Radar System Engineering

SEC. 69] EARLY AIRCRAFT-WARNING RADAR 177
energy was radiated backwards to make it uncertain, without special
arrangements, whether a target was in front of or behind a station.
The main receiving antenna consisted of a pair (ora stack of pairs)
of crossed dipoles, mounted on 240-ft wooden towers. Balanced pairs
of concentric feeders connected the dipoles to the field coils of a goniometer
whose rotor ~vas connected to the receiver. The final display was
on a 12-in. A-scope. The range of a target was determined from a scale
on the oscilloscope, and its azimuth by rotating the goniometer until the
echo disappeared. Ambiguities of 180° were resolved by the use of
— Main arrays
---- Gap- fdlmg
arrays
6 Transmitter dples wdh
reflectors, mean height 295 fi
2 Remwngd!~les, at 215M
4 TransmltMgdipoleswith
reflectorsat 95 fl
1 Recelvmgdipoleat 45 ft
n
Angle of elevation in degrees
l:l~. 6.14—Typical elevation pattern of CH radar, east coast of England, 1939. \Vave.
length = 10.1meters.
reflectors mounted near the receiving antennas. These reflectors could
be switched in or out of circuit by remote control from the ground. From
their effect on the echo, the operator could deduce whether the target
was in front of or behind the station.
The performance of CH stations was controlled by the reflections
from the ground of both the transmitted and the received signals. The
antenna patterns of the transmitting and receiving arrays were not
identical and there were large gaps in the vertical coverage of the stations.
In order to minimize the importance of the gaps, separate auxiliary
‘‘ gap-filling” transmitting and receiving arrays were installed to allow
aircraft to be followed through the gaps produced by the main arrays
(see Figs. 6.14 and 6.15). It was desirable that the ground surrounding a
station should be flat for several miles in every direction; few stations had
really ;deal sites. Ilven when all possible precautions had been taken,