How does a radar see an aircraft? In this live 8 GHz experiment, SkyRadar demonstrates radar signatures, RCS measurements and iSAR imaging.
An aircraft does not reflect radar signals equally in every direction. Its wings, fuselage, tail and other structural features contribute differently to the received echo, depending on the angle from which the radar observes it.
These variations form what is commonly called the aircraft's radar signature. By measuring the radar response as the aircraft rotates, we can investigate its angular reflectivity and, with additional signal processing, reconstruct an image of its scattering structure.
In this video, SkyRadar demonstrates the process using a rotating aircraft model, the NextGen 8 GHz Pulse Radar and the FreeScopes iSAR application. The experiment uses real RF measurements rather than simulated radar returns.
Video: A live radar experiment demonstrating the measurement of an aircraft model's angular radar signature, its representation in different coordinate systems and the generation of an inverse synthetic aperture radar (iSAR) image.
The laboratory setup consists of an aircraft model mounted on a motorised rotating platform and a stationary radar measurement system. Two separate information streams are used: one provides the angular position of the aircraft, while the other provides the received radar measurements.
As the aircraft rotates, the radar observes the target from successive aspect angles. The strength and distribution of the reflected signal change because different parts of the aircraft contribute to the radar return.
By correlating the radar measurements with the angular position of the model, FreeScopes can display the resulting radar signature and process the measurements into an iSAR image.
The video presents three different ways of looking at these measurements: a radar signature plotted in decibels, a polar representation of the angular response and a two-dimensional iSAR image.
Although these representations originate from the same experiment, they describe different properties of the measured target.
Radar Cross Section (RCS) describes how strongly an object scatters radar energy back towards a radar, expressed as an equivalent reflecting area. It depends not only on the physical dimensions and shape of the object but also on frequency, polarisation, viewing angle and material properties.
In a calibrated measurement, RCS is commonly expressed in square metres or in decibels relative to one square metre (dBsm). A relative radar signature, by contrast, can show changes in received reflection strength without necessarily representing absolute RCS values.
In our experiment, the aircraft rotates through successive aspect angles. The radar records how the reflected signal varies with orientation, producing an angular scattering signature.
This signature can be displayed as a curve in decibel coordinates or as a polar diagram. The polar representation makes the dependence on the aircraft's orientation particularly visible.
The same data can also be projected into a PPI-style display. However, this is a representation of the angular radar signature, not a conventional surveillance PPI showing the geographical position of a moving aircraft.
These distinctions matter because identical measurement data can appear quite different depending on the selected coordinate system, angular reference and amplitude scale.
A radar signature tells us how the overall radar response changes with viewing angle. Inverse Synthetic Aperture Radar (ISAR, or iSAR) goes further by using measurements acquired from different aspect angles to reconstruct the spatial distribution of radar scattering within the target.
Conventional synthetic aperture radar (SAR) typically exploits movement of the radar platform relative to a scene. In ISAR, relative target motion, including rotation, provides the changing observation geometry required for image formation.
In the SkyRadar experiment, the radar remains stationary while the aircraft model rotates. The changing aspect angle provides the angular diversity needed for image reconstruction.
By processing the collected radar measurements, the iSAR application generates a two-dimensional representation of the target's scattering structure. The resulting heat map indicates regions contributing differently to the radar return.
This is not an optical photograph. It is a radar image reconstructed from electromagnetic measurements. Bright regions correspond to stronger radar scattering contributions under the particular measurement conditions.
The distinction is fundamental: the angular radar signature describes how strongly the target reflects at different orientations, while the iSAR image provides spatial information about the scattering regions responsible for those reflections.
One of the learning objectives of the experiment is understanding how the representation of radar measurements influences their interpretation.
A radar signature plotted against angle in decibels emphasises changes in reflection strength. A polar diagram makes the angular dependence more intuitive, but can give a different visual impression because radial distances represent measured amplitudes.
A PPI-style projection introduces another coordinate convention. The angular zero reference and direction of rotation need to be understood before comparing such displays.
Finally, the iSAR heat map is not simply another visualisation of the same RCS curve. It results from image-processing methods that use the radar measurements acquired over a range of target orientations.
Understanding these differences is relevant to radar engineering, target characterisation and radar-based object recognition.
The experiment also demonstrates how SkyRadar's FreeScopes environment allows users to construct and modify radar processing applications.
Processing and visualisation components are selected from a repository and placed onto a graphical canvas using drag-and-drop operations. Their parameters can then be configured individually.
In the video, the radar signature, polar diagram and iSAR heat map are displayed within the same application environment.
This approach allows trainees to examine different representations of measured radar data without having to develop an entire application from the beginning.
For engineering students, researchers and defence specialists, the objective is not merely to generate an image. It is to understand the relationship between the physical target, the measurement geometry, the received signals and their subsequent processing.
Simulators are useful for explaining radar imaging principles under controlled conditions. Physical experiments add the behaviour of an actual RF measurement chain, including background noise, reflections from the laboratory environment and practical limitations of the measurement setup.
The NextGen radar operates in the 8 GHz frequency range with low transmitted power. The video also deliberately retains the ambient sounds of the laboratory rather than replacing them with a studio narration.
The result is an experimental demonstration in which radar signatures and iSAR images are derived from measured signals rather than generated from an idealised target model.
This creates opportunities to investigate how target geometry, rotation, processing parameters and measurement conditions affect the resulting radar information.
Conventional radar detection establishes whether a target is present and estimates properties such as range, direction or velocity. Radar signature analysis and imaging introduce additional information about the target's scattering characteristics.
These properties are relevant to target classification, recognition and the development of advanced radar processing methods, including AI-assisted interpretation of radar data.
The experiment illustrates a progression from a physical radar reflection to an angular scattering signature and finally to a reconstructed radar image.
The aircraft model rotates. The radar measures its changing reflections. The processing system reconstructs information that cannot be obtained from a single observation angle alone.
Understanding this relationship is an important step towards interpreting what a radar can reveal about an object beyond its presence and position.
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