German firms had magnetron patents during the 1930s. Were captured British magnetrons different then what they already had?
There are several types of Magnetron. The magnetron is a "diode" it only has two functional terminal (ignoring the heater). The basic type is the split anode magnetron invented by Habann of Jena IN 1924 based on a primitive magnetron developed by Hull of GE in 1922. The type Randall and Boot developed is the multicavity magnetron however this was known to the Germans, Russians and Japanese.
A basic vacuum tube diode has a heated cathode at the centre to boil of electrons and has a cylindrical positively charged anode surrounding the cathode to attract them. In a split anode magnetron the concentric anode cylinder is split and a magnetic field run down the axis. The electrons traveling out from the cathod to the anode are curled around by the magnetic field and interact with the anode segments to form a resonant effect.
Another type is the mulitcavity magnetron, known as a 'rad' or 'wheel' magnetron to the Germans and Mandarin to the Japanese. In this the anode is metal and looks like say 8 or so cavities in the shape of say gear teeth or mandarin segments. French were using these to develop radar at the outset of WW2.
Randall and Boots magnetron had a very efficient cavity, it was a hole with narrow slots rather than relatively open mandarin are square gear tooth like segments.
The story goes that Randall frequented a second had book shops on Saturday afternoon, found a book on Hertz's experiments and a formula which gave the resonance of a loop of wire as 7.94 times its diameter. He wondered whether he could make the loop of wire 3 dimensional along with Boot and they came up with the idea of boring a hole and having narrow slots.
The British magnetron was actually based on a 6 shot revolver cylinder which had the correct dimensions for 9cm radiation (with minor adjustments) and was made on the same tooling. (9cm produced 15 degree beam width with a 75cm dish aerial, this is why 9cm was chosen as the beam was narrow enough to avoid sweeping the ground and till fit in a Mosquito or Beaufighter)
So it was the efficiency of this arrangement that was stunning.
The Japanese at systematically studied their 'mandarin' and 'chrysanthemum' multitcavity magnetrons and came up with exactly the same arrangement actually ahead of Randall and Boot about 1 year earlier. Their M3 magnetron of 10cm 10kW water cooled (glass envelop) magnetron was productionised as the M312 and used in the Type 22 radar in 1942 on the cruisers Ise and Hyugu in mid 1942. In 1943 it was in mass production and about 300 produced. Some were given extra side antennas for fire control. These radars only stayed in the Japanese Navy.
The Japanese moved much much slower than the British despite their primacy, some researchers were even arrested for buying the magnet materials on the black market! They never introduced PPI.
So the British innovations were:
1 efficient cavity configuration
2 later developed 'strapping' which quadrupled power (the Japanese also developed)
3 British immediately recognized the technical and tactical value of their invention and had the researchers to develop the receivers. This was unique.
They had taken 80 physicists before the war and introduced them to Chain Home so that they could be used if war broke out.
The Germans were fairly successful with their 50cm radars and were really left wanting for little till 1943 when Wurzburg was jammed by windows.
The Germans became obsessed with developing tunable magnetrons, also started to run out of resources to engineer new radars.
As I pointed out a 18kW 18cm magnetron is respectable and could have made a radar as is a 3.7cm tunable 4kW unit. In 1940 the Sanitas company had a 100W continuous wave 18cm magnetron that probably could have done about 4 kW in pulse mode. (power goes up with either number of cavities or magnet power) but they didn't recognized its potential.
There was one other factor. The Germans developed standard triodes to the max to the point they could produce microwaves at considerable power.
What prevents normal triodes (with a control grid between cathode and anode) from working at ultra high freqencies is
1 The transit time of the electrons between anode and cathod exceeds the period of the wavelength.
2 the leads become highly inductive and capacitive and block and short out high frequency signals.
To overcome 1 they developed techniques to get electrode gaps down to a few thousands of an inch.
To overcome 2 they made the whole tube in coaxial technology using anular electrode entering through ceramic seals.
These tubes could produce about 12kW, perhaps 18kw in a gas atmosphere) at 9cm, greater powers at higher wavelenghts.
The idea was to go to radars operating at about 25cm and 110kW. These radars were about 80% complete when they were suspended due to resource issues in 1942 though the 3m dish track locking Mannheim K radar did eventually get built for the German navy as a 1.5m dish version known as FuMO 231 Euklid FLAK radar (for German destroyers).
These disk triode tubes such as the LD6 are STILL in production and formed the backbone of soviet radar till 1970.
See here.
http://www.cdvandt.org/BIOS-30.pdf
If you can read German:
http://www.jogis-roehrenbude.de/Buecher/Hist_Leseprobe.pdf
See page 13 at the end of the page.
"So entstand bereits im Jahre 1940 ein Impulsmagnetron einer Leistung
von 18 kW bei 18...20 cm. Und bis 1942 schaffte man ohne Kenntnis des
späteren Beutegutes, des Rotterdam-Tastmagnetrons CV64, eine Eigenentwicklung für
4,5 cm/3 kW zu bauen, brach dann jedoch eine konsequente
Weiterentwicklung ab."
"The result was as early as 1940, a Impulse magnetron of power of 18
kW at 18 ... 20 cm. In 1942 they managed without the knowledge of the
later captured Rotterdam-magnetron CV64, developed a 4.5 cm / 3 kW but then
terminated from a logical development. "
From You can check Review article: Microwave tube development in Germany
from 1920-1945 by H. Döring. (Pay document unfortunately)
"The most important tube, the multi-cavity magnetron, was already in
existence in Germany in 1937. For example, Telefunken built an eight-cavity
magnetron operating at 1.5cm and capable of delivering 50mW ouput CW. At Sanitas
a water-cooled magnetron was developed to deliver I00W CW at 25cm. At
this time, such tubes were called 'Radmagnetron' ('Rad' meaning 'wheel' in
German). A tube developed in 1'938 at Lorenz A G by F. Herriger for a wavelength
of 8cm is shown in Fig. 18. However the advantages of this particular design
for pulse operation were not fully appreciated in Germany at the time."
A 100W CW can probably be produce to about 4kW impulse (1 microsecond or so) and greater if more powerful magnets or more cavities used.
Note: Lovell pointed out that the British almost canceled their magnetron work due to resource issues at the height of the battle of Britain.
http://rsnr.royalsocietypublishing.org/content/58/3/283.full.pdf
video of Bernard Lovell (H2S developer) talks about how the British magnetron was almost canceled !)
Bernard Lovell - A secret report by Hackenberg on the Cavity Magnetron - Web of Stories (Lovell talks about magnetron development and German knowledge of it)
Bernard Lovell - Differing attitudes towards science between Germany and the Allies - Web of Stories