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Using Calibration to Optimize Performance in Crucial Measurements
In today’s wireless world, signal and spectrum analyzers face several challenges. Increasing bandwidth requirements of technologies such as WLAN 802.11n, WiMAX and LTE require more analysis bandwidth. Intense price competition forces the manufacturers of wireless equipment to cut costs wherever possible, including production and test costs. Therefore, faster measurement speed is necessary to attain shorter test cycles and the best price for a given performance level. Furthermore, the increasing complexity of modern wireless standards requires test equipment that can be easily operated so that results are achieved faster and with fewer possibilities for mistakes occurring.
The new mid-range R&S FSV signal analyzer is designed to fulfill all these requirements and to provide a future proof, extremely fast signal-analysis solution. With up to 40 MHz of analysis bandwidth, more than 1000 sweeps/second, a user-friendly touch screen and a wealth of dedicated analysis packages for all major wireless standards, it offers an attractive price/performance ratio that helps users increase the effectiveness of their development, device characterization and production.
The signal analyzer comes in versions that cover the 9 kHz to 3.6 GHz and 9 kHz to 7 GHz frequency ranges, with additional frequency models scheduled to follow in the near future. The instrument’s frequency range can be extended down to 20 Hz. At low frequencies it uses a mode with direct A/D conversion of the RF signal. This eliminates the performance degradation that can occur on some signal or spectrum analyzers at low frequencies, which is caused by local oscillator feed-through and the phase noise of the local oscillators.
With its fully digital backend, the R&S FSV combines spectrum analyzer and signal analyzer capabilities. It uses a 16-bit 128 MHz DAC to digitize the last IF, with a memory that enables the recording of up to 200 MSamples of signal. The standard analysis bandwidth of 28 MHz covers the IEEE 802.16e (Mobile WiMAX) standard and the developing LTE standard as well as all of today’s mobile communications standards. The optional 40 MHz bandwidth supports the analysis of IEEE 802.11n signals, and also serves designers for satellite communications and satellite TV.
The new signal analyzer has a resolution bandwidth range from 1 Hz to 10 MHz. In addition, 20, 28 and optional 40 MHz bandwidths are available in Zero span. A very frequent task is the accurate power measurement on wideband burst signals such as WLAN or WiMAX signals. A standard swept channel power measurement is difficult to set up because it requires the gated mode with stable triggering. With its 20, 28 or 40 MHz-wide filter, the instrument can measure the power in Zero span, and it can be triggered with the internal video trigger. A dedicated time domain power measurement function allows users to define exactly which part of the burst will be measured (see Figure 1).
Accurate power measurements are enhanced by the low level measurement uncertainty of the R&S FSV of 0.3 dB up to 3 GHz and only 0.4 dB up to 7 GHz (a 95 percent confidence level in total). Especially for frequencies between 3 and 7 GHz, the signal analyzer’s measurements come closer to power meter accuracy than those of current analyzers, which often show an amplitude flatness in the range of 1 to 2 dB above 3/3.6 GHz. This means that test set ups in production and development can be simplified. Two examples would be 802.11a analysis at 5 GHz in the ISM band at 5.8 GHz, or the 3.4 to 3.8 GHz bands of WiMAX. In the test set up, power meters can be omitted in many cases.
The R&S FSV is designed specifically for speed and design considerations, but this design objective went beyond sweep time and sweep repetition rate. Other considerations included measurement functions that automate those measurement sequences that are typically used in production set ups. This minimizes the remote-control overhead.
Table 1 gives an overview of speed benchmarks. With up to 500 sweep repetitions in manual operation and up to 1000 in remote operation, the new signal analyzer is up to four to five times faster than other currently available signal analyzers. This high sweep rate is important for more than just production applications. Whenever accurate and repeatable power measurements require averaging, or when a certain number of averages is required by a standard specification, this sweep rate will allow development engineers to achieve their results in a much shorter time.
All resolution filters are implemented digitally to assure that their behavior is very well known and that they can be swept faster than analog implementations. An optimized Fast Fourier Transform (FFT) sweep using a wide acquisition bandwidth further decreases the time needed to sweep a given frequency range. This is especially important for all kinds of spurious emissions measurements where the analyzer has to search in a wide frequency range for low level signals.
Sensitivity requirements can often be met only by using narrow resolution filters in order to get the noise floor down. However, reducing the bandwidth by a factor of two increases the required sweep time by a factor of four. This is the reason why spurious measurements are known to be quite time consuming. Table 2 compares the sweep time for a 10 MHz span for a currently available conventional analyzer and the R&S FSV. It shows how much faster the new signal analyzer lets the user perform this task.
A typical measurement task on a production line for wireless devices is the alignment of output power. Several power levels have to be checked on the same frequency. The R&S FSV will perform this measurement in one single remote sweep. Testing of harmonics is another measurement that is frequently required in production. The new instrument does this automatically in manual operation with its harmonics function. In remote operation, the list mode ensures the fastest measurement times for this and other tasks. The list mode allows users to perform measurements at 300 different frequencies with unique analyzer settings at each frequency, all with just one control command. The signal analyzer very quickly tunes to the different frequencies. For the measurement of the power at a fundamental frequency plus 5 harmonics it needs only 21 ms.
As Microsoft Windows becomes commonplace in the test and measurement world, a mouse and an external keyboard is coming into common use, even when there are space restrictions such as on a typical lab bench. The R&S FSV integrates a mouse and keyboard into its touch screen display so that an extra keyboard or mouse can be omitted. The mouse is simply replaced by the natural pointer—the finger. The external keyboard is emulated by an on-screen keyboard.
It should be noted that a touch screen offers numerous possibilities for speeding up manual operation. For example, it makes switching between operating modes very fast. Users simply touch the correct tab, or set up a dedicated measurement application such as for 3GPP by touching on a block of a signal flow block diagram, which opens the corresponding settings (see Figures 2 and 3).
The signal analyzer does not, however, force the user to use the touch screen. The function can be switched off and all functions can be operated in the standard key-oriented manner. In this case, several specialized hard keys guarantee fast and easy operation. Any questions regarding the function of keys or the corresponding remote control commands can be clarified with the online help function, which is context sensitive. Relevant information is found faster than in printed manuals. Undo/redo of up to six interactions makes it easy to correct mistakes.
Another form of help in setting up the instrument is the AUTO SET function, which determines the signal’s frequency and level, and tunes the analyzer accordingly at the press of a single key. Many dedicated measurement routines are standard in the basic instrument. For example, ACP measurements can be performed for many different standards; CCDF measurements, spurious emissions testing, spectrum emission mask measurements or harmonic measurements are done automatically. Up to six traces, each of which can be active at the same time, and up to 16 markers support the evaluation of the results.
Users who already have the R&S FSP or R&S FSU integrated into test systems will benefit from the compatibility mode of the R&S FSV, which emulates both instrument families. Table 3 shows the analysis possibilities for dedicated standards or signals. The most important standards were covered with the first product version.
Thanks to its RF performance (see Table 4)—a T.O.I. of typically 18 dBm, a phase noise of typically –110 dBc/Hz at 10 kHz offset and a noise floor of better than –155 dBm (1 Hz)—the R&S FSV has positioned itself at the top of mid-range signal analyzers. In addition, its 40 MHz analysis bandwidth, its analysis capabilities and its speed either equals or outperforms high-end instruments.
RS No. 301
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