Radiation shielding device

Details Radiation shielding device Radiation shielding device

1996-12-02

2001-05-29

Wimer, Michael C. (Department: 2821)

Communications: radio wave antennas

Antennas

With electrical shield

C343S7000MS, C343S795000

Reexamination Certificate

active

06239766

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a radiation shielding device and in particular relates to radiation control means for antennas.
BACKGROUND OF THE INVENTION
Antennas for use in telecommunications operate at many different frequencies. Transmit and receive wavebands may be separated so that interference between the signals is reduced, as in GSM and other systems. Intermodulation products may, however, still result, and transmit and receive signals may interfere between themselves. Intermodulation products in receive band signals are particularly undesirable; the operating capacity is reduced and/or the callers cannot clearly communicate, whilst operators face lost calls and accordingly a reduction in revenue.
One form of layered antenna (an antenna having ground planes, feed networks and dielectric spacers arranged in layers) is known from British Patent GB-B-2261554 (Northern Telecom) and comprises a radiating element including a pair of closely spaced correspondingly apertured ground planes with an interposed printed film circuit, electrically isolated from the ground planes, the film circuit providing excitation elements or probes within the areas of the apertures, to form dipoles, and a feed network for the dipoles. Typically, there is a linear arrangement of a plurality of such aperture/element configurations are spaced at regular intervals co-linearly in the overall layered/triplate structure to form a linear array. This type of antenna lends itself to a cheap yet effective construction for a linear array antenna such as may be utilised for a cellular telephone base station, with the antenna arrays being mounted on a frame.
One of the problems which arises during operation is that spurious signals are emitted from mounting apertures and other surface features associated with the reflector plane, for instance, mounting bolts which couple some of the radiated energy, and coaxial cable connector ports. Further, the coaxial cable and/or the cable termination assembly may also radiate spurious signals. The effect of all these unwanted signals is that they will couple with other radiating elements to form intermodulation products. In receive mode these intermodulation signals can severely impair the received signal quality, since they will be of a power level comparable to the received signal strength. In a transmit mode the output power will be reduced to a certain extent and these intermodulation products can affect the beamshape in an indeterminable fashion.
Careful design of the dimensions of the apertures and the elements coupled with the design of the electrical characteristics of the feed network for the elements can give a measure of control of coupling, but for some applications this is not effective. In such cases the performance of the antenna has to be adjusted upon installation, which complicates such a procedure and does not, in fact, solve the problem of spurious radiative effects behind the antenna. These problems are not limited to layered (tri-plate) antennas.
OBJECT OF THE INVENTION
It is an object of the invention to ameliorate the above mentioned problems.
STATEMENT OF INVENTION
According to the present invention there is provided an antenna assembly comprising a support frame and individually mounted antenna elements, wherein a flexible insulator-conductor sheet is interposed between the antenna elements and the support frame. Radiation emitted rearwardly from each antenna is thus prevented whereby the generation of intermodulation products is substantially eliminated. Thus the antenna can receive signals which are not degraded by the presence of such intermodulation products due to radiation reflected from emissions radiated rearwardly of the antennas and each individually mounted antenna element operates independently. The use of a flexible metallised plastics sheeting is preferred since it is both low cost and simple. Apertures for coaxial cables and mounting bolts are required in the sheeting but, if not unduly large, will not compromise the effect of the sheilding.
In accordance with another aspect of the invention, there is provided a method of constructing an antenna arrangement, wherein, in the assembly of an antenna comprising a frame and a number of layered antenna elements, a flexible insulator-conductor sheet is inserted between the layered antenna elements and the frame, with apertures being defined therein to aid connection of coaxial feeder cables and attachment of the radiating elements with connecting means.
In accordance with a yet further aspect of the invention, there is also provided a method of receiving and transmitting radio signals in a cellular arrangement including an antenna assembly comprising a support frame and individually mounted layered antenna elements, wherein a flexible insulator-conductor sheet is interposed between the antenna elements and the support frame, wherein the method comprises, in a transmission mode, the steps of feeding signals from transmit electronics to the antenna elements via feeder cables and, in a receive mode, the steps of receiving signals via the antenna elements and feeder cables to receive electronics wherein radiative coupling effects from one antenna element coupling with another antenna element due to radiation emitted from the back plane and feeder cables are minimised.


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