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conclusion.
II. ANTENNA DESIGN
The structure of the proposed antenna is shown in Fig. 1. A
monopole patch antenna is used to obtain a wide bandwidth,
which is characterized by its partial ground plane. The struc-
ture of the monopole patch antenna typically consists of the
following main components: radiating element, ground plane,
dielectric substrate, and feed line. The radiating element is
a metal patch that is located on the top layer of a dielectric
substrate. In the top layer of the substrate, the rectangular
metal patch of the proposed antenna is fed by a microstrip
line. The ground plane of a monopole patch antenna is a
conductive layer that is located on the bottom layer of the
dielectric substrate. The ground plane serves as a reflecting
surface for electromagnetic energy radiated by the patch. The
dielectric substrate is a non-conductive material that separates
the radiating element and the ground plane. The feed line is a
transmission line that connects the monopole patch antenna
to the transmitter or receiver. The initial structure is based on
the basic shape of the rectangular monopole antenna shown
in Fig. 2(a) using the low-cost FR4 substrate, which has a
dielectric constant of 4.3, a loss tangent of 0.025, and a height
of 1.6mm. The microstrip feed line characteristic impedance
is set to be 50 ?. The overall dimensions of the proposed an-
tenna are 26mm × 19mm, and the initial parameters are given
in Table I. The reflection coefficient of the initial design is
shown in Fig. 2(b), whose -10dB bandwidth covers the range
(2.98-8.37) GHz. The conventional design equations for the
initial monopole antenna at a center frequency of fo=3.5 GHz
are as follows [21]:
W= c
2 fo er +1
2 results in a dual-band operation due to the presence of the two
L= c - 0.824h[ (ere f f + 0.3)( W + 0.264) ] (2)
v (ere f f - h + 0.8)
fo ere W
2 f f 0.258)( h
Zo = 120p
v f [ Wf + 1.393 + 0.667ln( Wf + 1.444)]
ere f h h
ere f = er + 1 + er -1 h -1
2 [1 + 12
f ]2
2 Wf
where W is the patch width, fo is the antenna resonant
frequency, L is the radiator length, er is the substrate dielectric
constant, ere f f is the substrate effective dielectric constant, h
is the substrate height, and Wf is the feedline width.
Abdulzahra, Alnahwi & Abdullah
Fig. 1. The proposed antenna structure.
TABLE I.
The initial dimensions of the proposed antenna
Parameter Dimension (mm) Parameter Dimension (mm)
19 Lp 9
Ws 26 Lf 12
Ls 9.5 Wf 3
Lg 11
Wp
The microstrip antenna is transformed into a planar monopole
antenna by the partial coverage of the ground plane to convert
it from ?g/2 resonator to ?g/4 resonator [21]. In Fig. 3(a),
the parameter values are modified by engraving 4×4.5 mm2
rectangular slot on the radiating patch. The reflection coef-
ficient also has wideband coverage with -10 dB bandwidth
covering the range (3-9) GHz as shown in Fig. 3(b). After
that, a slit of 1 mm width is inserted to make two unequal
monopole antennas as shown in Fig. 4(a). As can be seen in
Fig. 4(b), this step leads to a dual-band centered at 3 GHz and
6.4 GHz with -32.35 dB and -22.75 dB, respectively. Finally,
another slit is engraved on the shorter monopole as illustrated
in Fig. 5(a) to increase the length of the current path of the
antenna that leads to shifting the resonant frequency down to
3 GHz and 6 GHz as shown in Fig. 5(b). The PIN diode used
to switch the operation of the antenna is SMP1340-079LF.
The purpose of inserting the PIN diode is to accomplish the
(1) frequency reconfigurability as will be explained in the next
section. The ON-state of the PIN diode results in a complete
square ring with wideband operation, while the OFF-state
unequal monopoles.
(3)
(4)