# Free-Space Path Loss

### Key Takeaways

• Free-space path loss describes the attenuation of signal strength that occurs as an electromagnetic wave travels through open air or a vacuum.

• Free space path loss is fundamental in wireless communications and radio frequency engineering applications.

• While free-space path loss primarily affects wireless signal transmission, it can also indirectly influence aspects of PCB design.

A 3D plot of free-space path loss (FSPL)
(Source: Wikipedia User Sss41)

When radio signals travel through air or a vacuum, they get weaker the farther they go. This phenomenon is called free-space path loss (FSPL), which is crucial for making wireless communications work effectively.  Engineers have to plan for it when they build wireless communications systems.

The free-space path loss can be calculated using the Friis transmission equation, which is given by:

FSPL (dB) = 20 log10(d) + 20 log10(f) + 20 log10(4𝜋/c)

Where:

d is the distance between the transmitter and receiver in meters

f is the frequency of the signal in hertz

c is the speed of light in a vacuum

The equation considers how electromagnetic waves propagate across distances and how signals act differently depending on their frequencies. The longer the distance or the higher the frequency, the larger the FSPL gets, leading to a weaker signal.

## Free-Space Path Loss Applications

Free space path loss is fundamental to wireless communications and radio frequency engineering. Here's a quick overview of some key applications:

## Free-Space Path Loss and PCB Design

PCB design focuses on circuits' physical layout and electrical properties, while free-space path loss relates to wireless signal transmission.  However, FSPL can indirectly influence aspects of PCB design, for example:

• Antenna Design: Impedance matching between PCB traces and an antenna is vital for efficient signal transfer.  Calculating FSPL may impact the choice of antenna type and design parameters to make up for signal loss.
• Wireless Communication Modules: Knowing FSPL helps determine the necessary power levels to enable communication, which can influence the power supply and distribution network design on the PCB.
• Ground Plane Design: The ground plane design is critical for RF and wireless products.  FSPL factors could guide the arrangement of ground planes and component placement to reduce interference and improve signal integrity.
• Transmission Line Effects: As signals travel through PCB traces, transmission line effects like impedance mismatches, reflections, and signal distortion become significant.  Controlling trace impedance is key to minimizing signal degradation.
• EMC/EMI Considerations: Managing electromagnetic compatibility (EMC) and electromagnetic interference (EMI) is essential in ensuring that different components on the board don't interfere.  Understanding how electromagnetic signals propagate and lose strength over distance due to FSPL can inform grounding, shielding, and layout choices.
• Trace Lengths and Delays: FSPL also relates to signal delays. Engineers must consider the time it takes for signals to travel through traces, especially in high-frequency applications.

FSPL doesn't directly impact PCB layout and design; it does influence decisions on wireless communication modules, antenna design, and the overall performance of RF circuits. Designers must consider these factors to optimize their PCB for reliable and efficient wireless communication.