What Is Insertion Loss, and How Can It Be Reduced?

Transmitting data fromthe signal generationend accurately tothe signal receivingend is not easy. Data transmission quality can be affected by components, operation, and the external environment. Attenuation or signal weakening may occur in electrical or data transmission. All losses differ in nature; losses can take many forms, such as power loss, connection loss, insertion loss, and even return loss. In addition, in electronics, losses such as insertion loss are an important performance parameter measurement in link design.

What is insertion loss?

Insertion loss (Insertion Loss - IL) refers to the signal loss of a transmission link caused by inserting a component into a copper cable or fiber-optic link. It is a natural phenomenon that occurs in all types of signal transmission. Insertion loss measurements are usually expressed in decibels (dB) as the unit.

Insertion loss is a key parameter in fiber-optic and copper cabling. Ideally, it is a positive value, representing the ratio of signal loss by comparing input power with output power. Insertion loss can be tested using a tester.

Positive dB value: the lower it is, the better the performance. High insertion loss can seriously affect or even prevent correct signal transmission from one end to the other. Insertion loss is mainly affected by cable length and quality. It may also be affected by connection points such as splices and connectors in the cable link.

What is the difference between insertion loss and attenuation?

Signal attenuation refers to the total loss of a signal as it propagates through a medium, while insertion loss refers to the signal loss when a component is inserted into a communication system. These two terms are actually the same concept and can be used interchangeably in most cases. However, when using a tester to test the entire link,“insertion loss”is more commonly used.

RFRF systemsInsertion loss in an RF system is the attenuation of signal power when a device or component is inserted into a transmission line, quantifying the signal loss caused by the presence of the component. This loss may be caused by resistive loss, dielectric loss, or impedance mismatch. In RF systems, insertion loss is also called cable loss and increases with frequency and cable length. Insertion loss is a key parameter for verifying the performance of RF cables and antennas, especially in field testing.

Insertion loss formula

Insertion loss is a key performance parameter for copper cable and fiber-optic applications. It is usually a positive number and is calculated by comparing the input power of the signal at the source end with the output power at the far end. The lower the insertion loss, the better the performance. If insertion loss is too high, active equipment at the far end of the link may be unable to correctly receive and decode the signal. Because insertion loss is directly related to distance and the number of connection points, industry standards specify insertion loss limits and, for specific applications, specify limits on the number and distance of connections.

Lower insertion loss indicates higher component efficiency and minimal signal attenuation.

Insertion loss is expressed in decibels (dB) as the unit, and the calculation formula is as follows:

IL (dB) = 10 * log10(Pin / Pout)

where,Pin is the device under test's (DUT) input power, and

Pout is the output power of the device under test.

Why is lower insertion loss better?

Insertion loss must be as low as possible to ensure that the signal transmitted through the cable or device is strong enough to be accurately received and decoded by the device at the other end, thereby maintaining high performance and functionality of the communication link. High insertion loss causes signal attenuation, which can lead to communication errors, dropped connections, and even complete link failure. The main reasons for minimizing insertion loss include:

Signal integrity:To maintain signal power and quality as the signal travels through the network.

Performance:Low insertion loss ensures that active devices receive signals of sufficient strength, thereby avoiding errors and maintaining high communication speeds.

Distance and bandwidth:In fiber-optic and copper cables, insertion loss increases with distance and the number of connections. A lower loss budget enables longer transmission distances and supports higher frequencies and larger data volumes.

Reliability:Components with high insertion loss may prevent a link from operating normally, directly affecting system reliability and potentially causing severe communication failures.

What is a good insertion loss?

In short, the output signal level is always lower than its input level. In addition, the lower the insertion loss value, the better the performance; for example,0.3dB insertion loss is better than 0.5dB. In some cases, insertion loss may appear as a negative value.

As we introduced earlier, the insertion loss of a transmission line or coaxial cable refers to the energy dissipated in the cable. Insertion loss is also defined as the energy lost due to reflection mismatch between the source and the load. Ideally, the source (transmitter), transmission line (coaxial cable), and load (antenna) are all designed to have the same characteristic impedance, typically 50 or 75 ohms. In a two-port network, you can also use S parameter S21 or S12 to represent insertion loss. The ratio of the input signal to the output signal from one end of the cable to the other, or from one port to another port, represents the total insertion loss of the cable. Ideally, the insertion loss of a lossless cable is 0。

What factors affect insertion loss?

Incable signal transmission, insertion loss is usually affected bycableresistance. When the signal is incable, its attenuation varies with signal frequency. High signal frequency causes greater insertion loss.

Cable insertion loss may also be caused by other factors:

Cable length: One of the main factors affecting cable insertion loss is cable length. As cable length increases, insertion loss also increases due to signal attenuation over long distances.

Wire gauge: It is well known that the smaller the wire gauge,AWGis smaller, indicating that thecableis thicker and has better conductivity. Thickcableusually has lower insertion loss than thincablehas lower insertion loss. Therefore,28or27 AWGwire is typically used for short-distance transmission. In addition,Cable internal materialsSolid copper wire has lower insertion loss than stranded copper wire, making it the best choice for long-distance wiring.

Connector and cable quality: The quality of connectors and cables greatly affects insertion loss. High-quality cables and connectors with better shielding can minimize insertion loss. In addition, conductor material also plays a crucial role in signal transmission.

Temperature: High temperatures canaffect the conductor'sconductivity, therebyaffectinginsertion loss.

How to reduce insertion loss

In the field of electronic measurement, to achieve high-precision measurement, interference and loss during testing must be minimized. Therefore, how to effectively reduce insertion loss in testing has become a key problem that engineers urgently need to solve. At present, there are two main approaches: first, selecting suitable test cables; second, selecting appropriate connectors, thereby achieving a significant reduction in insertion loss.

When selecting test cables, I compiled the following table based on the specific requirements of different test scenarios:

Also note during use:

1. When testing weak signals, shorten the cable length as much as possible to reduce interference.

2. When testing high voltage, cables must be secured and kept away from areas where personnel are active.

3. For multi-channel synchronous testing, it is recommended to use cables from the same batch and of the same length to reduce errors.

When selecting connectors, the key is the connector between the device under test and the cable at the signal source end. In power testing in particular, the corresponding fixture must be matched according to the different package types of the device. A high-quality fixture can effectively reduce insertion loss, thereby improving the accuracy of the test experiment.

Given that power devices with various package types exist on the market, corresponding matching fixtures have also emerged. However, due to differences in manufacturing processes, there are significant differences in performance among fixtures from different brands. Therefore, selecting an efficient and practical fixture has become an important issue that engineers must seriously consider.

When selecting a fixture, the following table is organized by device package type and test conditions:

In summary, insertion loss is an important metric affecting the performance of various signal transmission systems; it directly relates to signal integrity, communication distance, system bandwidth, and operational stability. In engineering practice, scientifically selecting suitable cables and connectors, optimizing the installation process, and fully considering environmental factors are key measures for reducing insertion loss. Whether for low-voltage weak signals, high-voltage high-current applications, or high-frequency RF applications, corresponding loss-control strategies should be formulated according to the specific scenario. Against the backdrop of continuously developing high-speed communications and high-power electronics, low-loss transmission will become an important direction for future design, and continued attention to advances in materials and processes will provide strong support for further improving system performance.

Some content is reproduced from Keysight Technologies