Abstract: A planar antenna includes a first slotted waveguide serving as a power-feed unit, and a second slotted waveguide of planar type coupled with the power-feed waveguide, for radiating circularly polarized microwaves into space. The second waveguide has a metal plate in which a two-dimensional slot array consisting of a plurality of rows of slots is formed. An insulative layer is provided on the second waveguide to cover the slot array. A plurality of rows of metal patch radiators are provided on the insulative layer. These patch radiators are electromagnetically coupled with the slots, respectively, in such a manner that each radiator is directly excited by the corresponding slot through the insulative layer, thereby radiating circularly polarized microwaves.

Abstract: A primary radiator for circularly polarized wave in accordance with the present invention is equipped with conductor projections along the inner wall of the horn antenna in order to convert linearly polarized wave to circularly polarized wave within the horn antenna, without adapting the prior art generator of circularly polarized wave. Consequently, it becomes possible to reduce the axial length and the overall size of the radiator. Moreover, the conductor projections are constructed with their edge sections on the aperture end side of the horn antenna sloping down along the inner wall of the horn antenna, so that generation of higher order modes can be suppressed and a satisfactory directivity can be obtained.

Abstract: An antenna apparatus including a small loop antenna element fabricated by printed circuit method, a variable capacitor for matching the antenna element to broadcasting frequency and an amplifier for the received signal. The variable capacitor and the amplifier are mounted on a printed circuit board containing the loop antenna element and the variable capacitor is rotatably mounted on the board centrally of the loop antenna element. A second loop antenna element may be mounted either concentrically on the said side of the printed circuit board or on the other side of the board. A second variable capacitor cooperates with the second antenna element and a single manual element controls both capacitors.

Abstract: The invention is directed to a tunable loop antenna design which provides impedance matching between the loop antenna and a feed line despite variations of the resonant frequency f.sub.o over a wide range of frequencies. The antenna has a maximum length of one tenth of the wavelength, and comprises a loop conductor and a variable capacitor connected in series with the conductor for providing a resonant circuit. The loop area of the conductor, the circumferential length and equivalent radius thereof are adjusted so that the ratio of the resonant frequency f.sub.o of the antenna and the resonant frequency f.sub.m, at which the input admittance is a minimum, is within the range:0.5-f.sub.o /f.sub.m -3.0.

Abstract: The linear antenna array comprises three or more element antennae which are disposed along a straight line and a feed circuit network connected to the element antennae via an inversion circuit for inverting power in opposite phases. The feed circuit network comprises a plurality of power dividers having common ports connected to respective element antennae, and split ports of a number corresponding to a binomial coefficient, phase shifters respectively connected to the split ports, and a common power divider connected to the phase shifters.