# resonantFrequency

Calculate and/or plot resonant frequency of antenna

Since R2024a

## Syntax

``[fRES, zRES, Z, typRES] = resonantFrequency(object,frequency)``
``[fRES, sRES, S] = resonantFrequency(object,frequency,Method="Sparameters")``
``[fRES, ___] = resonantFrequency(___,Name=Value)``
``resonantFrequency(___)``

## Description

example

````[fRES, zRES, Z, typRES] = resonantFrequency(object,frequency)` calculates the resonant frequencies `fRES` and its corresponding impedances `zRES` and resonance type `typRES` (series or parallel) for the specified antenna object within a sweep of frequencies. `fRES`, `zRES`, and `typRES` are empty if no resonant frequency is detected within the frequency sweep, and `fRES` and `zRES` are vectors if there is more than one resonant frequency whereas `typRES` is a string array. `Z` is the vector of the entire impedance plot spanning across the sweep of frequencies.```
````[fRES, sRES, S] = resonantFrequency(object,frequency,Method="Sparameters")` calculates the resonant frequencies `fRES` and corresponding `S11` value `sRES` for the specified antenna object. `S` is the vector of the entire `S11` values spanning across the sweep of frequencies.```
````[fRES, ___] = resonantFrequency(___,Name=Value)` calculates the resonant frequency and other parameters using additional options specified by one or more Name-Value Arguments.```
````resonantFrequency(___)` plots the impedance for the specified frequency range and marks the resonant frequency on the plot.```

## Examples

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This example shows how to calculate and plot the resonant frequency of a dipole antenna using Impedance method and S-parameters method.

Calculate and Plot Resonant Frequency using Impedance Method

Create a dipole antenna operating at 75MHz. Calculate and plot the resonant frequency of a dipole over a frequency span of 50MHz - 100MHz.

```h = design(dipole,75e6); resonantFrequency(h,50e6:1e6:100e6);```

Calculate and Plot Resonant Frequency using S-parameters Method

Calculate and plot the resonant frequency of the same dipole, using S-parameters method, over the same frequency span.

`resonantFrequency(h,50e6:1e6:100e6,Method="Sparameters");`

## Input Arguments

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Antenna to calculate resonant frequency, specified as an antenna object.

Example: `dipole`

Frequency sweep in Hz to calculate the resonant frequency, specified as a positive vector.

Example: [50e6:5e6:80e6]

Data Types: `double`

### 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: `Method="Sparameters"`

Flag to enable parallel pool, specified as a logical value. The default value is `false`. Set the flag to `true` or `1` to enable the parallel pool. Use parallel pool to speedup the resonant frequency 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`

Method to use for resonant frequency calculation, specified as either `"Impedance"` or `"Sparameters"`. The default method is `"Impedance"`. When the method is specified as `"Impedance"`, zero-crossings of the reactance are used to find the resonant frequency, and `zRES` and `Z` are the outputs. When the method is specified as `"Sparameters"`, the negative peaks of `S11` are used to find the resonant frequency. The output `typRES` (whether the impedance is series or parallel) is only supported when the method is `"Impedance"`.

Example: `"Sparameters"`

Data Types: `string`

Threshold value for impedance when the `Method` is `"Impedance"` or `S11` when the `Method` is `Sparameters`, specified as a real scalar.

Example: -12

Data Types: `double`

Reference impedance in ohms to calculate the S-parameters, specified as a positive real scalar. The default reference impedance is 50 ohms. Valid only when `Method` is `Sparameters`.

Example: 75

Data Types: `double`

Logical flag to enable or disable data tips, specified as either `true` to enable or `false` to disable. By default, the data tips are enabled.

Example: `false`

Data Types: `logical`

## Output Arguments

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Resonant frequency in Hz of the specified antenna, returned as either positive scalar value for a single resonance or a positive vector for multiple resonances within the specified frequency sweep.

Example: 75.33e6

Impedances in ohms corresponding to the resonant frequencies, returned as real or complex scalars or vectors. `zRES` is empty when no resonance is found within the specified frequency sweep. And `zRES` is a vector when multiple resonances are found within the specified frequency sweep.

Example: 75

Data Types: `double`
Complex Number Support: Yes

`S11` values in dB corresponding to resonant frequencies, returned as a complex vector.

Data Types: `double`
Complex Number Support: Yes

Impedance values in ohms over entire frequency span, returned as a complex vector.

Data Types: `double`
Complex Number Support: Yes

`S11` values in dB for the entire frequency sweep, returned as a complex vector.

Data Types: `double`

Resonance type, returned as either `"Series"`, `"Parallel"` or `"Unclear"`. When the reactance in the impedance plot touches zero but does not cross it, resonance type is returned as `"Unclear"`.

Example: `"Parallel"`

Data Types: `string`

## Version History

Introduced in R2024a