CHPA
S
ERIES
D
OC
.01023245
R
EV
.R
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1-5
A low-level RF input signal is applied to the CHPA via a type “N” connector (isolator) located
at the rear of the enclosure. The isolator limits the input voltage standing wave ratio (VSWR) to
a level of 1.3:1 or less back to the source. The RF input is then routed to the SSIPA, which
includes an integrated PIN diode attenuator. The attenuator, controlled via the front panel, has
a control range of a nominal 20 dB with quick response and excellent linearity. Built-in memory
circuits return the attenuator to a previously set level in the event of prime power outages.
The SSIPA is designed to be transparent to final amplifier RF parameters and is temperature
compensated to minimize drift. As a result, the overall TWT CHPA gain is specified to be
stable within ± 0.25 dB/24 hours with 10 percent line voltage variations. The output of the
SSIPA is connected to an isolator that protects the SSIPA from TWT failure. The SSIPA and
TWT provide a combined subsystem gain of at least 75 dB at maximum rated power for the C-
band and 75 dB for the Ku-band.
The TWTs employed in this power amplifier feature air-cooled, dual depressed collectors for
efficient operation, and periodic permanent magnet (PPM) focused helix design. They are
designed especially for compact, lightweight applications involving satellite uplink service. The
output waveguide assembly interfaces to the TWT and protects the tube from abnormal or
transient conditions that could permanently damage the TWT. This assembly consists of a four-
port circulator, harmonic filter, receive reject filter, and three-port directional coupler. The
high-power isolator provides a low VSWR to the external waveguide run and antenna feed.
The isolator assists in protecting the TWT from excessive reflected power due to
damaged/broken waveguides or antenna components. The isolator is rated such that it will
safely dissipate all reflected power equal to the full rated output of the CHPA for the duration
of time until the protection circuits shut off the high-voltage power supplies. In addition, the
isolator is designed such that it can safely dissipate a VSWR mismatch of 2.0:1 (12 percent of
forward RF power) indefinitely.
The harmonic filter contained in the output waveguide assembly provides a minimum of 60 dB
attenuation at the second harmonic and 45dB attenuation at the third harmonic. The receive
reject filter serves as a high-pass filter cutting off below-band signals. Finally, the three-port
directional coupler provides one reflected power port coupled via a detector to the RF power
monitor assembly for reverse power protection, and two for forward power: one for the user to
monitor forward RF power via a type “N” connector on the front panel, and one for use by the
optional forward power metering circuit, which uses a similar detector to process the RF signal.
The RF sample port, calibrated in coupling ratio vs frequency, permits independent monitoring
of output power levels through the use of an external spectrum analyzer or portable power
meter. High reflected RF protection circuitry is standard. The reflected power metered reading
is displayed on the front panel. Settable low and high RF power alarms are also available.
The output and reflected power level readouts are also available for remote monitoring via the
optional CPI remote control panel or via the Computer Interface (CIF) port located at the rear of
the enclosure. The RF drive is adjustable via the Serial Remote and CIF port. Also, the RF
sample port, calibrated in coupling ratio versus frequency, permits independent monitoring of
CHPA output power levels through the use of an external spectrum analyzer or portable power
meter. The standard RF output interface, provided by the user, to connect the CHPA to the
external waveguide run is a CPR-137F (flange) termination for the C-band, and WR-75F for the
Ku-band.
