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Developers of wireless technology have historically relied on frequency domain equipment as their only source of feedback for high-speed wireless designs. With real-time oscilloscope bandwidths now topping 18 GHz, capturing and analyzing the full band of ultrahigh-frequency RF signals is possible due to rapid performance advancements in real-time acquisition technology. Real-time oscilloscopes offer unique advanced analysis capabilities not available using traditional frequency domain equipment for RF wireless technologies. Advanced analysis capability through statistical characterization techniques and customized processing can provide greater insight and increase design efficiency.

To enable capture of wireless RF signals, an amplified antenna configuration can be used. Using standard components from the TV industry, an RG6 video coaxial cable with F connector can be stripped to use as an antenna, and powered inline amplifiers connected in series to the BNC adapter on the oscilloscope will form an amplified antenna array capable of detecting the tiny wireless RF transmissions nearby. The connectivity of hardware configuration is as follows. The receiving antenna is connected to the in-line amplifier and power supply, and this structure is then connected via a BNC adapter to the oscilloscope input channel to form the amplified antenna array.

Figure 1 shows something you may not have seen before — an octal display depicting eight views of the same real-time wireless RF burst with varied zoom ratios. To see both the burst characteristic and waveshape requires a large amount of waveform acquisition memory. In the capture of the wireless RF signal example 10 million acquisition sample points were used. In the final zoom ratio 250,000:1, actual data sample points can be seen along the rising and falling edges of the RF signal. As shown, the high sample rate of the single-shot capture is more than adequate to accurately represent the true signal shape for this signal. The high-level view of the entire burst can be viewed along with the smallest details at the same time using this multi-zoomed, multigrid display technique.

In addition to time-domain views of an RF burst, the frequency domain view (FFT) can provide more insight into the fundamental frequency, harmonics and modulation characteristics of the RF signal. Figure 2 shows several types of analysis useful for RF performed simultaneously on the acquired traces. The FFTs shown in Figure 2 are applied to specific zoom areas.

When panned, the FFT result can change depending on the frequency content encompassed by the function. As the zoomed areas are panned throughout the original waveform region, the FFTs show the spectral content of a user-defined portion of the waveform, allowing isolation of frequency content of a portion of the burst separate from surrounding waveform data. Using a zoom trace as the source for an FFT, then positioning the zoom to isolate specific areas of the waveform, will allow the frequency domain view to isolate the portion of the waveform of interest.

The histogram in function F8 shows the statistical distribution of instantaneous pulse widths of each cycle captured in the RF burst. The track view in function F4 is plotting the instantaneous pulse width values for every cycle and is time-correlated with the 5:1 zoomed view. This track waveform has measurement results for its Y-axis and time for its X-axis. In this case, the track is plotting duty cycle as a function of position, and the X-axis scaling of the RF burst and the track are identical. As shown by comparing the track view and zoom view, pulse width is inversely correlated with amplitude in the RF signal. This unique view provides insight into the modulation characteristics. Any anomalies of the tracked parameter can be easily identified in the track view and isolated in the acquired waveform by multizooming the track and acquisition at the point of interest.

Function F5 shows a custom MATLAB script calculating a simple wavelet transform, running within the scope application and outputting its result directly into the scope's graticule. This type of customization can be used to apply digital filtering and other signal conditioning directly to the data both before and after the other analysis has taken place. Any process that can be described algorithmically can be applied to the RF analysis process.

When acquiring RF signals that contain an I (in phase) and Q (quadrature) component, math-on-math capability allows the scope to rapidly square, sum and rescale the waveforms to produce an instantaneous power output waveform. Automatic measurement parameters derive the maximum and mean values of the power waveform and can be divided to rapidly determine the ratio of peak to average power of the RF signal directly on the scope display.

Mike Hertz is a field applications engineer with LeCroy Corp. in Michigan. Before joining LeCroy, he was an applications engineer with Agilent Technologies. He has three U.S. patents pending in the area of oscilloscope measurement design. Hertz received a BSEE from Iowa State University and an MSEE from the University of Arizona.

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