Technical Insights > RF + Microwave

Spectrum Analyzers and Signal Generators: Do I need both?

2020-02-21  |  9 min read 

Why would I need both a signal analyzer and signal source?

You probably know that if you have a source, you need an analyzer to characterize it. To even see what signal your device is producing requires a signal analyzer. Likewise, you also know that if you have a receiver, you would want to send it signals using a signal generator to test the device’s reaction to both ideal and noisy signals to mimic a real environment. So, why would you need both a source and an analyzer? In this blog, I’ll tell you why pairing these instruments raises the bar for development and insights.

 

Testing Sources:

First of all, what is a spectrum analyzer?

Spectrum analyzers measure the magnitude of an input versus signal frequency. Vector signal analyzers measure the magnitude and phase of an input signal at a single frequency. A signal analyzer performs both functions together. Signal analyzers measure signals in the frequency domain, allowing us to see how much energy is present at particular frequencies. Today, they are used to view and demodulate complex signals, allowing users to fine-tune their EVM, amplitude flatness, and more. If you want to see what type of signal your device under test (DUT) emits, a signal analyzer provides a window to view performance.

While this provides essential measurements and insights into complex signals, having a verified signal to compare to allows further characterization. Using your analyzer, you know what’s coming out of your DUT; how are you supposed to know what you should be seeing? Comparing your signal to an ideal one is a valuable way to see small differences and discrepancies between the two. For example, if an ideal signal from a signal generator created in PathWave Signal Generation software produces an error vector magnitude (EVM) of less than 1%, but your signal produces an EVM of 4%, comparing your signal’s results to that of the signal generator can help you understand where the loss of precision comes from.

Testing Receivers:

Signal generators, also referred to as function generators or frequency generators, generate waveforms of various types for testing purposes. They are often used to provide a stable sine wave, or an oscillator in RF receiver testing. Signal generators can also provide fixed RF power to test RF power amplifiers to determine output flatness.

To test your receiver, you likely send it the ideal signals that, in a perfect world, your device would receive. However, you also know that the real environment in which your device will reside is noisy and contains interference. To ensure your DUT is robust enough to handle the real world, using a source to send both a carrier signal and added noise, such as added white Gaussian noise (AWGN), is essential.

When your receiver takes these signals in, it will react in a few possible ways. It will pass tests, fail tests, and even react unpredictably. To take the mystery out of what your device reacts to and why it reacts how it does, use a signal analyzer to open a window to what your device sees. When viewing the signal on a signal analyzer and your device, knowing when and how your device reacts to noise, pulses, loss, and more becomes much easier.

For example, imagine you send an LTE signal plus noise to your device using your signal generator. The device doesn’t react how you expected. Noise is a random signal, so it may be difficult to know what exactly is causing your device to fail. Being able to see inside the waveforms and know what causes your device to fail allows you to eliminate that discrepancy and plan for the worst-case scenarios.

Where do I start when looking for a pair of Keysight’s signal analyzers and signal generators?

While you can pair most of our analyzers and generators together, here’s a place to start on building a strong test bench depending on your application. By pairing two pieces of Keysight equipment together, you ensure seamless hardware and software integration.

These are general purpose pairings. For more specific applications and more detailed information, please see product details or contact us

  • CXA (N9000B) and CXG (N5166B)
    • This pair is best suited for basic parametric testing of components and verification of receivers. This cost-effective pair would do well in a manufacturing/verification environment, or in an education lab.

  • EXA (N9010B) and EXG (N5171B, N5172B, N5173B)
    • The EXA is the most cost-effective method for millimeter-wave measurements. The EXG source allows you to balance budget and performance, featuring high stability for microwave measurements. For a mmWave signal/source combination, pair the EXA with a VXG.

  • MXA (N9020B) and MXG (N5181B, N5182B, N5183B)
    • Using the MXA with the MXG allows you to catch elusive signals using full-band real-time spectrum analysis, ideal for a manufacturing environment. The MXG brings unmatched phase noise and spurious characteristics. For mmWave capabilities, pair the MXA N9021B with the VXG.

  • PXA (N9030B) and MXG (N5182B) or the VXG
    • The PXA allows you to capture signals up to 110 GHz using Keysight smart mixers. The ideal pairing for the PXA, and all of the analyzers, depends on application. For general purpose measurements, the MXG N5182BX07 uses a frequency extender to enter the 6-7.2 GHz range, especially relevant to 802.11ax signals.
    • For higher frequency capability and 5G applications, the VXG, a dual-channel 44 GHz vector microwave signal generator, can help. Using PathWave Signal Generation software, tackle 3GPP conformance test configurations and engineer custom solutions.

  • UXA (N9040B/N9041B) and UXG (N5191A-N5194A) or the VXG (M9383B)
    • Ideal for design or Aerospace and Defense applications, the UXA’s ultra-wide bandwidth ensures spectral purity of your design. Paired with the UXG, generate and monitor chirps and pulses to test your design with an off-the-shelf threat simulator.
    • With the VXG, a microwave signal generator, the frequency capabilities are extended, as well as a 2 GHz modulation bandwidth, ideal for satellite applications and wideband 5G carrier aggregation scenarios. If your application requires data transmission with a high bandwidth, the VXG is the best choice.

Conclusion

Having both a signal generator and signal/spectrum analyzer on your lab bench allows for deeper insights into device performance. Whether you’re designing or validating a device, having both a signal analyzer and signal generator allows you to create and view your signals and device’s reaction. By choosing them from the same provider, the software and hardware are optimized to work together.

If you’re looking to save 35% on your signal analyzer and signal generator pair, Keysight’s current software/hardware promotion can help you attain the complete RF solution for less. Find out more here.

 

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