Talk:Pulse-Doppler radar

message: I performed a major rewrite to describe most of the topic involving Pulse-Doppler radar. Nanoatzin (talk) 10:46, 30 January 2011 (UTC)
thread_title:  Major rewrite 

message: It is a common misconconseption that PW-"doppler" radar uses the doppler effect to measure object velocities. The doppler effect can only be used to measure average velocity across the entire beam, using continous-wave "pulses". PW-doppler instead measures the phase-shift between succesive pulses to determine radial velocities. Doppler_radar#Doppler_radar_as_weather_radar already mentions this. --Fredrik Orderud 01:18, 30 March 2006 (UTC)
thread_title:  "Doppler" incorrect 

message: I've taken the liberty of replacing the old content of this article with the old content of Pulse-doppler. This has been done because both articles discussed exactly the same subject, but the old Pulse-doppler radar was of very low quality, containing mostly vague and noninformative information. --Fredrik Orderud 21:05, 31 March 2006 (UTC)
thread_title:  Page move/content replacement notice 

message: The current content might be a good start, but it is vague on the theory, and does not provide much insight into the underlying principles of Pulse-"doppler" radars. Some suggestions for improvements might include:
* Clearify that the "intermediate frequency" used, is simply a complex demodulated and downsampled variant of the received RF-signal.
* Clearify that the "velocity ambiguity" problem is an aliasing problem, encountered when the phase-shift caused by radial object velocity exceeds pi/2 radians between succesive pulses.
* Move all "AWACS" specifics/examples into a separate examples-section.
--Fredrik Orderud 21:20, 31 March 2006 (UTC)
replies: text: I've now rewritten most of the article in an attempt to clearify the underlying principles, as well as adding relevant details. The article does, however, still need some figures to illustrate how target movement leads to translation of the incomming RF-signal, which in turn leads to a phase-shift in the IQ-data, which finally is interpreted as target motion. --Fredrik Orderud 00:06, 1 April 2006 (UTC)
replies: text:  I've included coverage of most of the theory of operation for medium PRF pulse-Doppler RADAR. It might be nice to include an update that describes how pulse-Doppler modifies the RADAR range equation. 29 January, 2011 Nanoatzin (talk) 12:14, 29 January 2011 (UTC)
thread_title:  This article really needs some work! 

message: It's "Pulse-Doppler." Doppler radars like CW and FM are not pulsed.
: Some CW is pulsed to eliminate bleed-over between the transmit antenna and the receive antenna. This is called interrupted CW. Bleed-over from the transmitter into the receiver causes saturation, and that degrades range performance. Shutting off the transmitter during receiver sampling period eliminates saturation. Pure CW that is not pulsed requires an active canceler to null the bleed-over signal. Interrupted-CW and pure-CW do not attempt to resolve range by pulsing the transmitter so CW only takes one set of samples to produce a single spectrum whether or not the transmitter is pulsed. 
: Pulse-Dopper uses multiple range samples to produce multiple spectra for multiple sampling intervals between transmit pulses. This allows a pulse-Doppler RADAR to resolve range. This is very different from just turning the transmitter on and off rapidly to avoid receiver saturation. 
: Interrupted CW is not pulse-Doppler and pulse-Doppler is not interrupted-CW. Different kinds of RADAR.Nanoatzin (talk) 15:08, 29 January 2011 (UTC)
thread_title:  Doppler Shmoppler 

message: While pulse Doppler radar works on phase shift an CW/FM work Doppler effect, both type of radars are called Doppler. Therefore it would be best to merge both article and explain completely the concepts. Pierre cb 14:02, 4 November 2006 (UTC)
replies: text: Good luck with that merge plan. There are some cosmetic similarities between the names but the pulse-Doppler process used to identify true target range with intermediate PRF is completely different from every other type of RADAR. The RADAR equation for predicted detection range is not even the same. Merger would confuse readers that are not already familiar with RADAR.Nanoatzin (talk) 13:35, 29 January 2011 (UTC)
thread_title:  Merge with [[Doppler radar]] 

message: I agree that range resolution, conceptually, is related to the spacing of time samples, but fundamentally I don't think it has anything to do with the PRF. According to this, if you have a really low PRF, then your range resolution increases (worsens)? But that's totally missing the point. You can have a low PRF but also have a really short pulse (low duty cycle on the radar transmitter). The short pulse is ultimately what determines range resolution, not the number of pulses you sample. You can have a really large number of time (range) samples, but if you're using long pulses, then returns from objects that are closer together than cT/2 are just going to smear together. You can't resolve them. Radar range resolution is fundamentally related to a short pulse, T, with range resolution equal to cT/2. You can use a short pulse in a high-PRF radar or a low-PRF radar.
Furthermore, almost any pulse Doppler radar is also going to be performing pulse compression (time compression) with a matched filter so that you can use longer pulses to get higher peak power while still maintaining fine range resolution. After pulse compression, the sinc^2 profile has a width 1/B where B is the bandwidth of, for example, a linear FM chirp pulse. When doing pulse compression, range resolution is now defined by c/2B.
For velocity resolution, it looks like the equation shown is just taking the filter size from a "filter bank" and converting that to a velocity using the Doppler equation. It's almost correct, but is not described well, nor is it related to the important aspects of pulse Doppler. After the FFT operation of pulse Doppler processing, you get a sin(Nx)/sin(x) peak in Doppler frequency with a width of PRF/N, where N is usually the number of pulses in your coherent processing interval (CPI), but sometimes can be larger if you zero-pad the FFT to estimate finer Doppler resolution. To convert to velocity, this equation listed is missing a factor of two. V_D = f_D \lambda / 2. So your velocity resolution is \frac{f_c PRF}{2 c N}. 
Willkeim (talk) 12:04, 14 November 2015 (UTC)
thread_title:  Range and velocity resolution equations seem incorrect 

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thread_title:  External links modified 

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thread_title:  External links modified (January 2018) 

message: The recent edit made by Cyfal to change 'lock criteria' to 'lock criterion' is grammatically correct, but doesn't appear to accord with common usage on the subject.  The few links that I've found appear to use 'lock criteria' as per the original text and the linked reference within the section provides a formula to determine the 'Lock criteria'.  As it stands, the term would still be wrong since that formula only seems to be based on that single calculation.  However, I'm wondering if that formula may in fact be an over simplification of what goes on in practical systems and in fact there may be several criteria and that any or all have to be satisfied.
My experience of Pulse-Doppler radar dates back to the early 70s, so I do not feel qualified to do anything more than ask the question.  I do however feel that the plural version should be used if that is in common usage in the Pulse-Doppler radar community - even if it is grammatically incorrect.
Anyone able to clarify this?  Terry C (talk) 09:22, 17 October 2021 (UTC)
thread_title:  Lock criterion or lock criteria?