Fig. 1 shows an overview of the antenna. Antenna is
printed on an FR4 substrate which size is W x L = 40 mm
x 65 mm with thickness of 1.6 mm and relative
permittivity of 4.4. The antenna consists of two ring
antennas. It has size WI x Ll = 30 mm x 40 mm. The
basis of the antenna structure is a ring monopole, which
has the radius Rl = 10 mm and R2 = 8 mm and the
dimensions of the ground plane is 30 nun x 12 nun with
thickness h = 3 mm. The antenna is excited by a 50 n
microstrip line with ring shaped tuning stub. The width of
the 50 n microstrip line is 3 mm and the gap of the CPW
line is G 1 = G2 = 0.5 mm. Dimension of the proposed
antenna are 65 mm x 39 mm.
Antenna always has more than one resonant frequency.
It depends on feeder or matching impedance. Normally, it
is not difficult to find first resonant frequency. In this
paper we want to have good second resonant frequency in
the same antenna. We will begin with an antenna which