Design Of Broadband Filter Antenna Based On Coplanar Stripline

Under the development trend of multi-function and miniaturization for the wireless communication systems,the integration design of antennas and filters which are the key components of radio frequency(RF)front-end system,has become the research focus recent years.In consideration of the large circuit area caused by the traditional cascading design as well as the disadvantages of microstrip line in the coplanar integration design of filter and antenna,two wideband filtering antennas based on coplanar strip lines are proposed with simple circuit structure in this paper.The first one is a novel wideband filtering antenna designed on the basis of asymmetric coplanar stripline(ACPS).By using ACPS as the feeding structure and adopting the impedance matching method,a wideband dipole antenna is constructed.Then,by loading parallel coupled transmission line resonators,two radiation nulls are respectively generated at the lower and the upper gain passband edges.According to the boundary conditions at the resonance,theoretical locations of the nulls can be predicted.The second one is a compact filtering Yagi antenna with broad operation band designed by introducing a coupled half wavelength resonator near the driven element.Then,by adjusting the size of the antenna,the inherent filtering property of the Yagi antenna is excited.Meanwhile,to improve the upper band frequency selectivity,a pair of U-shaped resonant stubs is simultaneously coupled with coplanar strip feeding line at both sides.Finally,the design of wideband filtering Yagi antenna is accomplished with parameter analysis and physical verification.The simulation and optimization of proposed two wideband filtering antennas were conducted by using the full-wave electromagnetic simulation software ANSOFT HFSS v.13.Fabrication and Measurement were carried out by taking the second design as the example.For the wideband filtering antenna based on ACPS,the results show that the wideband filtering antenna operates between 3.16 GHz and 6.27 GHz with the center frequency of 4.71 GHz and fractional bandwidth of 66%.By adjusting the length of strip line and the position of the resonant point,bandwidth of the proposed antenna can be controlled.For the wideband filtering Yagi antenna,good agreements are found between the tested and simulated results.The operating frequency band ranges from 3.64 GHz to 4.38 GHz,thus to a fractional bandwidth of 18.5%.The average gain of the fabricated antenna is measured as 6.4 dB.As expected,flat passband gain response is obtained with two transmission zeros.Due to good radiation and filtering performances of proposed two wideband antennas,it is believed that proposed designs have good prospect in wireless communication systems.