MDEV-868-PRC datasheet(47/55 Pages) LINX

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Microstrip Details

A transmission line is a medium whereby RF energy is transferred from

one place to another with minimal loss. This is a critical factor, especially in

high-frequency products like Linx RF modules, because the trace leading

to the module’s antenna can effectively contribute to the length of the

antenna, changing its resonant bandwidth. In order to minimize loss and

detuning, some form of transmission line between the antenna and the

module should be used unless the antenna can be placed very close (<1⁄8in)

to the module. One common form of transmission line is a coax cable and

another is the microstrip. This term refers to a PCB trace running over a

ground plane that is designed to serve as a transmission line between the

module and the antenna. The width is based on the desired characteristic

impedance of the line, the thickness of the PCB and the dielectric constant

of the board material. For standard 0.062in thick FR-4 board material, the

trace width would be 111 mils. The correct trace width can be calculated

for other widths and materials using the information in Figure 92 and

examples are provided in Figure 93. Software for calculating microstrip lines

is also available on the Linx website.

Trace

Board

Ground plane

Figure 92: Microstrip Formulas

Example Microstrip Calculations

Dielectric Constant

Width / Height

Ratio (W / d)

Effective Dielectric

Constant

Characteristic

Impedance (Ω)

4.80

1.8

3.59

50.0

4.00

2.0

3.07

51.0

2.55

3.0

2.12

48.8

Figure 93: Example Microstrip Calculations

Pad Layout

The pad layout diagrams below are designed to facilitate both hand and

automated assembly. Figure 90 shows the footprint for the smaller version

and Figure 91 shows the footprint for the encapsulated version.

0.420"

0.015"

0.028"

0.050"

0.060"

0.070"

0.015"

0.136"

0.100"

0.101"

0.060"

0.065"

0.090"

0.015"

0.420"

0.015"

0.028"

0.050"

0.520"

0.070"

0.015"

Figure 90: HUM-***-PRC Recommended PCB Layout

Figure 91: HUM-***-PRC-UFL/CAS Recommended PCB Layout

MDEV-868-PRC Datasheet(PDF) 47 Page - Linx Technologies

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