Coplanar waveguides have been increasingly used as feeding lines
in the design of microstrip antennas, especially when used in the
millimeter-wave applications. The reasons are that they have low
radiation leakages and that they allow shunt and series connections
on the same side of the planar substrate and avoid the use of via
holes. In addition, the substrate can be made relatively thick such
that the microstrip antenna integrated on the same substrate can be
made well-matched with good efficiency and improved bandwidth.
Open-end coplanar waveguide fed microstrip antennas have been
studied experimentally [ 11, [2]. Similar geometries of microstrip
antennas inductively and capacitively coupled to coplanar lines
have also been investigated experimentally [3]. So far, however,
only one theoretical analysis has been published [2]. Nevertheless,
due to some simplified assumptions and the convergence problems
encountered in the numerical calculations, there were only five
points shown on the reflection coefficient curve presented in
[2]. To thoroughly understand the characteristics of the coplanar
waveguide-fed microstrip antennas, five calculation points are not
good enough; more analysis work is required