Bel Project Report

RADAR

RADAR is an abbreviation of word RADIO DETECTING AND RANGING. It is an electromagnetic system for detection and location of object. It operates by transmitting a particular type of waveform.

An elementary form of radar consists of a transmitting antenna emitting electromagnetic radiation generated by an oscillator, a receiving antenna, and an energy detecting device or receiver.

A position of the transmitted signal is intercepted by a reflecting object (target) and is re-radiated in all the directions. The receiving antenna collects the returned energy and delivers it to a receiver, where it processed.

The distance to the target is determined by measuring the time taken by the radar signal to travel and comeback. The direction or angular position of the target may be determined from the detection of arrival of the reflected wave front.

WORKING OF A SIMPLE RADAR

A simple radar system, as found on many merchant ships, has three main parts. These are as follows: -

1. Antenna unit or the scanner2. Transmitter/Receiver3. The virtual display unit

The antenna is about 2 or 3 meters wide and focuses pulses of very high frequency radio energy in to narrow vertical beam. The frequency of the radio waves is usually about 10,000 MHz.

The antenna is rotated at the seed of 10 to 25 revolutions per minute so that the radar beam sweeps through 300 degree all around the ship out to a range of about 90 kilometers.

In all RADARS it is vital that the transmitting and receiving in the transceiver are in close harmony. Everything depends on accurate measurement of the time which passes between the transmission of the

pulses and return of the ECHO about 1,000 pulses per second are transmitted. Through it is varied to suit requirements.

Short pulses are best for short-range work, longer pulses are better for long range.

TYPES OF RADARS Based on its function, RADAR may be classified as follows:

1. PRIMARY RADAR2. SECONDRY RADAR

Primary radar locates an object by transmitting a signal and detecting the reflected echo. A secondary radar system is similar in operation to primary radar except that the return signal is radiated from a transmitter o board the target rather than by reflection.

In other words, secondary radar operates with a co-operative active target while the primary radar operates with a passive target. But in case such as controlling of air traffic, the controller must be able to identify the aircraft and know whether it is of a friend or a foe. It is also desired to know the height of the aircraft, so that on the same source but flying at different levels can kept apart.

To give the controller this information, second radar called secondary radar called a “secondary surveillance radar” (SSR) is used. This works differently and needs the help of the target aircraft. It senses out the sequence of pulses to an electronic black box, called a transponder fitted on the aircraft.

Secondary radar system consists of an INTERROGATOR and a TRANSPONDER. The interrogator transmitter in the ground station interrogates transponder equipped aircraft, providing a two way data link to separate transmits and receive frequencies.

The transponder, on board the aircraft, on receipt of a chain of pulses from ground interrogator, automatically transmits a reply. The reply, coded fro purpose of identification is received back at the ground interrogator where it is decoded and displayed on radar type presentation.

General Design

The functional Block diagram Radar Transmitter is shown in Figure 2.4.1.

Control Rack High Voltage Rack Microwave Rack

Fig. – 2.4.2

The transmitter is used to amplify the pulsed RF signal from 1W to 140kW while maintaining the phase noise (additive noise) to –60dBc/Hz at 100Hz away as demanded by the system. In addition, a failsafe mode of delivering 1.5 kW of peak power to antenna, in case of failure of liquid coolant, as redundant measure.

It employs Traveling Wave Tube (TWT) as final power amplifier.

The transmitter consists of three racks containing the following functional units: Control Rack, Microwave Rack, and High Voltage Rack. All racks have front panels with proper gasket for protection against EMI.

At the upper part of each unit, slip panels containing RF input, Transmitter pulse input, control and measurement connectors, control lamps, hour meters, CBs and high voltage meters are placed.

Low power amplifier stage (RF Driver), amplifies pulsed RF signal from 1 mW (0dBm) to 3-4 W which is necessary to drive TWT amplifier.

In RF Driver, transistor power amplifiers are used to amplify pulsed signal from 0dBm to 37 dBm. After that, an Isolator is used to protect the transistor power amplifiers against excessive reflections from TWT. The Isolator is connected to a Directional coupler, which is used to monitor the power available at the input of TWT.

The RF Driver power (approx. 3 to 4W) is given to the input of TWT, which amplifies the pulsed RF signal from 3 Watts to a level of 125 to 185 KW at the TWT output. High power RF plumbing components are connected at the output of TWT.

The output of TWT is given to an arc detector, output of which goes to a ferrite circulator. Ferrite circulator is used to protect the microwave tube against failure /damage due to reflected power in case of excessive VSWR at Antenna input port.

The output of Ferrite Circulator is given to High Power Dual Directional Coupler (DDC), which is used for measuring the Transmit and Reflected power. If Reflected power exceeds the specified limit of 2:1 VSWR, video signal is generated to cut off the RF drive through control and protection unit. The output of the DDC is given to Antenna.

3 Phase power supply is given to filter unit to reduce EMI/EMC interference. The output of Filter unit is given to Power Distribution unit to distribute power to various units of the transmitter.

Control and protection unit ensures the sequential switching ON of the transmitter, continuous monitoring and interlocking of various parameters, detection and indication of errors. All these are achieved by dedicated hardware and software.

Synoptic Panel unit consists of LEDs, switches and LCD display. LEDs are used to show the status of the transmitter. They also show the fault, if any, in the transmitter. LCD display, mounted on synoptic panel, is used to show the value of cathode voltage & current, collector voltage and current and Duty cycle. It also displays the Filament Voltage and current, Grid+ve and Grid-ve voltages and RF forward power.

High Voltage Rack is used to supply high voltage to collector and cathode of the TWT.

The Floating Deck Modulator (FDM) unit generates filament voltage with surge current protection and also generates grid+ve and grid–ve voltages. Switching of grid voltage as per pulse width and PRF requirements are also provided by FDM.

Cooling Unit is used to cool the various components of the transmitter.

The TWT, High Power Ferrite Isolator and high Voltage Power supplies are cooled with de-ionized water and ethylene glycol mixture (50:50). Liquid cooling distribution is realized in such a way that the liquid cooling unit will have minimal pressure on the connections. Forced air-cooling is employed to cool other components using ambient air which is properly filtered to ensure dust free air.

Electrical specifications:

1. Prime Power : 3 Phase, 415V 10% (line to line); 50 Hz

2. Microwave Tube : TWT

3. Frequency range : 3.1 to 3.5 GHz

4. Peak Power : 120 kW – 185kW at TWT output

5. Average Power : 4.0 kW at 140kW peak

6. Pulse Width (RF) : 32 s (normal), 6 s & 64 s (selectable)

8. Duty : 3.2% (max)

11. Protection : Crowbar protection to safeguard Tube and H V HVPSU

Modes of operation and control

The transmitter is designed to operate in the following modes

defined as adequate controlled states.

a) OFF : All subsystems switched OFF

b) Cold Standby : Only LVPSU’s, TWT heater and Grid biases a r are switched ON. No High Voltage applied.

c) Hot Stand By : High Voltages applied, No RF and No grid

Pulsing.

d) Transmission : RF power delivered to Antenna / matched l oa load.

Transmitter Control

a) Local : To control through control panel on the transmitter.

b) Remote control : To control from the operator console through control interface.

Dimension & Weight

(a) Packaging : Three Racks With front, rear n and side access.

(b) Size : 1800(H) 1900(W) 800(D)

(c) Weight : 1200 Kg (approximately).

Realization of the Transmitter

Fig 2.4.1 shows the general block diagram of the transmitter. The Transmitter is housed in three separate racks, which are individually shielded. The individual racks consist of:

(a) Microwave unit consisting of all microwave plumbing components, RF driver, monitoring and diagnostic circuits.

(b) Power Supply Unit consisting of two high voltage power supplies, FDM, Transmitter Control Circuits and Power distribution along with Line Filter Unit.

(c) Control and protection unit consist the Inverter, Control and P r o Protection circuits, Synoptic Panel, Control Panel and Monitoring P a Panel.

Microwave Unit

The block diagram for the microwave unit is shown in fig -2.4.3.

Fig. – 2.4.3

The microwave unit consists of the following functional assemblies:

(a) High power TWT amplifier

(b) TWT ion pump supply

(c) Ferrite isolator

(d) Dual Directional Coupler

TWT is the main power amplifier used in the transmitter. It amplifies the pulsed RF signal from 2W to a level of 125 to 185 KW at the TWT output.

Ion pump supply is a source of positive voltage about 3.3kV, intended to supply TWT ion pump.

Ferrite Isolator is used to protect the microwave tube against failure / damage due to reflected power in case of excess VSWR at Antenna input port.

High Power Dual Directional Coupler (DDC) is used for measuring the Transmit Power and reflected power.

High Voltage Power Supply Unit

The block diagram for this is shown in figure 2.4.5, and 2.4.6.

Fig. – 2.4.5

This unit contains the following functional assemblies:(a) Floating Deck Modulator(b)Cathode Unit(c) Collector unit(d) Heater Unit

(e) Blower Unit

High Voltage Rack

Fig. – 2.4.6

The main function of HV Rack is to provide the High Voltage Power supply to Cathode and collector for the TWT.

Cathode assy. provides the cathode supply TWT.

FDM provides filament supply, Grid Bias and Grid positive supply to the TWT. It also communicates with CPC via Optical links.

The collector assembly provides the collector supply and 33 KV DC supply required for the TWT Amplifier.

Heater unit is used for removing the moisture within the rack.

Blower unit provides cooling for cathode and collector assemblies.

Control Unit

The block diagram for this is shown in figure 2.4.7, and 2.4.8.

FIG 2.4.7 BLOCK DIAGRAM OF CONTROL UNIT

MONITORING PANEL

CONTROL PANEL

SYNOPTIC PANEL

CONTROL AND PROTECTION CIRCUIT

INVERTER

Control Rack

Fig. – 2.4.8

This unit contains the following functional assemblies:(a) Monitoring Panel(b)Control Panel(c) Synoptic Panel(d) Control and protection Circuit(e) Inverter

In the inverter, 3 Phase (415V, 50Hz) mains power is converted to DC of 550V using AC/DC Converter employing soft start and the resulting DC is used as input to power inverters.

The control and protection unit assures the sequential switching of the transmitter, continuous monitoring and interlocking of various parameters, detection and indication of errors, finally placing the transmitter in appropriate state, and switching off.

Synoptic panel is mounted in Control Rack, above CPC. It gives the LED indications for the fault and status signals generated by CPC. Green LEDs represent status signals, while Red LEDs represent faults..

The function of control panel is to control the power supply of various units such as Fans, Heater, and LVPSU. Inverter, Modulator, RF Drive Unit and SSPA.

The Monitoring Panel displays the cathode voltage (45KV) and collector voltage (33KV).

FDM (Floating Deck Modulator)

It consists of the following:

a) Filament Supply and Timer Card to generate Filament supply for TWT using fly back converter.

b) Grid –ve and Grid +ve supply Cards to generate Grid Bias and Grid positive supplies.

c) Switch Card to switch TWT Grid between +870V and –600V.

d) LVPSU Card to generate all low voltage power supplies +15, -15V, +5V and +24V.

FDM performs the following functions:

1. Generates Filament supply for TWT with surge current protection.

2. Generates Grid negative and Grid positive supplies.

3. Provides switching function (Switching of TWT Grid as per Pulse width and PRF requirement.

4. Communication to CPC on optical link.

All the circuitry necessary to achieve the above functions is floating at cathode potential of –45 KV DC and needs special consideration in engineering. All circuits are housed inside an equipotential surface.

Specifications of FDM: -

1. Voltage Generation :

Filament voltage : -8V to -11V (adjustable) Filament current : 10A with surge limited to 15A. Voltage regulation : 0.01 % Grid +ve voltage : 800V to 1100 V ( adjustable) Grid current : 25m A average (75mA pulsed) Voltage regulation : 0.01% Grid –ve voltage : -600V to -800V ( adjustable) Voltage regulation : 0.1%

2. Grid pulse :

Grid –ve current : 10m A average Pulse output : -600 V to + 1100V pulse Pulse width : 1μs to 76μs Pulse rise time : < 500 ns Pulse fall time : < 500 ns Pulse Droop : < 5V for 70μs PW

3. Protections :

All Power supplies are short circuit protected. All parameters are transmitted on optical links and TWT protections are taken care of by CPC.

FDM cards:

It consists of the following cards.

V to F card

This card contains 6 nos. of V to F converters (AD650), four of which are used to convert the Grid +Ve, Grid -Ve, filament voltage and filament current samples to the corresponding frequencies. This card consists of four optical transmitters for converting electrical pulses into light signals, which are transmitted to CPC by optical links and two optical receivers to convert light signals to electrical pulses, one of which is used for Grid on command.

Filament Supply and Timer card

The Filament supply is a – 10V/10A supply for the TWT Filament. It is a switched mode power supply and topology followed is Fly back converter. The supply operates at a frequency of 25 KHz and PWM scheme is followed for regulation. The switching device is protected against over currents by pulse to pulse current limiting using a current transformer and current limit comparator. The supply has electronic current limiting which limits the TWT initial surge current to 15A and operates in current control

mode until the Filament warms up. It is also provided with hard current limiting by means of a series limiting resistor which is bypassed by operating a relay after 5 min from initial power on.

LVPSU Card

LVPSU card generates all low voltage power supplies i.e. +15V, -15V, +5V and +24V. Three out of these four power supplies i.e. +15V, -15V, +5V are generated using DC-DC Converters.

Negative Grid Power Supply Card

The Grid power supply is a switched mode power supply and the topology followed is Fly back converter. The supply operates at the frequency of 25 KHz and PWM scheme is followed for regulation. The switching device is protected against over currents by pulse-to-pulse current limiting using a current transformer and current limit comparator IC 1526. The card is capable of generating output voltage of –550 to –650 V DC, 10mA.

Positive Grid power Supply Card

The Grid power supply is a switched mode power supply and topology followed is Fly back converter. The supply operates at the frequency of 25 KHz and PWM scheme is followed for regulation. The switching device is protected against over current by pulse to pulse current limiting using a current transformer and current limit comparator of IC 1526. This card is capable of generating output voltage of +700 to +1000 V DC, 25 mA.

Switch Card

The Switch card uses a Fast high voltage Push Pull switch of BHELKE make to switch the TWT Grid between +870V and –600V at required Pulse width and PRF, based on the input command. The circuit configuration enables availability of continuous Grid –ve at TWT Grid even if the bottom switch becomes faulty.

PROJECT REPORT

ON FLOATING

DECK MODULATOR

OF RADAR

SUBMITTED TO: - SUBMITTED BY:-

Ms. RAJ LAKSHMI SHUKLA SATISH KUMARMs. MEENAKSI AGARWAL B.TECH, FINAL YEAR E.T., 0309633086