=Paper=
{{Paper
|id=Vol-3058/paper75
|storemode=property
|title=Analysis Of High Power Ku Band Magnetron Based Radar Transmitter
|pdfUrl=https://ceur-ws.org/Vol-3058/Paper-107.pdf
|volume=Vol-3058
|authors=H S Chahar,Shilpa Jindal
}}
==Analysis Of High Power Ku Band Magnetron Based Radar Transmitter==
https://ceur-ws.org/Vol-3058/Paper-107.pdf
Analysis of High Power Ku Band Magnetron Based Radar
Transmitter
H S Chahar1 and Shilpa Jindal2
1
The Institution of Engineers (India), Kolkata
2
Department of ECE, CCET, Sector 26, Chandigarh
Abstract
The Magnetron is an efficient oscillating microwave device that is used to generate high-
power electromagnetic energy at microwave band in radar technology. A magnetron is
used in various applications due to its compact size, lightweight, low cost, long life and
have so many benefits compared to other cross-field oscillators or liner beam amplifiers.
Magnetron has few limitations also, like frequency instability and thermal variation
effect. Based on the previous literature survey, so many methods are adopted for multi-
cavity tuning, thermal stability, and amplitude and phase control of magnetron. In this
paper, we put focus on the coaxial cavity magnetron transmitter which is commonly used
in modern pulse Doppler and navigational radar technology. The purpose of this analysis
is to present a practical field report on the performance of a Ku band coaxial magnetron
based transmitter by measuring the key parameters especially concerning its tuning
mechanism, HV regulation and output peak power of magnetron with its safety
precaution, common faults, and their remedial action and maintenance of magnetron
transmitter by knowing the transmitter behavior with a brief on operation and design
concept of the magnetron and the radar transmitter.
Keywords 1
Magnetron, Microwave, Tuning, Radar, Transmitter, Regulation
1. Introduction
As the radar history, the invention of the magnetron transmitter was introduced in the late
1930s that can operate at the higher frequencies called microwaves. In the era of microwave
technology, there are various microwave devices for oscillating as well as amplifying the microwave
signal like various solid states MW transistors and other cross-field devices. These cross-field devices
were followed by linear beam tubes e.g. Klystron, TWT, etc. The klystron amplifier is capable to
amplify the high power level used in radar (several KW average powers) with good efficiency and
stability. The main disadvantages of the klystron are high power consumption and narrow bandwidth.
The traveling-wave tube (TWT) is a new advancement followed by klystron in the field of microwave
amplification systems. It has a better combination of wide bandwidth, power output, and gain at a
weak signal. But, the peak power levels are increased with decrease bandwidth. TWT has the
limitations of its cost, weight & size for high output power, complexity in construction & installation,
high power consumption, difficulty to repair & maintenance. Solis state transmitters, such as
the transistor are attractive due to their long life, ease of maintenance, and relatively wide bandwidth.
But, have some limitations like as accomplished only for relatively low power in short-range radar
application and no suited for high power long range at short pulses (micro sec) by an individual solid
International Conference on Emerging Technologies: AI, IoT, and CPS for Science & Technology Applications, September 06–07, 2021,
NITTTR Chandigarh, India
EMAIL: harikesh01011981@gmail.com(A. 1); er_shilpajindal@yahoo.com(A. 2).
ORCID: 0000-0002-7201-890X (A. 1); 0000-0001-5736-3636(A. 2).
©2021 Copyright for this paper by its authors.
Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
CEUR Workshop Proceedings (CEUR-WS.org)
stage. Short pulses are suited for radar operation because signal processing (pulse compression) is
required to achieve the desired range resolution.
Each kind of transmitter has its advantages as well as its limitations. In practical, a magnetron
transmitter is (efficiency is up to 70%), compact design, low cost, size & weight, long life, easy to
maintain, and suitable for short pulse-Doppler radar which is capable to detect the moving target in
presence of noise. Hence, such a type of radar-based transmitter is the backbone of radar systems
especially in pulse-Doppler radar for military radar applications and navigational equipment.
1.1The Area of analysis
A radar transmitter using a microwave oscillating device like magnetron requires a high-
power dc source up to several KV to generate RF output. The HV power source is a major
consideration part of a transmitter to obtain satisfactory performance. The pulse radar transmitter
produces the short duration high-power RF pulses of energy that radiates into space through the
antenna which calls for a suitable energy storage capacitor and inductors operating under high altitude
and humidity conditions. Hence, there is a vital need for specific high voltage engineering during the
design & construction of it to prevent the unusual loss and partial discharge effect.
The major attractive subunits of a magnetron transmitter under analysis are the HV unit with
its regulation used to overcome the pushing effect resulting in increasing the frequency stability of
magnetron and servo tuning mechanism performance with a deviation of its every spot of freq. LC
filter, HV transformer, rectifier and divider, protection assembly, PFN, fast-switching devices like
thyratron and magnetron are the other crucial part of the transmitter. In general, a liquid dielectric is
used for compact design HV transformer and PFN for a long time considering its ability to remove
heat by convection, good dielectric strength, and its insulation restoration properties to reducing the
EMI/EMC factor.
1.2 Industrial significant:
A magnetron is generally used in various MW applications mostly in radar sys to spot the
enemy target, submarine periscope, and ship in the dark used by military and naval forces of many
counties around the world. A magnetron is also used for home appliances such as microwave ovens,
for lighting such as sulfur lamps, in medical with MW radiation such as LINAC, and the industry for
lighting and heating purpose. The growing market of communication, medical and smart home
appliances are driving the growth of the global magnetron market significantly. Magnetron market
can be categories into two broad categories. First, by end-user type, second is by type. End-user types
can be categorized as telecom industry, aerospace industry, and defense industry, electronic and
mechanical industry. By type, the global magnetron market can be segmented into negative resistance,
cyclotron frequency, and cavity magnetrons.
1.3 Contribution
This project work is carried out on a real working radar transmitter to provide the actual field
performance report compared with its performance characteristics given by the manufacturer which is
helpful to design and construct such a magnetron-based indigenous radar or abroad and other various
fields like medical, industry and appliances. The field report on magnetron handling, maintenance,
and common faults finding of the transmitter are also helpful to reduce the failure rate and increased
the mission reliability of servicing radar. This performance report basis on measurement can be a
better input for developing a computer simulation program of the radar sys.
1.4 Organization of this paper
Chapter 1 comprises the introduction of a magnetron transmitter comparison with others, its
area of analysis, industrial significance, contribution, and organization of this paper. Chapter 2
contains a brief description of the magnetron transmitter with their performance characteristics on
which project work is carried out. Chapter 3 presents the measurement and result from the summary
carried out. Chapter 4 deals with its conclusion and the future scope of this study in the relative field.
Chapter 2: Transmitter having magnetron under analysis
This chapter comprises the details of the coaxial magnetron-based radar transmitter on which
the analysis is based.
Fig 1: Transmitter Unit
2.1 Transmitter performance characteristics: The high-power magnetron transmitter
system key parameter is summarized below.
Operating frequency 6 x spot microwave frequency (Ku Band)
RF peak power More than 90 KW
Input power 3 Phase, 220V, 400Hz
Filament voltage 6.3V
Cooling system High RPM blower, 400 Hz supply
RF duty cycle 0.1 %
Pulse width 0.26 micro sec
PRF 3750 Hz
Repetition frequency (Wobbling) 3750 to 2500 Hz
Load SWR 1.35
Warm uptime 3 min
trigger pulse amplitude 15 to 20 v
Trigger pulse duration 0.5 to 1 micro sec
Table 1: Technical description of the transmitter
2.2 Description of transmitter:
This transmitter subsystem is capable to transmit over the 6 x predetermined spot frequency
over a Ku band and is capable of being tuned for each frequency by a frequency control servo
mechanism. This transmitter unit consists of the following units.
(a) Sub Modulator comprises emitter follower, blocking oscillator.
(b) Modulator containing magnetron, thyratron, tuning mechanism, and PFN.
(c) High Voltage Unit with protection assy.
(d) HV Regulator for regulation of HV DC source for magnetron
(e) Power Supply Unit (-12V, -125V, +250V and, +1.5KV) and cooling system
Sub Modulator is responsible to shapes the trigger pulse of 0.5 to 1 micro sec with 15 to 20
volts and provides the amplitude and duration necessary to the control of the modulator. A modulator
is used to switch the RF energy and operate the magnetron in such a way that transmits for a short
pulse of duration. The high voltage unit provides the +20 KV to charge up the storage capacitor
through the charging resistor of the modulator necessary to the magnetron operation. The stabilization
of the power line is due to an automatic increase in high voltage, which is accomplished by the
regulator unit. A servo tuning mechanism is used to tune the magnetron over a stable local oscillator.
There are many analyzing assemblies shown in the figure below.
Fig 2: HV regulator Unit Fig 3: Thyratron
Fig 4 : Magnetron slot Fig 5: MAFC mechanism
.
Chapter 3: Measurement and results:
3.1 The Transmitter unit is tested and results are summarized as:
Connection Reading Remarks
Cathode to ground Very high resistance OC
Anode to ground Very high resistance OC
Filament Very low resistance SC
Table 2: Cold test of transmitter block
Ser Input power supply Regulator HV reading Remarks
No output
(160v to
230 v AC )
(a) 220v, 3 phase, 400 Hz 160 v 17 KV Pass
(b) 220v, 3 phase, 400 Hz 170 v 17.5 KV Pass
(c) 220v, 3 phase, 400 Hz 180 v 18 KV Pass
(d) 220v, 3 phase, 400 Hz 190 v 19.5 KV Pass
(e) 220v, 3 phase, 400 Hz >190 v Switch off the transmitter Transmission
due to energization of a troubled due to
safety circuit overloading of HV
rectifier.
Table 3: Testing of HV regulation circuit
Ser Freq channel Test signal strength (Rx sensitivity up to result
No 80dB for microwatt signal )
(a) F1 Max Tuned
(b) F2 Max Tuned
(c) F3 Max Tuned
(d) F4 Max Tuned
(e) F5 Max Tuned
(f) F6 Max Tuned
Table 4: Testing of a magnetron tuning circuit
Frequency channel RF output power (dBm) Results
F1 79.7 Pass
F2 79.7 Pass
F3 79.7 Pass
F4 79.6 Pass
F5 79.6 Pass
F6 79.5 Pass
Table 5: RF power measurements
General faults Probable reason Remedial action
Magnetron Arcing Waveguide arcing & Examine and check for corrosion,
Shunt diode failure pressure, dirt & Replace diode
Twinning Thyratron failure, trigger Replace the thyratron& check the trigger.
pulse missing
Magnetron Erratic HV DC failure Check HV transformer, rectifier, and
regulator & insulation resistances
Pulse collapse Defective storage network Check capacity
No transmission Mag temp too high or low Check cooling sys & adjust the mag
current
Table 6: Common faults finding
3.2 Waveform characteristics of the transmitter
Fig 6: Thyratron grid pulse Fig 7: Thyratron anode pulse
FIG 8: HT damping pulse Fig 9: AFC error voltage
3.3 Precaution and safety measures:General safety and radiation hazards of the high
power microwave measurement/repair are as under:
(a) Ensure, the p/s must be switched off before dissembling the parts/ components.
(b) HV unit capacitor charged up to 20 KV due to residual volt after SW off the p/s.
(c) During operation conditions, the transmitter door cover should be closed and the door
switch activates the transmitter as a safety circuit.
(d) Don't touch the transmitter block with a naked hand and neither put an electrical or
magnetic device nearby magnetron.
(e) Personal should never stand nearby and in front of radar ant during Transmission.
(f) It should be advised to avoid the end of an open waveguide when turned ON.
(g) EM energy radiated beam heats the skin causes may pain without lasting damage and
sign, while muscle, nerves, and blood vessels may be significantly damaged.
3.4 Maintenance: Handling of magnetron:
(a) Avoid any mechanical and vibrating shock directly it can damage the device.
(b) Avoid the direct contact of any magnetized and conductive materials.
(c) Maintain the space gap bet’s lead wires and chassis to avoid the HV breakdown.
(d) Operate the magnetron under specified operating conditions.
(e) Provide adequate cooling and limit the system which induced high VSWR.
(f) When installing the new magnetron, the filament should be warm up to 8 hrs. appx.
(g) Never operate the magnetron at operation direct unless the warm-up ready status (a
specified time) lamp glow of the system.
(h) Season the magnetron after a long period of storage.
(i) Dispose of the magnetron after it reached to end of life specified.
4. Acknowledgements
First, I would like to thank The Institution of Engineers (India), Kolkata, for allotment of this
project to become an associated member of this Institution after completing the course. With immense
pleasure, I would like to express my deep sense of gratitude to my project guide Dr. Shilpa Jindal,
Life Member of the Institution of Engineers (India) for his valuable guidance, encouragement, and
continuous supporting entire this study. I am highly indebted for his supervision, advice, and
cooperation by which, I could complete this analysis timely.
5. References
IoT is a network of physical objects or "things" that contain embedded technology to enable these
objects to collect data, creating opportunities for more direct integration between the physical world
and computer systems. In other words, the result of the IoT is automation in all fields (Santhi, 2016).
The idea of IoT was developed in parallel to Wireless Sensor Networks (WSNs), therefore,
Applications of the WSNs include monitoring a wide variety of ambient conditions like temperature,
humidity, vehicular movement, lightning condition, pressure, soil makeup, noise levels, in the military
for target field imaging, earth monitoring, disaster management, fire alarm sensors, sensors planted
underground for precision agriculture, intrusion detection and criminal hunting (Bakaraniya, 2012),
(Kaur, 2016), (Akyildiz, 2010). Applications of IoT frequently perform data analysis and real-time
predictive analytics. Hence, the integration of IoT technology with radar and other MW devices can
be new advancement in modern technology.
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