RF Calibration

What frequency ranges are covered by RF and microwave calibration?

How do RF and microwave and dc/lf calibration differ?

What parameters are measured in RF calibration?

Mismatch errors are major contributions to measurement uncertainty in RF calibration. These arise from the output and input matches of the equipment and from the cables and connectors used to interconnect the equipment. Using high quality metrology grade connectors and cables, and treating them with care are essential in minimizing these sources of error and uncertainty.

Many other parameters and characteristics are measured when calibrating RF and microwave test equipment, too numerous (and often instrument-specific) to discuss here.

How is RF calibration traditionally performed?

The equipment may be assembled as a system dedicated to a particular type of instrument, as a system capable of calibrating many workload instrument types, or simply collected from the lab inventory for a specific calibration task and dispersed when the task is completed.

Because so many system instruments are involved, there are many different setups required to make connections to the unit or device under test (UUT/DUT). Switching and multiplexing is not possible due to the measurement errors and uncertainty contributions that would be introduced by the switching, particularly at the higher frequencies.

The calibration process may be performed manually, or it may be automated using software to take control of the system instruments and the item being calibrated. Fully automated RF and microwave calibrations are rare due to the difficulty in automating signal switching without degrading measurement quality.

Traditional automated systems need frequent user intervention to change the interconnections. Consequently there are many opportunities for mistakes and highly trained staff is needed. Costly operator time is often wasted waiting for the next setup change.

What instrument types are typically found in an RF and microwave calibration system?

What is the RF and microwave calibration workload?

What is the opportunity to improve efficiency and reduce costs?

Further information

What are the traditional RF calibration solutions?

There are virtually no instruments specifically designed as RF and microwave calibrators (apart from the Fluke 9640A Series). RF and microwave calibration procedures are complex, involving many general purpose test instruments, accessories, components, cables, adapters and connectors. Calibration solutions are generally created by users developing and assembling their own systems. Automation is often provided by users writing their own software or employing commercially available test system automation software. Larger organizations may commission systems integrators to put together a calibration system. Some test equipment manufacturers offer software packages for calibrating their own RF and microwave products, which only allows use of their own products as calibration standards and cannot calibrate any other workload.

What RF calibration solution does Fluke Calibration offer?

Employing the Fluke 9640A Series RF Reference Source, specifically designed for RF calibration, as the core of an RF and microwave calibration system enables many system instruments and accessories to be replaced by just one. Its unique combination of features and performance makes the 9640A Series clearly superior to general purpose signal generators. Used manually or partnered with MET/CAL calibration software the 9640A Series can halve system costs, improve system capacity  by up to 25% and free up 50% of the system operators time to perform other value-adding tasks.

What factors should be considered when selecting a solution?

Efficiency

The time and costs to perform the calibration, including total calibration time, automated system run time, and operator time are key factors determining and improving efficiency .

In a typical automated RF calibration process, the operator must intervene frequently to change test setups. “Walk-away” automation can easily increase calibration system capacity by up to 25% and free up 50% more operator time, enabling staff to perform other tasks rather than waiting for the next automated system setup change. For example, the manufacturer’s calibration procedure for calibrating the Agilent E4407B spectrum analyzer requires 27 different test setups.

On the other hand, the 9640A Series, used with MET/CAL Plus Calibration Management Software, performs the major core of documented tests with a single setup. Only six additional setups are required to complete the calibration process. Calibration time is reduced from (typically) four-and-a-half to two hours.

The key efficiency improvement benefit is realized when partnering the 9640A with MET/CAL software.  For example, the E4407B MET/CAL procedure for the 9640A-LPNX allows for a total 90 minutes of “walk-away” time within the total two-hour runtime.

Workload coverage and degree of automation

Workload coverage refers to instrument type and its manufacturer; degree of automation means the extent to which a solution addresses its calibration and provides automation.

Spectrum analyzers are key workload items for any RF and microwave calibration lab. The 9640A provides the functionality and performance required for lower performance and mid range spectrum analyzer models. With its superior low phase noise performance, the 9640A-LPNX is capable of calibrating the high-end spectrum analyzers.

The 9640A Series performs 80-100% of all the tests required on high performance, high frequency spectrum analyzers. For workload with frequency requirements beyond 4 GHz, existing RF and microwave sources can be used alongside the 9640A Series to address the few remaining test points that require a higher frequency source.

The 9640A Series features and performance also make it ideal for other workload, including RF millivoltmeters, signal level meters, modulation analyzers, receivers and counter/timers.

Some RF calibration software packages are only capable of calibrating single-vendor UUTs and also require single vendor system instruments. With its expanding library of RF calibration procedures available, MET/CAL calibration software does not have this limitation.

Operator skill levels and opportunity for errors

RF and microwave calibration is complex, and finding skilled staff can be challenging. The staff possessing the required knowledge and skill have many tasks to perform, and freeing their time to tackle the tasks where utilizing those skill adds the most value is an important consideration in choosing a calibration solution.

Compatibility with existing standards, automation and processes

Use MET/CAL software’s Flexible Standards feature to automate the other instruments in your system. This capability allows you to substitute equivalent standards within the procedures, so you aren’t locked into a specific reference model. Flexible Standards support is available for popular microwave synthesizers including the HP8340, HP83630, Agilent E8254 and E8257, and other models from Anritsu and Rohde & Schwarz.

The 9640A models are designed to match or exceed the performance and functionality of the HP3335A and HP8662/3A in the calibration system. With HP3335A GPIB command emulation as standard in both 9640A models and optional HP8662/3A emulation in the 9640A-LPNX, replacing these popular but obsolete and difficult to maintain products becomes just a plug-and-play substitution. HP8662/3A GPIB command emulation is installed on the 9640A-LPNX as a “try before you buy” temporary license for easy rapid compatibility testing.

Simplicity and indirect costs

Systems with many instruments are complex and expensive to support and maintain. The reduction in system instrument count achieved with the 9640A brings many benefits. Metrology is significantly simpler, with fewer error sources and fewer uncertainty contributions. System support costs are reduced, as there are fewer instruments to calibrate and maintain.

On-site portability

A smaller, compact system is ideal for on-site use, reducing transport costs and also enabling a system to be easily taken to locations inappropriate for a larger system.

What other RF applications might benefit from a signal source with precision and performance improvements?

Many applications in R&D, manufacturing test, ATE, and scientific research require better performance than a general purpose signal generator. The 9640A Series RF Reference Source’s  unique combination of level and attenuation accuracy, signal purity and low jitter, frequency resolution, dynamic range and precision modulation deliver better performance than any high performance signal generator in these applications.