vswr

R2026b

Calculate and plot voltage standing wave ratio (VSWR) of antenna or array element

Syntax

vswr(object,frequency,z0)

vswRatio = vswr(object,frequency,z0)

[___,sweepobj] = vswr(___,SweepOption=Value)

[___] = vswr(___,Name=Value)

Description

vswr(object,frequency,z0) calculates and plots the VSWR of an antenna or an array element, over specified frequency range, and a reference impedance of z0 ohms.

vswRatio = vswr(object,frequency,z0) calculates and returns the VSWR of an antenna or array element, over specified frequency range, and a reference impedance of z0 ohms.

[___,sweepobj] = vswr(___,SweepOption=Value) uses the specified frequency sweep interpolation method to calculate the antenna or array element VSWR, and additionally returns the interpolation method type and rational fit parameters stored in a frequency sweep object sweepobj.

[___] = vswr(___,Name=Value) specifies additional options using one or more name-value arguments. For example, vswr(dipole,60e6:1e6:80e6,UseParallel=true) uses parallel pool to perform VSWR calculation at each frequency for a dipole antenna.

Examples

Plot VSWR of Antenna

Plot vswr (voltage standing wave ratio) of a circular loop antenna.

h = loopCircular;
vswr(h,50e6:1e6:100e6,50)

Calculate VSWR of Antenna

Calculate vswr (voltage standing wave ratio) of a helix antenna.

h = helix;
hvswr = vswr(h,2e9:1e9:4e9,50)

hvswr = 1×3

    3.6047    6.7230    3.3524

Input Arguments

object — Antenna or array to calculate VSWR

antenna object | array object | custom antenna | custom array | pcbStack object | installedAntenna object

Antenna or array to calculate the VSWR, specified as one of the following options:

• Antenna object from the antenna catalog.

• Array object from the array catalog.

• pcbStack object.

• installedAntenna object.

Example: dipole

frequency — Frequency to calculate VSWR

positive scalar | positive vector

Frequency to calculate the VSWR, specified as a scalar for a single frequency or a vector for a frequency range in Hertz.

Example: 75e6

Example: 50e6:1e6:100e6

Data Types: double

z0 — Reference impedance

50 (default) | scalar

Reference impedance, specified as a scalar in ohms.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: Sweepoption="interp"

UseParallel — Option to enable parallel pool

false or 0 (default) | true or 1

Option to enable parallel pool, specified as a logical value. The default value is false. Set this option to true or 1 to enable the parallel pool. Use parallel pool to speed up the VSWR calculations at multiple frequencies for computationally large antennas and arrays. To use this feature, you need a license to the Parallel Computing Toolbox™.

Example: UseParallel=true

Data Types: logical

SweepOption — Sweep interpolation method

"direct" (default) | "interp" | "interpWithGrad" | frequencySweep object

Sweep interpolation method, specified as one of the following:

• "direct" — Compute VSWR using all the specified frequencies.

• "interp" — Interpolate the sweep using rational fitting to compute VSWR with minimum possible set of frequency points within the specified frequency range.

• "interpWithGrad" — Interpolate the sweep using rational fitting with gradient calculations to compute VSWR with minimum possible set of frequency points within the specified frequency range.

• frequencySweep object — Interpolate the sweep using parameters such as error tolerance, number of frequency points, and number of iterations that you set in the frequencySweep object.

Frequency sweep interpolation methods use rational fitting to interpolate results over the frequency range defined by two or more specified frequency points.

When you use an interpolating sweep, the frequencies at which the vswr function computes and plots the results can differ from the frequencies in the input frequency vector. The effective set of frequencies depends on SweepOption:

• If SweepOption is a frequencySweep object, the effective frequencies are determined by its NumFreqs property.

• If SweepOption is "interp" or "interpWithGrad", the number of frequency points depends on how many frequencies you provide:

  • If you provide more than 30 frequencies, the sweep uses your frequencies directly.

  • If you provide 30 or fewer frequencies, the sweep uses the default of 100 points across the band.

Sweep Interpolation Methods

Method	When to Use	Trade-off
"direct"	Results at all specified frequencies	High computational cost; slow for large sweeps
"interp"	Faster results with automatic accuracy control and fewer simulations	No control over number of frequency points
"interpWithGrad"	Faster results with gradient information for optimization	Slightly more expensive than "interp"
frequencySweep object	Manual control over frequency resolution, error tolerance, and number of iterations	Requires manual tuning; no adaptive refinement

To use this feature, you need an RF Toolbox™ license.

Example: [vswRatio,sweepobj] = vswr(dipole,[10e6:1e6:180e6],SweepOption="interp")

Data Types: string

Output Arguments

vswRatio — Voltage standing wave ratio

scalar | NumFreq-by-1 vector | 2-by-NumElem | NumFreq-by-NumElem matrix

Voltage standing wave ratio, returned as one of the following:

• a numeric scalar for an antenna with a single analysis frequency

• a NumFreq-by-1 vector for an antenna with a range of analysis frequencies

• a 2-by-NumElem vector for an array with 2 analysis frequencies

• a NumFreq-by-NumElem matrix for arrays with a range of analysis frequencies

NumFreq is the number of specified frequencies and NumElem is the number of array elements.

sweepobj — Frequency sweep interpolation parameters

frequencySweep object

Frequency sweep interpolation parameters, returned as a frequencySweep object.

Tips

• Interpolating frequency sweeps may report results at frequencies that differ from the frequencies you specify. If you require results at exact frequencies, either use the default direct sweep, or set the NumFreqs property of the frequencySweep object greater than or equal to the number of frequencies you provide.

• When using the "interp" or "interpWithGrad" sweep options, provide more than 30 frequency points to have the sweep use your frequency resolution exactly; otherwise the sweep defaults to 100 points across the band.

Version History

Introduced in R2015a

R2026b: Use frequency sweep interpolation to calculate VSWR

Use the new SweepOption name-value argument to interpolate the frequency sweep for the VSWR calculations. The interpolation methods use rational fitting or rational fitting with gradient information.