| The waveguide slot antenna has the advantages of compact structure,large power capacity,low loss,and high aperture efficiency.It is widely used in the field of communication and aerospace.In recent years,all kinds of radar and wireless communication systems have great demand for high-performancewaveguide slot array antennas,especially with high gain,low sidelobe and large bandwidth.Aiming at the realization of high-gain and broadband waveguide slot array antenna,this paper mainly investigatesthe broadband design process and decoupling structure of a two-dimensional standing-wave fed waveguide slot array antenna.The main contents is as follows:First,the radiationmechanism,the equivalent circuit,the resonant and the non-resonant waveguide slot array,and the Elliott' design formulas for a waveguide slot array are introduced.After that,the paper briefly introduce our proposal-by combiningthe "overload1' technique with Ansoft HFSS to realize the broadband design of a two dimensional resonant waveguide slot array antenna with decoupling structures.Then,the X-band 8 x 8-element waveguide slot array is designed as an example.This paper describes in detail the how to decompose the overall array into subarrays and how to combine the "overload" technique with Ansoft HFSS to realize the broadband design.By introducingthe partially-corporate feeding network,the overall 8 x 8-element array is decomposed into 2×2 subarrays.Then,the design of the overall antenna is simplified into the independent design of the subarray of radiation slots,that of the coupling slots,and the feeding network.The "overload" technique is adopted in the subarray design of radiating slots first.That is,basedonthe realization of the traditional matching condition,the lateral offset of each radiation slot is further increased.Then the value of the normalized input admittance at the center frequency will be greater than 1 and the equivalent circuit is overloadedas well as mismatched.When the operating frequency deviates from the center point,there will existtwo frequency points in the upper and lower frequency band,where the value of the normalized input admittance will be close to 1.Therefore,when the "overload"techniqueis adopted,the phenomenon of double resonance can be observed in the frequency response of the reflection coefficient.Finally,the bandwidth of impedance matching is significantly improved.Similarly,by increasing the rotation angle of the coupling slot,the "overload" as well as the double resonance is achieved.In addition,When combing the subarrays of radiating slots and coupling slots into a 4 x 4-elementsubarray,byusing the weakcoupling effect among them,we can furtherachieve the triple resonance and improve the bandwidth.As the simulation results of the 8x8 element array antenna,the matching bandwidth for the reflection lower than-12 dB is 12.4%,and the bandwidth for the aperture efficiency higher than 80%is 12.2%.Furthermore,as an exploration of antenna decoupling structures,a small array antenna,4x4-element waveguide slot array loaded with open-ended air cavities on the top side is designed in the X-band as well.The function of the open-ended air cavities is to weaken the mutual coupling among the radiation slots.Their three-dimensional dimensions are optimizedto realizethe radiation slot with open-ended cavity under the periodic boundary condition is equivalent in term ofits equivalent admittance to a single radiation slot under the radiation boundary condition.Aprototype antenna is planned to by fabricated bydirect metal laser sintering.With the consideration of potential problems especially in fabrication and measurement,we also investigate the effects of feeding aperture and the antenna overall dimension.After further optimization,tan antenna with a10%matching bandwidth for the overall reflection lower than-20 dB,and a 10.4%bandwidth forthe aperture efficiency higher than 80%is realized. |
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