This application note is about the STM32W108 product family from STMicroelectronics. It mainly discusses the advantages of using a PCB antenna and the methods for designing and implementing a PCB-printed antenna. Well designed and implemented PCB-printed antennas have a similar performance to SMD ceramic antennas, but the PCB-printed antennas have a larger size, resulting in increased PCB cost. However, the increased cost of the PCB is smaller and less expensive than a SMD ceramic antenna. The document also introduces the STM32-RFCKIT RF control kit, which is based on an STM32W108xx RF microcontroller and uses a PCB-printed antenna for RF communications.
This document details the design and implementation of a low-cost printed circuit board (PCB) antenna operating at 2.4 GHz, specifically tailored for the STM32W108 RF microcontroller family. The note explains that while PCB antennas offer reduced overall module costs compared to SMD ceramic equivalents, they require careful layout considerations regarding substrate parameters and impedance matching.
All electrical parameters were measured at connection to the Band Pass Filter with a frequency span covering frequencies from 2.4 GHz to 2.5 GHz.
The recommended substrate has a core thickness of 711.2 µm and a dielectric constant (εr) of 4.4.