What is a Good Return Loss Value and How Can it be Calculated?

October 30, 2020 Cadence PCB Solutions

Key Takeaways

  • Learn how to calculate Return Loss Value.

  • Gain a greater understanding of how Return Loss affects signal quality and connectivity.

  • Learn about the correlation between Return Loss Values and Voltage Standing Wave Ratios.

 Parabolic Antenna With A High Return Loss Value.

Big parabolic antenna

In the field of electronics, the term loss often has a dual but opposite meaning. Therefore, depending on the context, a loss can be good or bad. Although, in most instances, we typically perceive a loss as negative.

In general, not all losses are equal, and a loss can manifest in many forms, for example, loss of connectivity (Wi-Fi), a loss of power (electrical), or a return loss (signal transmission). Furthermore, in electronics, a loss such as an insertion loss is an essential performance parameter measurement in some designs (fiber-optic links). In this article, we will discuss what an acceptable measurement parameter (return loss) is and how it affects performance and functionality.

What is Return Loss?

The measurement of the amount of light reflected back toward the source is called return loss, and it is expressed in decibels (dB). This measurement parameter is always a positive number, and a high return loss is a favorable measurement parameter that generally correlates to a low insertion loss. Similarly, reflectance, which is also a measurement parameter that expresses reflection in decibels, is a negative number, and if it is excessive, it is not a favorable measurement parameter.

Return loss is the loss of signal power due to signal reflection or return by a discontinuity in a fiber-optic link or transmission line. This impedance mismatch can be with a device inserted in the line or with the terminating load. Moreover, return loss is the relationship between both the reflection coefficient (Γ) and the standing wave ratio (SWR). Incidentally, if you increase the return loss, it will correlate to a lower SWR.

Return loss is a measurement parameter that expresses how well a device or line matches. A high return loss is advantageous as it will result in a lower insertion loss.

In today’s electronics practices, in terms of use, return loss is preferable to Voltage Standing Wave Ratio (VSWR) since it affords better resolution for smaller values of reflected waves. Typically, we represent Voltage Standing Wave Ratio as a ratio of a specific number in comparison to 1. VSWR and SWR are generally interchangeable.

Understanding Return Loss Values

Return loss is the measurement of the reflected wave or signal strength traveling or returning back to a transmitter from an antenna. However, the forward wave, or incident wave, travels from a radio transmitter to an antenna. There is also a reverse wave or reflected wave reflected from an antenna or even another connectivity element back to a radio transmitter. Reflections propagate back and forth in a line, but most assessments only consider the effects of the initial reflection because the back and forth energy attenuates until it is untraceable.

Once the VSWR is known, return loss can be calculated as follows:

Return Loss = 20 ∙ log10 ()

Generally, a higher return loss value is preferable. If we measure the power of a reflected signal from an antenna near a radio transmitter, the measurement of the reflected signal’s amplitude at this juncture compared to the initially transmitted signal’s amplitude (before reflection) provides the return loss value.

Furthermore, a higher return loss value signifies less reflection in the wires. A better VSWR value results in a higher return loss, and if the VSWR degrades, then the return loss decreases as well. For this reason, we desire a loss in this instance, and a high return loss is preferable.

It is important to closely observe both the VSWR and return loss values since they substantially affect wireless connectivity, especially if they have considerably undesirable values. Examining return loss values allows us to assess efficiency and performance more accurately, and failing to mon. It can also help us determine if there are impedance mismatches at the pins of the receiver and transmitter, as well as the connectors, vias, and various other discontinuities. 

Return loss, generally speaking, is an essential assessment tool in understanding signal performance. For instance, if the return loss is 10 dB, then the return is 10% of the power. Different systems utilize different acceptable return loss limits, but 15 dB or better is a standard system limit for antenna systems and cable.

In an ideal scenario or a perfect system, the return loss equals infinity since there is no reflection. However, in the real world, systems are inherently imperfect, and as a result, there will always be some level of return loss.

Communications Tower With A High Return Loss Value.

Communications tower

With Cadence’s industry-leading suite of design and analysis tools, the best circuit analysis program, PSpice, is at your disposal. Cadence offers designers and production teams a greater understanding of return loss values and how signal quality can be optimized in all designs. To learn more about why a high return loss value is critical to signal transmission quality, take a look at OrCAD PSpice Simulator.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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