Research On Open-ended Waveguide Array Antennas And Low Cross-polarized Patch Antenna

Modern wireless systems have higher requirements for each component.For example,in satellite and missile-borne applications,the antenna efficiency is often required to be as high as possible within a given limited space.In addition,the antenna needs to have a lower profile to further reduce the volume.However,the traditional microstrip antenna,which is widely used,suffers from high losses when large arrays are constructed.Therefore,in recent years,arrays and antenna elements with low-loss characteristics have received widespread attention in the wireless field.Waveguide slot antennas filled with air medium usually have low loss,but the current research has two defects:（1）The radiating part and feeding network of the waveguide antenna are usually layered,resulting in high assembly accuracy and high profile height.（2）For the series-fed waveguide slot array,the beam direction changes with the frequency,and a stable beam cannot be achieved in broadband.The research on low cross-polarized antennas is also a current research hotspot,and it is a challenging problem for patch antennas to achieve low cross-polarization while meeting other performance requirements.To solve these problems,this paper systematically studies open-ended waveguide array antennas and low cross-polarized patch antennas.The main innovative work is as follows:1.A single-layer low-loss waveguide array antenna based on an open-ended waveguide is proposed.The feeding methods of waveguide arrays can be divided into the coupling between the radiating layer and the feeding layer or the H-plane waveguide feeding.Considering the shortcomings of these schemes,this paper proposes a scheme of an E-plane waveguide network that provides direct feed to the elements.This network has a compact structure,short feed line,and small aperture size.Since the entire feed network is cut along the E-symmetry plane without cutting off the currents,the leakage loss is very small when it is processed into two parts and then combined into one.To solve the problem that the feed waveguide directly excites the radiating element,a scheme of using an E-plane waveguide whose normal direction is parallel to the array to excite the open-ended waveguide element whose normal direction is perpendicular to the array is proposed.In this scheme,the feed waveguide is placed to one side of the centerline of the excited waveguide element.At this time,the aperture fields of the two adjacent radiating elements excited by the E-plane waveguide exactly have the same amplitude and phase.To verify the accuracy of the simulated results,a16×16 single-layer planar waveguide antenna array operating at 60 GHz was simulated and fabricated.According to the simulated results,the radiation efficiency of the antenna is above97.5%in the operating band ranging from 57 to 66 GHz.The measured results are in good agreement with the simulated results.Within the relative bandwidth of 16.4%,the aperture efficiencies of the antenna exceed 80%,which is the highest among the current waveguide slot array antennas.At the operating frequency of 61.5 GHz,the realized gain of the array antenna reaches 32 d Bi.The values of the cross-polarization in the two main planes are less than-30d B.The array can be applied in various frequency bands.At present,it has been applied in the Ku band,V band,U band,and W band.2.A broadband multi-band antenna based on an open-ended waveguide is proposed.Based on a detailed analysis of the frequency characteristics of the basic open-ended waveguide structure,the impedance bandwidth can be further expanded by changing the internal dimensions of the cavity and adding a waveguide converter between the waveguide cavity and the feed waveguide.The simulated results show that the bandwidth can be adjusted to 33%.On this basis,a multi-band modulation of the open-ended waveguide antenna is carried out using a non-radiating groove loading technique.The loaded groove introduces a notch and an additional resonant point to achieve broadband dual-band characteristics.The proposed dual-band antenna can adjust all resonant points and notches independently through different parameters.To verify the correctness of the simulated results,a single element antenna and a 2×2 array are processed and tested,where the 2×2 array adopts the array design method and fabrication method described in Chapter 2.For the element antenna,the measured impedance bandwidth of the two bands exceeds 22.2%and 14.2%,respectively,fully covering the 26/28GHz（24.25–29.5 GHz）and 39 GHz（37–40 GHz）bands of 5G millimeter wave.In addition,this chapter also designs,processes,and tests a tri-band antenna by loading two non-radiating grooves with different sizes on the narrow wall of the open-ended waveguide cavity.It should be noted that the above two works are only application examples of this frequency response control scheme.Different requirements of practical applications can be reasonably met by using the non-radiating groove loading technology.3.A broadband circularly polarized antenna based on an open-ended waveguide is proposed.By loading two radiating stubs on the wide wall of an open-ended waveguide,the TE₀₁ mode whose field direction is perpendicular to that of the TE₁₀ mode of the main waveguide is excited.The two radiating stubs act in the lower-and higher-frequency bands,respectively,and their change in size and position can be used to adjust the difference in amplitude and phase between the two field components.To achieve impedance matching,a matching window is cut between the stub acting at the lower frequency and the waveguide cavity so that the frequency range of the axial ratio bandwidth and the impedance bandwidth essentially coincide.In addition,a corresponding 2×2 array was designed based on the low-loss array construction method in Chapter 2.The measured results of the machined phototype show that the element antenna has a wide impedance bandwidth of 50%and a 3 d B axial ratio bandwidth of 50%,covering all frequencies from 24 GHz to 40 GHz.The measured gains of the element antenna are 6.7 d Bic and 6.9 d Bic at 28 GHz and 38 GHz while those of the proposed array are 12.3 d Bic and 13.9 d Bic,respectively.In addition,a broadband dual circularly polarized antenna element based on an open-ended waveguide is proposed as an extension of the work above.The proposed cross-shaped element structure consists of two rectangular open-ended waveguides crossed as two arms.The distance from the two ends of each arm to the center of the cross is unequal,and this unequal design eliminates the high axial ratio point in the operating band,resulting in a wide axial ratio bandwidth.The proposal of this element lays the foundation for the construction of subsequent large-size dual circularly polarized arrays.4.A patch antenna with wide band,low cross-polarization and high gain is proposed.The structure adopts the aperture-coupled feed method,that is,the energy from the microstrip line at the bottom is coupled to excite the upper shorted patch through the coupling slot curved in the center of the ground.This excitation method can effectively suppress the two sources of cross-polarization:the higher-order modes and the fringing field along the non-radiating edges at the fundamental mode.The resonant points of the patch and the coupling slot together realize the broadband performance,and the additionally loaded matching stub further expands the bandwidth of the antenna.The non-radiating edges of the proposed patch are loaded with two shorting walls.The shorting walls allow the patch to detach from the dielectric substrate,thus reducing the dielectric loss and improving the gain.Due to the change in the boundary conditions of the patch,the working mode of the proposed antenna is changed to TM₁₁ mode,so its working frequency is determined by the length and width of the patch.Therefore,the beam widths in the E-plane and H-plane of the antenna can both be adjusted in a certain range.In this study,an antenna structure with an operating frequency of 12.5 GHz has been processed and measured.Its relative bandwidth can reach 35%,and its gain,as well as the cross-polarization,can reach 11.2 d Bi and-40 d B.The beam widths in the E-plane and H-plane can be adjusted in the ranges of 30°to 50°and 50°to 60°,respectively.