board. Because the loop antenna uses the ground plane as a dipole,
most of the radiation comes from the PCB. Since the total length has to be half a wavelength, as explained earlier, with a quarter
24 March 2025
www.electronicsworld.co.uk
wavelength on one side and the same on the other. As the wavelength varies with frequency, the required length of the PCB varies, and if the PCB is too short for a given frequency, the loop antenna will not work as expected. Because of these two factors, loop antennas are the most engineering-intensive embedded antennas, requiring experienced RF engineers to design them. Ceramic Patch Antennas Patch antennas work better for GPS applications if you know
that the device will always face the sky. Tey have a high gain and a circular polarisation. However, if the device position is arbitrary like a wearable, for instance, then a chip antenna is a good alternative as they have an omnidirectional radiation pattern.
The importance of antenna design An antenna is designed for a wanted operating frequency, which means that it can be used for any standard or application if it covers the frequency band. For example, a dual-band 2.4/5 GHz antenna can be used for Bluetooth, Bluetooth Low Energy (LE), and Wi-Fi, and just for 2.4 GHz applications like Zigbee and Thread. Every time you have a dip in your VSWR or your return loss
at a particular frequency, it means the antenna is resonating at that frequency. If the antenna is not tuned at the right impedance or at the right frequency of the radio module, it will create an impedance mismatch at the antenna input – a return loss, see Figure 3. Tis impedance mismatch will result in power being reflected from the antenna back to the radio. If this is the case, you may have to increase the output power of the radio module, which, for battery-powered IoT devices, will result in the battery draining faster. In addition, the budget link between the IoT device and the receiver will be weaker. Terefore, it is important to match the impedance to minimise
the return loss, enabling you to reduce the output power of the radio module and increase the battery life and, of course, the budget link will be much stronger. Te goal is to have the VSWR as close as possible to one, or the return loss less than -10 dB at the wanted resonant frequency. Suppose you choose an embedded wireless module with the
matched antenna ready to integrate onto the main PCB. In that case, TTI Europe has pre-certified cellular, Wi-Fi, Bluetooth, Bluetooth LE, LoRa and UWB solutions. Te benefits of choosing a module are the shortened design time, improved performance and lower overall cost. Whether deciding between a custom RF design or a ready-made wireless module, TTI Europe has a dedicated team of RF specialists who can provide technical advice and guidance. TTI Europe offers a wide range of different antenna types.
Antenna components are designed for specific applications, have better performance, and are more compact than PCB antennas. Find external, adhesive, or chip antennas for Wi-Fi, Bluetooth, ISM, Zigbee, GPS, LPWAN, Cellular, RFID, and NFC applications. Antennas are available from Abracon, Amphenol, JAE, Kyocera AVX, Pulse Electronics, Taoglas, TE Connectivity, and more.
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