Study Of The Serpentine Waveguide Feed Ln Frequency Scanning Antennas

The serpentine feed is the core of a frequency scanning antenna feed system, which produce proper amplitude and phase distribution for the antenna arrays. Most of all, it make the beam scanning over a large angle range by means of changing operating frequency. The formulas and steps for designing a waveguide serpentine feed is presented. In particularly, the method of key components is given. The effect of all components to the phase and reflection of the system is analyzed. Further more, some methods solving these problems are discussed.The author抯 major contributions are as follows.1.With the performance requirement(the pattern of the antenna, the rang of scanning angle, the maximal sidelcbe level and the beam ~vidth)givcn, a method is presented to determine the basic parameters of a serpentine feed, which includes the distance and ~vaveguide length bet~veeii t~vo couplers, the size of the arrays and the number of components. Finally, in view of the absorbed po~ver of the terminated load and the realizablity of couplers, a proper eclectic distribution of coupling degree of couplers is computed synthetically.2.A small, light, compact, ~vide band and high performance H-T coupler with lognitudinal dualslot is presented. In the case of thin slot, taking the effect of wall thickness into account, the coupler is analyzed with the slots replaced by equivalence magnetic current using the equivalence principle. The integral equation system is fonned and calculated by the moment method. The results of calculation and experiment indicate that the coupler is excellent in the chacteristics. On the other hand, the coupling degree can be enhanced by the method of enlarging the slot.3.A ~vaveguide H-T coupler with a large aperture and an inductive post is analyzed where the magnetic current distribution is assumed on the aperture and the current on the surface of the post. The result of calculation and experiment meet the requirement.4.Since the sinuous feed has a large number of 1 80?bends, the design of the bend is quit critical. The impedance match must be extremely good because at the frequency that the antenna beam ~vork on the broad-side position, the reflcctions from all the bends add in phase to produce a large input VSWR. In addition, a poor design of thc bends leads to high-power breakdown. A optimized design of the bend is made using the high frequency simulation software.5.The coupler and the bend cause a phase change in the wave transmitted past the coupler in the sinuous feed and also a phase change in the coupled po~ver. A analysis of these effect to the pattern is presented. In the mean time, the method of correcting the phase errors is given by shortening or lengthening the section of sinuous feed line between couplers from the normal value.6.The reflection characteristic of a serpentine is analyzed where the coupler is replaced by the equivalent of two ports loss network. Various methods for solving these problems are described.The design method of a serpentine feed is presented systematically. The key components are designed and calculated in detail. So, one can conveniently design a high performance sinuous feed rapidly following the steps in this paper.