Custom FM Waveform

Custom FM pulse waveform

Since R2023a

• 

Libraries:
Phased Array System Toolbox / Waveforms

Description

The Custom FM Waveform block generates a custom FM pulse waveform with specified pulse width, pulse repetition frequency (PRF), and sweep bandwidth. The block outputs an integer number of pulses or an integral number of samples.

Ports

Input

PRFIdx — PRF Index

positive integer

Index to select the pulse repetition frequency (PRF), specified as a positive integer. The index selects the PRF from the predefined vector of values specified by the Pulse repetition frequency (Hz) parameter.

Example: 4

Dependencies

To enable this port, select Enable PRF selection input.

Data Types: double

FreqOffset — Frequency offset

scalar

Frequency offset in Hz, specified as a scalar.

Example: 2e3

Dependencies

To enable this port, set Source of Frequency Offset to Input port.

Data Types: double

Output

Y — Pulse waveform

complex-valued vector

Pulse waveform samples, returned as a complex-valued vector.

Data Types: double

PRF — Pulse repetition frequency

positive scalar

Pulse repetition frequency of current pulse, returned as a positive scalar.

Dependencies

To enable this port, set the Output signal format parameter to Pulses and then select the Enable PRF output parameter.

Data Types: double

Coeff — Matched filter coefficients

vector | matrix

Matched filter coefficients, returned as a vector or matrix.

Dependencies

To enable this port, select Enable Matched Filter Coefficients Output.

Data Types: double
Complex Number Support: Yes

Parameters

To edit block parameters interactively, use the Property Inspector. From the Simulink^® Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Sample rate (Hz) — Sample rate of the output waveform

1e6 (default) | positive scalar

Sample rate of the output waveform, specified as a positive scalar. The ratio of Sample rate (Hz) to each element in the Pulse repetition frequency (Hz) vector must be an integer. This restriction is equivalent to requiring that the pulse repetition interval is an integral multiple of the sample interval.

Programmatic Use

Block Parameter:SampleRate

Type:double

Values:positive scalar

Default:1e6

Method to specify pulse duration — Pulse duration as time or duty cycle

Pulse width (default) | Duty cycle

Method to set the pulse duration, specified as Pulse width or Duty cycle. When you set this parameter to Pulse width, the pulse duration is set using the Pulse width (s) parameter. When you set this parameter to Duty cycle, the pulse duration is computed from the values of the Pulse repetition frequency (Hz) and Duty Cycle parameters.

Programmatic Use

Block Parameter:DurationSpecification

Type:string

Values:string

Default:'Pulse width'

Pulse width (s) — Time duration of pulse

50e-6 (default) | positive scalar

The duration of each pulse, specified as a positive scalar. Set the product of Pulse width (s) and Pulse repetition frequency to be less than or equal to one. This restriction ensures that the pulse width is smaller than the pulse repetition interval. Units are in seconds.

Example: 300e-6

Dependencies

To enable this parameter, set the Method to specify pulse duration parameter to Pulse width.

Programmatic Use

Block Parameter:PulseWidth

Type:double

Values:string

Default:50e-6

Duty cycle — Waveform duty cycle

0.5 (default) | scalar in the range [0,1]

Waveform duty cycle, specified as a scalar in the range [0,1].

Example: 0.7

Dependencies

To enable this parameter, set the Method to specify pulse duration parameter to Duty cycle.

Programmatic Use

Block Parameter:DutyCycle

Type:double

Values:positive scalar

Default:1e6

Pulse repetition frequency (Hz) — Pulse repetition frequency

1e4 (default) | positive scalar

Pulse repetition frequency, PRF, specified as a scalar or a row vector. Units are in Hz. The pulse repetition interval, PRI, is the inverse of the pulse repetition frequency, PRF. The value of Pulse repetition frequency (Hz) must satisfy these constraints:

• The product of Pulse width and Pulse repetition frequency (Hz) must be less than or equal to one. This condition expresses the requirement that the pulse width is less than one pulse repetition interval. For the phase-coded waveform, the pulse width is the product of the chip width and number of chips.

• The ratio of sample rate to any element of Pulse repetition frequency must be an integer. This condition expresses the requirement that the number of samples in one pulse repetition interval is an integer.

You can select the value of PRF by using block parameter settings alone or in conjunction with the input port, PRFIdx.

• When the Enable PRF selection input parameter is not selected, set the PRF using block parameters.

  • To implement a constant PRF, specify Pulse repetition frequency (Hz) as a positive scalar.

  • To implement a staggered PRF, specify Pulse repetition frequency (Hz) as a row vector with positive values. After the waveform reaches the last element of the vector, the process continues cyclically with the first element of the vector. When PRF is staggered, the time between successive output pulses cycles through the successive values of the PRF vector.

• When the Enable PRF selection input parameter is selected, you can implement a selectable PRF by specifying Pulse repetition frequency (Hz) as a row vector with positive real-valued entries. But this time, when you execute the block, select a PRF by passing an index into the PRF vector into the PRFIdx port.

In all cases, the number of output samples is fixed when you set the Output signal format to Samples. When you use a varying PRF and set Output signal format to Pulses, the number of output samples can vary.

Programmatic Use

Block Parameter:PRF

Type:double

Values:positive scalar

Default:1e6

Enable PRF selection input — Select predefined PRF

off (default) | on

Select this parameter to enable the PRFIdx port.

• When enabled, pass in an index into a vector of predefined PRFs. Set predefined PRFs using the Pulse repetition frequency (Hz) parameter.

• When not enabled, the block cycles through the vector of PRFs specified by the Pulse repetition frequency (Hz) parameter. If Pulse repetition frequency (Hz) is a scalar, the PRF is constant.

Programmatic Use

Block Parameter:PRFSelectionInputPort

Type:logical

Values:positive scalar

Default:off

Source of simulation sample time — Source of simulation sample time

Derive from waveform parameters (default) | Inherit from Simulink engine

Source of simulation sample time, specified as Derive from waveform parameters or Inherit from Simulink engine. When set to Derive from waveform parameters, the block runs at a variable rate determined by the PRF of the selected waveform. The elapsed time is variable. When set to Inherit from Simulink engine, the block runs at a fixed rate so the elapsed time is a constant.

Dependencies

To enable this parameter, select the Enable PRF selection input parameter.

Programmatic Use

Block Parameter:SimulationTimeSource

Type:enum

Values:Derive from waveform parameters, Inherit from Simulink engine

Default:Derive from waveform parameters

Frequency modulation — Wavefform requency modulation function

length-M real-valued vector | function handle | cell array

Waveform frequency modulation function, specified as a length-M real-valued vector, function handle, or cell array.

• If the FrequencyModulation property is a vector, it specifies samples of the instantaneous frequency at M points as [f₁, f₂, …, f_M]. The waveform sweeps the specified frequencies such for the k^th pulse with start time t_k and duration T_k, the instantaneous frequency at time

  $$t_m=t_k+(m-1)T_k/(M-1)$$

  is equal to f_m where t_k ≦ t_m ≦ t_k + T_k and m = 1...M. The instantaneous frequencies between time t_m and t_m+1 are found by linearly interpolating between f_m and f_m+1. The resulting custom FM waveform can be considered as a piecewise LFM waveform consisting of M-1 LFM sections of equal duration.

• If the FrequencyModulation property is a function handle, the function must have the following syntax: f = fmFcn(t)where f is the instantaneous frequency at time t. t is the time at which to compute the instantaneous frequency. The values in t are between 0 and the pulse width.

• If the FrequencyModulation property is a cell array, then the first cell must be a function handle as specified above. The remaining entries in the cell array are the additional input arguments to the function, if any.

Programmatic Use

Block Parameter:FrequencyModulation

Type:char, string, function

Values:char. string

Default:Hyperbolic

Data Types: char | string

Envelope function — FM signal amplitude envelope

Rectangular (default) | Gaussian | Hamming | Chebyshev | Hann | Kaiser | Taylor

FM signal amplitude envelope function, specified as Rectangular, Gaussian, Hamming, Chebyshev, Hann, Kaiser, or Taylor.

Programmatic Use

Block Parameter:Envelope

Type:enum

Values:Rectangular, Gaussian, Hamming, Chebyshev, Hann, Kaiser, or Taylor

Default:Rectangular

Source of Frequency Offset — Source of frequency offset

Property (default) | Input port

Source of frequency offset, specified as Property or Input port.

• When set to Property, the offset is determined by the value of the Frequency Offset parameter.

• When set to Input port, the offset is determined by the value of the FreqOffset port.

Programmatic Use

Block Parameter:FrequencyOffsetSource

Type:enum

Values:Property, Input Port

Default:Property

Frequency Offset (Hz) — Frequency offset

0 (default) | scalar

Frequency offset, specified as a scalar. Units are in Hz.

Example: 2e3

Dependencies

To enable this parameter set the Source of Frequency Offset parameter to Input port.

Programmatic Use

Block Parameter:FrequencyOffset

Type:double

Values:scalar

Default:0

Output signal format — Format of the output signal

Pulses (default) | Samples

The format of the output signal, specified as Pulses or Samples.

If you set this parameter to Samples, the output of the block consists of multiple samples. The number of samples is the value of the Number of samples in output parameter.

If you set this parameter to Pulses, the output of the block consists of multiple pulses. The number of pulses is the value of the Number of pulses in output parameter.

Programmatic Use

Block Parameter:OutputFormat

Type:enum

Values:Pulses Samples

Default:Pulses

Number of samples in output — Number of samples in output

100 (default) | positive integer

Number of samples in the block output, specified as a positive integer.

Example: 1000

Dependencies

To enable this parameter, set the Output signal format parameter to Samples.

Programmatic Use

Block Parameter:NumSamples

Type:double

Values:positive scalar

Default:100

Data Types: double

Number of pulses in output — Number of pulses in output

1 (default) | positive integer

Number of pulses in the block output, specified as a positive integer.

Example: 2

Dependencies

To enable this parameter, set the Output signal format parameter to Pulses.

Programmatic Use

Block Parameter:NumPulses

Type:double

Values:positive scalar

Default:1

Data Types: double

Enable PRF Output — Enable output of PRF

off (default) | on

Select this parameter to enable the PRF output port.

Dependencies

To enable this parameter, set Output signal format to Pulses.

Programmatic Use

Block Parameter:PRFOutputPort

Type:enum

Values:off on

Default:off

Enable Matched Filter Coefficients Output — Enable output of matched filter coefficients

off (default) | on

Select this parameter to enable the Coeff output port.

Programmatic Use

Block Parameter:CoefficientOutputPort

Type:enum

Values:off on

Default:off

Simulate using — Block simulation method

Interpreted Execution (default) | Code Generation

Block simulation, specified as Interpreted Execution or Code Generation. If you want your block to use the MATLAB^® interpreter, choose Interpreted Execution. If you want your block to run as compiled code, choose Code Generation. Compiled code requires time to compile but usually runs faster.

Interpreted execution is useful when you are developing and tuning a model. The block runs the underlying System object™ in MATLAB. You can change and execute your model quickly. When you are satisfied with your results, you can then run the block using Code Generation. Long simulations run faster with generated code than in interpreted execution. You can run repeated executions without recompiling, but if you change any block parameters, then the block automatically recompiles before execution.

This table shows how the Simulate using parameter affects the overall simulation behavior.

When the Simulink model is in Accelerator mode, the block mode specified using Simulate using overrides the simulation mode.

Acceleration Modes

Block Simulation	Simulation Behavior
	Normal	Accelerator	Rapid Accelerator
Interpreted Execution	The block executes using the MATLAB interpreter.	The block executes using the MATLAB interpreter.	Creates a standalone executable from the model.
Code Generation	The block is compiled.	All blocks in the model are compiled.

For more information, see Choosing a Simulation Mode (Simulink).

Programmatic Use

Block Parameter:SimulateUsing

Type:enum

Values:Interpreted Execution, Code Generation

Default:Interpreted Execution

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2023a