Transmission Characteristics And Applications Of Post Wall Coplanar Waveguide And Coplanar Stripline

With the rapid development of wireless communication technologies,microwave systems and circuits are advancing to wider bandwidth,higher integration,reduced size,more cost effectiveness,lower weight,lower power consumption and multiple functions.This places stringent requirements on microwave and millimeter wave transmission lines,increasing their complexity and diversity.Comparing with other conventional planar transmission lines,coplanar waveguide and coplanar stripline have an advantage that the electric fields in them are mainly horizontally polarized,it also facilitates the installation of lumped elements and provides good electric connection with probe testing equipment.They are widely used in modem microwave and millimeter wave systems.However,coplanar waveguide and coplanar stripline have the shortcomings of high characteristic impedance,narrow range of available impedance,difficulty in matching to 50 ohm systems,narrow slot width,high demand on precision during the manufacturing process,small power capacity and serious crosstalk.This dissertation proposes two new transmission line structures,namely Post Wall Coplanar Waveguide(PWCPW)and Post Wall Coplanar Stripline(PWCPS).PWCPW and PWCPS not only inherit the advantages of conventional coplanar waveguide and conventional coplanar stripline,but also provide the benefits of moderate impedance,wider available impedance range,higher power capacity and smaller crosstalk.The proposed PWCPW and PWCPS can be used to increase the performance of microwave and millimeter wave systems and antennas.This dissertation covers both the theoretical foundation of PWCPW and PWCPS and their practical applications in microwave networks and antenna.The main contributions are summarized below:1.Firstly,two new transmission lies structures,Post Wall Coplanar Waveguide(PWCPW)and Post Wall Coplanar Stripline(PWCPS)are proposed in this dissertation.The proposed transmission lines solve the problems that conventional CPW and CPS encounter,including high impedance,small available impedance range,high precision demand in manufacture,small power capacity and serious crosstalk.Secondly,a novel decomposition method for calculation of the characteristic impedance of PWCPW and PWCPS is proposed.By using this method,PWCPW is decomposed into two components,namely the conventional suspended waveguide part and two parallel-plate waveguide part.Next,the characteristic impedance for these two parts are calculated by using existing formulas.Lastly,the characteristic impedance for PWCPW is calculated by connecting the characteristic impedance for these two components in parallel.The same way can be used to calculate the characteristic impedance for the PWCPS.The characteristic impedance for asymmetrical PWCPW and asymmetrical PWCPS can also be derived using the same method.This method accounts for the physics of the proposed transmission line structures,is easy to implement and enables quick analysis and design.Numerical simulations are performed using full wave electromagnetic software to verify the accuracy of the analytical formulas.Thirdly,transition between different transmission lines,such as microstrip-PWCPS,PWC.PW-PWCPS and SMA-PWCPS reversed polarity structures are proposed.Experiments are carried out to investigate the characteristic of the proposed PWCPS and PWCPS.Transmission and reflection characteristics in the frequency range of 10 MHz to 20 GHz are measured.These results are then transformed into time using the Fourier transform.Then comparisons are made between PWCPW and conventional coplanar waveguide,PWCPS and conventional coplanar stripline.The differences are well demonstrated in time domain with the normalized Euclidean distance and its numerical characterization matrix based on the signal space.The results in both the frequency and time domain show that the proposed PWCPW and PWCPS have excellent transmission characteristics and outperform their conventional counterparts.2.Several power dividers based on PWCPW and PWCPS structures are proposed.Firstly,two narrow band Wilkison power dividers and one wideband band power divider using multiple stepped impedance transformers are realized using PWCPW and PWCPS,which further proves the accuracy of the analytical expressions for characteristic impedance of PWCPW and PWCPS.Numerical methods are used to achieve designs with optimal performance.The optimization goals are derived from the normalized Euclidean distance and its numerical characterization matrix based on the signal space and then are used to optimize the in-phase and out of phase power dividers for ultra-wideband and pulse applications.Prototypes of these power dividers are manufactured and measured in the frequency domain using vector network analyzer,demonstrating a good agreement with simulation results.The measured results are transformed to the time domain to examine performances.Both the results in frequency domain and time domain indicate good performances of the designed power dividers.The effectiveness of the time domain designing methods is verified.It also proves that PWCPW and PWCPS transition structures provide higher flexibility and can be used in the design of various microwave components.3.Antenna based on PWCPS are proposed.A Gaussian tapered slot antenna using PWCPS with improvement of cross polarization for ultra-wideband applications is proposed and experimentally verified.As Gaussian curve can be sub-divided into exponential gradual section,linear expansion section and retarded expansion section,it is suitable for the feed,radiation and resistance-load for ultra-wideband antenna respectively.A rhombus shape PWCPS presents easy matching and resistance-load.The antenna can be fed by a coaxial connector directly.The post wall coplanar stripline form a rhombus-like shape,which presents easy matching and resistance-load and it can be fed by a coaxial connector directly.It is demonstrated by both simulation and measured results that the proposed antenna can work within the bandwidth of 1.5 GHz to 20 GHz with a return loss less than-10 dB.Terminal resistors are used to absorb the reflected signal and it greatly reduces the reflected signal.A maximum realized gain of 12 dBi can be achieved in the specified frequency range.Compared with the conventional or antipodal tapered slotline antenna,the metallic post-wall exhibits symmetry,thus it can lower the cross-polarization level.The experimental results show that the broadside cross-polarization levels is lower than-22 dB in the entire frequency band.In summary,new transmission lines PWCPW and PWCPS have been proposed and studied in details.Analytical formulas for calculation of the characteristic impedances have been presented and verified.Transition structures for interfacing with PWCPW and PWCPS,power dividers and an antenna have been designed,numerically simulated and experimentally studied.It has been demostrated that the PWCPW and PWCPS transmission lines have good impedance and transmission characteristics and offer high flexibility.This study lays foundations for the applications of the PWCPW and PWCPS structures in microwave system.