29B6: Russian FMOP OTH Radar "Kontainer"

Russian Air and Space Defense Forces began deployment of a network of 29B6 over-the-horizon (OTH) radars, code-named "Kontainer" in the early 2013. The Russian 29B6 radar is generally less wide than PLUTO, typically around 14 kHz width.

observed on 19475.0 Khz
bandwidth about 14Khz,
modulation: FMOP (Frequency Modulation On Pulse)
sweep-rate: 50 sps

Both the British PLUTO and the Russian 29B6 most often use the sweeprate of 50 sps .This yields a maximum unambiguous range (since neither radar encodes the sweeps) of 3000 km.  The 29B6 uses FMOP (Frequency Modulation On Pulse) while PLUTO uses FMCW (Frequency Modulated Continuous Wave): while they sound somewhat similar they are slightly different, with the 29B6 having a slightly “rougher” sound than PLUTO,  moreover Russian 29B6 can be harder to visually or aurally define the edges of, so it could be reportsed with a wider width than it is actually using.

The first one began "experimental-combat" operations in Kovylkino, Mordovia, on 2 December 2013. The radar is reported to have a range of about 3000 km, which allows it to detect aircraft over large part of Europe.
 
video clip introducing the new 29B6 OTH radar installation:
http://tvzvezda.ru/news/forces/content/201312031334-4e99.htm
 

The Kolkino radar station, using the first modernized 29B6 radar, is able to track aerial targets flying as far aways as Denmark. Earlier the radar had a research role only, and even if full operational capability is expected within 2 years, the new system is already keeping an eye on what flies west of the Russian border. Another 29B6 radar should be installed in the far eastern Russian territories, achieving operational status in 2018.

The radar is made of 150 antenna masts, data transmission systems, transmitters and receivers, power station and control building. The peculiarity of the system is that it is able to detect both high altitude targets, such as ICBMs (Inter Continental Ballistic Missiles), as well as low altitude flying air traffic, at very long distances, well beyond the line of sight.
Based on the Russian claims reported by Defence24.pl, any aircraft with a radar cross section comparable to the one of a Cessna light plane would be detected by the new radar, even if it is flying at low altitude. Even a fighter jet taking-off in the Netherlands could be seen by the new surveillance station!

http://www.russiadefence.net/t2547p105-russian-radar-systems

http://www.defense-aerospace.com/articles-view/release/3/150118/russia-deploys-new-over_the_horizon-radar.html

PLUTO: UK RAF FMCW OTH Radar

The British Royal Airforce is operating the so-named PLUTO OTH Radar in their base in Akrotiri, Cyprus. It is often on 10, 21 and 28 MHz HAM bands with sweeprates of 25 and 50 sweeps/sec, sometimes 12.5 sweeps/sec. 

bandwidth about 20 Khz,
modulation: FMCW (Frequency Modulated Continuous Wave)
sweep-rate: 50 sps

 
 Below, the radar heard on 8070.0 Khz, 20 Khz bandwidth but with a sweep-rate of 25 sps:

OTH radars can detect and track aircraft, missiles in the atmosphere, and even large ships within the coverage fan as long as the objects are at least 500-1000 km from the radar and no more than about 5000 km, with the best coverage in the 1000-3500 km range.
The area covered by such radars is usually a fan extending in a line perpendicular to the transmitter array and as much as 50 degrees to either side, for a total fan width of up to 100 degrees. Although some OTH radars have a much narrower fan (ca 60 degrees), the alignment of the receiver arrays at Agios Nikolaos suggests that this system does have a wide fan. 

PLUTO transmitter SITE, north From Akrotiri (Cyprus)

This image shows approximately what the fan for the Pluto radar might look like, assuming that it is as wide as estimated above. The concentric arcs are at 1000 km intervals and the radiating lines are at 10 degree intervals. As can be seen, the fan covers little or none of Syria, Lebanon, Jordan, and Israel, but provides good coverage of Iraq, Iran, the Gulf States, part of Saudi Arabia, and most of Afghanistan, Pakistan, and the former Soviet Stans, and possible coverage of part of India. The Russian launch areas at Baikonur and Kapustin Yar are probably covered, as is the Persian Gulf and much of the Arabian Sea.

The receiver element, typically one or more long, linear arrays of antennas, is usually somewhat distant from the transmit site, as much as 100 km. In the case of this system, the receivers are likely to be at the other British Sovereign Base Area, Agios Nikolaos. There are three long white rectangular areas visible in the low-res GE imagery of Agios Nikolaos that might be the system's receive arrays.

 

hopping sounder (10Khz bw, 10 sps)

observed on 19845 Khz (cf), hopping its working frequency.

I used first the oscilloscope to get a measure of the distances between two consecutive sweeps:

The sounder is 100 msec delay between the sweeps, so (1000 msec/100 msec) = 10 sweeps per second (or 10 sps). The sweeps can also be observed, and measured, in the frequency domain: as expected, the sweep rate is 10 sps (100 ms distance between two sweeps). Modulation is FMOP.

This signal hops frequencies in a specific manner. It starts moving up the band in various intervals then it goes back and starts again, overlapping Amateur and broadcast shortwave bands.

OTH radar: FMCW principles

Frequency Modulated Continuous Waveform (abbreviated  FMCW) radar differs from pulsed radar in that an electromagnetic signal is continuously transmitted. The frequency of this signal changes over time, generally in a sweep across a set bandwidth. The name chirp is then a signal in which the frequency increases (up-chirp) or decreases (down-chirp) with time. In some sources, the term chirp is used interchangeably with sweep signal, or simply sweep.

A variety of waveforms is possible since the transmitter frequency can slew up and down as follows: sine wave, sawtooth wave, triangle wave and square wave.

A linear chirp waveform; a sinusoidal wave that increases in frequency linearly over time

Spectrogram of a Linear Chirp. The Spectrogram plot demonstrates the linear rate of change in frequency as a function of time, in this case from 0 to 7 kHz repeating every 2.3 seconds. The intensity of the plot is proportional to the energy content in the signal at the indicated frequency and time ( "LinearChirp" by Spyrogumas - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons)

The difference in frequency between the transmitted and received (reflected) signal is determined by mixing the two signals, producing a new signal which can be measured to determine distance or velocity (the received signal is mixed with the emitted signal and due to the delay caused by the time of flight for the reflected signal, there will be a frequency difference that can be detected as a signal in the low frequency range).

FMCW radar is then an indirect method of distance measurement. The transmitted frequency is modulated between two known values,f1 and f2,and the difference between the transmitted signal and the return echo signal,fd, is measured. This difference frequency is directly proportional to the transit time and hence the distance.

The bandwidth of an FMCW radar is the difference between the start and finish frequency of the linear frequency modulation sweep (sweep width). The amplitude of the FMCW signal is constant across the range of frequencies. A wider bandwidth produces narrower difference frequency ranges for each echo on the frequency spectrum. This leads to better range resolution. The sweep width determines the spatial resolution of the radar: sweeps must be shorter than the time it takes for the signal to travel between the target details; otherwise, the sweeps overlap in the receiver.

The sweep repetition frequency (sweep-rate, sps) determines the maximum unambiguous range to the target. The next (non-coded) sweep cannot be sent until the previous sweep has traveled to the target and back. (Coded sweeps can be sent more frequently because coding can be used to associate responses with their corresponding transmitted sweep.)

Short sweeps with a low repetition rate maximize resolution and unambiguous range and high sweep power maximizes the radar’s range in distance. 

Below some measurements of a FMCW OTH-B radar signal, obtained by analyzing the recorderd signal with Signals Analyzer (great software by radioscanner.ru

To approach this kind of transmissions you should run an (at least) 20Khz bandwidth receiver, such an SDR, and record the signal in a .wav file using 48 Khz sample rate value. The analysis is then run off-line, by play-backing the recordered signal.

Synthesized system are not sweeping the frequency continuously, but rather step the frequency with a set of discrete frequency points. Thus, these systems are also called Stepped Frequency Continuous Waveform (abbreviated SFCW) radar. The synthesized signal source assures very precise frequency control, which is important for the accuracy and repeatability of measurements.

phased array antenna

In antenna theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions. Usually, the spatial relationship of the individual antennas also contributes to the directivity of the antenna array.  One common application of this is with a standard multiband television antenna, which has multiple elements coupled together and in radar applications.

 

 

Phased array may be used to point a fixed radiation pattern, or to scan rapidly in azimuth or elevation. Simultaneous electrical scanning in both azimuth and elevation is also possible.

 

"A phased array antenna is composed of lots of radiating elements each with a phase shifter. Beams are formed by shifting the phase of the signal emitted from each radiating element, to provide constructive/destructive interference so as to steer the beams in the desired direction. 

 

The main beam always points in the direction of the increasing phase shift. Well, if the signal to be radiated is delivered through an electronic phase shifter giving a continuous phase shift then the beam direction will be electronically adjustable. However, this cannot be extended unlimitedly. The highest value, which can be achieved for the Field of View (FOV) of a planar phased array antenna is 120° (60° left and 60° right). With the sine theorem the necessary phase moving can be calculated.

 

One of the fundamental difficulties in designing a phased array is that significant portions of the wave power transmitted by one element of the array can be received by the surrounding array antenna elements. This effect, which is known as array mutual coupling, can result in a substantial or total loss of transmitted or received radar signal, depending on the coherent combination of all of the mutual-coupling signals in the array.
The amplitudes and phases of the array mutual-coupling signals depend primarily on the shape of the radiating antenna elements, the spacing between the array elements, and the number of radiating elements. There are as many different design possibilities for phased arrays as there are dozens of different radiating array elements to choose from, and the spacing and number of radiating elements can vary widely, depending on the scanning requirements." [1]

[1] https://www.radartutorial.eu/06.antennas/Phased%20Array%20Antenna.en.html