Abstract: It is the object of the present invention to provide a fixed earth station in which many antennas can be placed in a site area limited to one-several tenth of the conventional one.On a rotatable base 2, a plurality of antennas 1a to 1e are mounted. A control unit 4 controls the rotation angle of a drive unit for driving the base by the previously known orbital parameters of communication satellites. Further, the azimuth angle and the elevation angle of the respective antennas are controlled by antenna control units 5a to 5e, and the antennas catch and track communication satellites having appeared in the sky. As a result, the rotation angle of the base 2 can be set so that a beam accessing a satellite of a low elevation angle is not intercepted by other antennas. In addition, the area in which the antennas are placed can be reduced to about 1/50 of the conventional one.

Abstract: A PSK signal which is subject to frequency fluctuation and noise is demodulated through a quasi-coherent detection process with a fixed local frequency oscillator (5) noise elimination process using a low pass filter (17,18) after frequency adjustment, and a frequency and phase regeneration process using a PLL circuit (20). The PLL circuit (20) is updated by the estimated center frequency of a received signal by using an FFT (fast Fourier transform) circuit (11), a power spectrum means (12,13,14), and a frequency estimation circuit (15) estimating the center frequency based upon the fact that the modulated signal component exists only on a high level portion of the frequency spectrum.

Abstract: A PSK signal which is subject to frequency fluctuation and noise is demodulated by using a regenerated carrier signal and a regenerated clock signal which are derived from the output of bandpass filters (19, 24) for increasing the carrier to noise ratio C/N. The center frequency of bandpass filter is determined by converting the received time domain signal to a frequency domain signal by using a FFT (fast Fourier transform) circuit, and estimating the center frequency on the frequency spectrum based on the fact that the modulated signal component exists only on a portion which has a high level on the frequency spectrum.