Waveguide Components

WAVEGUIDE COMPONENTS
C-BAND MAGNETRON
BMG (Indonesia) – 224IDC – HW-Factory Training
Neuss, October 2017
PRINCIPLE OF WAVEGUIDES
For all kind of transportation of electrical energy in any frequency range electrical
conductors are used. Most conductors are simple wires. For higher frequencies often
coaxial cables are used. There are also some other kind of lines, like strip-lines, microstrip-lines or Lecher-lines.
For frequencies above 1GHz waveguides are much more useful.
They have their typical advantages:
• Waveguides have extremely low losses in comparison with other lines in the same
frequency range
• Waveguides can transport very high power signals without arcing or damage due to
high voltage
• Waveguides are completely RF-shielded
For lower frequencies waveguides have large dimensions, so that coaxial cables are the
better solution. For low power transmission above 1GHz also the other types of lines can
be used. Mostly they are more flexible and cheaper than waveguides.
This causes that waveguides are used for high-power transmission above 1GHz to
connect the transmitter with the antenna.
The transmitter-tube (Magnetron / Klystron) has a waveguide flange, which is connected
with the feed-horn of the antenna. The microwave-pulse passes the waveguide from the
transmitter-tube through all the waveguide components to the antenna.
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MAGNETRON
The transmitter tube is a mechanically
tuned coaxial Magnetron. This tube
acts as a high power RF generator.
This is the beginning of the waveguide
path to the antenna. The waveguide of
the magnetron has a window. The
window keeps the vacuum inside the
tube, while the RF-energy is passing.
Inside the magnetron this waveguide is
connected to the tube collector cavity
equipped with pick up loops.
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AIR PRESSURE INLET
The straight waveguide part next to the
magnetron is the air pressure inlet.
From the dehydrator is delivered dry air
for the waveguide system, to take care
that no water is getting into the
waveguide path.
Otherwise it might be possible that
corrosion would lead to a bad voltage
standing wave ratio (VWSR) and to
high waveguide losses.
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DEHYDRATOR
Our C-band and S-band systems are pressure interlocked within the dehydrator unit.
When the outlet air pressure is below a set value (400-500mBar), the interlock
prevents the equipment from going to operate condition – transmitter is degraded to
“Standby-Mode”. One 19” rack mounted waveguide compressor dryer supplies very
dry air to the waveguide system, and maintains the required pressure. Small
leakages in the waveguide and a pressure relive valve near the antenna feed horn
will guarantee the removal of humidity.
Typical dehydrator:
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DEHYDRATOR
Typical Dehydrators are equipped with
• heated humidity absorbers
• Compressor
• pressure gauge, pressure controller
with low pressure alarm and interlock
circuit
• humidity indicator
• humidity alarm.
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WAVEGUIDE DRY AIR SYSTEM
In practice it has been found that most
waveguide runs with antenna are not
without leakage. Due to temperature
changes the waveguide will “breathe”
and wet air can enter into the system.
The water vapor transport also takes
place through small cracks. Water
vapor can also enter the waveguide
system by diffusion.
Air of less than required specification
will
degrade waveguides performance
with internal corrosion, VSWR
increase, arcing and ringing.
Therefore, it is recommended to
pressurize and ventilate waveguide
systems with (very) dry air. It has
usually less than 20% of humidity.
Here some examples of waveguide
damages due to humidity:
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ARC SENSOR
At the left side of the transmitter cabinet the
waveguide run arrives from the Magnetron
tube and leads up to the cabinet roof. The
waveguide part next to the transmitter
cabinet is an H-bend with an Arc-Detector
inside.
The Arc-Detector consists of a light sensitive
semiconductor which will receive light
through a small hole inside the waveguide,
when an arc occurs.
If an arc was detected this status will be
stored until a reset of the detector is sent by
the control system.
The detection of an arc can be simulated by
an LED, which is integrated inside the
detector electronic. The light sensitive
components are working within the infrared
spectrum.
Additionally the H-bend is covered in lead to
provide x-ray shielding.
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FLEXIBLE WAVEGUIDES
Flexible waveguide components are:
• Flexible/twistable waveguide
• Flexible only waveguide
• A flexible waveguide consists of an inner core, two connecting flanges and a
protective outer neoprene jacket.
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WAVEGUIDE BENDS
•
•
•
The rectangular waveguide usually is operated with the electric (E) field across the
narrow dimension and with the magnetic loops (H) field across the wide
dimension.
A waveguide bend with the plane of its electric field changed is called an „EBend“. With the plane of its magnetic field changed, the waveguide bend is called
„H-Bend“.
The distinction can be easily remembered readily if one thinks of the E-Bend being
bent in the Easy direction, and the H-Bend in the Hard direction.
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BIDIRECTIONAL LOOP COUPLER
The function of the directional coupler is to couple a part of the transmitted or received
power to an external output. In the same way the coupler can also be used to couple a
microwave-signal into the waveguide. The coupler has coaxial N-type female connectors.
In this way it is easy to combine them with measurement equipment.
Loop-couplers are a small and compact version of a waveguide couplers. They are used to
measure or sample the transmitter-power, or to insert an external signal and they are
applied for calibration purposes. With all couplers it is possible to measure the waveguidepower in forward (FWD) and in reverse direction (RVS). Standard output impedance is
50Ohm, nominal attenuation 30dB for C-band. Exact attenuation (for system operating
frequency) is to be verified in dedicated calibration data sheet.
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WAVEGUIDE SWITCH
The electromechanical driven Waveguide
switch in our systems is used to change
the operational mode of one standard
Dual Polarization Radar System.
The switch is driven by the WSCU, which
is also installed next to the Waveguide
switch on the roof of the cabinets.
The switch has four ports and consists of
a square aluminum block with a cylindrical
rotating insert. It has two positions :
port 1 & 2 and port 3 & 4 connected or
port 1 & 4 and port 2 & 3 connected
End-position-micro-switches give the
information to the WSCU if the waveguide
switch has reached a defined position.
The switch is a latched switch with an
operation voltage of 230V AC.
The manufacturer guarantees a minimum
number of 100,000 switching cycles. The
typical number is 1,000,000.
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POWER SPLITTER (MAGIC-T)
To operate the radar system in the dual polarization mode with a transmitted pulse in horizontal
and vertical polarization at the same time, the transmitter power has to be split.
This is made with the “magic T” next to the waveguide switch.
A magic tee has four ports. The port 1 is connected to the transmitter. Port 2 and port 3 are
identical. If RF-power is inserted to port 1 it will be split equally to port 2 and port 3.
To assure that the power is split equally the waveguide impedance must be correct at all ports. In
this case port 4 is not needed. There is no power at port 4, thus it is terminated.
Port 2 and port 3 are connected to the vertical and horizontal waveguide run.
A similar “magic T” is also used in the circulators to separate transmitter and receiver signals.
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CIRCULATOR
1
Transmitter
Circulator
4
Erroneous signals
(mismatching etc.)
2
Antenna
3
Receiver
In a pulse mode radar system, the transmit signal will be sent out as a pulse. After sending out
this pulse, the system needs to wait some time for the reception of any reflected echoes.
Like in most radar systems we use only one antenna for transmitting and for receiving of all
signals. In order to do this, we need a fast switch to connect the antenna during transmission time
to the pulses emitted from the transmitter and at all other time to the receiver.
In order to reach a long range, two design criteria are used:
1. The transmitter is as powerful as possible to travel long distances.
2. The receiver must be very sensitive, to detect even the smallest signals.
We use a four port ferrite circulator to achieve this. In this device any RF signal entering any port
is transmitted only to the next port in rotation.
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CIRCULATOR
1.
2.
3.
4.
Connection 1: Transmitter
Connection 2: Antenna
Connection 3: Receiver
Connection 4: Waveguide
absorber (dummy load)
5. Magic-T
6. Ferrite section
7. Hybrid coupler
This is a four-port ferrite component for high-power applications. The circulator consists of waveguides with
connections to the antenna, transmitter, and the receiver. There are 2 operating cases that must be differentiated:
1. Normal transmission and reception operation:
On transmitter input port 1 of the circulator, the transmission pulse is split into two identical arms with the same phase
angle in a so-called "Magic-T".
The transmission pulse then runs through the ferrite section of the circulator. This is where one of the arms is shifted in
phase. On the output of the ferrite part, both arms of the signal are shifted 90° in phase.
The output signals of the ferrite section are now reunified by a hybrid coupler in port 2 and relayed to the antenna.
In turn the signal received from the antenna is split by the hybrid coupler into 2 parts with 90° shift.
In the ferrite section of the circulator, one arm is provided with an additional 90° phase shift. Thus, transmission signal
and reception signal are phase shifted by 180° relative to each other. This shift is due to the fact that the received
signals run through the circulator in the opposite direction. The reception signals are then brought together again in the
"Magic-T". Then the signals reach the receiver port 3 through the E-plane of the "Magic-T".
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CIRCULATOR
1.
2.
3.
4.
Connection 1: Transmitter
Connection 2: Antenna
Connection 3: Receiver
Connection 4: Waveguide
absorber (dummy load)
5. Magic-T
6. Ferrite section
7. Hybrid coupler
2. The receiver protection against excessively high signal amplitudes:
The insolation between transmission path and reception path is approx. 30dB. If you
connect the receiver directly, a signal level 30 dB below the transmission level would be
applied. This would be too much power for the input stage. Consequently, a TR-limiter is
interposed at this point.
The TR-limiter blocks all excessively high signals upstream from the receiver, to be specific
in this case the transmission pulse. A signal reflected by the TR-limiter then reaches the
ferrite section via the "Magic-T. Here one part gets an additional 90° phase shift. Through
this measure the signal gets to port 4 in the hybrid coupler where the signal is transformed
in a waveguide absorber (dummy load) into heat. The same applies if, due to a mismatch
in the antenna or the RF-circuit, a transmission signal that is too high is reflected.
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LOW POWER DUMMY LOAD
The low power dummy load or waveguide absorber terminates the waveguide and is
used as dummy load. It contains a conical absorber wedge that transforms the
microwave energy into heat. Thus, reflected power from the antenna RF-circuit is
absorbed and does not get back into the transmission line.
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TR LIMITER
The TR cell is purely a passive element to protect the receiver from excessively high
input power. The TR cell consists of a TR tube that is filled with gas and the
downstream TR limiter (limiting unit).
TR Tube
The TR tube is filled with the radioactive hydrogen isotope tritium. If the permissible
input power is exceeded the gas ionizes and reflects incoming energy to protect the
receiver.
Limiting unit
The limiting unit limits the inflowing energy to a dimension that can be handled by the
receiver.
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COAXIAL ADAPTER
The coaxial adapter couples the reception signal from the waveguide in a coaxial line
that is connected to the receiver. For this the coaxial adapter is fitted with a low-loss
transition with a low standing wave ratio (VSWR = Voltage Standing Wave Ratio).
The coaxial output is designed as N-socket.
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ROTARY JOINT
The antenna movements require signal
transmission via continuously
moveable connecting elements. For
this the waveguide is coupled on both
sides to a rotary coaxial transition.
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DUAL POLARIZATION ROTARY JOINT
For dual polarization systems a dual
polarization rotary joint is required for
the azimuth axis. Here a principle
drawing of one dual polarization rotary
joint. The yellow marked part is the non
rotating one.
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WAVEGUIDE FLANGES
Waveguide flanges are used to connect waveguide components, both
electrically and mechanically. The Flanges which are used for this
system are:
Waveguide Form
Cover
Choke
Circular
UG 407
UG 406
Rectangular
CPR 187F (F=flat)
CPR 187G (G=groove)
8 Straight
Holes
Cover
Flange
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8 Threaded
Holes
Non-Contacting Short
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Choke Flange
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PRINCIPLE OF SINGLE POLARIZATION WAVEGUIDE RUN
Bidirectional
Loop Coupler
(Transmitter Coupler)
Transmitter
RVS
FWD
Circulator
Low Power
Dummy Load
Bidirectional
Loop Coupler
(System Coupler)
RVS
FWD
External Waveguide
Run to Antenna with
2 Rotary Joints
Bidirectional
Loop Coupler
(Antenna Coupler)
Antenna
RVS
FWD
TRLimitter
Waveguide
Coaxial
transition
Receiver
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IN DUAL POLARIZATION MODE
Vertical Polarization Waveguide
Receiver
Waveguide
Coaxial
transition
TRLimitter
Low Power
Dummy Load
RVS
Circulator
Transmitter
Coupler
Waveguide
Switch
RVS
FWD
RVS
FWD
Bidirectional
Loop Coupler
(System Coupler)
External Waveguide
Run to Antenna with 2
Rotary Joints
FWD
Bidirectional
Loop Coupler
(Antenna Coupler)
Magic-T
Feedhorn
Transmitter
Horizontal Polarization Waveguide
Circulator
Low Power
Dummy Load
Bidirectional
Loop Coupler
(System Coupler)
RVS
FWD
External Waveguide
Run to Antenna with 2
Rotary Joints
Bidirectional
Loop Coupler
(Antenna Coupler)
RVS
FWD
TRLimitter
Waveguide
Coaxial
transition
Receiver
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IN LINEAR POLARIZATION MODE
Vertical Polarization Waveguide
Receiver
Waveguide
Coaxial
transition
TRLimitter
Low Power
Dummy Load
RVS
Circulator
Transmitter
Coupler
Waveguide
Switch
RVS
FWD
RVS
FWD
Bidirectional
Loop Coupler
(System Coupler)
External Waveguide
Run to Antenna with 2
Rotary Joints
FWD
Bidirectional
Loop Coupler
(Antenna Coupler)
Magic-T
Feedhorn
Transmitter
Horizontal Polarization Waveguide
Circulator
Low Power
Dummy Load
Bidirectional
Loop Coupler
(System Coupler)
RVS
FWD
External Waveguide
Run to Antenna with 2
Rotary Joints
Bidirectional
Loop Coupler
(Antenna Coupler)
RVS
FWD
TRLimitter
Waveguide
Coaxial
transition
Receiver
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PARTS ON TOP OF RADAR CABINETS
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PARTS OF ANTENNA AND POSITIONER
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INTERNAL WAVEGUIDE – TOP VIEW DUAL POL
TX
Coupler
Low Power
Dummy Load
Magic
-T
(V) TR
Limiter
Circulator
(V)
Low
Power
Dummy
Load.
System
Coupler (V)
Cabinet Back
Antenna
connections
ITSG/UPConverter Unit
RF Frontends
TX Warning
Light
Waveguide
Switch
HaN, BMKG- 224IDC, Indonesia, October 2017
WSCU
(H) TR
Limiter
Low Power
Dummy L..
System
Coupler (H
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Cabinet Front
28
INTERNAL WG - FRONT VIEW DUAL POLARIZATION
Low Power
Dummy
Load
Low Power
Dummy
Load
Transmitter
Coupler
Antenna
connection
Flexible
Waveguide
ITSG/UPConverter
Unit
Arc Sensor
System
Coupler (H)
WSCU
Air Inlet
Circulator
(H)
Magnetron
RF Frontend
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INTERNAL WG SIDE VIEW DUAL POLARIZATION
Low Power Dummy
Load
Low Power Dummy
Load
Low Power Dummy
Load
WSCU
Flexible
Waveguide
TX Warning Lamp
Arc Sensor
Waveguide Switch
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Thank you for your attention
Hardware Training
[email protected]
Selex ES GmbH
Raiffeisenstrasse 10
41470 Neuss, Germany
Tel: +49 (0) 2137 782-0 www.selex-es.de