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- 1. TR MICROWAVE SIGNAL GENERATION Date of seminar : 15th Oct’ 2016 Tech park, SRM university, KTR campus Subject EC0302 & MICROWAVE AND RF DESIGN Topic MICROWAVE SIGNAL GENERATION Audience 5th semester students of ECE (part time), 2014-2017 batch Faculty & Guide Ms. P. Malarvizhi, Asst. Professor, ECE dept at SRM university Prepared & presented by K Sridharan, ECE (PT), 2014-2017 batch at SRM university Email: sridharan_kannan@srmuniv.edu.in 1
- 2. Objective In this seminar, students should able to understand the use of various microwave tubes & solid state semiconductor devices which are used to Generate or Amplify Microwave signals ranging from 300MHz to 300GHz 2
- 3. Contents 3 The Electromagnetic Spectrum Various Frequency ranges Use of each Frequency range Microwave Frequency and Band designation Generation of Microwave signal Microwave Tubes Microwave solid state devices Generation of Microwave signal using Microwave tubes Generation of Microwave signal using Solid state devices Comparison of Microwave signal generated using Microwave Tubes and solid state devices TRAPATT diode (the seminar topic) Applications of solid state devices Measuring of Microwave signal using Spectrum analyzer
- 4. The Electromagnetic spectrum Increasing wave length Increasing energy • The electromagnetic spectrum is the term used by scientists to describe the entire range of light that exists. From radio waves to gamma rays, most of the light in the universe is invisible to us! • “Light is a wave of alternating electric and magnetic fields which is only visible to us!” 4
- 5. Various Frequency ranges Radio Frequency Microwave Frequency Infrared light, ultraviolet light, X-rays and gamma-rays Audio Frequency Frequency Wavelength Designation Abbreviati on 3–30 Hz 105 –104 km Extremely low frequency ELF 30–300 Hz 104 –103 km Super low frequency SLF 300–3000 Hz 103 –100 km Ultra low frequency ULF 3–20 kHz 100–10 km Very low frequency VLF 20–300 kHz 10–1 km Low frequency LF 300 kHz – 3 MHz 1 km – 100 m Medium frequency MF 3–30 MHz 100–10 m High frequency HF 30–300 MHz 10–1 m Very high frequency VHF 300 MHz – 3 GHz 1 m – 10 cm Ultra high frequency UHF 3–30 GHz 10–1 cm Super high frequency SHF 30–300 GHz 1 cm – 1 mm Extremely high frequency EHF 300 GHz & >3 THz 1 mm – 0.1 mm Tremendously high frequency (Tera Herts) THF 5
- 6. Use of each Frequency range Abbreviation Example uses ELF Communication with submarines SLF Communication with submarines ULF Submarine communication, communication within mines VLF Navigation, time signals, submarine communication, wireless heart rate monitors, geophysics LF Navigation, clock time signals, AM longwave broadcasting (Europe and parts of Asia), RFID, amateur radio MF AM (medium-wave) broadcasts, amateur radio, avalanche beacons HF Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony VHF FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications, land mobile and maritime mobile communications, amateur radio, weather radio UHF (Microwave) Television broadcasts, microwave oven, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as land mobile, FRS and GMRS radios, amateur radio SHF (Microwave) Radio astronomy, microwave devices/communications, wireless LAN, most modern radars,communications satellites, cable and satellite television broadcasting, DBS, amateur radio EHF (Microwave) Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio,directed-energy weapon, millimeter wave scanner THz or THF Experimental medical imaging to replace X-rays, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications, remote sensing, amateur radio 6
- 7. Microwave Frequency Band designation Band Frequency Range Origin of Name I up to 200 MHz Unknown G 200 to 250 MHz Unknown P 250 to 500 MHz P for "previous", as the British used the band for the earliest radars, but later switched to higher frequencies. L 0.5 to 1.5 GHz L for "long" wave. S 2 to 4 GHz S for "short" wave. Don't confuse this with the short wave radio band, which is much lower in frequency C 4 to 8 GHz C for "compromise" between S and X band. X 8 to 12 GHz Used in WW II for fire control, X for cross (as in crosshair) Ku 12 to 18 GHz Ku for "kurz-under". K 18 to 26 GHz German "kurz" means short, yet another reference to short wavelength. Ka 26 to 4-0 Ka for "kurz-above". V 40 to 75 GHz V for "very" high frequency band (not to be confused with VHF) W 75 to 110 GHz W follows V in the alphabet 7
- 8. Microwave signal generation Following devices are mainly used to generate microwave signals ranging from 300MHz to 300 GHz Microwave Tubes Microwave solid state devices Klystron Amplifiers Microwave Transistor & FET Reflex Klystron Oscillators Gunn oscillator Magnetron Oscillators IMPATT diode Helix TWT Amplifiers TRAPATT diode (seminar Topic) BARITT diode PIN diode TUNNEL diode 8
- 9. Generation of Microwave signal using Vacuum Tubes Microwave Tubes Klystron Amplifiers Reflex Klystron Oscillators Magnetron Oscillators Helix TWT Amplifiers 9 These Microwave Tubes works as per velocity modulation principle
- 11. Klystron Amplifiers Klystron is one of the high power vacuum tubes used in radar system as amplifier and oscillator. It is similar to pipe organ tube where air in the tube vibrates and produces sound energy of desired frequency. In klystron, instead of air, electrons are used which vibrate at desired frequency inside the glass tube and generates microwave energy. Klystron Frequency In the range of 100GHz & above Bandwidth 2-4% Power output Up to 50MW Amplification Up to 60 Db Function as Microwave oscillator and small-band power amplifier Two-cavity klystron Invented in 1937 11
- 12. Reflex Klystron Oscillators Low power klystron tube with a single cavity, which functioned as an oscillator . It was used as a local oscillator in some radar receivers and a modulator in microwave transmitters the 1950s and 60s, but is now obsolete, replaced by semiconductor microwave devices. Reflex Klystron Frequency 4GHz – 200GHz Bandwidth 2-4% Power output maximum 3W in X- band to 10mW at 220GHz. Amplification Up to 60 Db Function as Microwave oscillator & Amplifier 12 Note: Reflex Klystron is replaced with Gunn diode now
- 13. Magnetron Klystron Magnetron It can be used both as amplifier and oscillator. It can only be used as oscillator. Application: It is used in TV transmitter, radar and particle accelerators. Here it is used as high power, narrowband stable amplifier. Application: It is used in microwave ovens, operating at 2.45 GHz. It is also used for RF heating when operating at 900MHz or 2.45GHz. Magnetron Frequency Up to 95 GHz Bandwidth Any mega hertzes Power output Up to 10MW Amplification No amplification Function as High power oscillator as one Frequency Picture of Magnetron used in Microwave oven 13
- 14. Helix Travelling wave Tube <-- Electron gun <-- RF output <-- RF Input <-- Magnets <-- Attenuator <-- Helix coil <-- Vacuum Tube <-- Collector • A traveling-wave tube (TWT) is a specialized vacuum tube that is used in electronics to amplify radio frequency (RF) signals in the microwave range. • In TWT, radio waves interact with the electron beam while traveling down a wire helix which surrounds the beam • Radio wave is amplified by absorbing power from a beam of electrons as it passes down the tube Helix TWD Frequency Up to 95 GHz Bandwidth 10-20% Power output Up to 1MW Amplification Up to 50 Bb Function as wide band, low Noise voltage amplifier Picture of Helix TWT Among all methods of microwave generation >50% of the time, TWT is used for microwave signal amplification 14
- 15. Comparisons of velocity-modulated tubes 15
- 16. Generation of Microwave signal using semiconductor solid state Devices 16 Since it become impractical to generate low power microwave signal using vacuum tubes, semiconductor solid state Devices used to generated low power microwave signal
- 17. 17 Microwave solid state devices Microwave Transistor & FET Gunn oscillator IMPATT diode TRAPATT diode (seminar Topic) BARITT diode PIN diode TUNNEL diode Semiconductor solid state Devices
- 18. Pictures of various Microwave solid state devices 18 GUNN GUNN GUNN GUNN (assembled with Horn antenna) GUNN IMPATT diode GUNN PIN diode
- 19. 19 Specifications Gunn diode Impatt diode Trapatt diode Baritt diode Bandwidth 2% of RF center frequency 1/10th of RF center frequency - Narrow Operationg frequency 1 to 100GHz 0.5 to 100GHz 1 to 10GHz 4 to 8GHz Efficiency - 3% in CW, 60% in pulsed mode 20 to 60% pulsed mode Low(about 2%) Output power few watts (continuous wave), 100 to 200Watt(pulsed) 1 Watt(CW), 400Watt(Pulsed) Several 100Watt(pulsed) Low(mWatt) Noise figure - High, 30dB High, 60dB Less noisy than IMPATT diode(<15dB) Basic semiconductors GaAs, InP Si, Ge, GaAs, InP Si Si, metal Construction n+ n n+ GaAs single crystal n+ pip+ reverse bias p-n junction p+ nn++ or n+ p p+ reverse bias p-n junction p-n-p or p-n-i-p, or p-n metal or metal-n-metal forward bias p-n junction Harmonics - Less Strong Less Ruggedness Yes Yes Yes Yes Size Small Small Small Small Application Oscillator Amplifier, Oscillator Oscillator Local Oscillator Comparison of GUNN, IMPATT, TRAPATT, BARITT
- 20. 20 Impatt diode Trapatt diode Baritt diode In the year 1958 WT read discovered concept of avalanche diode. From this, it has been discovered that diode can produce negative resistance at the microwave frequencies. This is achieved by using carrier impact ionisation and drift in the high field intensity region of the reverse biased semiconductor region. From this concept, three diodes impatt diode, trapatt diode and baritt diode have been found. Full name Impact ionisation Avalanche Transit Time Trapped Plasma Avalanche Triggered Transit Barrier Injection Transit Time Develoed by RL Johnston in the year 1965 HJ Prager in the year 1967 D J Coleman in the year 1971 Operating Frequency range 4GHz to 200GHz 1 to 10GHz 4GHz to 8GHz Principle of operation Avalanche multiplication Plasma avalanche Thermionic emission Output power 1Watt CW and > 400Watt pulsed 250 Watt at 3GHz , 550Watt at 1GHz just few milliwatts Efficiency 3% CW and 60% pulsed below 1GHz, more efficient and more powerful than gunn diode type 35% at 3GHz and 60% pulsed at 1GHz 5% (low frequency) , 20% ( high frequency) Noise Figure 30dB (worse than Gunn diode) Very high NF of the order of about 60dB low NF about 15dB Advantages • This microwave diode has high power capability compare to other diodes. • Output is reliable compare to other diodes • Higher efficiency than impatt • very low power dissipation Less noisy than impatt diodes • NF of 15dB at C band using baritt amplifier Disadvantages • High noise figure • high operating current • high spurious AM/FM noise • Not suitable for CW operation due to high power densities • high NF of about 60dB • upper frequency is limited to below millimeter band • Narrow bandwidth • limited few mWatt of power output Applications • Voltage controlled Impatt oscillators • low power radar system • injection locked amplifiers • cavity stabilized impatt diode oscillators • used in microwave beacons • instrument landing systems • LO in radar • Mixer • oscillator • small signal amplifier Comparison of IMPATT, TRAPATT, BARITT
- 21. GUNN diode 21 GUNN diode The Gunn diode is not like a typical PN junction diode. Rather than having both p-type and n-type semiconductor, it only utilises n-type semiconductor where electrons are the majority carriers. When a voltage is placed across the device, most of the voltage appears across the inner active region. As this is particularly thin this means that the voltage gradient that exists in this region is exceedingly high. The device exhibits a negative resistance region on its V/I curve as seen below. This negative resistance area enables the Gunn diode to amplify signals. This can be used both in amplifiers and oscillators. However Gunn diode oscillators are the most commonly found.
- 22. IMPATT diode 22 symbol An IMPATT diode (IMPact ionization Avalanche Transit-Time diode) is a form of high- power semiconductor diode used in high- frequency microwave electronics devices. They have negative resistance and are used as oscillators to generate microwaves as well as amplifiers. They operate at frequencies between about 3 and 100 GHz or more. A main advantage is their high-power capability. These diodes are used in a variety of applications from low-power radar systems to proximity alarms. Principle of operation :Avalanche multiplication
- 24. 24 Principle of operation : Plasma avalanche TRAPATT diode
- 25. TRAPATT diode 25 Principle of operation : Plasma avalanche • Essentially the TRAPATT normally used as a microwave oscillator, but has the advantage of a greater level of efficiency - typically the DC to RF signal conversion efficiency may be in the region of . 20 to 60%. • Typically the construction of the device consists of a p+ n n+, although where for higher power levels an n+ p p+ structure is better. • For operation the TRAPATT is excited using a current pulse which causes the electric field to increase to a critical value where avalanche multiplication occurs. At this point the field collapses locally due to the generated plasma.
- 26. TRAPATT diode (structure) 26 Principle of operation : Plasma avalanche
- 27. TRAPATT diode (principle of operation) 27 AT the instant of time at point A, the diode current is turned on. Since the charge carriers present are those caused by thermal generation, the diode initially charge up like a linear capacitor, driving the magnitude of the electric field above the breakdown voltage. When sufficient number of carrier is generated, the particle current exceeds the external current and the electric field is depressed throughout the depletion region, causing the voltage to decrease. This portion of the cycle is known by the curve from point B to point C. During this time interval the electric field is sufficiently large for the avalanche to continue and a dense plasma of electrons and holes is created. The voltage decrease to D. The holes produced in the avalanche rapidly reach the p+ contact taking no part in process but the electrons are released into N region where they do not combine with either doner or holes. Principle of operation : Plasma avalanche
- 28. 28 The electron drift at their maximum velocity across the N region and current continuous to flow in the external circuit which they are in transit. When this current pulse actually arrives at the cathode terminal, the ac voltage is at its negative peak and the second delay of 90. (90 degree) has taken place. This time depends upon the velocity and the thickness of the highly doped N+ layer. A large time is required to remove the plasma because total plasma charge is large compared to the charge per unit time in the external current. At point E plasma is removed. As the residual charge is removed, the voltage increases from point E to point F . At point F all the charge generated internally has been removed. From point F to G the diode charged up again like a fixed capacitor. At point G the diode current goes 0 for half period and the voltage remains constant VA until the current comes back on and the cycle repeats. TRAPATT diode (principle of operation) Principle of operation : Plasma avalanche
- 29. TRAPATT diode (Typical parameter) 29 Principle of operation : Plasma avalanche
- 30. Frequency Vs. power of various Microwave sources: GaAs: Gallium arsenide 30
- 31. Applications of microwave solid state devices 31
- 32. Application of TRAPATT diode 32 Instrument landing system How the localiser and glide path work together to provide vertical and horizontal guidance to pilots Shows the different decision heights that apply to different approaches. • used in microwave beacons • instrument landing systems • LO in radar
- 33. Application of IMPATT 33 • Voltage controlled Impatt oscillators • low power radar system • injection locked amplifiers • cavity stabilized impatt diode oscillators
- 34. Application of Gunn Diode 34 Radar Gun is used to measure the speed of moving vehicle & cricket ball etc…
- 36. 36 Spectrum Analyser: Spectrum Analyser is used to measure Micro wave signal. The measured Microwave signal is represented in Frequency Domain
- 37. Time Domain Vs Frequency domain: 37
- 38. Microwave signal display on Spectrum analyzer 38
- 39. 39 Thank you