Return Loss to Insertion Loss Calculator
Convert return loss into reflection coefficient, reflected power, VSWR, delivered power, and mismatch insertion loss for RF cables, antennas, duplexers, filters, splitters, and high-speed network test points.
Mismatch insertion loss assumes reflected power is unavailable to the load. It does not replace a full S21 insertion loss measurement for filters, cables, attenuators, or active devices.
Formula Breakdown
| Return loss | Reflection coefficient | Reflected power | Mismatch insertion loss |
|---|---|---|---|
| 6 dB | 0.501 | 25.12% | 1.252 dB |
| 10 dB | 0.316 | 10.00% | 0.458 dB |
| 14 dB | 0.200 | 3.98% | 0.176 dB |
| 20 dB | 0.100 | 1.00% | 0.044 dB |
| 26 dB | 0.050 | 0.25% | 0.011 dB |
| 30 dB | 0.032 | 0.10% | 0.004 dB |
| Measurement source | Typical impedance | What return loss means | Practical calculator use |
|---|---|---|---|
| VNA S11 on an antenna feed | 50 ohms | How much source power reflects at the antenna input | Estimate mismatch loss before feedline and antenna efficiency losses |
| Coax certification or sweep test | 50 or 75 ohms | Connector, bend, water, and transition mismatch along the path | Translate a return loss limit into reflected power and VSWR |
| Filter, duplexer, or cavity port | 50 ohms | Port match at the passband frequency being tested | Add mismatch loss to measured S21 only when building a conservative budget |
| Ethernet cable analyzer | 100 ohms balanced | Pair impedance discontinuities versus frequency | Use reflected percentage as a quick severity comparison, not a protocol pass rule |
| Formula | Expression | Units | Notes |
|---|---|---|---|
| Reflection coefficient | Gamma = 10 ^ (-RL / 20) | Ratio | Voltage-wave magnitude reflected from the mismatch |
| Reflected power | Percent = 100 x Gamma squared | Percent | Power reflection is the square of voltage reflection |
| Mismatch loss | ML = -10 log10(1 - Gamma squared) | dB | This is the insertion loss caused by mismatch alone |
| VSWR | VSWR = (1 + Gamma) / (1 - Gamma) | Ratio | Only valid for Gamma below 1; ideal match is 1.00:1 |
| Scenario | Common target | What to watch | Useful result card |
|---|---|---|---|
| Wi-Fi bridge antenna feed | 15 to 20 dB | Adapters and pigtail bends near the radio | Total budgeted loss |
| Cellular filter or duplexer | 18 to 26 dB | Port tuning across the whole passband | Mismatch insertion loss |
| CATV or MoCA splitter port | 14 to 20 dB | 75 ohm connectors, splitters, and terminators | Reflected power |
| 10GBASE-T jack and patch pair | Frequency dependent | Pair balance and connector impedance steps | VSWR equivalent |
| Microwave dish or waveguide | 20 dB or better | Flanges, moisture, alignment, and frequency sweep width | Acceptance status |
This calculator uses the standard one-port mismatch equations. Lab-grade uncertainty work may also need source match, load match, phase, calibration kit quality, and ripple analysis.
When you are measuring an RF connection, the signal that dont reach the load is the signal that matters most in relation to your calculations. Return loss tell you how much power reflects back from the connection rather than traveling forward in the link. This reflected power creates a loss in the signal referred to as mismatch loss.
Converting return loss to mismatch loss, therefore, allow you to determine whether the RF link will have enough power to meet the power budget, or whether it will fall short of its requirements. The equation for return loss and the equation for mismatch loss are relate to one another. Return loss is expressed in decibels.
How to Find Mismatch Loss from Return Loss
As the match between the components within the system increase, the return loss increases as well. For a perfect match of component, the return loss would approach infinity (as no power would reflect off of those components). Instead, however, the connection of components to the load will always reflect some power.
To determine the reflected power within the system, the math squares the reflected portion of the wave. This same number is utilized in the mismatch loss equation. RF Return Loss to Mismatch Loss calculator can handle the mathematics for you so that you can enter the return loss value, the VSWR value, the percentage of the power that the load reflects, or the value of the reflection coefficient of the load.
Each of these values will produce the same result (as they all represent the same physical quantities of reflected power), but the entry of each of these value will change the mathematics that the calculator performs to arrive at that result. When engineers work with these values, they are often most interested in the number for mismatch loss. Mismatch loss is invisible to a power meter, yet it is still a loss of power that the system delivers to the load.
Cable loss, filter insertion loss, and other form of loss are considered “visible” losses because a meter can measure them directly, yet mismatch loss is not one of those measurable losses. Instead, it depend upon the quality of the termination of the load connected to the system. Changing the antenna to which the system is connected, retuning a cavity within a component, or even replacing a connector will result in a change to the mismatch loss value of that system.
Additionally, the RF Return Loss to Mismatch Loss calculator allow you to also enter a target value for the return loss of the system, as well as a buffer. This buffer accounts for the errors in the measurement of return loss, the effects of temperature, and the error introduced in adapters. RF systems often have a specific operating frequency.
Return loss is a value that is obtained at a specific frequency, and it will change if the system operate at a different frequency. The calculator allows you to enter the frequency at which you measured the return loss of your components. As with the value for impedance, the designer of the system must enter this value so that the reflection coefficient is not compared to the wrong reference point.
Furthermore, the designer can enter the number of transitions along the signal path. While the number of transitions will not impact the calculation of the mismatch loss of the system, the number of transitions will impact how the system is accepted or reject as meeting the required performance of the system. For example, if a return loss value is considered to be marginal at a single component, the same return loss at six connectors will have a different performance then the same mismatch loss at a single connector.
Another consideration of power budgets for RF links is the relationship between dissipative loss and mismatch loss. Many RF links will have other losses in addition to that cause by mismatch loss. For instance, many links will include loss due to the attenuation of the cables, the insertion of filters along the signal path, or the insertion of splitters into the signal path.
Each of these losses is measured with a matched load. In calculating the power budget for a link, it is necessary to calculate both dissipative loss and mismatch loss of that link, and to sum them together to determine the total loss that will be experienced by the signal traveling along that path. By determining mismatch loss by itself, engineers can more easy determine where to invest effort to improve the RF link.
For instance, if the mismatch loss is already low with the link, additional effort to improve the connectors will yield diminishing return. In contrast, if mismatch loss is the dominant loss along the path of the signal, then engineers should focus upon the termination of the load. Tables are provided on this page to assist engineers in understanding the relationship between return loss, reflected power, and mismatch loss.
For example, a return loss of ten decibels indicates that approximately ten percent of the power is reflected by the load, and the mismatch loss of that link is approximately half a decibel. Additionally, a return loss of twenty decibels indicates that reflected power is one percent of the incident power, and that the mismatch loss of the link is only a few hundredth of a decibel. These return loss to mismatch loss benchmarks allow engineers to understand if their measured return loss is typical or atypical for a given component.
Additionally, these tables help to explain the reason for the requirement of a certain level of return loss at higher frequencies (because even small amounts of reflected power at those frequencies has a significant impact upon the power budget of the link). Common mistake in measuring RF systems are treating return loss as a single value. For example, technicians may only measure the best return loss value for a system, ignoring those lower return loss values at the edge of the frequency band.
Instead, you should compare a return loss of the system to both a target return loss and a buffer. For example, if the measured return loss of the system is higher than the target return loss (even after the buffer is applied), the systems return loss is considered to be acceptable. In contrast, if applying the buffer to the target return loss creates the same value as the measured return loss, the system may deserve another look at the return loss of the system across the operating band.
Because of temperature variations, vibrations, and the other form of mechanical stress upon an RF system, return loss can change. For example, connectors may become loose along the path of the signal, cables can flex, or the dielectric constant of some of the components of the system may shift. None of these variable are accounted for in the calculator, as they are all dependent upon the specific system that is evaluated.
However, the buffer allows for the inclusion of these factors; a conservative buffer allowance accounts for the known variations in real-world systems as compared to lab measurement of those systems. Thus, while a conservative buffer does not guarantee that an RF link will meet its performance requirements, it does reduce the chance that the engineers will consider a link with a marginal match between the components and the load to be an adequate RF link. Finally, the most value of the conversion of return loss to mismatch loss is in the development of a complete power budget for the RF link.
By determining the power budget of the link, it is possible to determine if the remaining budget for the link is sufficient to account for the losses in the cables, filters, and for temperature variation in the link. Thus, while the RF Return Loss to Mismatch Loss calculator is not a device that replace a network analyzer for mapping the frequency response of a system, the calculator is useful in removing the arithmetic difficulties that will allow engineers to focus upon the engineering of those systems.
