Technical Information

TI-002 Rev.4

Mar. 10, 2023

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Nisshinbo Micro Devices Inc.

Contents listed in this document are subject to change at any time.

Magnetron life time

Nisshinbo Micro Devicesʼ advanced cathode design has extended the magnetronʼs life time to

sometimes beyond the life of the radar equipment. Our X band 2, 4 and 6 kW patented ESAC (Extended

Surface Area Cathode) magnetrons are operating in many shipboard and airborne radar in excess of

15,000 hours, hence very little replacements are required for these low power types. Our higher power

magnetrons also contain long life cathodes and improved with our thermal control techniques. They also

obtain an extremely long lifetime. This includes our 25 kW X and 30 kW S band shipboard radar

magnetrons and our high power line of coaxial, vane and strap, and hole and slot type magnetrons used

in airport surveillance radar, vessel traffic control radar, meteorological radar and medical and industrial

linear accelerators.

1. Life end mechanism

Each magnetronʼs cathode has a special coating to enhance performance. Over time this material is

consumed during normal operation. However, under improper operating conditions this consumption is

expedited. The consumption ratio is the function of the anode current density and the cathodeʼs

temperature. As these increase beyond specification the lifetime of the magnetron decreases. Reduced

emitter material causes low emission ability and unstable oscillation. This reduction in performance can

be detected by the radar operator by recognizing loss of long range targets and difficulty in tuning the

radar due to unstable oscillation. The consumption of material is dependent on current density and

temperature, hence conditions of; average output power, heater voltage, load VSWR, anode temperature,

and rrv (rate of rising of voltage) will affect the life time of the magnetron.

2. Operating condition effect

1) Average output power

Basically a magnetronʼs life time is extended by operating at low average output power at low duty

cycle as compared to high output power at long pulse and high duty cycle. All of Nisshinbo Micro Devicesʼ

life test data is measured at the most severe operating conditions; high average output power, maximum

pulse length and a high duty cycle. Under normal operating conditions our customers can expect from

1.5 to 5 times longer life time than our life test data shows, if the magnetron is mainly operated under

the middle or short pulse conditions.

2) Heater voltage

Cathode temperature is depended on heater voltage, electron back bombardment, ambient

TI-002 Rev.4

temperature, and cathodeʼs heat conductive design. Some of our high power magnetrons required heater

voltage reduction at normal operation because electron back bombardment increases the cathode

temperature on high power magnetrons. A heater voltage reduction schedule is listed in our specification

sheet and should be adhered to in order to avoid short life. This reduced heater voltage keeps the cathode

temperature within its limit. Please accurately adjust the heater voltage to the center of the specified

voltage value both during preheat and during the operation period.

3) Load VSWR

A low VSWR of the transmission waveguide line extends the life time. A good matched circulator and

waveguide line, including the antenna are important to maintain good lifetime of the magnetron. Please

ensure a low VSWR at least under the specified level in each specification.

4) Environmental temperature

The magnetronʼs lifetime is affected by the environmental temperature. High environmental

temperature beyond specification increases the cathode temperature thereby reducing the life of the

magnetron. So it is important that the magnetronʼs specified anode temperature be kept under the

absolute maximum rating in any operating condition. Environmental temperature effects on a

magnetron can be reduced by thick waveguide flange connecting to chassis, using heat sinks, fans, or

other methods or cooling devices.

5) rrv (rate of rising of voltage)

Mismatched rrv from the modulator to the magnetron causes mode shift oscillation. The less efficiency

of this mode shifted oscillation degrades the cathode. A degraded cathode causes unstable oscillation.

The rrv should be kept within the limits of the specification sheet of each magnetron.