Evaluation of a wideband monopole antenna with tunable stop notches

A multiple band-notched monopole antenna is proposed where active and passive components allow the control of the filtering frequencies. The monopole antenna covers a frequency range from 500 MHz to 6 GHz with the exception of GPS bands LI 1.575 GHz and L2 1.227 GHz. Three U-shaped stop notches are created at the radiator to block the unwanted interference. The use of the varactor diodes is also applied in the design to tune the rejected resonant frequencies. The radiating element is made of low-cost and flexible Copper-Clad Mylar substrate. The radiating structure is composed of two circuit layers sandwiching the dielectric substrate. One layer contains the radiating structure with the slots while the other layer has the biasing tracks and active components. The substrate is thin enough to be able to make the diodes as if they were connected at RF frequencies but isolated from the top layer at DC frequencies. The antenna design is placed over a large ground plane to assess the potential use on a large platform such as a vehicle. Simulation and measurements results are included. CST Microwave Studio™ has been used for the simulations. Both simulation and fabrication results show the antenna operates well at all working frequencies (reflection coefficients below −10 dB) except at GPS bands. Furthermore, the notch filters can be tuned and adjusted further using the reconfigurable capabilities of the antenna. The application envisaged is to be able to dynamically reject frequencies for a variety of satellite navigation systems, covering not only the frequencies for GPS but potentially also for GLONASS, COMPASS, Galileo and IRNSS.