Power Amplifiers and Their Applications in Radar Transmitter

Power Amplifiers and Their Applications in Radar Transmitter: 

Power Amplifiers and Their Applications in Radar Transmitter

Abstract: 

Abstract Radars are very complex electronic and electromagnetic systems. Radar systems are composed of many different subsystems, which themselves are composed of many different components. Here we will only discuss power amplifiers and their utility in radar system.

Introduction: 

Introduction The radar transmitter subsystem generates the radiofrequency (RF) energy required for the detection and tracking of a remotely situated target of interest. Targets may include aircraft, ships, missiles etc. The radar transmitters basically consists of three basic elements: RF Power Source Modulator Power Supply

RF Power Source: 

RF Power Source Power sources are further classified into two groups Oscillators Amplifiers

Power Amplifiers: 

Power Amplifiers Klystron Traveling Wave Tube (TWT) Extended Interaction Klystron (EIK) Crossed-Field Amplifier (Amplitron) Solid State Transistor Amplifier Twystron Gyrotron Grid Controlled Vacuum Tube Interaction Amplifier and others…

Klystron: 

Klystron A power amplifier tube used to amplify weak microwave energy (provided by a radio- frequency exciter) to a high power level for a radar transmitter. A klystron is characterized by high power, large size, high stability, high gain, and high operating voltages. Electrons are formed into a beam that is velocity modulated by the input waveform to produce microwave energy. A klystron is sometimes referred to as a linear beam tube because the direction of the electric field that accelerates the electron beam coincides with the axis of the magnetic field. Klystrons provide a coherent transmitted signal appropriate for Doppler radar and pulse-compression applications.

In a Klystron: 

In a Klystron The electron gun produces a flow of electrons. The bunching cavities regulate the speed of the electrons so that they arrive in bunches at the output cavity. The bunches of electrons excite microwaves in the output cavity of the klystron. The microwaves flow into the waveguide, which transports them to the accelerator. The electrons are absorbed in the beam stop.

Klystron Application: 

Klystron Application Klystrons can be found at work in Radar Satellite Wideband high-power communication Television broadcasting EHF satellite terminals High-energy physics (particle accelerators and experimental reactors). They are used in many operational radars, for example, NEXRAD (Next Generation Weather Radar) and TDWR (Terminal Doppler Weather Radar).

Traveling Wave Tube: 

Traveling Wave Tube Traveling wave tubes (TWTs) amplify radio frequency waves by converting electron beam energy into microwave energy. They use a slightly different principle than klystrons , and are therefore able to amplify over a very broad frequency band. Traveling wave tubes consist of three elements an electron gun for generating the electron beam the RF circuit, where the beam interacts and amplifies radio frequency waves the collector, where the spent beam is collected and dissipated.

Travelling Wave Tube: 

Travelling Wave Tube

TWT Applications: 

TWT Applications There are many areas in which TWT amplifiers are used. They are an ideal form of RF amplifier for satellites and as a result they are extensively used for satellite transponders where low levels signals are received and need to be retransmitted at much higher levels. In addition to this TWT amplifiers are used in microwave radar systems where they are able to produce the high levels of power required. Traveling wave tube, TWT technology is also used for electronic warfare applications

Extended Interaction Klystron (EIK): 

Extended Interaction Klystron (EIK) Extended Interaction Klystron (EIK) technology preserves the ruggedness and high power capability of the conventional Klystron. The EIK can be considered as a refinement of both two- klystron and TWT The EIK is a velocity modulated tube as linear beam device which combines the advantages of both tubes, the ruggedness and high power capability of a klystron and the larger bandwidth of a TWT. It achieves enhanced power, bandwidth and efficiency at millimeter frequencies through the introduction of cavities with multiple coupled gaps.

Extended Interaction Klystron (EIK): 

Extended Interaction Klystron (EIK) Interaction gaps Permanent Magnet Cooling Collector Electron Gun ladder

Crossed-Field Amplifier (Amplitron): 

Crossed-Field Amplifier (Amplitron) The Crossed-Field Amplifier (CFA), is a broadband microwave amplifier that can also be used as an oscillator (Stabilotron). The CFA is similar in operation to the magnetron and is capable of providing relatively large amounts of power with high efficiency, whereas magnetron is an oscillator. In contrast to the magnetron, the CFA have an odd number of resonant cavities coupled with each other. These resonant cavities work to as a slow-wave structure: an oscillating resonant cavity excites the next cavity. The actual oscillation will be lead from the input waveguide to the output waveguide. The electric and magnetic fields in a CFA are perpendicular to each other (“crossed fields”).

Amplitron: 

Amplitron Waveguide output Waveguide input Attenuator Cathode Anode with odd resonant cavities

Solid State Amplifiers: 

Solid State Amplifiers Solid State transmitters are employed in radar sets nowadays. At constant phases several MESFET- power amplifiers operates parallelly by means of simple power splitters and adders. The high performance is assembled by many low-power amplifiers (or amplifier modules).The modules are feed in phase by power splitters. Its respective output powers then are in phase summed up to the complete transmit power. To achieve adequate range with relatively low pulse power, the pulses are intra-pulse modulated often . MOSFET Power Amplifier MOSFET Power Amplifier Power splitter Power Adder Cluster 1 Cluster 2

Microwave Power Module : 

Microwave Power Module A Microwave Power Module (MPM) is a microwave device used to amplify radio frequency signals to high power levels. It is a hybrid combination of solid-state and vacuum tube electronics, which encloses a solid-state driver amplifier (SSPA), traveling wave tube amplifier (TWTA) and electronic power conditioning (EPC) modules into a single unit. Their average output power capability falls between that of solid-state power amplifiers (SSPAs) and dedicated Traveling Wave Tube (TWT) amplifiers. They may be applied wherever high power microwave amplification is required, and space is at a premium.

MAP Applications: 

MAP Applications Microwave power modules are used in Active phased array antennas Radar transmitters where relatively low power, but long pulse widths are needed (such as Synthetic Aperture Radars) Commercial and military satellite communications

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