FR2472282A1 - Wide bandwidth car whip aerial - is formed by open coaxial line with inner conductor earthed and outer excited to provide direct and capacitive propagation - Google Patents

Abstract

The aerial has a length equal to or less than a and of a wavelength a much wider passband than normal. It comprises a copper core conductor (2) electrically connected to an earth reflector plane (3) formed by the car body. The conductor is surrounded by an insulator such as glass fibre in turn enclosed in an outer metal conductor cylinder open at its extreme ends. At its lower end adjacent the car body the cylinder is connected to external circuitry to transmit or receive electromagnetic signals. The form of the aerial provides two modes of electromagnetic propagation, directly by way of the outer conductor and capacitively by way of the inner conductor, to provide an improved bandwidth.

Description

It is well known that the radio characteristics of an antenna

  thin whip type can only be used in a very narrow frequency range which is substantially equal to 5% of the tuning frequency Fo when the antenna is dimensioned at 1/4 of the tuning wavelength A. methods used to widen the bandwidth of such an antenna go to the detriment of the desired objective since they consist in increasing in

  large proportions of the length-to-diameter ratio or by the addition of cir-

complicated compensation at the base.

The present invention describes a simple and original method which makes it possible to considerably broaden the bandwidth of a whip antenna without modifying its length-to-diameter ratio or altering its characteristics.

of transmission.

  An antenna in accordance with the invention will be described using

diagrams attached.

Figures 1 and 2 show the principle of realization of an antenna

according to the invention.

  Figure 3 shows the sectional view of a vertical whip antenna conform

To the invention.

  Figures 4 and 5 show the views of an embodiment according to the invention

and operating in the VEF bands.

  The vertical conductor (2) whose lower end (5) is electrically connected to a metal plane (3) forming a ground plane is surrounded by an insulating cylinder (4) coated on its outer lateral surface with a conductive cylinder ( 1) open & its ends; the lower end (6) of the conductive cylinder (1) is excited or collects the radiofrequency currents so that two distinct waves (P1) and (P2) of different and harmonic speeds are

propagated and radiated.

  RATIONALE z the process developed consists in carrying out a line of trans-

open coaxial mission & its upper end and excited At its base so that the coaxial element is connected to the ground of a reflective plane, possibly being the body of a mobile, the external conductor being excited directly by the radio frequency currents of so that there is propagation and radiation of two distinct waves is a guided wave propagating inside the coaxial and

  radiated by capacitive effect and a surface wave propagate along the con-

  external conductor and radiated directly.

It can then be seen that as a function of the value of the dielectric permittivity of the coaxial medium (4) and for a value of the relative permittivity Er equal to 4 the ratio of the reflected wave to the direct wave or coefficient of reflection remains very low and less than 0.33 in a frequency range greater than 50% of the frequency for which the height of the antenna (h) corresponds to a quarter of the working wavelength. 2472282 I1 is & note that for Er = 4 the ratio of propagation velocities of interior and exterior waves is 2 since _ A __ _ The applications of such a process are numerous and susceptible of

important development.

- civil and military aviation

  - fixed and land mobile transmissions ...

  FIG. 3 represents an antenna in accordance with the invention, the excitation of which

  is carried out in (8) via an insulating bushing (7).

  FIGS. 4 and 5 show different views of an embodiment in accordance with the invention and operating in the aviation band 118 - 150 MHz with a statioemn wave ratio lower than 2 and a comparable radiation efficiency

with the Ao / h whisk of Ame diam & ire.

Its diameter 9 is 5 m and its height h is 45 cm. (2) is a copper conductor of diameter I m embedded in the mass of the fiberglass whip (4). (1)

  is the "external braid reyStue of a heat shrinkable sheath (11).

(9) is a rademe profiled in insulator which holds the elements of the antenna in place * t protects them. The excitation is carried out by the coaxial connector (13)

  fixed on the fixing plate (3) fitted with shaped parts (12) for the

chage of the filling material (10) ensuring the sealing.

  The antenna is fixed to the aircraft cabin by means of the fixing screws

(15), the neoprene flat seal (14) allowing sealing at the interface.

Claims (3)

  I / Antenna for emitting or receiving electromagnetic fields of a height equal to or slightly less than 1/4 of the working wavelength Xv and characterized in that the radiating element of the whip type is formed by a coaxial line open, the tme of which is connected at its lower part to a metallic plane called the ground plane while the conductive outer sheath is excited or collects the radiofrequency currents so that two propagation isodes are created allowing a considerable widening of the band from   the antenna thus formed and without altering its radiation characteristics.   2 / antenna according to claim 1 characterized in that the radiating element is inclined or curved relative to the vertical so as to provide a grip on the minimum wind.   3 / Antenna according to claims 1 and 2 characterized in that the element radiant and food are included in a radome.