Radar System Engineering

SEC.11.12] ILL US1’IiA TI VE EXA hlI’LES OF R-F IIEADS 431
of one oft he radars. Figure 11“31 shows the interior detail of one of these
compartments; in the other, the items are the same but are mounted the
other end up. The pulse from the modulator comes in through the pulse
connector on the end of the case. For the long-range search set the
power from the modulator is about 2 Mw, or about 10 kv on the 50-ohm
cable. This power goes in parallel to the primary of the pulse transformer
and to a despiking network consisting of a 50-ohm resistor and a 400-~pf
condenser in series to ground. The network provides a transient load
for the modulator while the voltage is rising but before the magnetron
starts to draw current.
On the long-range search set, a 4J32 magnetron furnishes 0.8 Mw of
r-f power. The pulse length is 1 psec and the repetition rate is 39o pps.
Since the peak voltage at the cathode is about 28 kv, good clearance must
be maintained. The magnetron output is in 1~-in. OD coaxial line, but
an immediate transition is made to standard waveguide l+ by 3 in. with
0.080-in. wall. Since both the coaxial line and waveguide are operating
not very far from the voltage-breakdown point, a specially tapered “doorknob”
transition is necessary. A small air gap in the choke-flange
coupling between the transition section and the waveguide outJet absorbs
the tolerances in the magnetron mounting. The whole magnetron highvoltage
compartment is tightly closed in operation. The small upper
compartment is mainly taken up with the fluted case of the pulse transformer.
The antenna waveguide of the other radar goes through in
front and the directional coupler is put in this convenient place.
In the central section are the two duplexer sections and the two
receivers. The duplexer section for the search radar stretches across the
lower part of the case. Nearest the magnetron is the AFC attenuator
and mixer. The mixer is of the type shown in Fig. 11.25, Sec. 11.8. One
coaxial cable brings r-f power from the local oscillator, which is mounted
in a well-shielded compartment in the receiver box. The other carries
the i-f signal to the AFC discriminator and control circuit in the same box.
Next along the guide and on the opposite side are the two ATIt tubes,
of the untuned 1ow-Q type, spaced one half of a guide wavelength apart.
This gives a broadband characteristic. 1 The resonant windows are
made a part of the broad face of the waveguide. A half wavelength
farther down the guide, and on the same side as the AFC attenuator, is
found the duplexer T. The TR cavity is iris-coupled, both on the input
side from the end of the waveguide and on the output to a coaxial mixer
which is otherwise the same as the AFC mixer. As in the AFC case, i-f
cables connect the mixer with the local oscillator and the proper parts
of the receiver.
The last part of the duplexer section is an r-f switch used in testing
1Microwave Duplaxrs, Vol. 14.