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.