The second is only claiming 0.2 millirad accuracy for the tracking, the initial error is +/- 2.5° (that’s the radar beamwidth) but of course it will be reduced by further scanning and filtering. But that’s true of the signals received by a RWR as well.
How can you applied Monopulse or CROSCO to a RWR?
In an AESA radar, signals from all the elements are summed and then processed. Because the signals emitted by all elements are coherent (all the same signal with the same phase shifts perofrmed in emission and reception), this summing results in a much bigger signal than what each individual element sees (e.g. for a linear array of N elements, you multiply the gain by N²).
Coherent wave mean the signal are at the same frequency and same phase, but ESA radar rely on destructive/instructive interference to steer their beam, so there must be a phase difference between elements
Number of elements in the phase measurement context will not significantly improve accuracy overall. It will only result in averaging the same incertitude level per elements over a greater number. By virtue of statistical distribution it could potentially give a slightly better average compared to averaging on a lesser count. In no way , this would be any significant in magnitude.
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Increase number of elements will increase AoA accuracy because it will reduce phase ambiguity
The phase interferometry method yields accurate AoA calculations; however, when antenna separation is greater than λ/2 , the phase difference can be greater than π. Interferometers can only calculate phase differences between −π and π, allowing for multiple answers, or ambiguities, when calculating the AoA. Additional techniques to resolve ambiguities are needed in order to make this technology viable for direction finding.The AoA calculation is valid so long as d, the distance from the emitter to the midpoint between the antennas, is much larger than s
The greatest technical difficulty in implementing the phase interferometry method of direction finding is resolving ambiguities. Phase interferometers can only measure phase differences between −π and π. Phase differences outside of this range result in ambiguous solutions and, without additional information, the true AoA cannot be determined. The simplest way to remove ambiguity is to place the interferometer’s two antennas less than λ/2 apart; however, this cannot be used for our application. For a 12 GHz signal, the maximum X band frequency, half of the wavelength is 1.25 cm. Placing the antennas this close together would require the antennas to be less than 1.25 cm wide in order to not physically overlap one another. Using antennas this small would result in a small effective aperture and poor signal gain. Additionally, when the separation between the antennas is small, the phase difference becomes more susceptible to noise and the measurement loses accuracy. Combining amplitude comparison and phase interferometry techniques provides another method of solving ambiguities with two antennas. The amplitude comparison provides a rough, but unambiguous angle of arrival, which can be used to determine which of the several ambiguous angles produced by phase intereferometry is the true AoA. The amplitude method can be accomplished with directional antennas, or by placing an asymmetric gain medium placed between two omnidirectional antennas. The scattering box reduces the amplitude of the received signals by varying amounts dependent upon the incident angle. Asymmetric boxes allow unique determination of every AoA. The scattering box method allows for 360◦ field of view (Zhou et al., 2011). Due to the time constraints of the project we focused on solving the ambiguities with only the phase interferometry method rather than combining the phase interferometery and amplitude comparison methods.The problem of ambiguity can also be mitigated by moving from two antennas to three antennas. The antennas are placed in a line with differing spacing as shown in Figure 18.
The three antennas are treated as two pairs; the short baseline of antenna 1 and antenna 2 and the long baseline of antennas 1 and 3. Adding the third antenna helps mitigate some of the issues with placing smaller antennas half of a wavelength apart. The system maintains its overall accuracy by measuring the angle of arrival based on antennas 1 and 3, which are far enough apart to be resistant to noise, after ambiguities are removed by antennas 1 and 2. In cases where the antennas cannot be placed half a wavelength apart using three antennas still helps remove ambiguities. The phase difference can now be calculated between the first and second and first and third antennas giving two sets of ambiguous results. Comparing these results reduces the ambiguities to only those angles that appear among the possible angles for both pairs of antennas. This method is further improved by taking the geometry of the antennas into account. The maximum number of full phase changes that can occur between a pair of antennas, and therefore the number of ambiguities, n is shown in Equation 27
where s is the distance between the antennas, λ is the minimum wavelength of the signal and θmax is the maximum angle of arrival for the system
Technically speaking if you have 2 receiver on the wing tips , and you keeping yaw left and right , you can have that kind of Doppler shift different , however, i can own see this method working again a stationary emitters , because if you known the emitter is stationary , you know your own speed and you know your yaw rate then technically speaking you will know how much Doppler shift will be induced due to motion of each wing tip.
You can create different Doppler shift between 2 sensors in that case but you wont be able to computes the range because both sensors are in the same angular direction in respect to the radar , FDOA need angular seperation to estimate transmitter location.
What are the numbers? 9.47 m2 and 8.12 m2 – front area. Diameter = 2 * √ (9.47 m2 : π)
I know you mean frontal area, but i ask where do they come from?
Your drawing seem to mis noticeable bump on T-50
it is not fake, but i won’t give you his cell phone so as you can check. He is more active on tweeter. BTW he useparcimonuously FB. Wouldn’t change the articles on defesanet btw.
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