Preparing the design¶
So, you're ready to start designing your product. Carefully read through this section, as it will guide you to the best possible performance of your product.
Reference design files¶
A complete reference design including PCB layout and PCB design guidelines is available from LumenRadio to make integration easier. Please send your inquiry to LumenRadio for details.
Internal or External Antenna¶
For short distances the internal antenna will perform well. But if the design is to be placed inside a metal enclosure, or if there is a need to cover longer distances, an external antenna is necessary. An external antenna must at least be designed for operation between 2.4 – 2.48GHz with a 50 Ω characteristic impedance.
If the internal antenna is considered, the product case needs to be of a RF transparent material. The circuit board that will hold the MiraOne module needs to be designed so that the internal chip antenna radiates efficiently. Avoid any ground planes near the antenna chip.
When placing MiraOne on a circuit board:
- Place the module as close to the host circuit board edge as possible with the antenna pointing outward.
- Note the absence of ground plane near the chip antenna on the module's circuit board.
- Remove any copper from the main board as specified in section “Layout Examples”
- Avoid using metal structures such as mounting hardware close to the antenna chip.
Layout considerations for the main board¶
MiraOne has been specifically designed in order to achieve good RF performance. In order to maintain this, there are some guidelines that we would like to stress:
The use of ground planes also on the main board cannot be emphasized enough. Good decoupling of any high speed digital circuitry is a must. Many embedded type microprocessors today have clock frequencies with clocks or overtones that reach well into the GHz range. It is perfectly possible for an embedded design to pass any EMC certification and still cause disturbances that will block the RF reception of the TiMo module. The sensitivity of the MiraOne receiver better than -100dBm therefore it is recommended to keep disturbances well below this level in the frequency range of operation, to achieve a good signal to noise ratio.
A near field probe connected to a spectrum analyzer will show if there are any disturbances present on the 2.45 GHz band generated by the microprocessor or any other device that is placed on the main board. Pay special attention to readymade LAN-products, such as "Server in a RJ connector". They pass EMC certifications, but some of them radiate badly on 2.45 GHz. If disturbances can be seen on a spectrum analyzer - then the MiraOne module will have impaired reception.
MiraOne has a supply voltage decoupling on the circuit board. The supply voltage still needs to be adequately filtered. If any disturbance or intermittent communication failures occur - check the supply voltage for drop-outs, switch supply ripple, etc.
- The TOP layer inside the footprint must be free from copper. There is a ground plane on the MiraOne module, but there are also supply lines. It is an unnecessary risk to rely on solder mask lacquer for isolation.
- The area around the antenna must be kept clear from copper on all layers as depicted in the picture below.
Minimum dimensions for ground plane clearance for optimum antenna performance are shown below:
LumenRadio operates a full RF laboratory in Sweden and can offer design verification and testing services – please contact LumenRadio for advice.