Research On Ultra-wideband Band-notched Antenna With Controllable Notched Bandwidth

Since the Federal Communications Commission (FCC)’s allocation of thefrequency band3.1-10.6GHz for ultra-wideband communication, short-range andshort-pulses UWB Wireless Communications develops rapidly. As the “ear and eye”of the system, the ultra-wideband (UWB) antennas was studied widely due to itsattractive merits, such as small size, low cost, and easy manufacture. However, overthe entire UWB frequency band, there are some other existing narrow band systemswhich may interfere with UWB operations. To solve the problem, all kinds of UWBantennas with band-notched characteristic are proposed recently. As the key elementof UWB system, the characteristics of the antenna will influence the performance ofthe whole system. Therefore, the researches on UWB antennas are meaningful andvaluable.The UWB antenna with band-notched characteristic requires that the antenna isnot only an antenna, but also with function of filter. The tradition approaches onlycreated one single filtering frequency and the selectivity is poor. Sometimes in orderto suppress the bandwidth of300MHz, but with mismatch in the vicinity of1GHz.This paper based on the concept of band-stop filter, discusses the operating lawof more than two resonators and proposes four band-notched antennas and anantenna-filter. Compared with the previous work, the selectivity of the four antenna isimproved, but with a compact size. Generally speaking, the ratio of-5dB notchedbandwidth to-10dB notched bandwidth is only0.42. But in this paper, the ratio of-5dB notched bandwidth to-10dB notched bandwidth is more than0.7, even0.79.Theproperties of the proposed antenna remain unchanged compared with the traditionalstructure of band-stop filter but decreasing a quarter wave-length.A method of designing band-notched UWB antenna based on controllablereflection zero is proposed. Firstly, the law of reflection zero is presented and theproduction and working law of reflection zero are discussed and then the way todesign UWB antenna with good selectivity is presented. The feasibility of thismethod is proved to be correct through three antenna examples. This method can beapplied in UWB antenna with arbitrary shapes to design UWB antenna with sharpband-notched characteristic.