الفهرس 
Review of Hybrids and Power DividersOnly 14 pages are availabe for public view
 |  | from | 198 |  |  |
| | | from | 198 | | |
Abstract
Power dividers may be classified into many categories such as
directional couplers, hybrid junctions, multi-stage multi-way power
dividers, sector power dividers, Wilkinson power dividers, etc. This
thesis is mainly concerned with the branch-line coupler which is one
type of hybrid junctions. These components are used for wide range of
applications such as power division, power combining, signal mixing
and as a feeding network in various antenna systems.
The conventional branch-line coupler (BLC) consists of four
quarter-wavelength transmission lines of loop structure. It has the
property that when all ports are matched, the power entering from one
port will be divided into other two ports and the fourth port is isolated.
However, the conventional branch-line coupler has many disadvantages
such as occupying huge area when it is fabricated on a thin substrate, or
under the M[C or MMIC technology. It also suffers narrow bandwidth
and the existence of higher order modes. One of the problems that are
related to the BLC is that when loose coupling is required for example -
J 0 dB coupling.the width of the microstrip line will be very small which
complicates the fabrication process and reduces the power handling
capability. Many techniques are used to reduce the size of the hybrid
junction and to get rid of other limitation such as using artificial
transmission lines, using space-filling fractal curves, using quasi-lumped
element approach, using vertically installed planar couplers, using folded line, using meandering and multi-meandering, using defected