Understanding RF Power De-embedding

Introduction:

RF power de-embedding involves a mathematical process of compensating for network components’ effects in measurements. It’s crucial to ensure accurate referencing of RF power measurements.

The Essence of RF Power De-embedding:

RF power de-embedding entails compensating for losses or gains in your setup that might interfere with Device Under Test (DUT) measurements. Components like attenuators, filters, amplifiers, or switches within your setup might affect measurements but aren’t relevant to the DUT’s application. RF power de-embedding involves a mathematical process of manipulating measurements by adding or subtracting network components. This method is pivotal because it ensures precise referencing in RF power measurements.

Understanding RF Power De-embedding

We’ll delve into the theory behind RF power de-embedding, exploring its purpose and methodologies. The essence lies in correcting measurements by compensating for potential losses or gains within your setup. The aim is to obtain accurate readings from your Device Under Test (DUT) without the interference of superfluous series or shunt components that may exist within your evaluation board. These components—such as attenuators, filters, power amplifiers, or switches—though integral to your setup, might not reflect the actual application of your DUT. Therefore, the goal is to eliminate the impact of these components in the measurements, ensuring the readings align with the real-world circuitry your DUT will operate within.

RF Power De-embedding Equipment Insights

S-parameters are not imperative for RF power de-embedding. Contrary to the assumption that a Vector Network Analyzer (VNA) is necessary for this process, de-embedding can be achieved using scalar power measurements.

Often, confusion arises among those less familiar with RF processes when encountering S-parameters. While power de-embedding shares some similarities with S-parameter de-embedding, the distinction lies in the focus on phase. S-parameter de-embedding demands meticulousness due to phase variations influenced by factors like frequency and transmission line lengths.

In contrast, RF power de-embedding doesn’t require the same level of precision in phase adjustment. While precision remains essential, it’s not as critical as in S-parameter de-embedding. You can conduct RF power de-embedding without the need for an expensive VNA; instead, an RF signal generator and a power meter can serve the purpose effectively. Even within manufacturing settings, de-embedding can be accomplished using scalar power measurements. A Digital Voltmeter (DVM) referencing milliwatts suffices to assess the losses incurred within your setup or the specific components you intend to de-embed from your measurements.

Establishing the Reference Plane in RF Power De-embedding

When providing RF measurements, one of the initial queries you’ll encounter is about your reference plane—where exactly are you capturing this data? Is it at the ports of your Device Under Test (DUT), your evaluation board, or within your test setup? Articulating a clear answer to this question is crucial. Ideally, the focus should be on measuring solely at the RF ports of your DUT. However, it’s essential to consider the practical application of your product. Sometimes, testing exclusively at the DUT’s ports might not align with the real-world scenario. For instance, components two and three might be part of your evaluation board but are integral for the DUT’s proper functioning. Consequently, in practical application, your DUT would typically be accompanied by these components. Hence, your reference plane might encompass both these components, while components one and four might solely serve the testing purpose within your setup. Always prioritize the application context of your product when determining the reference plane for measurements across all the RF ports you’re utilizing.

Practical Application of Reference Plane: High-Power Filter Case Study

Consider a practical scenario: let’s say we’re evaluating a high-power application filter as our Device Under Test (DUT). Typically, RF sources don’t provide high power levels as they cater to various applications. To test this filter at high power levels, you might require a Class A PA or a driver PA to amplify the RF source output. Incorporating an isolator becomes crucial to safeguard the Class A PA from potential reflections or issues with the filter under test. At the filter’s output, both fixed and variable attenuators play pivotal roles. They help manage signal attenuation, ensuring the measurement equipment isn’t overwhelmed by the power output from the Class A PA, thus preventing damage.

Now, let’s determine the reference plane for this setup. Beginning with the filter’s input, setting the reference plane at the isolator isn’t ideal since the isolator serves a protective function not pertinent to the filter’s application. Instead, the reference plane should shift to the input or RF ports of the filter.

Similarly, for the output, setting the reference plane at the attenuator’s end isn’t practical as the attenuator won’t feature in the actual application. Shifting the reference plane from the attenuator to the output port of the filter is more suitable. Here’s the critical step: measuring the complete gain or loss from the RF source to the RF filter’s cable and accounting for losses from the filter’s output to the measurement equipment. These losses, inclusive of attenuators and transmission lines, must be factored in to calibrate the measurement readings. Adjustments should compensate for losses or gains within the setup.

For instance, if the test plan specifies a 40 dBm signal at the filter’s input, understanding the total gain becomes crucial. This knowledge aids in setting the Class A PA gain or RF source power to attain the desired input power level. As the signal traverses through various components, such as transmission lines and attenuators, the measurement equipment doesn’t merely read the 40 dBm minus the filter’s inherent losses; instead, it reads the overall losses including attenuators and transmission lines. Thus, compensating for these losses ensures referencing measurements accurately to the filter’s RF ports.

Summary: The Crucial Role of Reference Plane in RF Power De-embedding

In summary, RF power de-embedding involves the manipulation of network components within measurements. It’s akin to compensating for the losses or gains within your setup, aligning measurements with the RF ports of your Device Under Test (DUT). This adjustment is essential as every setup incurs its own losses or gains, typically manifesting as losses that need proper correction. Determining where de-embedding is essential—whether at the RF ports or involving specific components linked to your DUT’s application—is crucial. Always consider your product’s application context when establishing the reference plane. This step is pivotal in the measurement process. It directly contributes to accurately gauging losses. If the reference plane is inaccurate, all subsequent measurements could be flawed. An incorrect reference plane might lead to misinterpretations, resulting in discrepancies in dB readings. Precise measurements hinge on correctly assessing losses and ensuring the reference plane aligns accurately.

Learn more about this topic by taking the complete course ‘Introduction to RF Testing Fundamentals and RF Test Architecture – RAHRF412’. Watch the course videos for more detailed understanding. Also checkout other courses on RF system and IC design on https://rahsoft.com/courses/. Rahsoft also provides a certificate on Radio Frequency. All the courses offer step by step approach.