Abstract: Accordingly to the present invention, when an incidence angle of a direct wave or a satellite elevation angle reaches a predetermined value, signals from two (or more) antennas, which are disposed at positions where variations in the field intensities of radio waves recevied by the two antennas are negatively correlated (i.e. when the received signal level of one of them is low, the received signal level of the other is high) or uncorrelated (i.e. the variations are not related to each other), are successively or discretely switched at a suitable switching period, by which burst-like errors are spread with time to perform the de-interleave or interleave function in decoding transmitted signals.

Abstract: A microstrip antenna of two-frequency separate-feeding type for circularly polarized waves is disclosed, in which four radiation conductors are disposed on a dielectric plate mounted on a conducting ground plane and each radiation conductor has its marginal portion partly short-circuited via a short-circuiting conductor to the conducting ground plane and is supplied at its feeding point with power via a feeder passing through the conducting ground plane and the dielectric plate. The four radiation conductors are composed of two pairs of radiation conductors of different sizes adjusted so that two desired frequencies can simultaneously be used for transmission and for reception, respectively, the conductors of each pair being arranged to generate a circularly polarized wave.

Abstract: A quadrifilar helix antenna according to the present invention incorporates four helix conductors wound around an axis in the same winding direction. Each of the helix conductors has a linear conductor which is parallel to its axis at either end or both ends of the helix conductor. The present antenna reduces the effect of multipath fading due to sea-surface reflection in mobile satellite communications.

Abstract: An interference cancellation system has a combiner which removes an undesired component from a main signal including both a desired signal and an undesired signal received by a main antenna. A power sensor measures output power of a main signal. A weight control circuit is coupled with an output of the power sensor. An auxiliary antenna receives an undesired signal. A variable complex weight control circuit adjusts an undesired signal from the auxiliary antenna according to the output of the weight control circuit to provide an input signal to the combiner. The variable complex weight control circuit operates so that the output power becomes a minimum.