AN ELECTROOPTIC BFN FOR ARRAY ANTENNA BEAM FORMING

This paper proposes a new type of optically controlled BFN (beam formi ng network), an electro-optic BFN using an optical waveguide structure . In this BFN, antenna beam forming is performed using conventional op tical variable phase shifters and conventional optical variable direct ional couplers. An electro-optic BFN can easily utilize monolithic int egration capability that will be advantageous to microwave stabilizati on. In order to discuss practical applicability, microwave characteris tics and beam forming characteristics were examined using an experimen tal BFN fabricated on a LiNbO3 substrate. Resulting from electro-optic lightwave control, linear phase shifting and variable amplitude distr ibution were measured at various microwave frequencies. Without any ot her control except for optical offset frequency locking and applying c onstant voltages, typical short term fluctuation in L-band microwave w as measured to be within 3 degrees(p-p) in phase and 2.5 dB(p-p) in am plitude, respectively. For the first time, an electro-optic BFN was su ccessful in performing beam forming in an L-band array antenna as well as coaxial cables. It was also verified that radiation pattern measur ed in 60 degree beam steering using the experimental BFN was comparabl e to that calculated using conventional microwave BFNs. The experiment al results show the feasibility of utilizing an electro-optic BFN in f uture advanced microwave/millimeter-wave array antenna systems.