Broadband Microwave Mode Forming Network

This task relates generally to stripline microwave antenna feed systems and moreparticularly, to a compact low-profile wideband microwave antenna mode formingnetwork. It is used in conjunction with airborne microwave electronic warfare andcommunication systems for purposes of providing instantaneous direction finding andmulti-beam jamming of microwave signals; it includes a number of 90 or 180-degreehybrid couplers along with a number of fixed phase shifters, which are usuallyelectrically interconnected via phase-trimmed coaxial cables. However, suchcommercially available mode forming networks generally involve a rather large,heavy and complex packaging arrangement, especially those networks that arecapable of providing a large number of beams. The complex packaging associatedwith prior networks typically includes a large number of electrical componentsarranged in a bulky layout and coupled to one another by way of crossovertransmission lines. Typical circuit layouts further require multilayer signalinterconnections, which may become unwieldy, cause the feeds to exhibit highinsertion loss due to ohmic, and mismatch loss. In addition, the commerciallyavailable networks are generally capable of operating effectively over a very limitedfrequency range. For instance, typical operating ranges include frequencies between7-15 GHz or 12-18 GHz. Such limited frequency ranges are usually rather narrow andgenerally do not extend into higher frequencies such as those exceeding 20 GHz.Current and future trends in airborne electronic warfare and communicationtechnologies require that provide increasingly wider instantaneous bandwidths. Inaddition, there is an increasing need to provide for a larger number of antenna modesor beams in a smaller more lightweight package. Furthermore, it is desirable todecrease the costs associated with manufacturing such as the costs generally involvedin attempting to meet stringent cable phase-trimming requirements. It is thereforedesirable to provide for an improved low-profile mode-forming network, which iscapable of. operating over wide instantaneous bandwidths. More particularly, it isdesirable to provide for a mode-forming network, which is capable of providing alarge number of antenna modes in a small lightweight package that exhibits ratherlow energy loss.Coupler is widely used in microwave circuits. The influence of its capability cannot be ignored for the capability of the whole circuit. It is very important to make a broadband coupler with high performance. According to the special request of the task, an appropriate method is selected by using the characteristics of offset parallel-coupled strip transmission Lines directional coupler. After a series of analyses and simulations, a satisfying result is finally found out in the broadband 2-18Ghz.90 degree fixed; phase shifter is improved but based on the theory of schiffman broadband phase shifter.