Ansys HFSS and STK for Communications and Radar Analysis

STK Pro, STK Premium (Air), STK Premium (Space), or STK Enterprise
You can obtain the necessary licenses for this training by contacting AGI Support at support@agi.com or 1-800-924-7244.

Pictures, graphs, and data snippets are used as examples only. The results of the tutorial may vary depending on the user settings and data enabled (online operations, terrain server, dynamic Earth data, etc.). It is acceptable to have different results.

Capabilities covered

This lesson covers the following STK Capabilities:

  • STK Pro

Problem statement

In this lesson, you will learn how to use custom antenna and radar cross section (RCS) files to obtain a realistic simulation. You will use that simulation to analyze radio communications and radar tracking.

The lesson's scenario models how an aircrew could fly a Diamond DA-40 trainer from Buckley AFB to Pueblo Memorial Airport. An airport surveillance radar (ASR) is located at the City Of Colorado Springs Municipal Airport and will track the aircraft. Controllers located at Pueblo Memorial Airport will establish voice communications with the aircraft prior to landing. You want to determine when controllers can track and communicate with the aircraft.

Solution

You can use STK Communications capability, STK Radar capability, and Ansys HFSS generated antenna and RCS files to simulate the scenario.

What you will learn

When you complete the scenario, you will know when the ASR system can track the small aircraft and when air traffic controllers can communicate with the aircrew. Based on the capabilities you will use, you will have a basic understanding of the following:

  • How to use external Ansys HFSS generated antenna and RCS files in STK
  • Data contained in the HFSS generated files

Video Guidance

Watch the following video. Then follow the steps below, which incorporate the systems and missions you work on (sample inputs provided).

Starter scenario

A partially created scenario has been created for you so you can focus on the portion of this lesson about HFSS Generated files in STK.

  1. Launch STK ().
  2. Ensure that the Welcome to STK dialog is visible in the STK Workspace.

Signing in to access the SDF

You can access your scenarios or objects from the STK Data Federate (SDF).

  1. Click Open a Scenario () in the Welcome to STK dialog box.
  2. Change the Location to STK Data Federate at the bottom of the Open dialog window.
  3. Click Guest in the top-right corner to sign into your account.
  4. Click Switch User... when the SDF Server Login dialog box opens.
  5. Enter your Account name and Password on the Log In: AGI SEDS dialog box.
  6. Click Log In.

Opening the starter scenario

  1. Browse to Sites>AGI>documentLibrary>STK12>Starter Tutorials.
  2. Select STK_and_HFSS.vdf (v1.0).
  3. Click Open.

Saving a VDF as a SC (scenario) file

When you open the scenario, STK creates a directory with the same name as the scenario in the default user directory (e.g. C:\Users\username\Documents\STK 12). The scenario will not save automatically. When you save a scenario in STK, the file will not change its file type automatically. In other words, if you open a Visual Data File (VDF), the default save format will still be a VDF. The same is true for a scenario file (*.sc). If you want to save a VDF as an SC file (or vice-versa), you must change the file format when you are performing the Save As procedure.

  1. Open the File menu.
  2. Select Save As...
  3. Click STK User in the Save As window.
  4. Select the STK_and_HFSS folder.
  5. Click Open.
  6. Change Save as type: to Scenario Files (*.sc).
  7. Click Save.
  8. Click Yes to confirm.

Save often!

Understanding the starter scenario

Prior to modifying the scenario, you should become familiar with the objects already created in the starter scenario.

  1. Bring the 2D Graphics window to the front.
  2. Look at the flight route of the aircraft.

The aircraft's flight route starts at an altitude of 1,000 feet near Buckley AFB, climbs to 10,000 feet while passing over the Black Forrest VORTAC navaid, and then descends to 1,000 feet as it approaches Pueblo Memorial Airport. An air surveillance radar is located at the City Of Colorado Springs Municipal Airport which will track the aircraft. Air traffic controllers are located at Pueblo Memorial Airport. They will establish communications with the trainer aircraft.

If you want to know more about how exactly to create a flight route in STK, check out the Level 1 STK training lessons to learn all of STK's fundamental features.

In this scenario, you are not using visual or analytical terrain. You are using the WGS84 for altitude reference. The Aircraft object is using the Great Arc Propagator.

Ansys HFSS SBR+ radar cross section files

The radar cross section is the measure of a target's ability to reflect radar signals in the direction of the radar receiver. Efficient modeling of the radar cross section (RCS) in Ansys HFSS SBR+ can help determine or control proper radar signature characteristics of commercial and military platforms (such as aircraft, ships, ballistic missiles, submarines, ground vehicles, and satellites). Ansys HFSS can compute a Complex RCS for targets based on their geometry and material characteristics. It exports complex RCS data in the CSV file format.

Each run of HFSS produces results for one signal source polarization. For example, a signal source model with horizontal (H) polarization computes RCS returns for the H-H (H incident and H reflected signal polarization) combination and for V-H (H incident and V reflected signal polarization). V is the vertical polarization. A second run produces data for V signal polarization and computes RCS returns for the V-V (V incident and V reflected signal polarization) combination and for H-V (V incident and H reflected signal polarization).

Using the Ansys HFSS CSV file format in STK

STK can use each data file independently when processing single polarization type. However, you can combine the exported files to produce a Complex Scattering RCS Matrix for [HH, HV, VH, VV] RCS Values. STK reads the column headers in the CSV format files and parses the data in each column: the RCS data frequency value, the polarization scattering matrix element (H-H, V-H, H-V, V-V), Phi angle start value (degrees), and Phi angle stop value. STK then computes the Phi angle step value. The first column of the CSV file represents the theta angle values. Each row corresponds to the RCS data row in the scattering matrix. The starting, ending, and step size for the theta values are determined by reading the first column data.

The following conditions apply:

  • The scattering matrix data is expected to conform to a polar coordinate frame with uniform step size for Theta and Phi angles.
  • The RCS data reference axis is the X-axis of the target body.
  • If you use two files to import the full scattering matrix, the two files must have the same matrix size, Theta angles, Phi angles, and step size.
  • The frequency values listed in the two RCS data files must be same.

Viewing the CSV file's contents

You can view two example sample files for 2.8GHz, one for H_Incident and one for V_Incident.

  1. Open Windows File Explorer.
  2. Browse to your scenario folder (e.g. C:\Users\username\Documents\STK 12\ STK_and_HFSS).
  3. Right-click on MD4-200_H_Incident_2p8GHz.csv.
  4. Select Open.

    5. The first column represents the theta values. The column header row (first row of the CSV file) shows the polarization, the frequency values, and the Phi angle values. The data in column two and beyond are complex RCS data values in the format a + bi.

    H_Incident sample

  5. Close the MD4-200_H_Incident_2p8GHz.csv file.
  6. Return to your scenario folder.
  7. Right-click on MD4-200_V_Incident_2p8GHz.csv.
  8. Select Open.

    9. V_Incident sample

  9. Close the MD4-200_V_Incident_2p8GHz.csv file and Windows File Explorer when finished.
  10. Return to STK.

Configuring your aircraft's properties to use HFSS CSV files for analysis

You need to configure the Aircraft object's properties so that you can use the HFSS CSV files analytically.

  1. Right-click on DA_40 () in the Object Browser.
  2. Select Properties ().
  3. Select the RF - Radar Cross Section page in the Properties Browser.
  4. Clear Inherit at the top of the page. This enables you to set the RCS settings for the Aircraft () object instead of inheriting the settings from the Scenario () object.
  5. Open the Compute Type: shortcut menu in the Band Properties frame.
  6. Select Ansys HFSS CSV File.

Loading the H Incident Ansys HFSS CSV file for analysis

You will use a nominal H incident HFSS CSV file that is provided for your analysis.

  1. Click the Primary Pol File: ellipsis ().
  2. Click STK User.
  3. Select your scenario folder.
  4. Click Open.
  5. Select MD4-200_H_Incident_2p8GHz.csv.
  6. Click Open.

Loading the V Incident Ansys HFSS CSV file for analysis

You will use a nominal V incident HFSS CSV file that is provided for your analysis.

  1. Click the Ortho Pol File: ellipsis ().
  2. Click STK User.
  3. Select your scenario folder.
  4. Click Open.
  5. Select MD4-200_V_Incident_2p8GHz.csv
  6. Click Open.
  7. Click Apply to accept your changes and keep the Properties Browser open.

Visualizing the radar cross section in the 3D Graphics Window

You can view the Aircraft object's RCS in the 3D Graphics window.

  1. Select the 3D Graphics - Radar Cross Section page.
  2. Select Show Volume in the Volume Graphics frame.
  3. Set the following:
    4. Option Value
    Show as wireframe on
    Scale (per dBsm): 2 m
    Minimum Displayed RCS: -10 dB
    Set theta and rho resolution together on
    Theta - Resolution: 0.5 deg
  4. Click OK to accept your changes and to close the Properties Browser.

Viewing the RCS in the 3D Graphics Window

  1. Right-click on DA_40 () in the Object Browser.
  2. Select Zoom To.
  3. Bring the 3D Graphics window to the front.
  4. Use your mouse to object a good view of the aircraft and its RCS.

3D Graphics View of the RCS

Inserting the radar antenna servo system

You will insert a Sensor object to simulate a servo system for radar antenna positioning. You will lock the sensor onto the aircraft and constrain the sensor to point in a limited area.

  1. Insert a Sensor () object using the Insert Default () method.
  2. Select COS_Radar () in the Select Object window.
  3. Click OK.
  4. Rename the Sensor () object Servo_System.

Defining the sensor field of view

You will define Servo_System's field of view using a Simple Conic sensor pattern. You will use the sensor's field of view for situational awareness when Servo_System points the radar antenna at DA_40.

  1. Open Servo_System's () properties ().
  2. Select the Basic - Definition page.
  3. Set the Simple Conic - Cone Half Angle: value to 1 deg.
  4. Click Apply.

Targeting the aircraft

You will use the Targeted pointing type to point Servo_System to DA_40.

  1. Select the Basic - Pointing page.
  2. Set the Pointing Type: to Targeted.
  3. Select DA_40 () in the Available Targets list.
  4. Move () DA_40 () to the Assigned Targets list.
  5. Click Apply.

Setting range and elevation angle constraints

There are many types of radar systems. A typical airport surveillance radar's nominal range is 60 miles and the elevation angle of the beam can track from 0 to 30 degrees. Anything higher than 30 degrees is the cone of silence in which the radar cannot track the aircraft. Extend Servo_System's maximum range further than 60 miles in order to lock onto the aircraft when it's above the horizon.

  1. Select the Constraints - Basic page.
  2. Select both Min: and Max: in the Elevation Angle frame.
  3. Set the Min: value to 0 deg.
  4. Set the Max: value to 30 deg.
  5. Select Max: in the Range frame.
  6. Set the value to 150 km.
  7. Click OK to accept your changes and close the Properties Browser.

Inserting an airport surveillance radar

You will insert a Radar object to create an airport surveillance radar. You will model actual airport surveillance radar specifications that are easily available to the public.

  1. Insert a Radar () object using the Insert Default () method.
  2. Select Servo_System () in the Select Object window.
  3. Click OK.
  4. Rename the Radar () object ASR.

Modeling a monostatic radar

You will model a Monostatic radar with a Search/Track mode. This model resembles a common antenna for transmitting and receiving, along with detecting and tracking point targets.

  1. Open ASR's () properties ().
  2. Select the Basic - Definition page.
  3. Note that Radar Systems defaults to Monostatic.
  4. Note that Radar Monostatic Modes defaults to Search Track in the Mode tab.

Defining the waveform

The waveform in your system will use a fixed pulse repetition frequency (PRF), with a PRF of 1000 Hz (approximately). Radar systems often use multiple pulse integration to increase the signal-to-noise ratio. The PRF is the number of pulses of a repeating signal in a specific time unit. After producing a brief transmission pulse, the transmitter is turned off in order for the receiver to hear the reflections of that signal off of targets.

  1. Note the Waveform is set to Fixed PRF in the Waveform sub-tab.
  2. Note the default PRF value of 0.001 MHz (1000 Hz) in the Pulse Definition sub-tab.

Defining the pulse width

Pulse width is the width of the transmitted pulse (the uncompressed RF bandwidth is the inverse of the pulse width). Set the pulse width to one microsecond.

  1. Click the units () drop down next to Pulse Width.
  2. Select usec.
  3. Set the Pulse Width value to 1 usec.
  4. Click Apply.

Defining the antenna pattern

You can model the antenna using the cosine squared aperture rectangular antenna pattern. The antenna transmit frequency for this radar is between 2.7-2.9 GHz.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Models Component Selector ().
  4. Select the Cosine Squared Aperture Rectangular Antenna Model in the Select Component window.
  5. Click OK to close the Select Component window.

Setting the Cosine Squared Aperture Rectangular Antenna Model's properties

  1. Select Use Beamwidth.
  2. Set the following:
    3. Option Value
    X Dim Beamwidth: 5 deg
    Y Dim Beamwidth: 1.4 deg
    Design Frequency: 2.8 GHz
    Main-lobe Gain: (if required, turn off Computed) 34 dB
    Efficiency: 55 %
  3. Click Apply.

Defining the radar transmitter

The transmitter has a frequency range of 2.7-2.9 GHz and a peak power of 25 kW.

  1. Select the Transmitter tab.
  2. Select Frequency in the Specs sub-tab.
  3. Set the Frequency value to 2.8 GHz.
  4. Set the Power: value to 25 kW.
  5. Click OK to accept your changes and close the Properties Browser.

Computing the probability of detection

You will base the probability of detection (Pdet) on a value of 0.800000 or higher with one as the highest value.

  1. Right-click on ASR () in the Object Browser.
  2. Select Access... ().
  3. Select DA_40 () in the Access Tool's Associated Objects list.
  4. Click Compute.

Generating a Radar SearchTrack report

Now that you calculated Access between ASR and DA_40, you will generate a Radar SearchTrack report.

  1. Click Report & Graph Manager... under the Reports frame.
  2. Expand () the Installed Styles list if necessary when the Report & Graph Manager opens.
  3. Select the Radar SearchTrack report ().
  4. Click Generate...

SearchTrack integrated probability of detection

Look at S/T Integrated Pdet in the report. S/T Integrated PDet uses multiple pulses.

  1. Look at the first line in the report.
  2. Locate the S/T Integrated Pdet column. Pulse integration improves the ability of the radar to detect targets by combining the returns from multiple pulses which you can see in the S/T Pulses Integrated column.
  3. Notice that overall tracking is good. You can track the trainer aircraft for approximately 14 minutes.
  4. Close the report, the Report & Graph Manager, and the Access tool when finished.

Cleaning up your scenario

Next, you will determine communications between the trainer aircraft and air traffic controllers at Pueblo Memorial Airport. Turn off all 3D Graphic visuals for the RCS and the radar servo system.

  1. Open DA_40's () properties ().
  2. Select the 3D Graphics - Radar Cross Section page.
  3. Clear Show Volume in the Volume Graphics frame.
  4. Click OK to accept your change and to close the Properties Browser.
  5. Clear the Servo_System () check box in the Object Browser.

Ansys HFSS Far Field Data (.ffd) files

You can define a Far Field Incident Wave Source as a plain text data file with a .ffd suffix. The source can be dependent on the frequency. You will use a nominal frequency dependent Far Field Data file (.ffd) that is provided for your analysis. This .ffd file simulates a nominal blade antenna that has a design frequency of 1.2 GHz and was designed and created using Ansys HFSS.

  1. Open Windows File Explorer.
  2. Browse to your scenario folder (e.g. C:\Users\username\Documents\STK 12\ STK_and_HFSS).
  3. Right-click on Blade_Antenna.ffd.
  4. Select Open With.
  5. Select Notepad in the Apps list.
  6. Compare your .ffd file with the following format. (For frequency-dependent far field links, the data is supplied in blocks. The syntax for a frequency- dependent far field uses this format.)

    7. ThetaStart ThetaStop ThetaNumPoints

    PhiStart PhiStop PhiNumPoints

    Frequencies NumFrequencies

    Frequency FrequencyValue

    E_theta_real E_theta_imag E_phi_real E_phi_imag

    E_theta_real E_theta_imag E_phi_real E_phi_imag

    E_theta_real E_theta_imag E_phi_real E_phi_imag

    … repeat for all theta and phi sweep points

    Frequency FrequencyValue

    E_theta_real E_theta_imag E_phi_real E_phi_imag

    E_theta_real E_theta_imag E_phi_real E_phi_imag

    E_theta_real E_theta_imag E_phi_real E_phi_imag

  7. Close the Blade_Antenna.ffd file and Windows File Explorer.

Building your aircraft receiver

You will attach a Receiver object to your trainer aircraft.

  1. Insert a Receiver () object using the Insert Default () method.
  2. Select DA_40 () in the Select Object window.
  3. Click OK.
  4. Rename the Receiver () object Acft_Rx.

Using a complex receiver

You need to use a complex receiver model so that you can use the Ansys *.ffd formatted antenna pattern.

  1. Open Acft_Rx's () properties ().
  2. Select the Basic - Definition page.
  3. Click the Receiver Models Component Selector ().
  4. Select Complex Receiver Model in the Select Component window.
  5. Click OK to close the Select Component window.
  6. Click Apply.

Antenna model

You will change your antenna model to the ANSYS .ffd Format.

  1. Select the Antenna tab.
  2. Select the Model Specs sub-tab.
  3. Click the Antenna Models Component Selector ().
  4. Select ANSYS .ffd Format in the Select Component window.
  5. Click OK to close the Select Component window.

Importing the Blade_Antenna.ffd file

You will import the Blade_Antenna.ffd file that is provided for your analysis.

  1. Click the External Filename: ellipsis ().
  2. Click STK User.
  3. Select your scenario folder.
  4. Click Open.
  5. Select Blade_Antenna.ffd.
  6. Click Open.
  7. Change the Design Frequency: value to 1.2 GHz.
  8. Click Apply to accept your changes and keep the Properties Browser open.

Viewing the antenna pattern in the 3D Graphics Window

You can view the Receiver object's antenna pattern in the 3D Graphics window.

  1. Select the 3D Graphics - Attributes page.
  2. Select Show Volume in the Volume Graphics frame.
  3. Set the following:
    4. Option Value
    Show as wireframe on
    Gain Scale (per dB): 2 m
    Minimum Displayed Gain: -20 dB
    Set azimuth and elevation resolution together on
    Azimuth - Resolution: 0.5 deg
  4. Click OK to accept your changes and close the Properties Browser.
  5. Right-click on DA_40 in the Object Browser.
  6. Select Zoom To.
  7. Bring the 3D Graphics window to the front.
  8. Use your mouse to get a good view of the aircraft and the receiver antenna pattern.

3D Graphics Antenna Pattern

Inserting the Pueblo Memorial Airport Transmitter

You can insert a Transmitter object at IFS_Pueblo.

  1. Insert a Transmitter () object using the Insert Default () method.
  2. Select IFS_Pueblo () in the Select Object window.
  3. Click OK.
  4. Rename the Transmitter () object Pueblo_Tx.

Using the default simple transmitter model

A simple transmitter model uses an isotropic antenna.

  1. Open Pueblo_Tx's () properties ().
  2. Select the Basic - Definition page.
  3. Set the following:
    4. Option Value
    Frequency: 1.2 GHz
    Data Rate: 1 Mb/sec
  4. Click OK to accept your changes and close the Properties Browser.

Computing carrier to noise ratio (C/N)

You are determining an effective carrier to noise ratio (C/N) focusing on voice communications.

  1. Right-click Acft_Rx () in the Object Browser.
  2. Select Access... ().
  3. Expand () IFS_Pueblo () in the Access Tool's associated objects list.
  4. Select Pueblo_Tx ().
  5. Click Compute.

Using a Link Budget to finish the mission

Based on the receiver's capabilities, you want a C/N of 15 dB or higher.

  1. Click Link Budget... in the Reports frame.
  2. Locate the C/N (dB) column in the Link Budget report.

You have effective voice communications between the aircraft and the air traffic controller for approximately 24 minutes.

Saving your work

  1. Close any properties, reports, and the Access Tool.
  2. Save () your work.

Conclusion

In this lesson, you focused on analyzing an aircraft RCS using Ansys HFSS .csv files and analyzing a link budget using an Ansys HFSS .ffd blade antenna. You applied this analysis to determine how the ASR system can track the small aircraft and when air traffic controllers can communicate with the aircrew.

If you want to know more about radar and communication design, you can learn more in the Level 1 STK training lessons. Also, you can learn more online about Ansys HFSS.

You can find many videos on this subject by going to https://www.agi.com/. In the upper right hand corner of the web page, click the Search icon and search "HFSS" in the Search field.