Determine Linear and Nonlinear Characteristics of RF Chain
RF budget analysis can help you determine both linear and nonlinear characteristics within an RF chain. By computing the RF budget, you can verify whether key parameters—such as output power, signal-to-noise ratio (SNR), second- and third-order intercept point (IP2 and IP3), and noise figure (NF)—meet the system specifications at each stage of an RF cascaded system. Optimizing these performance parameters involves an iterative process that accounts for constraints like RF component selection, channel path loss, and nonlinear element stability[1].
You can use either the rfbudget object or the
RF Budget
Analyzer app to compute an RF budget for a chain of 2-port elements.
Compute RF Budget in Three Steps
To compute the RF budget:
First, specify the three system parameters as an input: carrier (input) frequency, input power, and signal bandwidth. These system parameters are used in Friis or harmonic balance (HB) analyses.
Second, describe or create an RF chain. You can build an arbitrary chain representing a transmitter or receiver by cascading elements such as amplifiers, modulators, transmission lines, filters, and antennas. For a list of supported RF elements, see Available elements for RF budget analysis.
These elements can be represented with datasheet parameters such as gain, noise figure, nonlinearities, and input and output impedances.
Finally, select the solver to compute the RF budget. You can choose either the Friis or HB solver in the
rfbudgetobject and in the RF Budget Analyzer app.
This figure lists the three required steps to compute an RF budget of a chain or cascade of elements.
Friis Solver and Harmonic Balance Solver
You can choose the Friis or harmonic balance solver to compute an RF budget based on your application. Consult this table for a summary of the features supported by the two solvers.
Summary of Features
| Feature | Friis | Harmonic Balance |
|---|---|---|
Compute:
| Yes | Yes |
| Compute second-order intercept points (IIP2 and OIP2) | No | Yes |
| Enable faster simulation speed | Yes | Determined by number of harmonics used for one- and two-tone analysis. You
can Use HarmonicOrder property to set the number of harmonics
to use for all the tones in HB analyses. |
| Account for intermodulation distortion effects | No | Yes |
| Account for noise folding effects | No | Yes |
Visualize RF Budget Analysis
After computing the RF budget, visualize the results. Consult this table to choose the right type of visualization option for your application.
| Visualize | Example |
|---|---|
| Budget results, S-parameters over stages and frequencies | Plot S-Parameters, Output Power, and Transducer Gain of RF System |
| Amplifier power characteristics | RF Transmitter System Analysis |
| One- and two-tone harmonic balance results of the RF budget chain | Visualize One-Tone and Two-Tone Analysis Results |
| Mixer spurs and spur-free zones of the IMT mixer element | Perform Frequency Planning to Find Spur-Free IF Bandwidths |
Export RF Budget Analysis
Iterate on the budget analysis by adding different components with various specifications. Once satisfied with the architectures, the number of stages, and the initial results, you can export the:
Per-stage and cascade values to the MATLAB® workspace.
System design to RF Blockset™ for circuit envelope and idealized baseband simulation. For more information, see Circuit Envelope vs. Idealized Baseband simulation in RF Blockset (RF Blockset).
System design to the RF Blockset Testbench as a device under test (DUT) subsystem and verify the results using simulation.
System design to an
rfsystemSystem object™.RF budget results to create a
phased.Transmitter(Phased Array System Toolbox) System object and aphased.Receiver(Phased Array System Toolbox) System object.
References
[1] Tripathy, Shiv. RF & μWave Measurements: For Design, Verification and Quality Control.. Independently published, 2019.
[2] Razavi, Behzad. RF Microelectronics. Upper Saddle River, NJ: Prentice Hall, 2011.
