The Design And Research Of Novel Millimeter-wave Butler Matrix Based On Substrate Integrated Suspended Line

For the new generation of mobile communication technology,5G millimeter-wave frequency band with sufficient spectrum resources is used to realize millisecond-level delay,ultra-large data capacity communication.However,the signals in millimeter-wave suffer from large propagation path losses and low diffraction ability.Therefore,millimeter-wave communication has also become a difficult point in the 5G research.Due to the advantages such as ease of implementation and accurate beam pointing,Millimeter-wave multi-beam antenna arrays have triggered widespread attention for many researchers.As an important building block of the multi-beam antenna,the beam-forming networks can effectively improve antenna gain,reduce interference between antennas and compensate for signal attenuation in millimeter-wave.With the trend of 5G technology of miniaturization,multi-function,and high integration,higher requirements have been put forward for the beam-forming networks.The Butler matrix is widely studied for its simple structure and low power consumption.Up to now,the designs of the Butler matrix are almost based on the microstrip line.Their corresponding performance will deteriorate as the frequency increases to millimeter-wave due to the large loss.The patch element with low insertion loss and high power handling characteristics has been widely applied.Moreover,it also has following excellent properties,such as ease of construction,low profile,and high mechanical strength.However,the radiation loss of the patch element will enlarge with the increase of frequency due to its semi-open characteristics.Substrate integrated suspended line(SISL)is a new kind of multilayer transmission line,and it features good properties,including low loss,high Q value,self-packaging,high integration,and fine high-frequency characteristics.It is especially suitable for integration with patch circuits to implement the millimeter-wave Butler matrix.To achieve the novel Butler matrix and its components with low loss,multi-function,and miniaturization in millimeter-wave band,according to the new topology,two prototypes of the Butler matrix based on the SISL flatform are proposed in this paper.In prototype I,the crossovers are removed and a non-standard phase difference of-180°?180° is obtained.In prototype II,both the crossovers and phase shifters are removed and the standard phase differences of ±45° and ±135°are obtained.Since the 3-d B coupler with an arbitrary phase difference is needed for the construction of the novel Butler matrix,two kinds of millimeter-wave couplers are firstly proposed by using the circular patch element.In the first coupler design,arbitrary coupling coefficient and phase difference of 0?180° can be achieved by using a circular patch with multiple radii and adjusting the port location,resulting in simpler design complexity.In the second coupler design,based on the double-radius circuit model,continuous variation of coupling coefficient can be implemented by adjusting the radius ratio and quadrature phase characteristics is realized.The simulated results show that the insertion loss of the two couplers is only 0.1 d B at 26 GHz.Similarly,to meet the construction requirements of the Butler matrix and improve the flexibility of the Schiffman structure,a Schiffman differential phase shifter loaded with open-stubs is proposed.The insertion loss is 0.3 d B at the center frequency,and the phase error maintains within ±1.1°.Through the comparative analysis,good agreement between the measured results and simulated results of the two Butler matrices is shown.Moreover,the proposed Butler matrix realizes good properties of low cost,miniaturization,and high integration.