How should I connect the pins which are not intended to be used on Si4x6x / EZR32?
How can I make the frequency bandwidth of PCB antennas wider?
In some cases/applications the BW of printed antennas might not be sufficient. This article summarizes some design tricks on how to make a printed antenna wider bandwidth.
- Increase the board size (e.g. GND plane in the case of monopole-type antennas). Avoid using RF modules that have smaller size than quater-wavelength. Small modules generally have poor antenna gain and narrow bandwidth (due to the high Q factor).
- Increase the board thickness. Of course, it's typically limited by design.
- Decrease the dielectric constant of the PCB. Select PCB material with low epsilon value.
- Use wider and/or tapered traces in the PCB antenna structure.
- Use coupled traces in the PCB antenna structure. Coupled structures typically have wider frequency bandwidth.
- Do some tricks in the external antenna matching network. I.e. use more components to do the match (to stay within a given constant Q ellipse on the Smith Chart); create resonators in the matching network. Also, see Bode-Fano, Youla matching techniques.
A number of antenna types can inherently be matched to the desired input impedance (typically, 50-ohm single-ended) without using any external tuning component (e.g. printed inverted-F antenna). However, board size, plastic enclosures, metal shielding, and components in close proximity to the antenna can affect antenna performance. For best performance, the antenna might require tuning that can be realized by two ways:
It is typically a preferred solution when layout modification is not required on a custom design. To accomplish this, Silicon Labs generally recommends to ensure SMD placeholders for external antenna tuning components, where the suggested external antenna matching structure is a 3-element PI network. You can achieve a good match using as a maximum of two elements (with one series and one shunt component) of the PI network. Any unknown passive impedance can get matched to 50 ohms on this PI network, since all L, C, L-C, C-L combinations can be realized on it and therefore any de-tuning effect can be compensated out.
Note that every implementation of an antenna design might require different combinations of inductors and capacitors.
Recommended 3-element PI network for external antenna matching purposes:
The PART and ROMID reply fields of the PART_INFO command are sufficient to identify EZRadio/PRO part number and revision according to the following table.