Laird LYRAS BLE Wireless Radio Module User Manual

Laird LYRAS BLE Wireless Radio Module User Manual

Layout and Placement

For optimal performance of the LYRA S the following guidelines are recommended:

• Place the module 1.50 mm from the edge of the copper “keep-in” area at the middle of the long edge of the application PCB, as illustrated in Figure 10.
• Copy the exact antenna design from Figure 10 with the values for coordinates A to L given in Figure 11.
• Make a cutout in all lower layers aligned with the right edge and the bottom edge of the antenna as indicated by the yellow box in Figure 12.
• Connect all ground pads directly to a solid ground plane in the top layer.
• Connect RF_2G4 to ANT_IN through a 0-ohm resistor.
  • The 0-ohm gives the ability to test conducted and to evaluate the antenna impedance in the design.
• Place ground vias as close to the ground pads of the LYRA S as possible.
• Place ground vias along the antenna loop right and bottom side.
• Place ground vias along the edges of the application board.
• Do not place plastic or any other dielectric material in contact with the antenna.
  • A minimum clearance of 0.5 mm is advised.
  • Solder mask, conformal coating and other thin dielectric layers are acceptable directly on top of the antenna region.
    
    Figure 1: Recommended Layout for LYRA S
    
    Figure 2: Antenna Layout With Coordinates

Table 1: Antenna Polygon Coordinates, Referenced to Center of LYRA S

Point|

LYRA SC22HNA2

---|---

A

| (2.87, 2.13)
B|

(2.54, 2.13)

C

| (2.54, 3.69)
D|

(3.36, 4.51)

E

| (7.75, 4.51)
F|

(7.75, 4.15)

G

| (6.84, 4.15)
H|

(6.21, 3.52)

I

| (4.26, 3.52)
J|

(3.97, 3.81)

K

| (3.10, 3.81)
L|

(2.87, 3.58)

MWloop

| 4.88
Hloop|

4.15

Note: 1. All coordinates and dimensions listed in mm.

Figure 3: Antenna Clearance in Inner and Bottom Layers

Best Design Practices

The design of a good RF system relies on thoughtful placement and routing of the RF signals. The following guidelines are recommended:

• Place the LYRA S and antenna close to the center of the longest edge of the application board.
• Do not place any circuitry between the board edge and the antenna.
• Make sure to tie all GND planes in the application board together with as many vias as can be fitted.
• Generally ground planes are recommended in all areas of the application board except in the antenna keep-out area shown in Figure 12.
• Open-ended stubs of copper in the outer layer ground planes must be removed if they are more than 5 mm long to avoid radiation of spurious emissions.
• The width of the GND plane to the sides of the LYRA S will impact the efficiency of the on-board chip antenna.
  • To achieve optimal performance, a GND plane width of 55 mm for LYRA S22A is recommended as seen on Figure 13.
  • See Antenna Typical Characteristics for reference.

Figure 14 illustrates non-optimal layout examples scenarios that will lead to severely degraded RF performance for the application board.

Figure 4: Illustration of Recommended Board Width

Figure 5: Non-Optimal Layout Examples

Radio Performance vs. Carrier Board Size

For many applications, the carrier board size is determined by the overall form factor or size of the additional circuitry. The recommended carrier board width 55 mm for the LYRA S is thus not always possible in the end-application. If another form factor is required, the antenna performance of the integrated antenna will be compromised but it may still be sufficiently good for providing the required link quality and range of the end-application. Figure 16 shows the total efficiency of the integrated antenna for different carrier board sizes. As can be seen the best performance is achieved for the carrier board size of 55 mm x 25 mm for the LYRA S, with relatively constant performance for larger boards and rapidly declining performance for smaller boards.

The performance of all the sizes tested will be adequate for more than 15 m line of-sight range and all of the sizes are thus usable.

WARNING: Any antenna tuning or change of the loop dimensions will void the modular certification of modules with modular certification. In that case, a Permissive Change to the modular approval is required.

Figure 6: Efficiency of the Integrated Antenna as Function of the Carrier Board Size for LYRA S22A

Proximity to Other Materials

Placing plastic or any other dielectric material directly in contact with the antenna may cause performance degradation. A clearance of minimum 0.5 mm is recommended to avoid excessive detuning of the antenna. Solder mask, conformal coating, and other thin dielectric layers are acceptable directly on top of the antenna region. Any metallic objects in close proximity to the antenna will prevent the antenna from radiating freely. The minimum recommended distance of metallic and/or conductive objects is 10 mm in any direction from the antenna except in the directions of the application PCB ground planes.

Proximity to Human Body

Placing the module in contact with or very close to the human body will negatively impact antenna efficiency and reduce range. Furthermore, additional certification may be required if the module is used in a wearable device.

References

• Ezurio | Laird Connectivity is now Ezurio

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