How to Calculate the Transmit Power of a PCB Antenna

How to Calculate the Transmit Power of a PCB Antenna

Introduction

PCB antennas are a popular choice for wireless communication devices due to their compact size and ease of integration into PCB designs. Transmit power is a critical specification for any wireless device that uses a PCB antenna. In this article, we will explain how to calculate the transmit power of a PCB antenna and what factors can affect it.

Calculating PCB Antenna Transmit Power

The transmit power of a PCB antenna can be calculated using the following formula:

Transmit Power (dBm) = Pout (dBm) + Gant (dBi) - Lcable (dB) - Lboard (dB)

Where:

Pout = output power of the wireless module in dBm

Gant = antenna gain in dBi

Lcable = loss in the cable connecting the module to the antenna in dB

Lboard = loss due to the PCB trace and surrounding components in dB

Note that all values in the formula are in decibels (dB), which is a logarithmic unit of measurement used to express power ratios. The result is also in dBm, which is a measure of power in decibels relative to one milliwatt.

Factors Affecting PCB Antenna Transmit Power

There are several factors that can affect the transmit power of a PCB antenna. These include:

1. Antenna Gain: The antenna gain is a measure of the antenna's ability to focus the radiated energy in a particular direction. As the gain increases, so does the power transmitted in that direction.

2. Cable Loss: The cable connecting the wireless module to the antenna can cause signal attenuation, which can reduce the transmit power.

3. PCB Trace and Component Loss: The trace length and width, as well as the surrounding components on the PCB, can cause signal loss. This can be minimized by careful PCB design and layout.

4. Regulatory Limits: Regulatory bodies like the FCC in the United States limit the maximum allowed transmit power for wireless devices. It is important to ensure that the PCB antenna's transmit power does not exceed these limits.

Conclusion

Calculating the transmit power of a PCB antenna is a critical task for any wireless device. The transmit power is determined by the output power of the wireless module, the antenna gain, and the losses due to the cable and PCB trace. Careful consideration of these factors can help to ensure that the PCB antenna's transmit power meets regulatory requirements and performs optimally.