Theory And Design Of Compact Filter Antenna

With the arrival of the 5th Generation Wireless Communication era,communication equipment is developing in the trend of miniaturization,integration and multi-function.Multiple network standards coexist in one communication system,which is easy to cause mutual electromagnetic interference and reduce the performance of the communication system.The filter antenna has both the radiation characteristics of the antenna and the filtering characteristics of the filter.The integrated design of them can effectively improve the anti-interference ability of the system,and can reduce the volume of the RF front-end,reduce the loss of dis-matching,and improve the efficiency.In some situation,devices are required to switch between different frequency bands such as 4G,5G,and WLAN.The frequency reconfigurable antenna can integrate antennas of different frequency bands into one antenna,which can not only solve the problem of mutual compatibility between antennas,but also save space,reduce costs,and meet the requirements of equipment miniaturization.This paper mainly studied on filter antenna.Reconfigurable technology is also used on filter antenna.The main work of this paper is demonstrated as follows:(1)The design method of parallel coupled line filter and monopole antenna based on equivalent circuit model is studied,and the design principle and idea of filter antenna are analyzed.On this basis,a hairpin-shaped wideband filter antenna is proposed with a fractional impedance bandwidth of 33.9%,flat gain in the passband,steep passband edge,and whose stopband attenuation is above 20 d B,showing good filtering characteristics.(2)A frequency reconfigurable antenna is designed.By adding parasitic cells at the feed end or between the second and third order coupling units,radiation zeros are introduced and stop bands are generated.In this way,conversion from wideband to dualband can be realized.By controlling the state of the PIN diode,the antenna can be switched between WLAN and indoor 5G frequency bands.Compared with other types of frequency reconfigurable antennas,the overall design is more compact,and the introduction of parasitic cells does not cause an increase in size.(3)An ultra-wideband filter antenna fed by coplanar waveguide is designed.The filtering structures are directly loaded on the radiation patch or feeding structure of the UWB antenna,which will not increase the size of the antenna.The filtering of the specific communication frequency band is realized without decrease the radiation performance of the antenna.By embedding a complementary split resonant ring,a microstrip resonant unit or adding short stubs,the frequency bands of 3.3 GHz-3.6 GHz,5.15 GHz-5.85 GHz and above 10.6 GHz are effectively filtered out,excluding the antenna from interference of domestic 5G commercial bands and WLAN bands.