Aerospace and Electronic Systems Magazine June 2017 - 53

Czekal/ a and Samczyn´ski
underwent acceptance trials in 1961, and its production started immediately at the RAWAR factory.
The new search radar, named JAWOR (great maple tree) operating in the L-band (around 1,300 MHz), had a ca. 180 km range on
an IL-28 aircraft, with 0.5 probability of detection and a scan rate
of 3 rpm (Figure 10). The radar offered important innovations in
comparison to the earlier NYSA-C. A hydrogen thyratron of Polish
manufacture was employed in the magnetron modulator instead
of a rotating spark gap. A travelling wave tube was used at the
receiver front end, having a noise figure of 10 dB. The transmitter
produced 3 μs wide pulses of 1.1 MW peak power at a repetition
frequency of 400 Hz.
A sophisticated mechanism was implemented to make the transmit/receive system capable of changing its operating frequency. The
local oscillators in the receiver system, using crystal oscillators and
frequency multipliers, were tuned by means of a system of cams
driven by an electromagnet. The RF pre-selector was tuned with
an electric motor, and the magnetron was tuned to the changing
local oscillator frequency in an automatic frequency control loop.
The entirety of this sophisticated system was employed to provide
just a single spare operating frequency. The user manual stated that
the radar featured "fast tuning within the range of four operating
frequencies covered by two magnetrons"; there were therefore only
two operating frequencies available without replacing the magnetron. The re-tuning time was 1 second (Figure 10, bottom left).
JAWOR's antenna had about a 6 m span, and its reflector parabolic shape spoiled in the bottom part to form a cosec2 type beam in the
vertical plane. The beam width in the horizontal plane was 2.4°. The
maximum azimuth side lobes were 15 down according to the radar's
technical specification. The antenna could rotate at a rate adjustable
in two ranges: 1 to 6 or 2 to 9 rpm. For transportation, the antenna was
dismantled and carried on a trailer; a system of quick-fastening locks
enabled the crew to construct it in a dozen or so minutes.
In the JAWOR radar, moving target indication (MTI) was implemented for the first time in Polish radar history, operating with a
staggered PRF. The required signal delay by the pulse repetition interval (PRI) was accomplished with the use of mercury delay lines.
The 30 MHz intermediate frequency (IF) signal was first converted
to ca. 8.5 MHz, then applied to a piezo-electric transducer to convert it into an acoustic wave that, at the second end of the line, was
converted back to the original electric form. The direct and delayed signals were subtracted, resulting in the cancellation of fixed
echoes, or clutter. The delay lines, some 3 m long, were arranged
under the floor of the radar cabin (Figure 11, left).
There is an interesting story about the mercury delay lines in
this radar. According to the requirements, the radar had to operate in
temperatures down to minus 40° C. But the freezing temperature of
mercury is minus 39° C. The military representatives supervising the
development of the radar equipment in the factory were very strict
in enforcing the requirements so a special heating system had to be
incorporated enabling the mercury to be melt at minus 40° C.
The radar cabin was mounted on a Czechoslovak TATRA
truck, which towed a trailer with the antenna in parts. The JAWOR radar was the first to accommodate IFF equipment. The
primary radar antenna reflector was used for IFF action, with
two IFF dipole radiators fixed on both sides of the feed horn.
JUNE 2017

Figure 10.

Top. JAWOR warning radar. Bottom left. Local oscillator tuning mechanism: 1-microwave frequency tripler; 2-electromagnet; 3-frequency
doubler; 4-oscillator and initial frequency multiplexers; 5-cam system.
Bottom right. PPI console of the JAWOR radar.

Figure 11.

Mercury delay line and MTI processing unit of the JAWOR radar.

IEEE A&E SYSTEMS MAGAZINE

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