In the paper, the low-frequency band radiation performance of the stepped aperture slot antenna is mainly determined by the narrow slot of the L-shape, and the radiation performance of the antenna in the high-frequency band is mainly depended on the resonator.
Figure 3 shows the reflection coefficient of the simulation of the stepped aperture slot antenna.
Figures 3(b), 3(d) and 3(e) depict the radiating surface, aperture slot arrangement and feed line structure correspondingly.
As an EM wave travels from the source of the antenna to the feed line, aperture slots, radiating element and is excited in free space, the EM wave is encountered by a different impedance match at each interface.
A small aperture slot
on the ground is oriented to excite the magnetic field between the feedline and patch.
The aperture coupled microstrip antenna has the flexibility in design parameters due to various shapes of aperture slot
and patch which gives more freedom in antenna design.
Some common feeding mechanisms such as probe feed, aperture slot
, microstrip line and coplanar line can be used with the DRAs .
A truncated square aperture slot
is located on another side of the FR-4 substrate.
The performance parameters of the proposed design are to be achieved by aperture couple feeding mechanism and implanting inverted U-shaped slotted structure stepped at the corners and dimensions of the aperture slot
. The resonant frequencies at different return losses throughout the band can be achieved by varying the dimensions of the slots as well as stub length of the feedline.
On the other hand, an electromagnetic coupled structure such as reported by  will be very hard to switch because there is no specific coupling mediator between the patch and the feed line, unlike the aperture slot
as proposed here.
The aperture slot
array consists of 4x5 = 20 equal slots, with a size of 15 mm x 2.5 mm each.
The geometrical dimensions of the two aperture slots
which excites the first and last CDRAs are [L.sub.1] = [L.sub.2] = 20 mm and width [w.sub.1] = [w.sub.2] = 4 mm.