The applet shows the cumulative effect of concentrated clutter along a received pulse to illustrate the temporal and spatial variation of received signal amplitude and phase. These clutter induced signal variations impact the performance of both amplitude and phase comparison DF systems.
Fixed frequency, frequency modulation-on-pulse (FMOP), and phase modulation-on-pulse (PMOP) radar types (drop-down menu selection) are modeled.
The upper display simulates a ground site containing a moveable target surrounded by a position-adjustable 25-point clutter area with adjustable RCS together with moveable radar transmitter and an ESM receiver pair.
The target (green), radar (red) and ESM receiver antenna pair (blue) may be repositioned by mouse-clicking and dragging them to new positions.
The actual spacing and vertical offset from the pair center are also scrollbar adjustable.
Moving, or clicking and dragging, the mouse in this display lists the mouse x-axis and y-axis (range) position, together with the point target relative path delay.
Clicking the mouse in the upper display area selects different random clutter positions and RCS for the 25 components while maintaining a constant distributed RCS.
The RCS of the point target and the size and distributed RCS of the clutter area are scrollbar adjustable.
Clutter returns are displayed in the other three plots; detailed amplitude/time (bottom display), amplitude difference between a pair of linearly spaced antennas/time (center lower display), and the equivalent interferometer-measured instantaneous angle of the phase front normal/time (center top display). Interferometer running azimuth data is also highlighted on the power/azimuth circular display (center right). Note the front-rear interferometer ambiguity as the clutter targets are moved behind the interferometer - rearward targets are mirrored in the forward direction.
The bottom display shows the total received signal (blue curve) from the upper receiver of the pair and the contributions of the point target (green) and the clutter area targets (orange).
The middle display signals are color-coded similarly.
The radar parameters, ERP, frequency, pulse width, antenna beamwidth and antenna pointing direction (line indicator) are adjusted using the scrollbars. 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. The display range is also scrollbar adjustable.
All target and clutter points giving bistatic returns above the ESM threshold level are highlighted in magenta.
Moving or clicking and dragging the mouse in the lower display lists the mouse x-axis (time) position, the corresponding upper receiver signal power, the receiver pair power difference and the indicated azimuth.
Clicking the mouse in any of the lower plots causes the ESM-measured azimuth line to be displayed on the upper plot corresponding to the x-position (sample time) of the mouse. The azimuth is also highlighted by a larger point on the power/azimuth circular display.
Greater pulse return detail is available by increasing the number of display points and or scale magnification.

User Notes:
For fine variation of receiver position and immediate display update, use the Rx Pair y-Offset scrollbar.
The amplitude difference plot can be related to amplitude comparison DF systems to determine the order of DF errors due to clutter.
Note that the perfect interferometer (very accurate phase measurement and no ambiguities; except for the intrinsic front-back ambiguity) is little affected by clutter and although the antenna model does exhibit phase reversals in nulls, it is unaffected as these traverse the aperture (why?). Real interferometer phase measurement systems can however be affected by amplitude unbalance.
With complex modulation radars (FMOP and PMOP, selected using the drop-down menu), 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.
Data saved to the Data Console is the total received signal detected voltage; this can be extracted and loaded in the Fourier Error Analysis Applet to evaluate the clutter amplitude spectrum.
When the radar illuminates the clutter area, note how sensitive the DF measured along the pulse is to vertical position offset.
For detailed examination use the timebase expansion facility.
The applet shows that in seriously cluttered environments, the importance of careful selection of timing along a pulse to optimize the DF measurement accuracy.
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.