Abstract: An antenna circuit which is improved the deterioration of amplitude characteristic in a strong electric field, an antenna circuit for AM broadcasting which can surely inhibit and damp FM-band signals in the strong electric field and amplifies to output AM-band signals, and an antenna circuit for AM/FM broadcasting in which AM-band signals are not damped by means of an FM-band filter. In the first antenna circuit, the output signal of an antenna (10) is supplied to the base of a transistor Tr2 forming a current amplification type amplifier having a high-input and low-output impedance and the emitter of the transistor Tr2 is grounded through a coil L6 and connected to an FM receiver (16) through a band-pass filter (38). In the second antenna circuit for receiving AM broadcasting, an input terminal is connected to an AM amplifier circuit (36) through coils (L7) and L8 in series and to the gate G of a field effect transistor FET.

Abstract: A ground conductor plane 1 and an excitation electrode 2 are provided substantially in parallel with each other. Two electrodes 3a and 3b for respectively radiating a linearly-polarized wave are provided substantially in parallel with the ground conductor plane 1, with the excitation electrode 2 interposed therebetween. The radiation electrodes are provides in close proximity to the excitation electrode 2 such that one end of each of the radiation electrodes 3a and 3b establishes capacitive coupling with respect to the excitation electrode 2. The other ends of each of the radiation electrodes 3a and 3b are grounded such that the directions in which electric fields are to be excited becomes substantially orthogonal to each other. For instance, a feeding section 4 is provided in flush with the ground conductor plane 1 and is electrically connected to the excitation electrode 2 via a feeding electrode 5.

Abstract: An antenna for mounting on a vehicle which restrains damping of a signal voltage by reducing a stray capacitance of a signal path and has an improved antenna characteristic and a short physical length, and an antenna element which is suitable for an antenna for mounting on a vehicle and is flexible by using a helical coil of a large winding diameter are provided. In the antenna for mounting on a vehicle, with respect to a band signal having a short wavelength of a plurality of band signals to be transmitted/received, an antenna element is caused to resonate with a physical length shorter than ¼ of the wavelength of the band signal. A linear line portion is provided at the proximal end, and the antenna element is provided at a predetermined distance from vehicle body and a conductive member of the same electric potential as the vehicle body. The stray capacitance between the proximal end portion of the antenna element and the vehicle body is small, and a signal voltage is outputted without being damped.

Abstract: The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Abstract: A motor-driven antenna device in which an antenna element (10) has a short protruding length so that the outer dimension of the entire device is reduced, and in which damping of an AM-band signal by a signal path is restrained with a small stray capacitance. A rack cord (12) to be meshed with a pinion gear (24) is connected to a proximal portion of the antenna element (10) made of a helical coil over its entire length, and the antenna element (10) is caused to protrude and move to be housed by rotational driving of a motor drive section. The rack cord (12), the motor drive section and the pinion gear (24) are housed in a case (14), and a guide (26) to which the rack cord (12) is abutted and moves while bending is provided in the case (14). Thus, the rack cord (12) is abutted and moves to the guide (26) by the movement of the antenna element (10).

Abstract: The antenna element (1) of a long conductor is formed with at least one returned portion (1a) arranged substantially in parallel to a longitudinal direction of the antenna element. In practice, a physical length of the antenna element in the longitudinal direction is determined to such a length as to be substantially resonated in a first frequency band, and the at least one returned portion (1a) is formed in such a way as to be resonated in a second frequency band twice higher than the first frequency band on the basis of an electric coupling with the adjacent antenna element.