# rfinterp1

Interpolate network parameter data at new frequencies

## Syntax

``objnew = rfinterp1(objold,newfreq)``
``objnew = rfinterp1(___,'extrap')``

## Description

example

````objnew = rfinterp1(objold,newfreq)` interpolates the network parameter data in `objold` at the specified frequencies, `newfreq`, storing the results in `objnew`. `rfinterp1` uses the MATLAB® function `interp1` to interpolate each individual `(i,j)` parameter of `objold` to the new frequencies. NoteIf any value of the specified frequency is outside of the range specified by `objold.Frequencies`, then `rfinterp1` function inserts `NaNs` into `objnew` for those frequency values. ```
````objnew = rfinterp1(___,'extrap')` also interpolates the network data, but if any of the frequency values you specify in `newfreq` are above the final frequency of the network parameter object, `objold.Frequencies(end)`, then the function extrapolates flat using the final value of the network parameter data `objold.Parameters(:,:,end)`. If any of the frequency values you specify in `newfreq` are below the first frequency of the network parameter object, `objold.Frequencies(1)`, then the function extrapolates linearly between ```conj(objold.Parameters(:,:,1)) ``` and `objold.Parameters(:,:,1)`. This ensures that the network parameter data of the new object, `objnew.Parameters` approach real values as in `newfreq` approach `0`. ```

## Examples

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Read the data from the file `default.s2p` into an S-parameter object.

`hnet = sparameters('default.s2p');`

Interpolate the data at a specified set of frequencies.

```freq = [1.2:0.2:2.8]*1e9; hnet2 = rfinterp1(hnet,freq)```
```hnet2 = sparameters: S-parameters object NumPorts: 2 Frequencies: [9x1 double] Parameters: [2x2x9 double] Impedance: 50 rfparam(obj,i,j) returns S-parameter Sij ```

## Input Arguments

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Data to interpolate, specified as an RF Toolbox™ network parameter object. `objold` must be one of the following types of network parameter objects: S-parameters, t-parameters, Y-parameters, Z-parameters, h-parameters, g-parameters, or ABCD-parameters.

Interpolation frequencies, specified as a vector of positive numbers ordered from smallest to largest.

## Output Arguments

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Interpolated data, returned as an RF Toolbox network parameter object of the same type as `objnew`.

## Algorithms

The function uses the MATLAB function `interp1` to perform the interpolation operation. Overall performance is similar to the RF Toolbox `analyze` function. However, behaviors of the two functions differ when `freq` contains frequencies outside the range of the original data:

• `analyze` performs a zeroth-order extrapolation for out-of-range data points.

• `rfinterp1` inserts `NaN` values for out-of-range data points.

## Version History

Introduced in R2012b