One example of software-programmable platforms can be seen in the Aeroflex PXI 3000 series (Fig. 3). The product range includes a broad choice of PXI chassis and modular PXI instruments for wide-bandwidth RF signal generation, analysis, and conditioning for signals to 6 GHz. The series is supported by the PXI Studio application software for the waveform generation and vector signal analysis of complex wireless communications systems. According to Bill Burrows, Business Development Manager for Aeroflex International, “The Aeroflex PXI 3000 series addresses wireless parametric measurements for all of the existing cellular and wireless broadband technologies on a single platform. By building a wideband, generic signal source and signal analyzer, we are able to characterize its performance to the customer requirement by supplying a software application.”

The 3020 series compact, 3U-high precision PXI modular RF signal generators come with an integrated dualchannel arbitrary waveform generator (AWG). They serve RF test systems for design verification and manufacturing to 6 GHz. The signal generators provide RF output-power control ranging from –121 dBm to +17 dBm with modulation bandwidths to 90 MHz. They boast level accuracy of ±0.3 dB.

Those generators are complemented by RF conditioning modules and the 3030 series of RF digitizers. The digitizers are used with a 3010 series synthesizer module to provide precision conversion of RF signals into digital IF or I and Q data. When used with PXI Studio application software, the 3030 series RF digitizer family can perform vector signal analysis of RF signals for manufacturing and design verification. The digitizers span 250 kHz or 330 MHz to 3 GHz and 6 GHz. They offer a digitized bandwidth that is 36 or 90 MHz wide (1 dB) with 13- or 14-b analog-to-digital-converter (ADC) resolution. The digitizers sample at rates to 200 MSamples/s. They boast 75 dB spurious and intermodulationfree dynamic range, level accuracy that is typically 0.3 dB, and noise spectral density below -145 dBm/Hz.

Of course, not all aspects of an instrument can be software programmable. Mike Barrick, Anritsu’s Business Development and Global Account Manager, states, “All modern instruments are software programmable, with some instruments providing the user with access to manipulation of data once a measurement has been made. An example of this is the MS269X VSA, in which the user can install PC-based analysis tools that may implement user-specific functions ranging from filtering to custom data displays. Lower levels in an instrument, such as RF/baseband hardware and fundamental measurement algorithms, are related to underlying measurement accuracy, which must be specified by the instrument manufacturer. If user-implemented changes to the basic measurement algorithms were allowed by an instrument manufacturer, it is doubtful that the resulting data would be useful.”

In the excitement over new capabilities, it is easy to overlook the roadblocks that are inherent to the traditional RF test arena. Rohde & Schwarz’s Justin Panzer notes that high-performance requirements necessitate the careful selection of RF, IF, and LO frequencies, power budgets, and data-processing algorithms. Within this hardwaredefined context, however, he points out that instruments like the Rohde & Schwarz FSQ and FSV spectrum analyzers use SDR algorithms to take downconverted I/Q samples and demodulate many popular waveforms from LTE and WiMAX to Bluetooth and CDMA.

Of course, nonlinear S-parameters and the increasing reliance on SDR approaches are not the only developments forcing the evolution of test and measurement equipment. The test industry has to keep up with ongoing trends, such as the increasing integration of hardware and software and the trend toward millimeter-wave frequencies. Development also is largely being driven by the needs of the fourth-generation Long Term Evolution (LTE) standard. For example, test equipment must now incorporate aspects like multi-channel capability and new fading scenarios to simulate multiple-input multiple-output (MIMO) performance. Due to the great number of services that are now provided by digital broadcasters, mobile network operators, and other providers, the potential for interference between them is heightened. As a result, Panzer has seen impressive growth in the areas of interference hunting and spectrummonitoring applications.

Modern communications is creating a growing need for real-world testing as well. According to Graham Celine, Senior Director of Marketing at Azimuth Systems, “While statistical modeling of wireless conditions has been the norm for many years, the proliferation of the technology drives vendors to want to find methods to capture field conditions and recreate them in the lab. This is a complex and challenging operation.”

Thanks largely to communications, microwave testing also has to adapt as digital technologies become more critical to designs. For example, faster DSPs are causing ADCs and digital-to-analog converters (DACs) to be placed closer to the antenna. This proximity makes it critical for the system engineer to be able to diagnose and troubleshoot potential software errors. Converters also are being put on the same board as the RF front end. Because most RF front-end suppliers are not the same as those supplying the baseband receivers, Panzer notes that they need testing solutions that allow them to easily work together on product development. The increasing use of digital modulation also comes into play here, as it will increasingly create a need to accurately measure modulated signals.

Tektronix’s Darren McCarthy has seen a profound increase in the importance and advancements of wideband technologies supporting the spectrum efficiency and linearity of modern radars: “The ability to create spectrally efficient radar pulses is important as the NTIA and FCC work on the coexistence of commercial wireless frequencies and those frequency bands required for national infrastructure (aircraft landing and weather radars). The linearity of the chirp radars helps to improve the effectiveness of the technology.” Tektronix’s IPR measurement, impulse response, measures the time-side lobe response of chirp radar pulses and can detect distortions and nonlinearities due to impedance, amplitude, and phase distortions. It has replaced the use of component testing of constituent parts of the radar to give the true performance of the triple returns and other components of error within the radar transmit chain.

Clearly, test and measurement companies will continue to have to quickly adapt their equipment to meet the needs of future applications. Although the major drivers of tomorrow’s innovations may be hard to predict, it is very likely that today’s breakthroughs will spawn the next wave of developments. As stated by Aeroflex’s Bill Burrows, “The increasing use of software-defined instruments will blur the boundaries of our current instrument definitions. Such products as spectrum analyzers, power meters, and vector analyzers will merge into generic test platforms supporting all of the expected capabilities of these individual products. This will be aided by the increasing use of digital technology and, as the speed of ADCs continues to increase, these will get closer to direct connection to the RF domain. The result of this will be increased accuracy and analysis capability, allowing signal complexity to grow to provide the increased throughput that our information-fueled lives demand.”