Considerations for Spectrum Analyzer Selection

You are ready to measure a signal and know you need a Spectrum Analyzer. You know that Agilent, Anritsu, Rohde Schwarz, and Tektronix all offer instruments, but which one would be right for you? Where do you start?

Here are some key points to keep in mind when selecting the right Spectrum Analyzer for the job:

1. Frequency Range (Less than 1GHz, 1-3GHz, 3-13GHz, and above 13GHz)
   1. Fundamental frequency of the signal being analyzed. 
   2. Frequency of Harmonics generated by your signal – generally 3rd Order Harmonics (3f and 1/3f) will be sufficiently lower power level than the fundamental to allow characterization of your device.
   3. The lowest frequency you expect to see in the device.


2. Amplitude Range
   1. Displayed Average Noise Level (DANL) – you will want your lowest expected signal to be higher than the DANL of the Spectrum Analyzer.
      1. Some Spectrum Analyzers are equipped with Pre-Amplifiers to raise your signal above the noise floor prior to measurement.  If you need to measure extremely low levels, a pre-amplifier is recommended.
   2. Maximum Safe Input Level – it is important not to overdrive the Spectrum Analyzer, so attenuators may be required prior to input of your signal into the Spectrum Analyzer.
      1. The Spectrum Analyzer may also have internal attenuators, but this will not change the Maximum Safe Input Level.


3. Resolution Bandwidth (RBW)
   1. This specification will determine the ability of the analyzer to display signals close to the fundamental frequency at lower power.
   2. You may want a RBW small enough to find signals very close to the fundamental frequency at much lower level without having the signal lost in the "skirts" of the fundamental as displayed on the Spectrum Analyzer.
   3. Inter-modulation products can also appear close to the fundamental frequency and should be taken into account.


4. Analysis (Demodulation) Bandwidth
   1. Analysis (Demodulation) Bandwidth is the bandwidth around the center frequency which can be digitized for further analysis.
   2. Many digital demodulation schemes will require an Analysis Bandwidth wide enough to resolve the embedded I/Q data.


5. Frequency and Amplitude Accuracy
   1. It will be important to check these specifications, especially for Government and Industry Regulations and Requirements.


6. Software Options
   1. Modern Spectrum Analyzers are computer based and offer a wide range of signal processing capabilities.  Be sure to choose the options that will support your testing needs.  Examples of some Software Options are:
      1. Cellular Demodulation – WCDMA, UMTS, HSDPA, HSUPA, GSM, GPRS, EGPRS (EDGE), WiMAX, LTE, etc.
      2. EMC/EMI pre-compliance and compliance testing.
      3. Vector Signal Analysis.
   2. Phase Noise, Noise Figure and analog modulation options are often offered as well.


7. General Considerations
   1. Input connector type.
   2. Available outputs – video, printer, USB.
   3. Memory and trace storage – internal HDD, USB, removable HDD, CD/DVD.
   4. Portability / Battery Operation.

Once you have determined the Spectrum Analyzer required, you will need to plan your acquisition strategy. If your project is short-term then an equipment rental may be your best solution. Rental allows you to scale to project size and scope, minimize capital outlay and quickly replace a down unit. For long-term or repetitive needs, a lease or purchase may be a better option.

A few links are listed below to provide more detailed information.

Agilent Technologies – Spectrum Analyzer Selection
Anritsu – Spectrum Analyzers
Rohde Schwarz – Spectrum Analyzers
Tektronix – Real Time Spectrum Analyzers
TRS-RenTelco – Spectrum Analyzer Rentals