Research On Chebyshev Filtering Antennas With The Cavity Structure

Filters and antennas are critical passive components that are widely used in wireless communication systems.The conventional approach is to design filters and antennas separately and then to combine them in series to fulfil the design requirement?s?.Waveguide cavity components with integrated filtering and radiation functions are discussed in this thesis.This novel architecture makes the entire system more integrated and compact.This architecture can be applied to microwave high frequency band or even terahertz frequency band.In this thesis,extensive works have been done in this area and it can be elaborated as follows:?1?Based on the several presentation forms and properties of traditional antennas,a minimalized double-input double-output antenna based on monopoles is presented in this chapter.This antenna consists of two monopoles with a Complementary Split Ring Resonator?CSRR?between them to achieve a better isolation.The antenna is fed by a coupling microstrip line.The measurement shows the reflection loss is lower than–20 dB and the mutual coupling between the two antenna elements is lower than-24 d B at5.8 GHz.The measured gain is 5.1 dBi with a radiation efficiency of 82.8%.Besides,the other antenna parameters also perform well.?2?Waveguide cavity antennas are studied in this chapter.Firstly,a right-handed circularly polarized broad-band antenna based on substrate integrated waveguide?SIW?structure is designed,fabricated and measured.The antenna is fed by a rectangular waveguide.This antenna radiates from a centrosymmetry aperture in the middle of the SIW from an etched right-hand Archimedes spiral.The measured results show that the bandwidth of the antenna is 6 GHz?Fractional Bandwidth?FBW?=17.14%?under the condition of S₁₁?-10 dB and axis ratio?3 dB.Besides,the beam patterns of the antenna also perform well.In addition,due to the use of single-layer structure as well as single feeding,it also has advantages of compact configuration and low cost.Secondly,based on the coupling matrix theory,a 3^rd-order Chebyshev waveguide aperture filtering antenna is designed,by replacing the external quality factor of the filter by radiation quality factor of the antenna.The antenna is fed by WR-90 rectangular waveguide and centered at 9GHz.It consists of three resonators,they are coupled using irises which can be adjusted to control the coupling coefficients.An aperture is opened on the last resonator for radiation.The simulated results indicate that the optimized S₁₁agrees well with the theoretical results predicted by the coupling matrix.The optimized dimensions diviate less than 5%compared with the initial ones extracted the coupling matrix.The fractional bandwidth of the antenna is 5.56%and the gain is 6.58 dBi.The beam pattern is a sector,according with the aperture antenna's radiation feature.This antenna not only combines the characteristics of the filter and antenna,but also has a compact structure and is easy to fabricate.?3?Chebyshev filtering antenna array based on waveguide cavity structure is studied in this thesis and two devices are designed.The first one is a 3^rd-order 1×2 antenna array working at 10 GHz.The antenna is fed by WR-90 rectangular waveguide with the resonators coupled by overlapping the adjacent resonators,this aoviods the use of irises so the whole structure can be more compact.The two symmetrically designed resonators radiate through the apertures in the raditation end at the same time and in-phase to obtain a higher gain.This strucuture not only provides filtering and radiation at the same time,but also power division.The antenna is first fabricated using CNC milling,the measurement showed the fractional bandwidth is 10%under S₁₁?-15 dB with 9 dBi gain,but the beam patterns do not agree with the simulation well.It is found that this is caused by the 20um air gaps exists between the two adjacent layers.To address this,the antenna was refabricated using 3-D printing technology to avoild splitting.The measured results of the printed antenna matchs the simulation well.The other antenna proposed in this chapter is a 2^nd-order 2×2 filtering antenna array with 4 radiation rasonators fabricated by 3-D printing.The couplings are achieved by the dislocation of the adjacent resonators.The measured gain of the antenna 12.51 dBi,obtaining a higher gain but still compact.?4?Two filtering antenna arrays working at 300GHz band are discussed in this chapter.Both of them are based on multilayer sturture.The first antenna array have 2×4 radiation apentures and fed by a parallel feeding network.It employs a 1×2 2^nd-order antennas array as its basic radiation element.The array arrangement which yields the best gain and side lobe level performance is found in this work.The simulation shows the gain is 17.28 dBi and the side lobe level is reduced to-9.2 dB from the initial-6.1 dB.The second antenna array have 8×8 radiation apentures.It employs a 2×2 3^rd-order antenna array as its basic radiation element and fed by a series feeding network.The simulation results show the fractional bandwidth is 8.67%under S₁₁?-10 dB and the gain reachs 26.06 dBi.