Energy Density Antenna Apparatus For Mobile Radio Receiver

Abstract

An energy density antenna has a magnetic current antenna in the form of a slot in a conducting plate and an electric current antenna in the form of a unipole normal to the plate with the signals from each antenna independently coupled to separate square law detectors and combined to provide an output signal which is relatively immune to fading due to motion of the antenna through a standing wave pattern.

Description

BACKGROUND OF THE INVENTION

The present invention is related to an energy density antenna apparatus for mobile radio receiver, and more particularly to energy density antenna apparatus of electric current and magnetic current coupling type.

When vehicles such as automobiles equipped with radio receivers run among the mountains or between high buildings in big cities, there are such problems as fading by standing waves caused by the interference of incident waves reflected by buildings and the like, besides the fading due to insensitive areas of the radio waves due to obstacles in the wave paths.

Having examined the fading caused by these standing waves, we found that the maximum fading frequency fd is expressed by the formula: fd=2V/.lambda. (Hz.) when the vehicles run at a speed of V(M) per second in the coherent standing waves caused by the radio wave having the wave length of .lambda. (M). When the employed frequency is 1,000 (MHz), and the speed of the vehicle V=60(km./hr.), then fd.congruent.110 (Hz), which in turn will have a bad consequence to the communications by mobile radio.

Previously, these type of antenna generally used received either one of electric field or magnetic field of the radio wave only. This meant the prior type apparatus could not meet the aforementioned problem. Other apparatus such as energy density antenna apparatus in which dipole antenna and loop antenna are combined have been suggested to obviate this problem. Such a combination creates a difficulty in impedance matching because the rediation resistance of loop antenna at one-tenth wavelength is about 2.5.OMEGA., and the coaxial system ordinarily used has 50.OMEGA. impedance.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved energy density antenna apparatus for mobile radio receiver while eliminating fading by standing wave.

Another object of the present invention is to provide an energy density antenna apparatus for mobile radio receivers wherein it is easy to match the antenna apparatus with the feeder system in impedance to be connected thereto.

Still another object of the present invention is to provide an antenna apparatus in which the coupling between electric current antenna and magnetic current antenna is minimized.

Further, another object of the present invention is to provide an antenna apparatus suitable for loading in a space where there is a limit in thickness.

According to one embodiment of the present invention the, aforementioned fading caused by said standing wave can be eliminated by combining an electric current antenna and a magnetic current antenna which receive respectively and independently of each other electric field energy and magnetic field energy of the space where such electromagnetic field is and conducting a suitable gain adjustment thereon. This embodiment provides an antenna system in which the magnetic current antenna is used to match the slot antenna with the feeder line easily by the offset feeder method.

According to another embodiment of this invention, the coupling between the electric current antenna and magnetic current antenna is minimized because the former is placed within the latter.

According to still another embodiment of this invention, a cavity having a larger cross section than the area of the slot forming the aforementioned magnetic antenna is utilized. This will enable the effective loading of the apparatus because of its thinness of the body.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and features of the present invention will now be described references being made to the attached drawings in which:

FIG. 1 shows a simplified perspective view of one embodiment of the present invention;

FIGS. 2 and 3 show perspective views of the cavity of a magnetic current antenna to be utilized by the embodiment shown in FIG. 1 and;

FIGS. 4 and 5 show simplified perspective views of antenna according to another embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the accompanying drawings, FIG. 1 shows an energy density antenna apparatus of electric current and magnetic current coupling type in which an incoming wave receives along the direction of the Y-axis a plane wave having only Ez-Hx component and which is a linear polarized wave determined by three-dimensional Cartesian coordinates. In the drawings, antenna apparatus 10 is provided with conductive plate 11 on which are formed magnetic current antenna which is a slot antenna 12, and unipole antenna 13 adjacent to said slot antenna. Thus, the Ez component Ez-Hx component forming said plane wave is received by said unipole antenna 13 and fed to a square law rectifier 15 by way of coaxial cable 14. Hx component is taken out as the voltage induced by electric current Jy as it crosses slot 16 of said slot antenna 12 on the conductive plate 11. This is then fed to a square law rectifier 18 by way of coaxial cable 17. Reference numeral 19 indicates a summing amplifier which is fed with rectified signals obtained by said respective square law rectifiers 15, 18. The summing amplifier 19 adjust gains of these rectified signals suitably, and supplies a signal proportionate to 1/2(.epsilon..sub.o IE .sup.2 +.mu..sub.o HI .sup.2) as an output, wherein IE and HI designate electric field and magnetic field of incoming wave, respectively, E.sub.o designates dielectric constant in vacuum and .mu..sub.o designates permeability in vacuum.

FIGS. 2 and 3 of the attached drawings show perspective view of a cavity of magnetic current antenna utilized in one embodiment of present invention as shown in FIG. 1. FIG. 2 shows a slot shaped cavity 21 having an opening in a plane-shaped conductive plate 11 at one end thereof which is approximately one-half wavelength (.lambda./2) in length and one-fourth wavelength (.lambda./4) is width. FIG. 3 shows a cylindrical conductor 31 of an approximately one-sixteenth wavelength diameter having a slot 32 which is about one-half wavelength in its length alone the axis thereof.

FIG. 4 shows another embodiment of the present invention wherein the essential part of antenna apparatus to receive an incoming wave is composed of Ez-Hx-Hy components. Said antenna apparatus 10 is provided with a unipole antenna 43 at a cross point of slot antennas 41 and 42 located perpendicular to each other on the conductive plate 11. Each of the slots 44. 45 for slot antennas 41 and 42 are formed by locating them perpendicular to cavities 46, 47 having the same length and width, or having the same shape as those cavities shown in FIG. 2 or 3. When the unipole antenna 43 is placed at the cross point of slot antennas 41 and 42, the coupling of the two are maintained at minimum. However, this construction with a considerable depth in the air cavities 46 and 47 presents a problem in loading the apparatus onto vehicles.

FIG. 5 shows an embodiment of the present invention which tries to solve the foregoing problem by providing a box-type cavity 48 which would be open to each of slots 44, 45 and also be wide enough to embrace them in whole at the back of the plate 11. This will, thus, shorten the depth of the cavity 48. In this embodiment, it is also possible to provide the unipole antenna 13 in the slot 16 of the slot antenna 12 when receiving a plane wave. This also enables minimizing of the coupling of the two antennas.

In the embodiment above described, signals are to be fed from the unipole antenna and slot antenna by way of coaxial cable. The use of Lecher wires and the like in place of cable may be utilized.

The slot antenna utilized in the said embodiments will have the same characteristics as that of one-half wavelength dipole antenna having the diameter of a=D/2 , wherein D is the width of the slot. Accordingly, when unipole antenna and dipole antenna are designed in such a way as to have the width of each in the manner as described heretofore, unipole antenna and slot antenna having the same frequency bandwidth, same shrinkage rate and same impedance can be obtained.

Claims

What is claimed is:

1. An energy density antenna apparatus for mobile radio comprising an electric current antenna and a magnetic current antenna, said magnetic current antenna comprising a conductive surface having slot means therein resonant at the frequency of said energy and said electric current antenna being a linear conductor substantially normal to said surface; and separate coupling means for said magnetic and electric current antennas substantially matching the impedances of said antennas wherein electromagnetic energy may be obtained in proportion to energy density of the space in which standing wave is induced by multireflection of radio waves.

2. The antenna apparatus as set forth in claim 1 wherein the magnetic current antenna is a slot antenna approximately one-half wavelength long and one-fourth wavelength wide.

3. The antenna apparatus as set forth in claim 1 wherein said slot antenna is provided with a slot formed on a conductive plate and a box-shaped air cavity connected to and facing said slot.

4. The antenna apparatus as set forth in claim 1 wherein said slot antenna is provided with a slot formed on a conductive plate and an air cavity comprising of a cylindrical conductor having a slot formed correspondingly to said slot.

5. The antenna apparatus as set forth in claim 1 wherein said slot antenna is provided with a unipole antenna within a slot therefor.

6. The antenna apparatus as set forth in claim 1 wherein said slot antenna is provided with a cavity having a bigger cross section than the area of said slot formed on a conductive plate.

7. The energy density antenna apparatus for mobile radio as set forth in claim 1 comprising of square law rectifiers to which are fed signals received by said electric current antenna and magnetic current antenna respectively, and a summing amplifier to which are fed outputs of said square law rectifiers.

8. The antenna according to claim 1 in which said magnetic current antenna comprises a pair of orthogonally intersecting slots in a conducting plate and said electric current antenna comprises a unipole antenna normal to the plane of said slots and positioned at the intersection thereof.

9. Apparatus according to claim 8 and including a cruciform box-shaped air cavity connected to said plate and facing said intersecting slots.

10. Apparatus according to claim 8 and including a rectangular box-shaped cavity having a bigger cross section than the extended dimensions of said intersecting slots connected to said plate and facing said intersecting slots.