Microstrip patch antennas offer many practical advantages, such as being lightweight, having low profile, able to conform to the body of a host object, and relatively simple and inexpensive to fabricate compared with other types of antennas. One of the principal disadvantages of the microstrip patch antenna is its very narrow bandwidth, and many techniques have been suggested in recent years to improve the bandwidth of the antenna. The use of varactor diodes is one of these techniques implemented in practice. The varactor diode has a nonlinear capacitance characteristic which depends on the applied reverse bias voltage. Such a varactor diode can be mounted near the patch radiator's edge to maximize its tuning effect since the electric field is a maximum at that point. The paper investigates the effect of introducing a varactor diode on the performance of a microstrip patch antenna.
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