Vector network analyzers are often considered the kings of the electronic laboratory. With the ADL5961, Analog Devices introduces a one-stop-shop solution that provides the network analyzer analog front-end on a single chip.

Vector network analyzers are helpful for a wide variety of applications. They are mandatory for antenna matching and can determine the frequency behavior of connectors and the stability of power supplies. The Austrian company Omicron Labs built its existence on this application. Be that as it may, vector network analyzers require an analog front-end to interact with the device under test. In the case of the ADL5961, Analog Devices provides just that. Thanks to the frequency coverage ranging from 9 kHz to 26.5 GHz, the part applies to high-end test equipment.

Creating a One-port VNA with the ADL5961

The simplest vector network analyzer has one port, which it uses to determine some of the S parameters of the connected device under test. With the ADL5961, such a vector network analyzer can be created by following the schematics outlined in the figure below.

In addition to the digital processing required for analyzing the results, Analog Devices requires that the circuit designer provide radio and local oscillator frequencies. These can be generated from various parts - for example, the Würth 831018545 could be used for the LO. In contrast, various VCO-based oscillator integrated circuits can create the radio frequency. In addition, the ADL5961 analog front-end integrated circuit can also be cascaded to simplify the creation of multi-port vector network analyzers. In this case, the LO and offset signals are used to synchronize the individual devices, thereby limiting the amount of skew in the results returned to the digital back-end processor.

SPI Bus for Data Communication

The SPI bus can connect the ADL5961 front-end integrated circuit to the digital signal processors required in the back end. The datasheet, found at https://www.analog.com/media/en/technical-documentation/data-sheets/adl5961.pdf, provides extensive mathematical background information intended to simplify the development of the calibration algorithms required for accurate vector network analyzer measurements.

Even though the ADL5961 greatly simplifies VNA front-end design, the PCB layout can be challenging. Should software development take place in parallel to the design of the printed circuit board, the use of an evaluation board is highly recommended. In the case of the ADL5961, Analog Devices provides such a product under the SKU ADL5961-KIT-EVALZ — it presents itself as shown in the figure.

Running this board is simple—as shown in the figure below, an RF signal generator is needed to provide the operating frequency. The required board for communication with the PC is included in most SKUs.

Conclusion

If the task at hand requires the use of a vector network analyzer, deploying the ADL5961 integrated circuit is a surefire way to get the device off the ground quickly. Analog Devices' extensive experience in signal conditioning means that the performance parameters offered by the chip are first-class—in short, it is a component that can save hundreds of engineering hours.