Microstrip Patch Antennas for Broadband Indoor Wireless Systems ...

6.3 RECTANGULAR BROADBAND ANTENNA
L4
W4
W1
W
Feed Location
W2
L
L1
L2
Fig 13: Broadband using Rectangular Patches
The parasitic patch method was chosen because its mechanism of operations is
fashioned similar to the parasitic ring but without the restrictions suffered by the previous
method. In this method, instead of using parasitic rings, parasitic patches of similar
dimensions are placed around the base fed-patch. Operation of the parasitic are same as
the base patch as in the length of the parasitic patch determines the resonant frequency
and the width sets the bandwidth. The fig-13 shown above is a typical topographical
layout of a four parasitic element patch antenna. It is important to note that the parasitic
element dimensions are not identical to each other. By changing individual dimensions it
is possible to tune the antenna to achieve the best possible broadband solution. It is
important to keep in mind that, it is hard to notice the difference caused by altering the
dimensions of one parasitic element. But rather, all four elements need to be altered
together in a logical manner in order to achieve the overall broadband solution.
Initially when designing the antenna, all four parasitic elements had identical
dimension as the base patch. Subsequently the lengths of the parasitic elements were
altered until the required resonant frequencies were achieved. It soon became apparent
due to the addition of parasitic elements, the feed location needed to be changed in order
to provide the optimum input impedance match. Further research suggested this issue
could be resolved by shifting the feed location towards the bottom edge of the antenna [4,
pg 109]. The effect of shifting the feed location 3mm closer can be seen in fig 13. The
appropriate smith chart of the above occurrence can be found in Appendix-E.
W2
L3
15