Channel Quality Modulation Analysis 89600 VSA Software

Key Features

• Make group delay measurements using a simple wideband multi-tone stimulus signal
• Import and export the multi-tone stimulus definition from and to Keysight’s N7621B Signal Studio software
• Calibrate the input stimulus with measured signal data
• Perform simple and repeatable phase and magnitude channel response analysis
• Select from more than 40 Keysight measurement platforms to meet your specific design and test goals
• Channel quality modulation analysis now is part of the 89600 VSA software option 89601200C for basic vector signal analysis and hardware connectivity

Channel Quality Measurements

The 89600 VSA software Option 89601200C for channel quality measurements accelerates satellite payload testing with a wideband test approach for group delay. Satellite system design engineers can input a multi-tone stimulus to their device, then make quick and easy relative group delay measurements within an instrument span of up to 1 GHz using the UXA signal analyzer, and even wider bandwidth measurements with Keysight oscilloscopes and digitizers. 89601200C for channel quality measurements allows R&D engineers to measure and diagnose problems for signals generated on the test bench, as well as live signals over the air.

Key Benefits of Option 89601200C for Channel Quality Measurements

• Active channels can be notched out of the stimulus signal
• Source and receiver can be in different physical locations
• Works well with frequency-translating devices
• Measurement algorithms compensate for LO drift

Scalable Measurements Across Various Hardware Platforms

The 89600 VSA software provides seamless connectivity with over 300 Keysight instrument models, enabling a wide variety of solutions to fit the price, form factor, performance, and capabilities needed for your test environment. For example, some series of oscilloscopes enable very high bandwidth phase coherent measurements across multiple channels. On the other hand, much better dynamic range is achieved with some X-Series analyzers. For test environments where space comes at a premium, PXI-based solutions can offer a modular form factor.

Why use a multi-tone stimulus model?

Traditionally, characterizing channel quality figures of merit such as group delay has been done using network analyzers with precise methods and cable connections. Design engineers face increasing challenges when it comes to characterizing magnitude, phase, and group delay in passive, active, and frequency-translating devices over ever-wider bandwidths. On the other hand, the multi-tone stimulus test approach offers a simpler test setup and more stable group delay measurements, and thus has been broadly adopted by satellite system engineers. The 89600 VSA software’s channel quality measurement provides many ways to look at a wideband relative channel response, with a set of features for defining multi-tone signals, tracking drifts in frequency, phase, and amplitude. It also offers one-button stimulus definition update and fixed equalization response update functions to quickly eliminate measurement system frequency response variability, so you can focus on and troubleshoot aberrations in the DUT frequency response.

Measurement Example

To highlight the use of this equalizer, we present measured data on a cable at 28 GHz. Often, system impairments such as broadband IQ mismatch and IF gain (un)flatness prevents accurate measurement of a low-loss cable. But by looking at the difference between a straight-through calibration measurement and the actual device under test (DUT), we can isolate the frequency response of just the cable alone. Thanks to built-in algorithms in the VSA, these equalizer corrections may be applied quickly and conveniently, as will be shown below.

First, a multitone signal was created using Keysight’s Multitone Distortion Signal Creation bundle (part of the Signal Studio software). With this tool, you can create a multitone signal definition specifying the number of tones, tone spacing (Hz), phase distribution (random, constant, parabolic), center frequency, and amplitude. This stimulus definition can serve as the VSA reference channel response against which you can compare measured signals captured with your receiver front end (signal analyzer or oscilloscope, for example). The resultant waveform file was downloaded to an M8190A arbitrary waveform generator (AWG). The channel 1 and 2 modulation outputs of the AWG were connected to the wideband analog I and Q inputs of an E8257D PSG signal generator. Other vector signal generators like the MXG or EXG may also be used. The resultant 28 GHz modulated RF signal was sent to an N9040B UXA signal analyzer, although any broadband receiver (like an oscilloscope) with appropriate frequency range may be used.

First, we measure a thru connection, assumed to be lossless. Using the channel quality measurement personality of the 89600 VSA software, we observe the channel frequency response in different formats such as log magnitude (dB), linear magnitude, unwrapped phase (deg), group delay (ns), real (I), or image (Q). In hardware, it is challenging to create a perfectly uniform amplitude series of tones across a 1 GHz spectrum at 28 GHz. Thus, the measured channel frequency response is the measurement system impairment, as shown in figure 4.

If we replace the through connection with the DUT connection (in this case a cable), the resultant measured channel response is not discernible from the system impairments, as shown in figure 5.

Equalization and Measurement Corrections

We need to compensate for the system impairment frequency response and make subsequent measurements with this correction in place. Fortunately, the VSA enables a convenient way to do this using the “Channel Quality Properties” dialogue box, shown in figure 6.

The stimulus definition would normally come from the signal creation software’s ideal multi-tone definition. But due to the measured system impairments, we may redefine the stimulus definition by hitting the ‘Update’ button shown in figure 6. Subsequent measurements are compensated by the stored frequency response. Since the hardware connections have not changed, the resulting channel frequency response is perfectly flat in amplitude and phase, with zero group delay, as shown in figure 7.