The onboard antenna beam forming network (BFN) of the next-generation communication satellites must offer multiple beam forming and beam steering. The conventional BFN, which directly controls the array elements, is not suitable for a large-scale array antenna because of the difficulty of BFN control. This paper proposes a new BFN configuration that consists of three/four-way variable power dividers and a Butler matrix (FFT circuit). This BFN can offer continuous beam steering with fewer variable components. By introducing new techniques based upon excluding FFT periods and power evaluations by definite integration, the deviation in beamwidth is reduced by 75% or more and the maximum sidelobe level is improved by 10 dB or more.

Electric beam scanning reflector antennas provide beam scanning and pattern control, and can create narrow beams efficiently. However, they are not popular because the beam control circuit is large and difficult to realize. This paper proposes a new BFN configuration for cluster feeding of highly functional scanning antenna. The Enhanced PAttern Control nonswiTch (EPACT) BFN simplifies the beam control circuit and its control algorithm by using a fast Fourier transform (FFT) circuit, phase shifters, and a power divider. Furthermore, this paper proposes a design technique that uses modules to implement the FFT circuit and a method that optimizes amplifier placement to improve antenna efficiency. The design technique facilitates the manufacture of large-scale FFT circuits. The optimized amplifier location improves the antenna efficiency by eliminating the partial concentration of signal power.

Employing a triangular dielectric phase shifter simplifies the beam forming network of an offset beam array antenna because this structure achieves phase control in a single configuration. This paper proposes a design method for a low loss offset beam planar antenna that incorporates a triangular dielectric plate phase shifter on parallel microstrip feedlines. Our design method reduces the loss of the phase shifter by optimizing the microstrip line width. By using the proposed design equation, the optimum low loss phase shifter configuration can be easily established. In addition, this paper presents the actual design of a triangular plate considering size reduction. The results of experiments of the offset beam antenna indicate that our design method is effective in obtaining a simple, low loss, and compact configuration.