Radiolocation from born to modern times

1. Radiolocation from born to modern times Contents Scientific-technical basic of radiolocation A magnetron A klystron The lined type layout system Radar impulse system The creation of the modern radar system The Primary Surveillance Radar (PSR) and Secondary Surveillance Radar (SSR) Display Radar performance Phase array antennas

2. Radiolocating is the process of finding the location of something through the use of radio waves. It is similar to radionavigation, but radiolocation usually refers to passively finding a distant object rather than actively one's own position. Both are types of radiodetermination. Radiolocation is also used in Real Time Locating Systems (RTLS) for tracking valuable assets.

3. Properties of radiowaves for identification different objects was known in the end of XIX-beginning XX century, but the condition of the technical development of that time did not allow us to realize this ideas in equipment, suitable for practical use.Intensive growth of military aviation was effective push for the developing radiolocational methods identification of air target. Aircrafts of enemy were to have been earlier detect and on a large distance from the protection objects. • Invention of special electrovacuum devices, magnetron and klystron, determined rapid advancement of very-high frequency technology.

4. A magnetron • Magnetrons function as self-excited microwave oscillators. Crossed electron and magnetic fields are used in the magnetron to produce the high-power output required in radar equipment. These multicavity devices may be used in radar transmitters as either pulsed or cw oscillators at frequencies ranging from approximately 600 to 30,000 megahertz. The relatively simple construction has the disadvantage, that the Magnetron usually can work only on a constructively fixed frequency. • Physical construction of a magnetron The magnetron is classed as a diode because it has no grid. The anode of a magnetron is fabricated into a cylindrical solid copper block. The cathode and filament are at the center of the tube and are supported by the filament(Нить накала) leads. The filament leads are large and rigid enough to keep the cathode and filament structure fixed in position. The cathode is indirectly heated and is constructed of a high-emission material. The 8 up to 20 cylindrical holes around its circumference are resonant cavities. The cavities control the output frequency. A narrow slot runs from each cavity into the central portion of the tube dividing the inner structure into as many segments as there are cavities.

5. Cutaway view of a magnetron Resonant cavities Anode Cathode Filament leads Pickup loop

6. Aklystron • A klystron is a specialized linear-beamvacuum tube (evacuated electron tube). Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyneradar receivers and to produce high-power carrier waves for communications and the driving force for modern particle accelerators. • The pseudo-Greek word klystron comes from the stem form κλυσ- (klys) of a Greek verb referring to the action of waves breaking against a shore, and the end of the word electron.

7. Explanation Klystrons amplify RF signals by converting the kinetic energy in a DC electron beam into radio frequency power. A beam of electrons is produced by a thermionic cathode, and accelerated by high voltage electrodes (typically in the tens of kilovolts). This beam is then passed through an input cavity. RF energy is fed into the input cavity at, or near, its natural frequency to produce a voltage which acts on the electron beam. The electric field causes the electrons to bunch: electrons that pass through during an opposing electric field are accelerated and later electrons are slowed, causing the previously continuous electron beam to form bunches at the input frequency. To reinforce the bunching, a klystron may contain additional "buncher" cavities. The RF current carried by the beam will produce an RF magnetic field, and this will in turn excite a voltage across the gap of subsequent resonant cavities. In the output cavity, the developed RF energy is coupled out. The spent electron beam, with reduced energy, is captured in a collector.

8. Two-cavity klystron amplifier(дворезонаторний)

10. THE REFLEX KLYSTRON

11. The lined type layout system • Transponding and receiving stations were installed these types of machines onto automobiles and places them in a straight line on ground so that the distance between them did not exceed 35 km. This type of alignment of the radio stations formed an electromagnetic wall. When an aircraft crossed this wall, goals came up with the help of interfering direct and reflect signals.

12. Target Directional antenna Generator of impulse Transponder of radar Commutator “transmition – reception” Timer Receiver of radar Indicator Radar impulse system

13. Radar impulse system

14. The creation of the modern radar system • The principle of the mono-impulse radiolocation developed in the 40’s an RLS was used in a very good variant in tracking goals. This was a presicely measuring RLS which assured the accuracy of the tracking angle 0.34’. This result is not easy to overcome even up till today. • In the 40’s there was a fast crossing to bigger frequencies, from high frequencies to very high frequencies and ultra high frequencies. • The specific feature in the development of the radiolocation devices of the 50’s, was the return to low frequencies-high frequencies and ultra high frequencies. At first a powerful clysters energizer was used which changed the architecture of the RLS. That type of energizer assured more power then a magnetron. It allowed the use of more complicated signal in compare to the simple impulse sequence. The use of klystrons allowed a bigger power to the transponding devices in the parallel mode. • In the 50’s the principle of impulses under pressure for sent radio signals was first used. The method of pressuring impulses lies in the use of long impulses with an inner module, which gives the ability to accumulate energy, typical to long impulses, and also to achieve characteristics typical to short pulses. At this period the frequency and phase modulation was used. In the period of approbation of the RLS. • In 50s last century radiolocation systems were began developed on theoretical scientist fundamental. • Scientists developed very impotent theoretical conceptions: statistic theory of reveal, form of signal sound, indeterminate. Idea of matching filter («узгоджувальний фільтр») was used vary wide (its appered in 1943)

15. The Primary Surveillance Radar (PSR) and Secondary Surveillance Radar(SSR) There are two types of radar systems installed each ATC ground station. • The first, called the Primary Surveillance Radar, operates on the principle of sending a narrow beam of energy, which is reflected from the aircraft under surveillance, and measuring its distance by noting the time lapse between the radar pulse transmission and its received echo. • The second, called the Secondary Surveillance Radar, operates on the coded reply sent from the airborne radio beacon Transponder in response to an interrogation sent from the ground station. The PSR and SSR antennas are co-located and scan synchronized, and both radars are used in conjunction to develop the total air traffic situation display on a single CRT radar scope, called the Plan Position Indicator (PPI).

16. Display

17. Radar performance • Pulse Width- the duration of the pulse will be converted into a pulse in distance.  The range of values from the leading edge to the trailing edge will create some uncertainty in the range to the target.    The duration of the pulse also affects the minimum range at which the radar system can detect

18. Radar Frequency It have some affect on how the radar beam propagates.  • At the low frequency extremes, radar beams will refract in the atmosphere and can be caught in "ducts" which result in long ranges.  • At the high extreme, the radar beam will behave much like visible light and travel in very straight lines.   • Very high frequency radar beams will suffer highlosses and are not suitable for long range systems.    Beam-width • For the same antenna size, a low frequency radar will have a larger beam-width than a high frequency one. In order to keep the beam-width constant, a low frequency radar will need a large antenna. Maximum Range(Equation) • A radar receiver can detect a target if the return is of sufficient strength. Let us designate the minimum return signal that can be detected as Smin, which should have units of Watts, W.  The size and ability of a target to reflect radar energy can be summarized into a single term, s, known as the radar cross-section, which has units of m2.  If absolutely all of the incident radar energy on the target were reflected equally in all directions, then the radar cross section would be equal to the target's

19. Over-the-horizon radar (OTH) • OTH (sometimes also beyond the horizon, or BTH), is a design concept for radar systems to allow them to detect targets at very long ranges, typically up to thousands of kilometers. Several OTH radar systems were deployed starting in the 1950s and 60s as part of early warning radar systems. The most common method of constructing an OTH radar is the use of ionospheric reflection. Given certain conditions in the atmosphere, radio signals broadcast up towards the ionosphere will be reflected back towards the ground. After reflection off the atmosphere, a small amount of the signal will reflect off the ground back towards the sky, and a small proportion of that back towards the broadcaster. Only one range of frequencies regularly exhibits this behaviour: the high frequency (HF) or shortwave part of the spectrum from 3 – 30 MHz. The "correct" frequency to use depends on the current conditions of the atmosphere, so systems using ionospheric reflection typically employ real-time monitoring of the reception of backscattered signals to continuously adjust the frequency of the transmitted signal. Given the losses at each reflection, this "backscatter" signal is extremely small. • Since the signal reflected from the ground, or sea, will be very large compared to the signal reflected from a "target", some system needs to be used to distinguish the targets from the background noise. The easiest way to do this is to use the Doppler effect, which uses frequency shift created by moving objects to measure their velocity. By filtering out all the backscatter signal close to the original transmitted frequency, moving targets become visible. This basic concept is used in almost all modern radars, but in the case of OTH systems it becomes considerably more complex due to similar effects introduced by movement of the ionosphere itself. • The resolution of any radar depends on the width of the beam and the range to the target. For example a radar with a 1/2 degree beamwidth and a target at 120 km range will show the target as 1 km wide. Because of the long ranges at which OTH radars are used, the resolution is typically measured in tens of kilometers. This makes the backscatter system almost useless for target engagement, although this sort of accuracy is more than adequate for theearly warning role. In order to achieve a beamwidth of 1/2 degree at HF, an antenna array several kilometers long is required.

20. Phase array antennas Corporate fed phased array