The applet allows the three most common amplitude comparison DF algorithms to be compared under realistic conditions. Example patterns are included, but there is a facility for the user to input own antenna patterns for evaluation.
The Number of Ports is selectable over the range 4 to 24.
The model is based on a wideband detector-video receivers in the DF channels with no RF amplification. Log-video amplification is assumed for amplitude ratio and quadratic fit DF algorithms, but a square-rooting video amplifier is modeled for the arc-tangent algorithm. All video compression amplifiers are modeled with a successive-limiting chain with an equivalent input RF dynamic range to the detector of −40 to 0 dBm.
The detector tangential signal sensitivity TSS can be varied by adjusting the noise level scrollbar. (Note TSS = −40dBm is equivalent to an input RF noise level of −44dBm).
Video SNR performance is displayed with other key data on the main display. Compression amplifier error ripple performance (typically <1 dB peak-to-peak for a successive-limiting log-video approximation) can be input as an adjustable parameter.
The signal power level can be adjusted to illustrate the effect of low-level thresholds and high-level limiting effects on DF performance.
Adjusting the port gain error parameter demonstrates the effect of port gain imbalances. This chooses a random set of port gain offsets within the peak-to-peak decibel range set. Values chosen for each port are indicated at the bottom of the display with the antenna pointing directions. The random gain offsets are updated each time this scrollbar is modified or when the Number of Ports is changed, but not when other parameters or examples are selected.
Antenna element boresight gain is referred to 0 dBm.
DF port signals are quantized using the ADC bits scrollbar and the influence on DF performance is viewed by adjusting this entry.
Should the antenna patterns squint, which often occurs in practice Adjust Mean offsets can be input and used for calibration purposes. It is usual to adjust the value to equalize the magnitude of vertical and horizontal polarization squint offsets.
The Polarization radio buttons select between vertical and horizontally polarized antenna pattern examples loaded.
Drop-down menu example antenna patterns include a typical broad band Flat Spiral antenna with representative patterns at low (lf), mid-range (mf) and high frequency (hf) parts of the band. In addition, an ideal Gaussian-shaped pattern is included to investigate non-pattern impementation errors.
There is a Test field in the antenna drop-down menu for viewing user own data. User data is entered via the data console (Control+V) and activating the Load Test Data button. A loadable example file is Testfile. This can either be edited once opened or used as a data formatting guide to the load file specification.
The main display shows three coloured error plots for the three DF algorithms with summary analyses. Each algorithm is displayed separately by means of the Plot radio buttons at the bottom of the display area.
The vertical error axis automatically scales and adjusts to the data. The effects of noise, quantization, DLVA ripple, port gain errors, signal amplitude, and noise level are readily apparent.
Antenna pointing directions are indicated relative to the azimuth axis by the red V markers at the lower edge of the display.
The Error Mode button Fourier analyzes the error plots and prints the mode results to the Data Console.
Mouse movement in the azimuth-error space displays plotted data values with respect to the x-axis, azimuth position.

User Notes:
The example patterns are optimized for a six-port system, whilst the Gaussian pattern example adjusts its beamwidth optimally with the number of ports selected.
The display rescales as adjustments are made, but the error data summary displayed gives clearer evidence of the error magnitudes.
Limiting the system dynamic range to that of a single video DLVA enables the DF accuracy to be explored at the DLVA limits.
The system sensitivity is improved with RF amplification and the dynamic range extended by incorporating RF amplification and further DLVAs.