RF & Microwave Engineering EC30116 Branch: ECE (6th Sem) Dr. Gopinath Samanta Assistant Professor Department of ECE Engineering C V Raman Global University, Bhubaneswar Email: [email protected] Lecture Materials Prepared by Dr. G Samanta, CVRGU 1 UNIT – IV Two Cavity Klystron Amplifier Materials Prepared by Dr. Gopinath Samanta (Assistant 2 Professor, ECE, CVRGU) O-TYPE MICROWAVE TUBES Multi Cavity Klystron Cavity Resonant Klystron Reflex Klystron Linear Beam Tube (O-type) Helix TWT Forward Wave Coupled Cavity TWT Slow Wave Structure BWA Backward Wave BWO Materials Prepared by Dr. Gopinath Samanta (Assistant 3 Professor, ECE, CVRGU) KLYSTRON Materials Prepared by Dr. Gopinath Samanta (Assistant 4 Professor, ECE, CVRGU) KLYSTRON ▪ Klystron tube is a vacuum tube that can be operated either as an oscillator or as an amplifier at microwave frequencies. ▪ Configurations: ▪ Multi-cavity Klystron : Low power microwave amplifier o Two-cavity Klystron o Three-cavity Klystron ▪ Reflex Klystron : Low power microwave oscillator Materials Prepared by Dr. Gopinath Samanta (Assistant 5 Professor, ECE, CVRGU) • The term “Klystron amplifier” was designed by two brothers, namely Sigurd Varian and Russell at Stanford University. • The prototype and the demonstration of this amplifier is finished successfully on 30th august 1937 and published in the year 1939. • News of the klystron amplifier was influenced by the US and UK researchers which are working on radar device. • These amplifiers are one type of microwave vacuum tubes which are used as an amplifiers in some radar devices as amplifiers. • These amplifiers make use of the transit time influence by changing the velocity of an electron beam. • These amplifiers use cavities to modulate the electric field nearby the axis of the tube. Materials Prepared by Dr. Gopinath Samanta (Assistant 6 Professor, ECE, CVRGU) Two Cavity Klystron Amplifier https://www.watelectronics.com/klystron-amplifier-types-and-applications/ Materials Prepared by Dr. Gopinath Samanta (Assistant 7 Professor, ECE, CVRGU) REENTRANT CAVITY • At high frequency the inductance is reduced to a minimum by short wire. Therefore the re-entrant cavities are designed for use in klystrons and microwave triodes. • A re-entrant cavity is one in which the metallic boundaries extend into the interior of the cavity. Materials Prepared by Dr. Gopinath Samanta (Assistant 8 Professor, ECE, CVRGU) Structure of Two Cavity Klystron Materials Prepared by Dr. Gopinath Samanta (Assistant 9 Professor, ECE, CVRGU) MULTI CAVITY KLYSTRON Assumptions: • Transit time in the cavity gap is very small compared to the period of the input RF signal. • Input RF signal amplitude is very small compared to the dc beam voltage. • The RF fields are totally confined in the cavity gaps, zero in the drift space. • Electrons leave the cathode with zero initial velocity. • Space charge effects are negligible. Materials Prepared by Dr. Gopinath Samanta (Assistant 10 Professor, ECE, CVRGU) TWO CAVITY KLYSTRON Microwave Amplifier • Working Principle: Velocity and Current Modulation • Electrons Injection: From Cathode ✓ Electrons reach at first cavity with uniform velocity • Velocity Modulation: Occurs in the first buncher cavity by input RF signal. • Bunch Formation • Current Modulation Materials Prepared by Dr. Gopinath Samanta (Assistant 11 Professor, ECE, CVRGU) WORKING OF TWO CAVITY KLYSTRON Materials Prepared by Dr. Gopinath Samanta (Assistant 12 Professor, ECE, CVRGU) Potential energy is eV0 and ퟏ ퟐ kinetic energy of the 풆푽ퟎ = 풎풗ퟎ ퟏ electron is 풎풗 ퟐ ퟐ ퟐ ퟎ ퟐ풆푽 풗 = ퟎ m/s ퟎ 풎 풅 Transit Time is , 흉 = 풕품 − 풕ퟎ = 풗ퟎ 흎풅 Transit angle is , 휽품 = 흎흉 = 풗ퟎ Materials Prepared by Dr. Gopinath Samanta (Assistant 13 Professor, ECE, CVRGU) Applegate diagram Exit velocity of the electron after the buncher 휷풊푽ퟏ 휽품 cavity is: 풗 풕 = 풗ퟎ ퟏ + 풔풊풏 흎풕품 − ퟐ푽ퟎ ퟐ 휷풊 is beam coupling coefficient. Materials Prepared by Dr. Gopinath Samanta (Assistant 14 Professor, ECE, CVRGU) Applegate diagram showing two bunching process Materials Prepared by Dr. Gopinath Samanta (Assistant 15 Professor, ECE, CVRGU) VISUALIZATION OF THE WORKING OF TWO CAVITY KLYSTRON Materials Prepared by Dr. Gopinath Samanta (Assistant 16 Professor, ECE, CVRGU) SPECIFICATIONS OF TWO CAVITY KLYSTRON Materials Prepared by Dr. Gopinath Samanta (Assistant 17 Professor, ECE, CVRGU) THREE CAVITY KLYSTRON AMPLIFIER Materials Prepared by Dr. Gopinath Samanta (Assistant 18 Professor, ECE, CVRGU) APPLICATION OF KLYSTRON POWER AMPLIFIER Materials Prepared by Dr. Gopinath Samanta (Assistant 19 Professor, ECE, CVRGU) ✓ These amplifiers can generate far higher microwave power o/p than solid state microwave devices like Gunn diodes. ✓ Klystron amplifiers are used in modern systems, they are used from hundreds of MHz (UHF) through hundreds of GHz. ✓ These amplifiers can be found in satellite, radar, wideband high-power communication, medicine, high-energy physics. ✓ The Radar uses two klystrons that offer a total o/p power of 1 MW at 2380 Mega Hertz. ✓ Global Resource Corporation (GRC) currently using a klystron amplifier to convert the hydrocarbons in daily materials, coal, automotive waste, oil sands, diesel fuel, oil shale and oil sands into natural gas. Materials Prepared by Dr. Gopinath Samanta (Assistant 20 Professor, ECE, CVRGU).