VNA Reflections

Reflecting on the Year

December 27, 2012

The end of the each year brings with it a time of reflection – not from the signal perspective but a much larger aspect. As this year closes, I thought it appropriate to take a “measured” look at the year coming to a close and what 2013 might bring.

One thing that can be said about our industry is that it continues to raise the bar when it comes to designs. Signal integrity is more important than ever before. Applications such as cloud computing, smart phones, and LTE services that demand high bandwidth and utilize complex signal technologies are making designs and testing more challenging than ever before.

The broader use of higher frequency levels, including millimeter waves, is another trend that we saw in 2012. In fact, mm-wave frequencies are becoming more commonplace in commercial applications. This has made it imperative for test companies to develop solutions that can conduct highly accurate measurements at frequencies as high as 750 GHz.

Many of the challenges associated with these market conditions have been discussed in our previous blog posts. They have also been the impetus for developing solutions such as the VectorStar® line of Vector Network Analyzers (VNAs). Engineers have come to rely on high-performance test instruments to conduct complex measurements with the high accuracy they require.

These trends will certainly continue in the years ahead. As the calendar changes to 2013, it is obvious that signal integrity will continue to be of utmost importance to engineers designing communications devices, equipment, and systems. Test solutions will have to be able to accurately measure high-frequency designs and do so in a manner that is more efficient and cost-effective. So, in that respect, the more things change the more they stay the same.

There is one final thing to convey for the last blog of 2012. I wish everyone a wonderful New Year and prosperous 2013! We look forward to the challenges ahead of us and the opportunities that they present.

Methods to Optimize Millimeter-wave Testing

December 12, 2012

Increased bandwidth needs are affecting all sorts of markets. 4G systems pushing demand for higher data throughput – particularly in the backhaul infrastructure – and corporate bandwidth needs driving E-band (71 GHz to 86 GHz) point-to-point solutions are just the tip of the iceberg. Several millimeter-wave applications are broadening their commercial use, as well.

While having started in the luxury car market, 77 GHz automotive radar systems are becoming mainstream. A new WiFi or WiGig standard, IEEE 802.11ad, in development will offer very high data rates over the 57 GHz to 64 GHz frequency range. As millimeter-wave applications become more common, optimizing cost-of-test becomes important to bringing these technologies to market.

Vector Network Analyzers (VNAs), such as the VectorStar™ series from Anritsu, play a key role in helping the millimeter-wave test engineer evaluate prototypes by performing accurate measurements, whether testing at 75 GHz or 750 GHz. Selecting the correct VNA requires engineers to look at characteristics such as accurate power control, wide power sweeps, optimum noise figure range, and cost effectiveness.

Power Control

Let’s start with power control. In the past, millimeter-wave test systems relied on software-leveling techniques that could damage devices under test (DUTs) due to power level variations. Today, real-time leveling techniques offer very accurate power level control to frequencies as high as 750 GHz. The ability to control to levels as low as –55 dBm provides amplifier designers the best power accuracy and stability, as evident in Figure 1, and helps protect sensitive devices.

 

Figure 1

Another factor is that millimeter-wave signals are often at lower power levels than traditional RF or microwave applications. For amplifiers, it’s important that power measurements begin in the linear region of the amplifier. This may require a very low power level start for a power sweep. Accurate power sweep measurements utilizing real-time power level control up to 55 dB enables accurate linear gain and 1 dB compression measurements.

Noise Figure

It is often necessary to add pre-amplification and filtering in front of the measurement receiver to ensure the sensitivity required to make a quality noise figure measurement at millimeter-wave frequencies. If too little amplification is used, there may be too much jitter from the instrument A/D converter (see Figure 2). If too much power or amplification is applied, compression can impact the measurements. Selecting a test system that provides a wide noise figure measurement range enables greater configuration flexibility, simplifying the setup and offering the ability to more accurately test a wider variety of devices (Figure 3).

 

Figure 2

Figure 3

Cost of Test

Engineers can lower test expenses with banded millimeter-wave modules for specific applications. One example is a single millimeter-wave module driven by a VNA with a frequency range as low as 40 GHz, for applications up to 110 GHz. For frequencies ranging from 110 GHz up to 750 GHz, waveguide banded millimeter-wave modules can be driven by a VNA with a frequency range as low as 20 GHz. The VectorStar family features models for both these environments, and more.

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