Taking On Broadband Measurement Needs

The broadband channels that now characterize many modern communications standards have challenged test-equipment suppliers to generate and analyze more complex signals.

Development of broadband RF/microwave test equipment has been triggered in recent years by the expanding bandwidths of communications channels. Those increasing bandwidths are typically occupied by complex digital modulation formats, using in-phase (I) and quadrature (Q) signal components. As modulation formats become more complex , test equipment suppliers must deliver the tools to characterize the channels on those systems.

Wireless communications test is no longer the domain of traditional separate-function instruments; rather, the trend is to include as many necessary functions as possible within a single compact instrument housing. A popular example is the model CMW500 Wideband Radio Communications Tester from Rohde & Schwarz, which includes an RF/microwave signal generator, signal analyzer, power meter, and Fast Fourier Transform (FFT) analyzer within a rack-mount instrument housing (see figure). Having the multiple instrument functions within easy, programmable reach can greatly simplify the barrage of tests required to characterize wireless networks and their devices.

Of course, all-in-one wireless communications testers such as the CMW500 are not popular simply for the variety of their functions. With a standard frequency range of 70 to 3300 MHz, the CMW500 has been developed for characterizing third-generation (3G) and fourth-generation (4G) cellular devices, although it is also available with a frequency-extension option for pushing its signal-generation and analysis range to 6 GHz for checking WiMAX equipment.

The CMW500 tunes in frequency with 0.1-Hz resolution and provides adjustable output power characterized in terms of continuous-wave (CW) power or peak envelope power (PEP). It offers −130 to −15 dBm CW power and PEP to −15 dBm from 70 to 100 MHz; −130 dBm to −5 dBm CW power and as much as −5 dBm PEP from 100 to 3300 MHz; and −120 to −15 dBm CW power and as much as −15 dBm PEP from 3300 to 6000 MHz. Power levels are adjustable with 0.01-dB resolution. For output levels greater than or equal to −80 dBm, the level uncertainty is less than 0.01 dB. For output levels less than −80 dBm, the level uncertainty of less than 0.05 dB. Second harmonic levels are controlled to -30 dBc, third-harmonic levels to −40 dBc, and nonharmonic spurious levels to −60 dBc. The phase noise is better than −120 dBc/Hz offset 1 MHz or more from carriers of 70 to 3300 MHz, and better than −117 dBc/Hz offset 1 MHz or more from carriers of 3300 to 6000 MHz.

The built-in FFT analyzer allows spectrum measurements from 70 to 3300 MHz in standard units and to 6000 MHz as an option, using FFT lengths of 1k, 2k, 4k, 8k, and 16k and frequency spans of 1.25, 2.50, 5, 10, 20, and 40 MHz. It features peak and root-mean-square (RMS) detectors and can achieve a dynamic range of better than 100 dB through 3300 MHz and more than 97 dB through 6 GHz. The built-in power meter adds the capability to precisely read power levels from 70 to 3300 MHz, and to 6000 MHz as an option. The measurement range is −74 to +34 dBm CW power (to +42 dBm PEP) from 70 to 100 MHz; −84 to +34 dBm CW power (to +42 PEP) from 100 to 3300 MHz; and −74 to +34 dBm (to +42 dBm PEP) from 3300 to 6000 MHz.

Similarly, the E2010 Broadband Wireless Test Set from AT4 wireless covers frequency bands to 3 GHz and signal bandwidths as wide as 20 MHz with support for 2 x 2 and 4 x 2 MIMO antenna configurations. It includes a low-noise test signal generator, an integrated signal analyzer, and emulation for interference and channel fading. The multifunction instrument is straightforward to control by means of a touchscreen graphical-user interface (GUI). It enables LTE testing at full data rates of 100 Mb/s on downlink and 50 Mb/s on uplink with support of two cells within a single E2010. The company's S3110B LTE Mobile Test Application runs on the E2010, an early RF design validation tool with complete call control functionality and integrated RF measurement capabilities.

Many test-equipment developers have adopted a software-defined-radio (SDR) approach to creating broadband measurement solutions. By changing the software, such instruments can be readily modified to meet the requirements of different communications standards. For example, the model N9030A PXA signal analyzer from Agilent Technologies supports more than 25 different measurement applications using the company's 89600 vector-signal-analyzer (VSA) software. Software test modules are available for both frequency-division-duplex (FDD) and time-division-duplex (TDD) measurements of wireless and wired communications systems.

Of course, it also helps that the software is capable of analyzing instantaneous bandwidths as wide as 160 MHz, allowing the N9030A to handle all current and proposed communications-channel requirements over its frequency range.

But it is also just one example of a wide assortment of available SDR-based measurement solutions, with many other fine products available from numerous suppliers. These companies include Aeroflex, Azimuth Systems, Anite, National Instruments, Spirent Communications, and Tektronix.

Tools for on-site and in-field testing must deliver reasonable measurement accuracy, as well as pack many of the test functions found in a lab or production line. One example is the BTS Master MT8222B handheld analyzer from Anritsu Co., which weighs about 5 lbs with a rechargeable, field-replaceable battery, but incorporates numerous essential measurement functions. It is a cable and antenna analyzer from 400 MHz to 6 GHz, a spectrum analyzer from 150 kHz to 7.1 GHz, a power meter from 10 MHz to 7.1 GHz, a channel scanner from 150 kHz to 7.1 GHz, and a vector signal generator from 400 MHz to 6 GHz.

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