This paper presents a detailed
investigation utilizing a defected ground structure
(DGS) to a conventional edge-coupled microstrip
coupler with tight coupling level over a relatively
wide frequency band. A reasonable spacing
between microstrip coupled lines and stronger
coupling are achieved using this technique. A 20
dB initial coupler (over a fractional bandwidth of
35% with 1dB ripple) is converted into 8 dB
coupler with almost 3 times wider band by etching
off a single unit cell of rectangular and meandered
slot loop in the ground plane under the central part
of the coupling region. Optimum DGS dimensions
are related to coupler dimensions in easy to use
design curves. An efficient technique for
compensation of the significant unavoidable
mismatch resulting from the presence of the DGS
is applied and tested. Some coupler samples with
different DGS are fabricated, measured, and
compared with a conventional coupler counterpart
to verify the simulation results and illustrate the
improvements, very good agreements are
observed.