frequency bands, the matching circuit becomes much more complex. To assist designers, antenna suppliers such as Ignion offer software that makes the job much easier. Armed with knowledge of the pc board size, choice of chip antenna, frequency band requirements, and S11 parameters (the reflection coefficient for the system which is a proxy for the target efficiency), designers can use Ignion’s software package to not only design the matching circuits, but also determine the exact component values needed to approach the S11 parameter target. With the assistance of the software, provided the PC board is large enough, it’s possible to design an antenna system with just one embedded antenna and matching circuit that meets the needs of a full multiband system. However, if the PC board (and hence the ground plane) is small,
The nRF6943 is designed to assist engineers in the development of IoT devices using short-range wireless (Bluetooth LE), LTE-M/NB-IoT, and GPS.
gap between it and the other components, and at a distance from the mounting screw (Figure 2). The nRF6943 is designed to assist engineers in the development of IoT devices using short-range wireless (Bluetooth LE), LTE-M/NB-IoT, and GPS. Matching circuit design The most important part of the antenna system design is the impedance matching circuit, which sits between the chip antenna and the IoT device’s transceiver. The purpose of the matching circuit is to limit transmit/receive losses
by matching the impedance of the transmitter power sources with that of the antenna (typically 50 Ω for a low-power IoT product). The engineering task is to not only design the appropriate circuit topology, but also to select the appropriate inductor and capacitor values to ‘transform’ the voltage source impedance such that it matches the antenna impedance. The use of high-quality factor (Q) and tight tolerance components enhances performance. For a single operating frequency band, for example 2.4GHz, the design is relatively straightforward, but for an IoT product operating in multiple
Figure 2: The nRF6943 cellular IoT development board showing the position of the multiband antenna at the top, with wide clearance area (partially covered by white label) between the antenna and other components. Image source: Nordic Semiconductor
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