RADAR EQUIPMENT - SITES & SPECIFICATIONS

Martin Shough

AN/CPS-5

Long range surveillance radar, designed by Bell Telephone Laboratories and developed by General Electric. GE began producing the CPS-5 in January 1945 when it was designated as a medium range search radar for Aircraft Control and Warning applications, requiring a field crew of ten. It was introduced into the temporary LASHUP early warning net in the US where it was used in conjunction with the AN/TPS-10 heightfinder, remaining as part of the first permanent network at some sites. It was later manufactured by Bendix and had wide military aircraft control and traffic control applications. Its original design was for a gap free envelope of 60 miles radius to 40,000' but turned out to be effective for surveillance at ranges in excess of 200 miles. Some CPS-5 antenna installations are illustrated here.

At Lakenheath the CPS-5 receiver fed multiple PPI scopes manned by several controllers in the Radar Air Traffic Control Centre in the station Tower building. Additional on-site modifications were undertaken to improve efficiency for its ATC function. Modifications included an increase in the rotation rate and the fitting of a Moving Target Indicator. The CPS-5 was normally used with a CPS-4 heightfinder and CPX-2 IFF set in the mid-fifties; but in this ATC application although a heightfinder was on-site it appears to have been either disabled or disconnected.

AN/CPN-4

Short range airfield surveillance radar, part of AN MPN-11A Ground Controlled Approach (GCA) system manufactured by Gilfillan. Self-contained two-trailer transportable system, comprising operations trailer and power generator unit, set up adjacent to Lakenheath main NE-SW Runway 24. Adjacent standby trailer for off-duty crews. Same system installed at RAF Bentwaters. Some views of MPN-11A systems can be seen here.

The CPN-4 is used in conjunction with a blind-landing or precision approach radar. The fixed-azimuth PAR antenna electrically scans at 2/second through 20° azimuth, 7° elevation, around the centreline of the 3.5° glide slope. RF energy is fed in rapid alternation to azimuth and elevation elements of the PAR assembly by 'switching blades' in the antenna feed duct. Landing aircraft are guided by the surveillance radar operator onto the glide path on the PPI scope of the CPN-4, whence they are taken over by the finals controller who guides them down the centreline on the separate PAR scope. The latter shows two parallel displays of the narrow sector containing the glide path. Permanent strobes on these azimuth and elevation displays indicate glide slope and runway centreline respectively, with mile-markers graded nonlinearly from the runway out to a range of 10 miles.

AI Mk.21 Air Intercept Radar

Modified American APS-57, nose-mounted in RAF Venom NF.3
(Air Publication 2913D, Vol.1. 2nd Edition June 1955)

Displays: range/azimuth PPI & azimuth/elevation (C) scopes

Wavelength: 3 cm; 9.375 ± .030 GHz

Transmitter: 4J50 magnetron

Peak power: 200kW or 160 kW

Pulse Repetition Frequency: 300, 550 and 2,450 p.p.s, depending on range scale.

Pulse length: 2.25. 1.75 and 0.4 microsec. depending on range scale.

Beam width: 3° at half-power points in normal pencil-beam modes (cosecant² in ASV mode)

Antenna: parabolic dish with waveguide feed

Scan Rates: 7 scan modes -

• 1 ASV (surface vessel) search mode - cosecant² beam, elevation manually adjustable between +60° and -30°, azimuth sector-scanned between 15° and 85° either side of centreline at 0.41 cycles per sec.

• 6 pencil beam AI modes scanning operator-selectable sectors with azimuth limits up to 85° either side of centreline (170°) and elevation limits between +60° and -30°. Azimuth scan rates between 3.1 and 4.65 cycles per sec. Elevation scan rate 8.3° per sec.

Maximum range: 120 miles (200 miles for beacon operation)

Minimum range: 100 yards

Range marker accuracy (PPI scope): ± 2% (on 6 mile range scale for GGS.5 gunsight control the fixed range markers show 1/2 mile intervals)

Altazimuth resolution (C scope): ± 3°

Track-and-lock antenna: disabled

GGS.5 radar-ranging gunsight: fitted

(Note: See here for operation of radar controlled gunsight and an Opinion on the question of electronic 'range lock'.)

RAF Ground Controlled Interception (GCI) System

ROTOR Early Warning network, Neatishead Sector Operations Centre

Each GCI site (a nuclear strike-hardened bunker complex known as a 'Happidrome' after a wartime comedy show) employed at least five electronically independent radar transmitters whose outputs were integrated in several operator-selectable combinations. A brief description follows:

The master radar was an AMES (Air Ministry Experimental Station) Type 7 200MHz "3D" surveillance/heightfinder. Surveillance was supplemented by two Marconi radars: the Type 14 Mk.7 (or Mk.9) to fill gaps in low cover; and the Type 14 Mk.8 with a cosecant² profile to improve high cover. The Type 14 Mk.7/9 operated in synchronous 6 rpm rotation with the AMES Type 7, the 'pencil' beam of its single-curvature parabolic antenna aligned in the same direction; the Type 14 Mk.8 also operated in synchronous rotation but with the cosec² beam of its compound-parabolic antenna aligned to the reciprocal azimuth - i.e, looking 180° in the opposite direction. The inputs from these three radars could be selected and combined in different ways by the operator using a head-selector switch on the PPI console:

1) AMES Type 7 only;
2) Type 14 Mk.7/9 only;
3) Type 14 Mk.8 only;
4) AMES Type 7 plus the backward-looking Type 14 Mk.8, automatically switched between selectable 180° sectors, giving an effective 12 rpm at alternating frequencies.

All antenna drives were independent and could be desynchronised to any combination of scan rates between 0 and 6 rpm at will (older Type 7 installations were 0.5 to 8 rpm); also both Type 14s (but not the AMES Type 7) were capable of manual position control ("searchlight" operation) and sector scanning if desired - though this was rarely advantageous and scarcely ever used. The Type 14 Mk. 8 beam was shaped to improve high altitude coverage, and the improvement in low cover given by the Type 14 Mk.7/9 was dramatic, an effective horizon only 1/5 as high at 50 miles range (see below).

Some Type 14 antennas are illustrated here.

The range and azimuth resolution of the Type 14s was also much better than the Type 7; but their coverage patterns could not match the null-free vertical polar diagram achieved by the Type 7 over a wide altitude range. Guaranteed continuity of tracking was all-important for interception control, and mainly for this reason the AMES Type 7 remained the master radar. It was in effect an early 'phased array' 3-D system. By selecting the phase relationship of the top and bottom sets of antenna dipoles the operator could transmit different beam shapes whose overlapping vertical lobe patterns filled one another's nulls to give gap-free coverage. In reception mode the Type 7 would then automatically cycle through different phase combinations of the antenna dipole elements and provide height-finding by comparing the amplitudes of signals returned due to ground reflections. This output was displayed on a separate height console and was quite accurate at moderate elevations.

Some Type 7 antenna installations are illustrated here.

Some characteristic performance figures cited for the early model Type 7 master radar against bomber targets (courtesy Dick Barret, radarpages.co.uk and "Watching The Skies") are as follows:

Height finding accuracy was within +/- 500 ft between angles of elevation of 2.5^o and 20^o. Bearing accuracy is said to have been within +/- 1.5^o .

The improved Type 14 low cover figures can be compared with the above range/altitude minima: A bomber could be detected on the Type 14 at 20 miles when flying at 50 feet above the sea and at 50 miles when flying at 1000 feet. At 6000 feet the detection range was 90 miles.

Supplementary height-finding was provided by Marconi Type13 Mk.7 nodding-fan height-finders. At least two Type 13s were normally used simultaneously and were manually 'azicated' by turning a knob to place an intertrace marker strobe through the target on the PPI console, which controlled the Type 13 antenna bearing by means of a servo mechanism. The Type13 outputs were displayed on a separate height/range console. At Neatishead the full complement of available Type13 antennas was five, and the low-cover gapfiller radar was the Type 14 Mk.9 (see Air 29/3582 271 Signals Unit, RAF Neatishead, December 1956-58).

Some Type 13 antennas are illustrated here.

See this electromechanical schematic of the whole GCI system (courtesy of Bruce T. Neale, Consultant, Marconi Radar Systems Ltd.)

Four complete sets of consoles were parallelled in four isolated Interception Cabins, each manned as required by a Controller, a Corporal, a PPI tracker and a height reader. A further set of displays was provided adjacent to the Chief Fighter Controller's coordinating desk, which overlooked the plotting tables and flight status indicator board (see Chief Controller F.Wimbledon's description and sketch of the Neatishead layout and compare with these 'Happidrome' photographs). The Chief Controller could switch in to monitor any Interception Cabin as desired.

Detailed specs. of the complete ROTOR system (courtesy Bruce T. Neale, Marconi Radar Systems) are given below:

i. AMES Type 7 Surveillance/ '3-D' height-finder

ii. Marconi Type 14 Mk.7 (or Mk.9) surveillance, extended low cover

iii. Marconi Type 14 Mk.8 surveillance, extended high cover

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* Sector-scan and "searchlight" modes were in practice rarely used. Wear on the drive bearings was severe and the rotation-reversal process slow. It was usually considered more efficient to leave the antenna in rotation.

iv. Marconi Type 13 Mk.7 height finder (x2)

(Note: full specifications of Type 13 Mk.7 & Type 14 Mks.7 & 8 are contained in A.P.115H-300/1400-1.)

TPS-1D Defence Acquisition Radar

The TPS-1D, or 'Tipsy Dog', was developed by Bell Telephone laboratories from a wartime original through 'B' and 'C' variants. It was later manufactured by Western Electric. The TPS-1B achieved an effective range of 120 miles for a bomber at 10,000' and the TPS-1D exceeded this performance, becoming introduced (like the CPS-5) at a number of sites in the LASHUP early warning network from 1948. It continued in use as a gap-filler and supplemented the permanant Pinetree Line network during upgrade to FPS-3 sets in the period 1955-57. The TPS-1 (along with its TPS-10 heighfinder series), was a very widely used system in all variants for decades, being efficient, reliable, mobile and operable with a field crew of only two. It was operated world-wide by many countries, including in a limited rôle by the UK (where it was known as the RAF's Type 60 and 61), and was the backbone of the Swedish air defence network until 1984. It is still popular on the commercial market today from Radio Research Inc..

Second-generation development of the new TPS-1D variant, now fitted with MTI, was responsive to the need for a mobile battalion level US Army Air Defence Command radar. During the mid-fifties it was widely deployed with Anti Aircraft Artillery (Automatic Weapons) battalions as a tactical search radar for mobile and fixed air defence. At Lakenheath the local Army Air Defence Command Post operated by the 60th AAA (AW) Battalion is believed to have utilised TPS-1D search radar in coordination with 75mm Skysweeper radar-directed AA gun batteries for airfield defence.

T-38 Anti-Aircraft gun-laying radar

By 1956 anti-aircraft gunnery was widely supported by van-mounted or integral automatic tracking radars, and in newer generations of systems such as the M-91, introduced in 1953, the AA guns were electronically slaved to the radar. These types of radar all had visual displays, generally allowing the operator to disconnect the auto-tracking and manually bore-sight selected targets.

David Thayer, who worked with similar equipments in the US Army Signals Corps during the early 'fifties before becoming a radar propagation specialist with the National Bureau of Standards, was asked for comment on his experience with the SCR (Set, Complete, Radio) series and other AA tracking radars of this vintage. He stated:

I did work on the SCR-584. This was a van-mounted tracking radar, but it did not have "gun-laying" capability. A later model of the same radar, called the SCR-784, did, however, have gun-laying capability: it was, in fact, made for just this purpose. It was mounted on an open trailer and was meant to be coordinated with nearby AA artillery units. There was a later radar, brand new in 1953 when I first saw it, whose designation I no longer recall (I think it began with the letter "M" and the number began with a "9" [M-91]). It was an x-band, high-speed gun-laying radar with an automatic target acquisition mode. The one we saw was positioned alongside a two-storey building. While the instructor was demonstrating it an aircraft chanced to fly overhead, coming over the top of the building. The speed with which that radar swivelled its antenna to lock on to the aircraft was really impressive. It is quite possible that one of these radars could have been in use at Lakenheath within three years of the time I saw it - that is, in 1956. All of these radars include imaging systems (usually PPI and RHI scopes). In the case of the super-fast radar, the system allowed the operator to over-ride the automatic target acquisition feature so targets could be chosen at will. Once the operator had guided the antenna to a target on the scopes, the radar could be switched back into automatic mode.

M-91 was a self-propelled gunnery radar for a mobile fighting force. The AA guns and associated radars employed by the 60th AAA (AW) at a major SAC bomber base in 1956 were probably permanently emplaced. According to Col.William J. Lawrence, who served with the 91st AAA (AW) in Germany at this time and later with the reborn 60th Artillery Nike-Ajax missile regiment after the ARADCOM reorganisation of 1957:

It would not have been very likely to have used self-propelled equipment in a static role like air base defense.  There was an Air Defense Brigade in England in the 50s -- the 32d AAA Brigade.  I do know that some of their units were later equipped (circa 1955) with the 75mm Skysweeper AAA Gun. If we are talking about the time frame when B-47s were active, then I'm sure that any defenses of their airstrips would have probably featured the 75mm Skysweeper gun, later replaced by Nike Ajax missiles.  The Skysweeper  had its own fire direction radar, the T-38, whose parabolic dish could be set to rotate to provide surveillance and acquisition in the area around the gun.

It has not so far been possible to locate details of the T-38 radar, but some typical characteristics of similar radars can be summarised. The automatic aided tracking available on earlier equipments such as the SCR-584, and the similar-vintage AN MPG-1, could be manually over-ridden as with the M-91, and this would likely be true of the T-38. Typical maximum aircraft speed for auto-tracking on both the SCR-584 and the MPG-1 was nominally 700 mph. The maximum range of the SCR-584, 32,000 yards (18.18 miles), would be typical of most such tracking radars, and typical x-band frequencies (required for resolution because of the small size of their highly-mobile antennas) lie between approximately 5 and 10 GHz (3-6 cm). Short range permits high PRFs, and indefinite dwell-times in tracking mode lead to high energy-on-target.

The number and placement of T-38/Skysweepers around the airfield is unknown. Practise in automatic weapons battalions prior to the introduction of the Skysweeper in 1955 was to deploy four batteries of eight each towed 40mm guns and eight M55 quad .50 calibre emplaced or truck-mounted machine guns. Presumably a smaller complement of the much more powerful and radar-directed Skysweepers was required.