power dividers and directional couplers.pptx

The types of power dividers and directional couplers are given in the ppt.

1. Power dividers and directional couplers Prepared By A.Anitha,AP /SXCCE

2. Introduction Power dividers and directional couplers are passive microwave components. U sed for power division or power combining. P ower divider : A n input signal is divided into two or more output signals of lesser power . P ower combiner: Accepts two or more input signals and combines them at an output port.

3. Cont … The coupler or divider may have three ports, four ports, or more, and may be lossless. Three-port networks are in the form of T-junctions. Four-port networks take the form of directional couplers and hybrids. Power dividers provide in-phase output signals with an equal power division ratio (3 dB), but unequal power division ratios are also possible. Directional couplers can be designed for arbitrary power division, while hybrid junctions usually have equal power division . Hybrid junctions have either a 90◦ or a 180◦ phase shift between the output ports.

4. THE T-JUNCTION POWER DIVIDER It is a three-port network,used for power division or power combining . I t can be implemented in any type of transmission line medium. Figure shows some commonly used T-junctions in waveguide and microstrip line form.

5. Cont … The output line impedances, Z 1 and Z 2, can be selected to provide various power division ratios. Thus , for a 50 ohm input line, a 3 dB (equal split) power divider can be made by using two 100 ohm output lines . There will be no isolation between the two output ports.

6. Resistive Divider If a three-port divider contains lossy components, it can be made to be matched at all ports. An equal-split (−3 dB) divider is shown , but unequal power division ratios are also possible.

7. Disadvantages of lossless T-junction and resistive power dividers The lossless T-junction divider is not being matched at all ports. I t does not have isolation between output ports. The resistive divider can be matched at all ports, but even though it is not lossless, isolation is still not achieved .

8. Wilkinson power Divider A lossy three-port network can be made having all ports matched, with isolation between output ports. Eg : Wilkinson power divider It can be made with arbitrary power division This divider is made in microstrip line or stripline form .

9. WAVEGUIDE DIRECTIONAL COUPLERS They are four-port devices. Power incident at port 1 will couple to port 2 (the through port) and to port 3 (the coupled port), but not to port 4 (the isolated port ). Similarly , power incident in port 2 will couple to ports 1 and 4, but not 3. Thus, ports 1 and 4 are decoupled, as are ports 2 and 3. The fraction of power coupled from port 1 to port 3 is given by C , the coupling coefficient, T he leakage of power from port 1 to port 4 is given by I , the isolation, The quantity that characterizes a coupler is the directivity, D = I − C (dB),

10. Bethe Hole Coupler To couple one waveguide to another ,a single small hole is used in the common broad wall between the two waveguides. Such a coupler is known as a Bethe hole coupler .

11. T wo-hole coupler A single-hole coupler has a relatively narrow bandwidth. If the coupler with a series of coupling holes , increase this bandwidth. Two small apertures are spaced λg / 4 apart and couple the two guides is shown in figure.

12. Cont … A wave entering at port 1 is transmitted through to port 2, but some power is coupled through the two apertures. T he phase of the wave incident at the second aperture will be −90◦ Each aperture will radiate a forward wave component and a backward wave component into the upper guide. In the direction of port 3, both wave components are in phase. T he waves get cancelled in the direction of port 4 because the wave coming through the second aperture travels λg / 2 further than the wave component coming through the first aperture.

13. THE QUADRATURE (90◦) HYBRID Quadrature hybrids are 3 dB directional couplers with a 90◦ phase difference in the outputs of the through and coupled arms. It is made in microstrip line or stripline form . It is also known as a branch-line hybrid .

14. Coupled Line Directional Couplers When two unshielded transmission lines are in close proximity, power can be coupled from one line to the other due to the interaction of the electromagnetic fields. Such lines are referred to as coupled transmission lines .

15. Lange coupler Here four parallel coupled lines are used with interconnections to provide tight coupling. This coupler can achieve 3 dB coupling ratios More bandwidth is achievable. There is a 90◦ phase difference between the output lines so the Lange coupler is a type of quadrature hybrid.

16. THE 180◦ HYBRID It is a four-port network with a 180◦ phase shift between the two output ports. It can also be operated so that the outputs are in phase. A signal applied to port 1 will be evenly split into two in-phase components at ports 2 and 3, and port 4 will be isolated. If the input is applied to port 4, it will be equally split into two components with a 180◦ phase difference at ports 2 and 3, and port 1 will be isolated.

17. Thank You