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History of magnetrons

Introduction

A magnetrons is invented by Dr. Hull (USA) in 1921.
During the Second World War, the development of the pulse magnetrons had been accelerated for the use of a military radar.
After World War a large amount of works on the development and analysis of a magnetrons for other use than a radar or communication had been done.
Raytheon (USA) developed CW (Continuous Wave) magnetrons and produced the prototype of a microwave oven first in the world in 1949.
In 1955 Tappan (USA) started sales of a microwave oven for commercial and domestic use, and contributed for wide use of a microwave oven.

In Japan Toshiba and Sharp started the production of a microwave oven in 1962.
Mass production of Toshiba magnetrons started at Toshiba Horikawacho works.
Toshiba have the longest history for a magnetrons production among existing manufactures.

1.Development Period (1958-1965)

In 1958 Toshiba Research Center developed a microwave oven first in Japan which supplied to the Defense Agency.
The magnetrons 2M20 was developed for this first microwave oven, which refers to Raytheon magnetrons.
In 1960 Toshiba developed 2M21 which was used for a microwave oven installed in the buffet of Japan Railway.
However still the first step of designing a magnetrons was to analyze USA magnetrons and measure those dimensions by vernier calipers, and production quantity was several tens to hundreds per month.

[Image] 2M21(1960)
2M21(1960)
It was adopted for the dining car of the train for the first time in Japan.
Raytheon QK707 is a model.

[Image] 2M66(1966)
2M66(1966)
Prototype of magnetrons used for domestic microwave oven.

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2.Promotion Period (1966-1971)

In 1967 Toshiba originally developed 2M52 with a built-in permanent magnet and 2M53 of further compact type in 1969.
In the same period Matsushita, Hitachi and New Japan Radio had started the production of a magnetrons for a microwave oven according to expiry of basic patent of Raytheon on a magnetrons.
In 1969 sale of a microwave oven in Japan reached 380 thousand and microwave ovens have come into wide use.
In 1971 Toshiba magnetrons was introduced into Litton of USA, which is an epoch-making event to show Toshiba magnetrons Technology can compete to USA magnetrons manufactures.

3.Progress Period (1972-1983)

All USA magnetrons manufactures withdrew from the production, and 4 Japanese manufactures cover all demand of magnetrons for microwave ovens in the world.
Then competition among Japanese manufactures became keen.
To meet requirement for cost down and improvement in performance form customers Toshiba developed 2M57 in 1972, which shall be the standard of current magnetrons having a ferrite magnet and horizontal cooling structure.
In 1983 Toshiba developed 2M172A having 10 segments cavity (12 segments up to that time), which has been applied for all current magnetrons.
To supply better technical support to customers, Application Engineering group was newly established and we have introduced customer's requirement into the design of a magnetrons and advised the design of a microwave oven related application of a magnetrons such as microwave circuit.

[Image] 2M53(1969)
2M53(1969)

[Image] 2M57(1972)
2M57(1972)

[Image] 2M172A(1983)
2M172A(1983)

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4.Growing Period (1983-1987)

The spread of microwave ovens had begun in Europe and Korea in addition to USA and Japan where microwave ovens were popular.
According to the expansion of the market three Korean manufactures entered into the production of a magnetrons and a microwave oven.
Therefore competition among magnetrons manufactures became keener, then cost down and development of a magnetrons had been accelerated.
In 1988 the regulation for noise at 12GHz band became severer due to start of satellite broadcasting.
This frequency band is corresponding to 5th harmonics of oscillating frequency on a magnetrons.
In order to suppress harmonics radiation Toshiba developed 2M240 with coaxial type of the choke on the antenna, which is now the world standard as for the antenna structure.

5.Growing and Maturity Period (1990- )

Toshiba Corporation transferred the magnetrons production in 1990 and all magnetrons business in 1992 to Toshiba Hokuto Electronics.
In 2000 we transferred the magnetrons production to Toshiba Display Device Thailand which is the former company of Toshiba Hokuto Electronic Devices Thailand.
After business transfer to our company from Toshiba Corporation, we developed 2M282 of high efficiency magnetrons in 2000, and 2M253-Z of noise improved type in 2001. Corresponding to requirement from customers and revised legal regulation we have been developing new magnetrons.

[Image] 2M240 (1988)
2M240(1988)

[Image] 2M253 (1995)
2M253(1995)

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