Speed is as important as accuracy for production testing. With that in mind, Agilent Technologies (Palo Alto, CA) undertook major development programs for three different families of high-frequency test instruments. These extensive efforts resulted in the model N9020A MXA signal analyzer, a midrange signal and spectrum analyzer with high performance and blazing speed in four versions spanning 20 Hz to 3.6 GHz, 8.4 GHz, 13.6 GHz, and 26.5 GHz; the models N5181A MXG analog signal generator in three versions covering 250 kHz to 1, 3, and 6 GHz and the model N5182A MXG vector signal generator with wide modulation bandwidth in two versions spanning 250 kHz to 3 and 6 GHz; and the model E6601A Wireless Communications Test Set (see sidebar) .
The MXA signal analyzer platform (Fig. 1) is ideally suited for measurements on wireless communications devices to current and emerging standards. Although it has the measurement speed for the production line, it is also a powerful research and design tool for general purpose, aerospace, and defense applications as well. It features a user interface based on the familiar Microsoft Windows XP Professional operating system. The MXA is essentially a high-performance test instrument with an embedded personal computer: All measurement functions can be accessed from the front panel or via a universal-serial-bus (USB) keyboard and mouse.
The MXA signal analyzer family can be viewed as one instrument with four options, or four separate models: the N9020A-503 with frequency coverage from 20 Hz to 3.6 GHz, the N9020A-508 with frequency range from 20 Hz to 8.4 GHz, the N9020A-513 with frequency range from 20 Hz to 13.6 GHz, and the N9020A-526 with broad coverage from 20 Hz to 26.5 GHz well suited to military and aerospace needs. It employs an internal frequency reference with standard aging rate of 1 10-6/year and optional (Option PFR) aging rate performance of 1 X 10-7/year.
The MXA N9020A series analyzers combine traditional spectrum analysis with the wide instantaneous bandwidth needed to evaluate modern communications signals with advanced modulation formats. The standard models offer an analysis bandwidth (the bandwidth which is digitized for further analysis) of 10 MHz, which can be extended to 25 MHz with Option B25. All models feature impressive dynamic range, defined as the range from displayed average noise level (DANL) at the low end to the maximum input power at the high end. Since the MXAs can be ordered with an optional preamplifier, DANL performance
is specified with and without the preamplifier. Without it, the specified DANL is -150 dBm from 1 to 10 MHz, -151 dBm from 10 MHz to 2.1 GHz, -149 dBm from 2.1 to 8.4 GHz, and -147 dBm from 8.4 to 13.6 GHz. With the preamplifier turned on, the specified DANL is -161 dBm from 1 to 10 MHz, -163 dBm from 10 MHz to 2.1 GHz, and -160 dBm from 2.1 to 13.6 GHz. The MXAs can handle average input power levels to +30 dBm (1 W) with the preamplifier off and to +25 dBm with the preamplifier on.
The analyzers show signal levels in linear or logarithmic scales. To display logarithmic signal levels, for example, the MXA signal analyzers allow reference levels to be set from -170 to +30 dBm in 0.01-dB steps. To adjust high-level signals, the analyzers feature an input (electronic) attenuation range of 0 to 70 dB, adjustable in 2-dB steps. The linearity is what one would expect of a high-performance analyzer designed for advanced wireless testing, with typical third-order intercept (TOI) points of +17 dBm from 10 to 100 MHz, +18 dBm from 100 to 400 MHz, +19 dBm from 400 to 1700 MHz, +19 dBm from 1.7 to 3.6 GHz, +18 dBm from 3.6 to 8.4 GHz, and +18 dBm from 8.4 to 13.6 GHz. The analyzers, which are based on a 14-b analog-to-digital-converter (ADC) analyzer intermediate-frequency (IF) section, achieve a 72-dB wideband-CDMA (WCDMA) adjacent-channel leakage ratio (ACLR) of 72 dB.
AMAZING AMPLITUDE ACCURACY
In a signal or spectrum analyzer, amplitude accuracy is a function of many different factors and even instrument settings. (For more on signal-analyzer amplitude accuracy, don't miss the Agilent Technologies' White Paper elsewhere in this issue.) In the MXA instruments, the total absolute amplitude accuracy, from +20 to +30C and at any reference level, measured with 10-dB attenuation, resolution bandwidths from 1 Hz to 1 MHz, input signals from -10 to -50 dBm, and all settings auto-coupled except auto sweep time, is 0.28 dB at 50 MHz and 0.30 dB (with 95-percent confidence) from 20 Hz to 3 GHz.
These analyzers display the signal being measured without adding spectral content of their own, by employing a proprietary low-noise local oscillator (LO) and minimizing spurious generation. The measured phase noise for a 1-GHz carrier, for example, is typically -86 dBc/Hz offset 100 Hz, -100 dBc/Hz offset 1 kHz, -106 dBc/Hz offset 10 kHz, and -136 dBc/Hz offset 1 MHz from the carrier. Residual spurious responses are nominally -100 dBm, with LO related spurious typically -70 dBc, and other spurious products at -70 to -80 dBc.
The MXA signal analyzers include a built-in frequency counter with resolution of 0.001 Hz. The instruments perform a host of automatic measurements to speed and simplify wireless testing, including automatic channel power, occupied bandwidth, burst power, spurious emissions, spectral emission mask (SEM), adjacent-channel power, and histogram power statistics. Functionality includes 6 trace displays, 12 markers, trace math to manipulate measurement data, and auto-tune capability to simplify measurements. In addition to the measurement power and accuracy, these analyzers are fast, performing data transfers (601 measurement points) over a local-area network (LAN) in less than 5 ms. They can also execute a marker peak search is less than 5 ms, execute a center frequency tune and transfer in less than 51 ms, and complete measurement/mode switching in less than 75 ms.
The MXA signal analyzers can be used with optional test application software for a variety of different applications, including IEEE 802.16e WiMAX, WCDMA, HSDPA/HSUPA, and automated phase-noise measurements. Signal-modulation analysis can be performed on a variety of wireless formats, including digital video (DV), 2G, 3G, and 3.5G cellular, WiMAX, WLAN, and private-mobile-radio (PMR) applications. Other formats supported include Bluetooth, GSM, EDGE, TETRA 1 and 2, TD-SCDMA, and ZigBee.
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MXG SIGNAL GENERATORS
Speed is also a hallmark of the MXG signal generators. The test source family includes the model N5181A MXG analog signal generator and the model N5182A MXG vector signal generator (Fig. 2) . As with the MXA signal analyzers, each MXG signal generator can be thought of as a platform with a host of options, such as frequency range. The N5181A MXG analog signal generator is available with frequency ranges of 250 kHz to 1 GHz (Option 501), 250 kHz to 3 GHz (Option 503), and 250 kHz to 6 GHz (Option 506). The N5182A MXG vector signal generator is available with frequency ranges of 250 kHz to 3 GHz (Option 503) and 250 kHz to 6 GHz (Option 506). Any of these signal generators can be used at frequencies as low a 100 kHz, although the performance is not specified that low. The frequency resolution is 0.01 Hz for all models, with phase offset that can be adjusted in 0.01-deg. increments.
The MXG signal generators are optimized for manufacturing, with fast switching of frequency, amplitude, and even between waveforms. In SCPI or list/step modes, the MXGs achieve better than 5 ms typical frequency or amplitude switching. That performance can be improved to as good as 500 µs with a high-speed switching option (Option UNZ). They provide wide-dynamic-range amplitude control, with ranges of -127 to +13 dBm from 250 kHz to 2.5 GHz, -127 to +10 dBm from 2.5 to 3.0 GHz, -127 to +13 dBm from 3.0 to 4.5 GHz, -127 to +10 dBm from 4.5 to 5.8 GHz, and -127 to +7 dBm from 5.8 to 6.0 GHz. An electronic attenuator provides an attenuation range of 0 to 130 dB in 5-dB steps. Using the built-in automatic-level-control (ALC) circuitry, the MXG signal generators achieve absolute level accuracy of better than 0.6 dB from 250 kHz to 1 GHz, 0.7 dB from 1 to 3 GHz, and 0.8 dB from 3 to 6 GHz.
The single-sideband (SSB) phase noise offset 20 kHz from the carrier is better than -126 dBc/Hz at 500 MHz, better than -121 dBc/Hz at 1 GHz, and better than -104 dBc/Hz at 6 GHz. Harmonics are better than -30 dBc at and below 3 GHz and better than -44 dBc above 3 GHz. Nonharmonic spurious signals are less than -48 dBc though 3 GHz and better than -42 dBc from 3 to 6 GHz.
Both the analog and digital MXG signal generators provide generous analog modulation formats, including amplitude modulation (AM), frequency modulation (FM), phase modulation, and pulse modulation. The Agilent MXG vector signal generator family also includes vector modulation by means of external inphase/quadrature (I/Q) input signals or by generating I/Q modulation with a baseband generator. The vector signal generators can be equipped with a choice of optional internal baseband generator, with maximum sampling rates and bandwidths of 30 MSamples/s and 24 MHz (Option 651), 60 MSamples/s and 48 MHz (Option 652), or 125 MSamples/s and 100 MHz (Option 654). These digital waveform generators support waveform switching at rates of 900 µs or less (Option UNZ). Waveforms can be constructed with as many as 2000 sequences (depending upon memory).
DIGITAL MODULATION FORMATS
The MXG vector signal generators can provide the complex digital modulation formats used in modern wireless communications systems, including GSM/EDGE, WCDMA, mobile WiMAX, and wireless-local-area-network (WLAN) systems. The test sources offer outstanding ACLR performance, with a single-carrier specification of -71 dBc (and measured -76 dBc) and a four-carrier ACLR specification of -65 dBc (and measured -70 dBc). Such performance provides increased test margins and greater confidence in test results, especially when characterizing high-dynamic-range components such as multicarrier power amplifiers (MCPAs).
The vector signal generators work with the company's Signal Studio software to create complex test waveforms, including the standards-based signals used for WCDMA, cdma2000, WLAN, and mobile WiMAX testing. The generators feature simple self -maintenance; typical onsite calibration can be performed is less than one hour with a spectrum analyzer and a power meter. The MXG signal generators are fully compliant with the LXI class-C specification. They feature a wide range of interface possibilities, via 100 based-T LAN, GPIB, and two USB 2.0 ports.
Separately, the MXA signal analyzer and the MXG signal generator offer powerful measurement capabilities with enhanced test speed. Together, they can be combined into a versatile test system (Fig. 3) that is at home in both manufacturing sites and research labs. P&A: $25,900 and up (N9020A), $6200 and up (N5181A), and $16,000 and up (N5182A); stock.
Agilent Technologies, 1400 Fountaingrove Pkwy., Santa Rosa, CA 95403; (707) 577-1400, Internet: www.agilent.com