Abstract: A system for communicating between mobile units and an exchange station, with a radio frequency signal, in which an electric signal from a telephone exchange of the telephone station is converted into an optical signal with an electricity-to-light converter. The optical signal is carried via an optical fiber cable to a transmission communication antenna for emission, with amplification of the optical signal if necessary. The emitted signal is received by a receiving communication antenna, amplified with an optical amplifier if necessary, and converted to an electric signal with a light-to-electricity converter.

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: A radio wave receiving system comprises an antenna having at least two antenna elements, a phase shifter connected to at least one of the antenna elements, and a combiner for combining signals passed through the phase shifter and other signals not passed through the phase shifter. Through proper control of the mutual phase difference between signals from the aforementioned antenna elements by using the phase shifter, the system alters the polarization characteristic of the antenna in the direction of incidence of undesired reflected waves and consequently supresses the fading due to undesired reflected waves.

Abstract: A compact and light weight array antenna with a gain of approximately 13 dB comprises a plurality of axial-mode helical antennas with an antenna height of 0.4.about.0.6.lambda. (.lambda.: Wavelength) as element antennas, having cylindrical metallic rims with a rim height of approximately 0.25.lambda. surrounding each corresponding element antenna in order to suppress the characteristic degradation of the device caused by the mutual coupling of element antennas.

Abstract: An antenna system including a single directional antenna having a single directional gain pattern for receiving electromagnetic waves in a certain direction. The orientation of the directional gain pattern is varied to vary the gain of the antenna in directions other than the certain direction in which electromagnetic waves are to be received. The gain is varied at a frequency higher than that of amplitude variations superimposed on the received electromagnetic waves while maintaining the gain substantially constant in the certain direction in which electromagnetic waves are to be received. The antenna gain variations in the directions other than the certain direction are effective to reduce the amplitude of received undesired electromagnetic waves and thereby diminish amplitude variations caused by these undesired electromagnetic waves.

Abstract: A system for receiving through a single antenna apparatus a direct radio wave and reflected radio waves arriving from the same radio wave source, in which the resultant level of the direct radio wave and the reflected radio waves is detected under a condition where the directivity characteristic of the antenna apparatus is slightly altered at the arrival bearing of the reflected radio waves at intervals sufficiently shorter than that of fading perculiar to the paths of the direct wave and reflected waves, and the directivity characteristic of the antenna apparatus is modified at the arrival bearing of the reflected radio waves to raise the resultant level by the use of error voltages of the above intervals each indicative of the polarity of a difference between the directivity pattern of the antenna apparatus and an optimum pattern.