80
votes
Accepted
Will radar/lidar still work when every car is equipped with them?
You'd be surprised.
This is actually topic of ongoing research, and of several PhD dissertations.
The question which radar waveforms and algorithms can be used to mitigate interference is a long-...
- 90.4k
40
votes
How did old WW2-era radars accurately measure time delay and integrate this into an oscilloscope?
The basic PPI (plan position indicator) radar display — the kind that has a bright line that sweeps around a circular screen like the second hand on a clock — works on the principle that ...
- 170k
28
votes
How does LIDAR avoid getting confused in an environment being scanned by hundreds of other LIDAR?
Commercial LIDAR units modulate the light with a very long pseudo-random sequence.
The modulation is primarily to (1) have a modulation for determining distance and (2) to avoid interference with ...
- 1,870
13
votes
Accepted
Does this VCO produce a sine wave or square wave
This VCO outputs a frequency between 5.5 and 6.1 GHz.
It is sort of "implied" that the output signal will be a sinewave because:
a "decent" square wave at that frequency would need a signal ...
- 80.5k
10
votes
How does LIDAR avoid getting confused in an environment being scanned by hundreds of other LIDAR?
Depends on the LIDAR. My experience with it is out of date (over 10 years), but I cannot imagine that the basics have changed that much.
Most will be using a form of lock in to discriminate their ...
- 1,053
10
votes
Accepted
Radar received RF signal phase-shifted by 90 to obtain I/Q signals
What is idea behind this instead of classical way with shifted LO, what affect this produce, any useful link to read about this approach ?
If done perfectly, it really doesn't matter whether the LO ...
- 162k
9
votes
Accepted
What power limitations was chirped radar designed to overcome?
I'm not a radar expert by any means, but I think I understand the general concepts well enough to try to answer your questions.
What specific requirements on the peak and average powers and the ...
- 170k
9
votes
Accepted
Uniform Linear Array (ULA) beamwidth and angular resolution using FFT
Theoretical Derivation
The antenna electric field pattern of array antenna consists of isotropic radiator can be given by
where N is the number of antenna elements
d is the spacing between antenna ...
- 283
9
votes
How did old WW2-era radars accurately measure time delay and integrate this into an oscilloscope?
Did this require vacuum tubes?
A traditional analog scope is essentially a vacuum tube (the CRT) with the timebase sawtooth and signal being applied directly to the horizontal and vertical plates to ...
- 128k
9
votes
Accepted
How does one measure the Fourier components of a signal?
Is the signal split by many narrow band pass filters in paralell? Are these filters RLC circuits? Are there chips that contains many such filters in paralell?
No, these are typically collected as ...
- 90.4k
7
votes
Accepted
In heterodyn receiver circuits, why is the LO not chosen to match the target frequency?
There are receivers made on ICs today that use a mixer with an LO equal to the input frequency. Instead of 'heterodyne', they are called 'homodyne', for obvious reasons.
The big problem with these is ...
- 162k
7
votes
Will radar/lidar still work when every car is equipped with them?
This is a rather old problem in radar engineering, dating from the era of jet aircraft carrying guns and supersonic missiles. This Wikipedia article on Chirp compression gives some clues about how ...
- 71
7
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Will radar/lidar still work when every car is equipped with them?
There are military sonar and radar systems that see the world around them using reflections of "the other guy's" radar / sonar. They existed back in the days of 286 Intel processors... so it can be ...
- 71
7
votes
Can radar/lidar sensors for self-driving cars be designed to ignore deliberate interference?
You'd be surprised.
This is actually topic of ongoing research, several PhD dissertations and a lot of money invested in the auto radar jamming industry. Military researches were made for jamming/...
- 2,546
7
votes
Accepted
Why are many radar antenna arrays not rectangular but rather octagonal÷icosagonal?
There are several reasons for those shapes.
First, the cut off/rounded corners make it easier to fit into the nose of an aircraft. This is true of the phased arrays, both active and passive, that are ...
- 10.3k
7
votes
Accepted
Is it possible to build radar system for drones detection at home?
It will be expensive, since you'll need to hire an experienced RF engineer to design it, make the prototype, then pass the prototype through certification needed to legally operate it. And you'll ...
6
votes
Accepted
What detection method does phased array radar use?
As a question, it's bordering on the 'too broad' mark. However ...
An antenna array with phase-shift available at each element is 'only' a way of electrically steering the antenna. What signal you ...
- 162k
6
votes
Accepted
Why do the Duga-1 dipoles look like an array of birdcages?
This is a cage dipole antenna (or an array of cage dipoles to be exact). It works just like a dipole, but has a wider bandwidth. The thicker the dipole, the wider the bandwidth.
RF does not care if ...
- 8,901
6
votes
Accepted
Feasibility of rat-race as RF mixer without active devices
some sort of active device (sometimes diodes)
This suggests that you deem diodes to be active devices, so presumably a passive device means no diodes. In that case, a structure that's passive will ...
- 162k
5
votes
How did old WW2-era radars accurately measure time delay and integrate this into an oscilloscope?
The SCR-270 radar that was present at Pearl Harbor on December 7, 1941 had the following characteristics:
Transmit Frequency: 105 MHz
Pulse width: 10-25 µsec
Repetition rate: 621 Hz
Power Level:...
- 15.9k
5
votes
How the azimuth of the time base is synchronized with the azimuth of the rotating antenna?
Early radar sets used a pair Selsyn motors to transfer the rotary motion of the antenna platform to a sine-cosine potentiometer.
The terminals of the potentiometer were driven with complementary ...
- 170k
5
votes
Why do the Duga-1 dipoles look like an array of birdcages?
That second image shows a feed where you would expect it. It's a bit hard to see on all of the elements, and it's better to look at the high resolution original image. But they're definitely center ...
- 40.8k
5
votes
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What do you believe was meant by FEA?
"Finite Element Analysis"
Simulations that work over 3D surfaces by breaking everything up into a little triangular section, analyzing each one individually, and piecing everything together
- 55.3k
4
votes
Radar Snr improvement
There are very strong limits on what you can do to improve SNR. After all, your received signal consists of a low level reflected signal, and a noise signal in the same frequency range, that cannot be ...
- 162k
4
votes
Help reverse engineering RCWL-0516 microwave proximity detector module
R-CDS (parallel to R15) is part of the voltage divider for the photo resistor (LDR).
When it's bright, the LDR pulls the CDS line below 0.7V, disabling the trigger output (pin 9, VC). Thus, the ...
- 41
4
votes
Accepted
ADC and DSP Requirements for FMCW Radar
FMCW radar is a bit tricky, and your "IF frequency is up to 1 MHz" is a bit vague.
In an FMCW system, a target returns a signal that is delayed based on its range. The frequency difference between ...
- 170k
4
votes
How did old WW2-era radars accurately measure time delay and integrate this into an oscilloscope?
Consider the 12SK7 vacuum tube: gm of 0.002, plate resistance of 0.8MegOhms, grid capacitance of 6pF, output(plate) capacitance of 7pF.
Predict bandwidth by gm/C. Assume nodal C is 6p + 7p + 7p ...
- 33.8k
4
votes
Accepted
Radars and high frequency relation
To a first order approximation, you get directivity by making the aerials large with respect to the wavelength.
It is much easier to make a moderately directive antenna at say 24GHz then it is at ...
- 17.4k
Only top scored, non community-wiki answers of a minimum length are eligible