The radar to which you refer was in fact CYMBELINE, and was principally a mortar locating radar. Its primary  purpose was to track incoming mortars and determine whence they came, such that fire could be returned. 

I was marketing director of Thorn EMI radar division for a time in the eighties, and I know this radar very well. We sold many of them at home and abroad.  It was a strange beast, having a Foster scanner and equipped with a Wankel engine for power generation.

For more info, follow this link:   http://en.wikipedia.org/wiki/Cymbeline_(radar)

Input from Bernard de Neumann

Is COBRA (COunter Battery RAdar) a descendant?

Input from Richard Worby

In a word - YES! Whereas Cymbeline was a mortar locator, COBRA could locate multiple launches of various artillery munitions. It was very capable, but equally expensive. Hence the consortium of France, Germany and the UK which developed it. Thorn-EMI radar Division was part of this, but of course didn't remain T-EMI for long. First T-EMI ate MEL, whereupon I became a victim of rationalisation, (aka chucked out), then RACAL ate T-EMI, then Thales ate everybody. It's hard now to find traces of the companies we all grew up with.

Input from Alan Matthews 

I have the Data Sheets - K1 for EVA and K2 for PETA. These are from the "Marconi Radar Systems "  Catalogue of 1970/71 with 7 pages for the EVA and 5 pages for PETA

Input from Bob Mountford

PETA - I remember one on the A12 in Boreham in the lay-by opposite the pub, memory fails me as to the name. And once, on one of my journeys North to visit a  Cement works, I got lost somewhere around Goole. Saw a police car, pulled up to ask for directions, realised I was screening their PETA device as they became agitated  telling me to move on. I took my time and told them that it was made by Marconi and I worked for them. All the while cars were speeding by. Frustrated Fuzz!

Input from Mike Rignall
I can confirm that PETA was developed at Great Baddow in the early 60s under the guidance of Mervyn Morgan who led a Doppler radar group The equipment was given much publicity by the Autocar mag, that published a review of the device in August 1965 where its accuracy was confirmed - see here

The development was quite interesting, since it was one of the first radars to use transistors and, looking at the circuitry, it is fascinating to note that a valve , a 12AT7, was needed to get a high input resistance, no CMOS op amps in those days. Much early development was done in conjunction with the Lancashire Constabulary, but the first public demonstration was given to the Cambridge police. There was quite a tale to tell about this demo, since the prototype was tested at West Hanningfield early in the morning, and, when the PETA was loaded into the Hillman van, the display meter unit was overlooked and it got run over . Fortunately is was quickly repaired and Mervyn made great play of the ruggedness of transistorised equipment to the Cambridge police.

It is interesting that when the police became used to PETA, they trusted it. The radar did have two calibration oscillators built into it and, although not crystal controlled, they held their frequency to better than 1/4 MPH, which was less than the thickness of the pointer on the meter. When I look at the circuitry, I often think that now, in the days of op amps and umpteen bit processors, how the design would look. Most of the work was done with OC71 pnp transistors with an fb of 1Mhz. Now, with a solid state X band osc, how different it would look, no need for the ringing choke HV power supply to keep the klystron working, with all of the attendant system noise it generated.
Those were the days!

Input from Nick Pinnock
“The biter bit”, to use an old-fashioned phrase, or nearly so.
I remember arriving for work at the PCTA at Great Baddow one day in 1970, and a young colleague, an apprentice, recounted how he had been approaching the village rather fast that morning. “Yikes! Crikey! Goodness me! That’s a policeman with a Marconi grey box by the roadside,” he said to himself. (Since this is a family website, various expletives have been altered.)

A screech of brakes preceded his being apprehended by the fuzz, armed with a box he himself had helped to create, he said.
The police don’t get a very good press, do they? All they wanted to do was to calibrate his own speedometer, after all.

Input from Ian Gillis

In the early 1970's the UK Police Forces were seeking a replacement for PETA and a contract was placed by the Home Office for examination of a optical technique for speed measurement. A device with the required accuracy, known as OSCAR, was demonstrated to Police Forces but was not adopted by them, partly because they were reluctant to spend the time and effort involved in convincing magistrates and juries of the validity of a new technique, and partly because a very cheap form of electronic stop watch which could be used (albeit with less accuracy) by police officers in a vehicle became available at the same time.