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Microwave Coupler

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Microwave Coupler

  1. 1. 1 Microwave Couplers Presentation by: MD ERFAN (33108908) Masters in Electrical Communication Engineering
  2. 2. 2 Outline • Introduction • Directional coupler • Differences between couplers • Key specification • Losses • Types of coupler • Recent development • Summary • References Microwave Couplers
  3. 3. 3 COUPLERS •Passive device that divides and distributes power. •Couples part of the transmission power by a known amount out through another port. •Uses two transmission lines set close enough together such that energy passing through one is coupled to the other. Couplers is a device having 4 port , which couples the power from input port, to two out ports, while the fourth port is isolated. Microwave Couplers [13]
  4. 4. 4 Directional Couplers • Symmetric Device • Directional couplers • Ports 1&2 are Primary ports • Ports 3&4 are Secondary ports •Power is defined to a specific direction, while no power is reflected back at any port. •Power is divided between transmitted port and coupled port Microwave Couplers
  5. 5. 5 Differences [14] Microwave Couplers
  6. 6. 6 Forward Coupling • Energy that propagates down transmission line starts a parallel wave down to transmission line 2 . • Most common forward coupler is the multi-hole coupler realized in waveguide. • In this case the holes are spaced a quarter wave apart. • Asymmetric multi-section coupled structures provide forward-wave, in-phase response. [15] Microwave Couplers
  7. 7. 7 Backward Coupling • Reverse coupler • Energy that propagates down transmission line starts a reverse wave down to transmission line 2. • Single-section coupled transmission lines are always backward-wave couplers (and outputs are in quadrature) • Example: Lange coupler • Symmetric multi-section couplers provide backward-wave, quadrature response. [15] Microwave Couplers
  8. 8. 8 Key Specifications The key specifications for a directional coupler relay on its purpose. Each of them should be carefully evaluated to ensure that the meet assemble its intended use. Microwave Couplers
  9. 9. 9 Coupling Factor • Indicates the fraction of input power that is coupled to the output port. • Coupling is not constant, but varies with frequency. • Coupling values of 10 and 20 dB are most common. • Larger the coupling value smaller the coupled power. Microwave Couplers
  10. 10. 10 Coupling Factor • Directional couplers are specified in terms of the coupling accuracy at the frequency band centre. • The accuracy is due to dimensional tolerances that can be held for the spacing of the two coupled lines. • Another coupling specification is frequency sensitivity. • A larger frequency sensitivity will allow a larger frequency band of operation. Microwave Couplers
  11. 11. 11 Isolation Factor • Defined as the difference in signal levels in dB between the input port and the isolated port when the two other ports are terminated by matched loads. • Also defined between the two output ports. In this case, one of the output ports is used as the input; the other is considered the output port while the other two ports (input and isolated) are terminated by matched loads. Microwave Couplers
  12. 12. 12 Isolation Factor • The isolation among the input and the isolated ports may be dissimilar from the isolation between the two output ports. • For example, the isolation between ports 1 and 4 can be 30 dB while the isolation between ports 2 and 3 can be a different value such as 25 dB. • Isolation can be estimated from the coupling plus return loss. • Larger the bandwidth, higher the frequency, difficult to provide Isolation. • Higher the isolation, better the performance (Ideally Infinite) Microwave Couplers
  13. 13. 13 Directivity • Indicates the coupler’s ability to isolate the forward and backward waves. • How well the forward travelling wave in the primary couples only to a specific port in secondary. where P3 is the output power from the coupled port and P4 is the power output from the isolated port. • The directivity should be as high as possible (Ideally Infinite). Microwave Couplers
  14. 14. 14 Directivity • The directivity is very high at the designed frequency • More sensitive function of frequency because it depends on the cancellation of two wave components. • Waveguide directional couplers will have the best directivity. Ref: [13] Microwave Couplers
  15. 15. 15  SWR: Standing wave ratio for power dividers and couplers, 50 Ohm match over all frequencies. • Best performance • Minimize reflections Microwave Couplers
  16. 16. 16 losses Ref: [16] Microwave Couplers
  17. 17. 17 Main line loss • Indicates the power loss as the signal travels from Input port to Through Port. • Ratio of input power through Input port (port1) to power out of the Through Port(port 2). Microwave Couplers
  18. 18. 18 Coupling loss: • Indicates the portion of Mainline loss that is due to coupling some of the input power into the coupling port. • This loss is unavoidable • Very small value Microwave Couplers
  19. 19. 19 Insertion loss  Additional loss Causes: • reflections, • dielectric absorption, • radiation effects, • and conductor losses  Broadband designs tend to have higher insertion losses. Causes: • accumulate more dielectric, • Reflection loss • radiation, and • conductor losses 1) skin effect 2) surface roughness Microwave Couplers
  20. 20. 20 TYPES OF COUPLERS Microwave Couplers
  21. 21. 21 Bethe-hole coupler  One of the most common, and simplest, waveguide directional couplers is the Bethe-hole directional coupler Ref: [17] • Two parallel staked WG •Power pass through hole •Backward coupler •λ/4 a parted hole •Bandwidth extended Microwave Couplers
  22. 22. 22 Two couplers in series, in opposing directions, with the isolated ports internally terminated. This component is the basis for the reflectometer. Using internal, well-matched loads helps remove errors with poor terminations that might be present in real systems. Dual-directional coupler Microwave Couplers
  23. 23. 23 A hybrid coupler is a special case, where a 3 dB split is desired between the through path and the coupled path. Hybrid couplers There are two types of hybrid couplers 90 degree couplers and 180 degree hybrids (such as rat-races and magic tees). Microwave Couplers
  24. 24. 24 • 3 dB coupler divides the power equally (within a certain tolerance) between the output and coupled output ports Quadrature hybrid couplers 90° Hybrids or hybrid couplers are basically 3 dB directional couplers in which the phase of the coupled output signal and the output signal are 90° apart. Application: 1) Variable attenuators 2) Microwave mixers 3) Modulators 90° Hybrid Schematic Microwave Couplers
  25. 25. 25 180° Hybrid Coupler [7].  Depending on the junction three types:  Ring hybrid or rat-race  Tapered coupled line and  Magic-T hybrid.  Application: combiner and splitter. 180180oo Hybrid CouplerHybrid Coupler Four-port network with 180° phase shift output  The output are in phase Microwave Couplers
  26. 26. 26 • Four-port component • Coherent power by means of simple Tee junctions • E-plane and H-plane • split power equally • Tends to compensate phase velocities Lange Coupler [9].  Coupling is too loose to achieve 3 or 6 dB  90°phase difference between port 2 and 3 Advantages: Small Size and large Bandwidth Disadvantage: lines are very narrow and close together Application: power combiners and splitters The Lange Coupler and Magic T Wave guide-magic T [8] Microwave Couplers
  27. 27. 27 • Power Measurements • Frequency measurements • Signal levelling • Reflection coefficient measurements • Signal sampling • Signal injection • Measure incident and reflected power to determine VSWR Applications Microwave Couplers
  28. 28. 28 Recent Development Rat-race coupler 3D Phase Inverter Structure [11]. Top View Of Phase Inverter [11]. • Great features a 40% size reduction and over 60% bandwidth improvement • high port-to-port isolation in the D-band frequency range. • 90° and 180° output phase differences • Phase inverters are based on CMOS process • Performance dependent on phase inverter. Advantages: • Wide operation bandwidth •Acceptable return loss, •Good port-to-port isolation, •Excellent amplitude and phase imbalance in the whole D band frequency range. Based on novel phase inverter and developed in a standard CMOS process Microwave Couplers
  29. 29. 29 Summary • Couplers are often called directional couplers. • Directional coupler is ideally matched at all ports. • In waveguide technology, bethe hole couplers and multihole couplers are widely used. • Microstrip couplers are hybrid couplers, coupled line directional couplers and lange couplers. • Phase inverter can simultaneously increase bandwidth and can reduce size for the hybrid coupler application. Microwave Couplers
  30. 30. 30 References 1. http://publications.lib.chalmers.se/records/fulltext/143058.pdf 2. http://www.aps.anl.gov/asd/people/nassiri/USPAS2003/Lecture10.pdf 3. http://www.nikoha.co.jp/eg/highvacu_com_eg.html 4. Pozar, David M., Microwave Engineering, 4th ed.p.cm. 5. http://www.cernex.com/PRODUCTS_NEW/Coupler-PDF/Directional%20Couplers.pdf 6. http://news.thomasnet.com/fullstory/Quadrature-Hybrid-Coupler-has-compact-90-degree- design-605196 7. http://www.militaryaerospace.com/articles/2013/08/krytar-hybrid-coupler.html 8. http://www.aps.anl.gov/asd/people/nassiri/USPAS2003/Lecture10.pdf 9. http://www.amitecltd.com/photo-gallery2.html 10. http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6552367 11. http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6259758 12. ML Sismondi, GS Raghuvanshi, Basic Microwave Techniques and Laboratory Manual, 1st ed.1987 13. http://www.rtftechnologies.org/physics/fusor-mark3-ecrf-driver.htm 14. http://www.markimicrowave.com/Assets/appnotes/microwave_power_dividers_and_couplers_p rimer.pdf 15. http://www.microwaves101.com/encyclopedias/directional-couplers 16. http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/couplers.pdf Microwave Couplers
  31. 31. 03-Jun-14 31

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