Research On Novel Microstrip Filtering Antennas

With the development of wireless communication systems,the antenna,as an important component that directly determines the signal transmission and reception performances,has a very considerable research value.At the front end of a communication system,the antenna for receiving and transmitting signals is always accompanied by a bandpass filter for suppressing unwanted interfering signals.Traditionally,the antenna and bandpass filter are designed separately and then connected by a matching network,but this approach is complex,space-consuming,and lossy.Thus,filtering antenna,as an effective solution to this problem,has been proposed in recent years and still has high research value.By investigating domestic and foreign literatures in recent years,it is found that there is still of great value in designing the filtering antennas with low profile,high frequency selectivity,and wideband performances.Based on the above analysis,this thesis designs three kind of microstrip filtering antennas by using a parasitic element,a half-mode substrate integrated waveguide（HMSIW）cavity,and a special feeding structure.The design processes of these antennas are analyzed in detail.The main contribution is summarized as follows.1.A microstrip filtering antenna loaded with parasitic element structure is proposed,which solves the problems of complex structure and difficult processing of stacked filtering antennas.The proposed antenna achieves good filtering performance.Firstly,the size of the radiating patch is reasonably designed to operate at the desired frequency.Then,a radiation null at lower stopband is generated by connecting the symbiotic branch with the radiating edge of the radiating patch.And a pair of rectangular slots are etched on the radiating patch to generate another radiation null at the higher stopband.Finally,to further improve the gain of the proposed filtering antenna,a mushroom-shaped parasitic element is loaded.The design process and the generation principle of the radiation nulls of the proposed antenna are discussed in detail.The simulation results show that the-10 d B impedance bandwidth of the proposed antenna covers 2.69-2.73 GHz,the relative bandwidth is 1.4%,and the peak gain in the passband can reach 8.76 d Bi,and the profile is 0.014λ₀.The resonant frequencies of the two radiation nulls are located at 2.45 GHz and 2.95 GHz,respectively.The out-of-band rejection levels of the low-frequency stopband and the high-frequency stopband are24.2 d B and 19.7 d B,respectively.The proposed antenna with low profile and simple structure has two independently adjustable radiation nulls,which has excellent filtering and radiation performances.2.A band-pass filtering antenna combined with an HMSIW cavity is designed to solve the problem that most existing band-pass filtering antennas can only achieve high frequency selectivity at a single-side stopband.The antenna consists of a slot-loaded HMSIW cavity,two rectangular metal patches,and five shorting pins.The antenna has two radiation nulls on both sides of the passband.The interaction between the HMSIW cavity and the parasitic patch can generate a radiation null at the upper stopband edge of the passband,realizing high frequency selectivity.To improve the out-of-band rejection level of the upper stopband,a quarter wavelength slot is etched on the HMSIW cavity.The generation principles of the two radiation nulls at the lower stopband are the same,and both are realized by introducing short-circuit nails in the metal patch.The principle of the generation of radiation nulls is explained in detail by analyzing the currents of the proposed antenna.Finally,the proposed antenna is fabricated and measured.The measured results show that an-10 d B impedance bandwidth of 4.3%（2.74-2.86 GHz）,and the frequency selectivities of the low-frequency stopband and high-frequency stopband are 175 and 183 d B/GHz,respectively.The out-of-band rejection levels are 22 d B for the upper stopband and 9 d B for the lower stopband.3.Two microstrip filtering antennas loaded with novel coupling branches are proposed.Firstly,a microstrip filtering antenna with aψ-shape coupling branch is designed.The antenna has good filtering performance on both sides of the passband,but the impedance bandwidth is relatively limited.To solve this problem,a microstrip filtering antenna loaded with T-shape coupling branch is designed.The antenna adopts a simple feeding structure to achieve wide impedance bandwidth and stable gain.To verify the performance of the proposed antenna,the microstrip filter Iing antenna with theψ-shape and the T-shape coupling branches are simulated.The simulation results show that the filtering antenna loaded with theψ-shape coupling branch can achieve|S₁₁|<-10 d B at 1.96-2.01 GHz,and the out-of-band suppression on both sides of the passband can reach 22 d B.The filtering antenna loaded with the T-shape coupling branch can achieve|S₁₁|<-10 d B at 2.06-2.35 GHz,and its relative bandwidth is 13.2%.The average gain within the bandwidth is 4.4 d Bi,and the radiation performance is stable.