JPS591001B2 - Antenna System - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna system using a reflector, and particularly to an antenna system in which the reflector has a ventilated structure.

In some cases, antenna systems use reflective surfaces to focus the wave energy radiated by the feed elements.

In other cases, reflectors are used to suppress radiation in undesired directions from an array of antenna elements, thereby increasing radiation in desired directions.

In some systems, the antenna requires a reflector of considerable size, in which case the use of a so-called solid conductive surface without any apertures will cause the reflector to have considerable wind resistance. The power will be increased by 5.

When wind forces are applied to the antenna, it is necessary to use extensive mechanical structures to maintain the desired curvature of the reflector surface and prevent damage to the reflector.

Additionally, wind loads make it more difficult to rotate mechanically steered antennas, which naturally necessitates the use of high power motors for rotation.

To reduce this wind loading on the reflector, previous designs have used reflectors consisting of a grid of parallel conductive columns.

Although this type of reflector has low wind loads, a significant portion of the incident radiation leaks through its grid.

This reflector leakage is not a significant problem if the reflector is a curved converging reflector, but in the case of a planar array,
The radiation leaking through the reflector forms a highly undesirable focused four-backlobe.

April 1948, Bulletin of the IR
``The Radiation Resistance of Antennas in Infinite Arrays or Waveguides'' published in Vol. 36, No. 4.
t ion Re5i 5tance Of An A
ntenaIn An Infinite Array
In a paper titled ``Or Waveguide,'' the inventor, Harold A. Wheeler,
Mr. Wheeler, R.C., has shown that a reflective surface can be formed by an array of reflective elements consisting of half-wave length conductors; Hanson) in the 1966 Academic Press (Academic 0 Press)
Press), New York, Volume 366, “Microwave Scanning Antenna (Microwave Scanning Antenna)
ave Scanning Antennas)”.

However, such an array of reflective elements cannot be used to support antenna elements because the transmission lines that direct the wave energy to the elements detune the array.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a new and improved antenna system having a reflector that is of substantially ventilated construction.

Another object of the invention is to provide such an antenna system that reduces the amount of radiation leakage through the reflector.

Yet another object of the present invention is to provide the above antenna system in which the reflector has a conductive column and an antenna element is attached to the column.

According to the present invention, there is provided an antenna system which has a ventilation type structure and has an improved effect of suppressing radiation leakage through a reflector.

The antenna system of the present invention includes a reflective grid of substantially parallel conductive columns and a plurality of collinear arrays of reflective elements, the array being substantially parallel to and selective to the columns. will be distributed to

The antenna system further includes at least one linearly polarized antenna element for radiating wave energy such that the polarization of the antenna element is aligned substantially parallel to the column.

The antenna system of the present invention also includes means for supporting the antenna elements, posts and arrays.

When wave energy is radiated by the antenna element,
The reflective elements provide a suppression of radiation leakage through the grid of conductive columns.

Next, the present invention will be described in more detail with regard to embodiments of the present invention based on the accompanying drawings.

The antenna system of FIG. 1 includes a plurality of dipole elements 10, which are antenna elements for radiating wave energy.

These dipole elements 10 are mounted on conductive columns 11 forming a planar grid.

A collinear array 12 of reflective elements 13 is distributed on these conductive columns 11 .

These collinear arrays 12 and conductive columns 11 are held in place by support structures 14.

A planar grid of conductive columns and a collinear array are "cross-ventilated" structures, i.e. the distance between the columns and the array is
It should be larger than the cross section of the array and pillar, preferably much larger.

Conductive pillar 11, collinear array 12 and support structure 14
forms a planar reflector of wave energy.

The dipole elements 10 are all mounted on a conductive column 11 so as to face one side of the planar reflector.

The size and shape of this reflector are similar to the size and shape of a conventional non-ventilated (having no ventilation apertures) metallic reflector of a planar array of dipole elements.

The location and number of dipole elements 10 are selected based on principles well known to those skilled in the art of antennas, as are the amplitudes and phases of the wave energy signals provided to each dipole element 10. .

The dipole element 10 of the antenna of FIG. 1 is arranged so that the polarization of the element is parallel to the conductive column 11.

Linearly polarized elements other than dipole elements may be used in antenna systems embodying the invention, as long as the elements are arranged to have a polarization that is parallel to the conductive column 11.

For example, another type of antenna element that can be used is a resonant loop antenna.

FIG. 2 shows a typical dipole element 10 with a conductive column 11
This shows one technique for attaching the device to the device.

In this embodiment, the conductive pillar 11 is hollow,
A transmission line 15 supplying wave energy to the dipole element 10 may pass through this conductive column 11.

Such presence of the transmission line 15 does not have any influence on the radiation characteristics of the antenna system.

As long as the transmission line 15 is close to the conductive column 11 and is grounded to the column, the transmission line 15 is connected to the conductive column 11.
It will be clear to those skilled in the art that the antenna may be located externally to the antenna 1 and not substantially interfere with the radiated noisiness of the antenna.

FIG. 3 shows a portion of one collinear array 12 of reflective elements 13. FIG.

In the embodiment of FIG. 3, collinear array 12 is formed by using a non-conductive core 16 of insulating material.

A reflective element 13 is attached to the outside of this core 16.
The element consists of an elongated conductive cylinder.

The length, diameter, and spacing of this reflective element 13 are selected by the first
This is done so that the reflective element 13 is resonated so as to suppress radiation penetrating the grid of conductive columns of the illustrated antenna.

The reflective element 13 need not be cylindrical, but may have another shape that is more convenient for the particular embodiment.

In some applications, reflective element 13 may be an elongated strip of conductive material formed on a flat, non-conductive surface.

The resonance of the reflective element 13 is an important feature of the invention.

An elongated conductor whose length is effectively half a wavelength at the operating frequency is self-resonant, meaning that the current in a half-wave conductor in the presence of an electromagnetic field is substantially greater than the current in a continuous conductor. The matter is clear to those skilled in the art.

In the case of a half-wave reflective element, the inherent inductance of the conductor causes resonance due to its own self-capacitance;
Reflective elements have minimal impedance.

When placed in an electromagnetic field of wave energy of the appropriate frequency, the half-wavelength element carries the maximum amount of current.

This current produces secondary radiation that interferes with the incident electromagnetic field in a certain direction.

Because the current associated with the resonant reflective element is large, the interference with the incident wave energy is greater than the interference with the non-resonant element.

Therefore, the degree of interference between the incident wave energy electromagnetic field and the reflective element can be adjusted by selectively resonating or non-resonating the reflective element, that is, by adjusting the length of the reflective element. It's obvious.

The second-order radiation of the reflective element varies slowly with frequency, so that interference effects exist over a finite frequency band.

The collinear array of reflective elements 13 shown in FIG. 3a is
It consists of a conductive element 13 whose length is less than half a wavelength.

These elements can also be made resonant by appropriately adjusting the spacing between adjacent elements of the collinear array.

This spacing provides a capacitance that can be used to resonate with the shortened inductance of element 13.

The amount of secondary radiation from the collinear array in Figure 3a can be adjusted similarly to the secondary radiation of an isolated half-wavelength resonant reflective element.

The collinear array of FIG. 3a has more favorable characteristics than the half-wavelength collinear array because it has an inherently wider resonant bandwidth.

Bandwidth can also be increased by increasing the diameter of the reflective element, but this has the effect of increasing wind resistance.

An alternative array to the collinear array of FIG. 3a is shown in FIGS. 3b and 30.

In the array of FIG. 3b, the capacitance required to resonate with the inductance of reflective element 13 is provided by fixed capacitor 17.

The array of Figure 3c is of similar design to the array of Figure 3a but further includes a protective cover 18 of dielectric material;
This prevents a drop in array tuning due to deposits on the collinear array.

The operation of the antenna system shown in Figure 1 is as follows: collinear array 1
This will become clear after considering the characteristics of No. 2.

If there is no collinear array 12, dipole element 10
The linearly polarized energy radiated by the conductive column 11
is partially reflected and partially transmitted through the grid.

The collinear array 12 is selectively resonant such that the secondary radiation from the elements 13 of the array is of equal amplitude to the wave energy penetrating the grid of conductive columns 11.

The position of the collinear array 12 is selectively adjusted such that the phase of the secondary radiation from the reflective elements 13 is opposite to the phase of the wave energy passing through the grid of conductive columns 11.

In most cases, the collinear array 12 consists of conductive columns 11
and are on a common plane.

The secondary radiation from the collinear array 12 interferes with the wave energy penetrating the grid of conductive columns 11 and results in a substantial reduction in wave energy signal leakage through the reflector.

Accordingly, the collinear array 12 adjusts its amplitude and phase to completely eliminate wave energy leakage in a particular direction, or to substantially eliminate it over a particular range of angular directions.

It is usually desirable for the dipole element 10 of the antenna of FIG. 1 to radiate a single antenna beam.

In the embodiment of FIG. 1, since the spacing of the dipole elements is equal to the spacing of the conductive columns 11, this spacing is operative to avoid the presence of undesirable extra antenna beams, referred to as "grating suspensions". Usually chosen to be less than one wavelength in frequency.

Spacings of less than one wavelength typically allow leakage radiation to be substantially eliminated by placing a single column of reflective element in each space between adjacent conductive columns of the grid.

In this case, the reflective elements are most effective when they are placed equidistant from the closest pair of conductive columns.

A reflector having a structure such as that shown in FIG. 1 is most desirable when the antenna is in the form of a planar array of elements.

As shown in FIG. 4, without using the present invention, the element 10
has a desired main antenna beam 22 that is perpendicular to the plane of the grid 21 of conductive columns 11 when provided with wave energy signals of equal phase.

Leakage of wave energy through the grid 21 of the conductive columns 11 produces an antenna beam 19 in the opposite direction to the desired antenna beam 22, referred to as a "back lobe."

The wave energy signal passing through the grid 21 of conductive columns is
Being in substantially focused phase, the undesired beam 19 has a substantial amplitude relative to the desired beam 22.

If the collinear array 12 of reflective elements 13 is distributed in the grid 21 of conductive columns 11, the extent of radiation leakage through the grid 21 of conductive columns 11 is substantially reduced.

The unwanted beam 19 is substantially reduced in size as the radiation leakage through the grid 21 of the conductive columns 11 is reduced and a beam 20 is formed, which beam 20 is free from the main beam 22. It has a small swing width.

Utilizing the ``tuned'' common collinear array of the present invention is much more effective in reducing backlobe radiation than is the use of corresponding conductive columns in place of the array.

Experiments have shown that the back lobe radiation of an antenna with conductive columns instead of a collinear array is only 13 dB below the desired antenna beam 22 amplitude.

In the same configuration, using a tuned collinear array, backlobe radiation was suppressed to 35 dB below the desired antenna beam 22 amplitude.

In this experiment, the ground plane consisted of 0.20 wavelength diameter conductive columns separated by 0.88 wavelengths at the operating frequency.

The reflective element was a conductive cylinder with a diameter of 0.05 wavelength and a length of 0.26 wavelength.

The reflective element was tuned by adjusting the gap between the elements, which was a Wo, 01 wavelength.

One linearly polarized antenna element was used, which was placed 0.20 wavelength from one conductive column.

The invention applies advantageously to planar arrays of radiating elements such as that shown in FIG.

However, it will be apparent to those skilled in the art that the present invention may be used to form a substantially ventilated reflector for use in other antenna systems.

One such alternative embodiment projects wave energy into a converging reflector as well as a reflector in a substantially ventilated configuration.

Consists of linearly polarized antenna elements. Yet another example is
It consists of a non-planar array of antenna elements having non-planar reflective surfaces constructed in accordance with the present invention.

These alternative embodiments do not have a critical need for the minimal radiation leakage present in planar arrays where the radiation leakage through the reflector forms a convergent bank lobe; It has the advantage of having a greater gain than reflectors which are essentially ventilated structures made by.

Although reference has been made to transmit antenna systems in the description of the various embodiments above, it will be apparent to those skilled in the art that the principles of the invention are also applicable to receive antenna systems.

Accordingly, the claims should be construed as applying to both transmitting and receiving antenna systems, regardless of the actual language used therein.

[Brief explanation of the drawing]

1 depicts an antenna system constructed in accordance with the present invention; FIG. 2 depicts one suitable technique for mounting antenna elements to a conductive pole; and FIG. 3 depicts a collinear array of reflective elements. and FIG. 4 are top views showing the operation of the antenna of FIG. 1. 10...Dipole element, 11...Conductive column, 12...Collinear array, 13...
...Reflection element, 14...Support structure, 15.
...Transmission line, 16...Non-conductive core, 17...Fixed capacitor, 18...
Protective cover, 20... Beam, 21...
・Crid, 22...Main beam.

Claims (1)

[Claims] 1. An antenna system having a reflector having a ventilated structure and improving the effect of suppressing radiation leakage penetrating the reflector, the antenna system comprising a reflective grid of substantially parallel conductive columns;
a plurality of collinear arrays of reflective elements and at least one linearly polarized antenna element for radiating wave energy arranged such that the polarization of the antenna element is substantially parallel to the conductive column; means for supporting the antenna element, the conductive columns, and the collinear array, the collinear array being substantially parallel to and selectively disposed between the conductive columns. and the dimensions of the collinear array and the position of the collinear array relative to the conductive columns are such that the amplitude and phase of secondary radiation from the collinear array interferes with wave energy incident on the reflective grid of the conductive columns so that the An antenna system selected to suppress leakage of the radiated wave energy through the reflective grid of conductive columns.