The applet models the effect of ground clutter in the radar-ESM environment for fixed frequency, frequency modulation-on-pulse (FMOP), and phase modulation-on-pulse (PMOP) radar types (drop-down menu selection). Clutter returns are displayed as a detailed amplitude/timebase plot.
The upper display simulates an area half-filled with a fixed grid of equal (30 dBm²) clutter targets together with a radar transmitter and, an ESM receiver, embedded. Smaller targets are simulated by an equivalent reduction in transmitter power.
Both radar (red square) and ESM (blue square) may be repositioned by mouse-clicking and dragging them to new positions.
There is provision for one mobile clutter target (heavy black square spot), with variable RCS, also to be similarly repositioned.
The radar parameters are adjusted using the scrollbars. For added realism, the radar antenna pattern is a modified sin(x)/x characteristic with first sidelobes of –24 dB and a minimum sidelobe level of –60 dB. Radar antenna pointing direction (red sector indicator) is rotated using the relevant scrollbar and all main beam and sidelobe targets giving bistatic returns above the ESM threshold level are highlighted in magenta.
The display range is scrollbar adjustable.
The lower displays shows the total ESM received power (blue) as a function of time, referenced to the direct path signal. The first black pulse is the received signal from the direct path (antenna sidelobe signal when the radar is not pointed at the ESM, lowest level = –60 dB). The second black pulse is the signal reflected from the black-spot mobile target.
Clicking and dragging the mouse in the lower display lists the mouse x-axis position and the data amplitude.
The display plot is magnified referenced to the central Time Strobe position to enable observation of received signal pulse detail. Greater pulse return detail is available by increasing the number of display points. The Time Strobe window range T is controlled by the Timebase magnification Scrollbar and the Strobe is positioned relative to the window extent by the Time Strobe Scrollbar. Strobe Power lists the ESM received power at the strobe instant.
All data values may be modified and the display updated using scrollbars and drop-down menus.

User Notes:
At any ESM sensitivity, increasing the display range shows that moderate targets at quite large ranges are detectable. Strictly, this only applies to free-space clear paths (air-to-air or ground-to-air) as horizon diffraction loss is not modeled. Ground-to-ground line-of-site ranges are usually terrain limited, while in the naval case, the horizon is determined by the transmitter/target/receiver heights.
The applet still indicates the regions and extent of clutter likely to have an impact on the ESM anti-radar performance.
Larger or smaller distributed targets are simulated by adjusting either the radar ERP or the ESM sensitivity.
The littoral ESM performance is simulated by moving both radar and ESM positions into the clear (sea) region.
Increasing the ESM sensitivity by a factor of 10 increases the range of significant clutter targets by the square root, whilst allowing targets a factor of up to 10 times smaller to become visible.
Very high sensitivity ESM systems need special techniques to make visible small wanted signals within an extensive clutter signal.
With complex modulation radars (FMOP and PMOP), the clutter return appears more noise-like due to the bistatic returns from multiple or distributed clutter targets overlapping. When these radar types are selected, an extra scrollbar is activated for control over the chirp pulse time-bandwidth product or the rate of random 180^o phase changes per microsecond along the pulse.
For detailed examination of the clutter signal with complex signal modulations, use the Time Strobe scrollbar to select the position, then the Timebase Magnification and/or number of Display Points as required.
RF data can be saved to the Data Console for spectrum analysis of the clutter distorted received signal. The spectrum is displayed using the Fourier Transform Error Analysis applet. For this, selected and copied data from the applet Data Console is pasted in the Error Analysis applet Data Console. Once loaded the spectrum is viewed using the User Data entry in the Data Source drop-down menu. The displayed mode bin-width = 1000/inc/points MHz, where, inc is the Time increment value in the Data Console saved data, and points is the Display Points drop-down menu value selected. The spectrum peak position is determined by the Frequency setting and may be considerably folded due to sub-Nyquist sampling. Spectrum data can be saved to the Data Console and extracted for further analysis as required.