Reduction of near field interference by beam controlling in a transmit phased array antenna

A method of reducing the electromagnetic interference over a broad frequency range by controlling the excitation phase of the element antennas for beam shaping in a phase array used in such systems as wireless LAN is discussed. In this method, an optimum excitation phase of each element antenna is determined by means of the output power minimization algorithm [1] with a directional constraint based on the amplitude and phase data of each element antenna in the far and near fields in the array configuration. The method presented here not only reduces the interference in the near field but also can maintain the radiation level in the desired direction in the far field. In regard to the reduction of interference in the near field by controlling the phase of the transmitting phased array, a method based on the output power minimization with a directional constraint is discussed. Also, in an experiment with an eight-element patch array antenna, the confirmed reduction of the interference is 13.2 dB with a bandwidth of 500 MHz at the frequency of 9.55 GHz and 31.7 dB at the center frequency only. Further, a method is presented for eliminating the effect of quantization error when a digital phase shifter is used for phase control, and its effectiveness is confirmed. (C) 2000 Scripta Technica.