Reasearch And Design Of Kinds Of Filtering Antennas Based On Microstrip Feed

Filtering antenna is a kind of multifunction antenna with the characteristics of radiation and filtering at the same time. It adopts the method of co-design to integrate the filter and the antenna together at the front part of radio frequency(RF) system, which will restrain the working property within the specific bands. That's to say, the filtering antenna designed can reduce not only the unnecessary losses between the devices, but also the additional matching network directly cascaded between the filter and the antenna. Its unique characteristic of miniaturization, broadband and multi-functions, can provide greater space for the wireless communication system. Given this, at the beginning of this thesis, the working principle and design methods of the filter and the antenna are separately expounded. Then aiming for the application areas, the analysis and study on the micro-strip antenna with filtering characteristics are carefully carried to make them share the same system. And the following aspects mainly refer to the work on the filtering antennas designed, which concentrate on the research and design of the multi-functional antennas with linear polarization and circular polarization.Firstly, aiming for the flaws in traditional cascading design of the filter and the antenna, the method of co-design is adopted to propose a kind of filtering antenna with low-pass property. In the design, according to the design objects about the working frequency, polarizing character, and radiation pattern, the defected ground structure(DGS) is etched on the ground of the dual-band antenna to realize the low-pass character. The simulated results show that the embedded DGS can effectively reduce the radiation signal produced by the patch-T, whose pass-band can cover the bandwidth of WLAN 2400 MHz, WCDMA 2100 MHz, LTE 2300/ 2500/ 2600/ 2800 MHz etc. Besides, at the center frequency of 2400 MHz, the filtering antenna with the DGS has a good radiation pattern of omni-direction. In addition, the test results of the filtering antenna are basically consistent with the ones of simulation, and can be well applied to the terminals of wireless mobile system.Secondly, according to the application standard of the beidou antenna with circular polarization, the multi-layer design method is utilized to integrate the power dividers with filtering characteristic with the radiation patch, which will put forward a filtering antenna working on the bandwidth of beidou B1 frequency and GPS L1 frequency. In the design, the phase-shifted network without and with L stub are analyzed to compare its filter performance. Then the two feeding network are respectively used at the bottom of the antenna to go on the total simulating optimization, which can be used to observe the radiation affects of the two antennas designed. The simulation results show that the feed network loaded with L stub has a better performance to gain an out-of-band restraint. The filtering antenna designed has a character of circular polarization, which has an impedance bandwidth of 64.4%, and an axial ratio(AR) bandwidth of 55.6%.Then remove the L stub of the filtering antenna, and rotate the circularly polarized(CP) antenna for 90 degree to obtain an improved CP antenna. Taking other methods to construct the filtering antenna into account, two orthogonal slots with bow-tie aperture are embedded into the upper patch to separate the radiation area into several parts. The etched slots would be used to resonate with the improved CP antenna to put forward a new filtering antenna. The simulation results show that the bandwidth of the improved filtering antenna ranges from 1.15 GHz to 2.06 GHz, which can be better applied for the terminals of beidou system(BDS), whose broad bandwidth can even realize the functions of compatibility and interoperability with other Navigation Systems.Finally, the performance of the circularly polarized antenna with filtering character is tested, according to the theory of the polarimetric decomposition. Herein, the test principle and the test procedure are listed before the measure process move forward. Then export the results measured and compare with the simulated results, which are used to verify the radiating performance of the filtering antenna.