RADIOWAVE ANTENNA SYSTEM

Abstract: The present invention presents a radiowave antenna system, which includes means for the concentration of said means, like a parabolic reflector or a Luneburg-type lens. A primary feed (14), which receives the concentrated radiowaves, is supported by a tubular or hollow structure (11). This tubular structure (11) houses electronic means (13), such as a low noise converter (LNC). By the arrangement according to the invention, the length of a needed feeder line can be reduced, or such a line can even be avoided. Thereby time and money for the assembly can be saved and performance is improved.

Description: Radiowave_Antenna_Svstem The present invention relates to an antenna system including a radiowave concentration means, like a reflector, a lens or the like, and a primary feed antenna, which is located at a focal point, where incoming radiowave beams are concentrated. It is generally known, to use antenna systems, which include a parabolic reflector and a feed horn provided at the focal point of the parabolic reflector, for receiving radiowave si gna Is . From US 4 742 359 it is known, that said feed horn can be replaced by a helical antenna with two ends whereby the first end is linked to a feeder line. For the purposes of the fol¬ lowing explanation it s understood that the said feeder line is aligned with the axis of the said helical antenna. Such a helical antenna may be bu lt as a so-called endfire helical antenna, where under maxi um received power conditions the direction of the signal power flow at the said first end is in the same direct on as the received radiation. Such a helical antenna can also be bu lt as a so-called backfire helical antenna, where under maximum received power condi¬ tions the direction of the signal power flow at the said first end is in the opposite direction to the received radia¬ t on. In the said US patent an antenna system is presented, which comprises a reflector, a primary helical antenna having a coi l with a pair of ends, said coi l located at the focal point of said reflector so that the axis of the helical anten¬ na coincides essent ally with the axis of said reflector. A feeder line couples the antenna system with an external cir¬ cuit, so that primary helical antenna represents a backfire helical antenna coupled with said feeder line at the nearer end from said reflector and the other end of the helical antenna is free standing, and said feeder Line is a coaxial cable. A typical semi-rigid coaxial cable has an insertion loss of 1,5 dB/m at a frequency of 12 GHz, which is used for current direct reception of satellite TV-signals. In systems, which are state of the art, a length of nearly 0,1 meter is re¬ quired, for a reflector of a diameter of 40 centimeter, re¬ sulting in a total cable loss of nearly 0,15 dB. This value adds directly to the noise figure of the antenna system ( typi¬ cally less than 1,4 dB) and will be substantially higher at higher frequencies, such as the 22 GHz band proposed for future satellite TV systems. It is an object of the present invention to provide a compact antenna system, for receiving electromagnet ca L, preferably microwave, signals, where the use of a feeder line for micro¬ waves between a primary feed antenna and external circuits can be reduced to a great extent or even be avoided. The antenna system according to the present invention inc¬ ludes a concentration means, such as a reflector, e.g. parab¬ olic, or a microwave lens, e.g. Luneburg-li ke. The said con¬ centration means concentrates received microwave beams at one focal point or at several focal points respectively and at each of these focal points a primary feed is provided, which is supported by a hollow structure, which may be tubular, circular, rectangular, or the like. This structure houses electronic means, e.g. a low noise converter (LNC), which convert, filter and/or amplify signals received by the said primary feeds. By arranging the said electronic means inside the tubuLar structure the use of expensive feeder lines, such as a semi¬ rigid coaxial cable, can be reduced to a great extent or even be avoided. Additionally respective links or connectors can be avoided. The antenna system according to the invention allows fewer mechanical parts, a lighter weight, and reduced costs relative to the prior art. Additionally insertion losses of such a cable ca be reduced or avoided respectively, whereby the noise figure wi ll be improved and the performance of the antenna system can be increased. If the tubular structure is provided with an adjustment mecha¬ nism the feed position can be changed to suit concentrat on means with different focal points, e.g. by the use of reflec¬ tors of d fferent diameters. The use of helical coi ls has the advantage that they can be changed very easi ly, whereby the reception of signals with right-hand or left-hand circular polarization is possible. The use of backfire helical antennas has the advantage that such an antenna system is quite compact. If parts of the said electronic means are integrated and realized as part of an integrated circuit, e.g. as Monolithic M crowave Integrated Circuit, or as part of a hybrid circuit, space and more costs can be saved. As especially in known systems using a microwave reflector, the quantity of feeder line needed is high, this invention can preferably replace such systems. Further features, advantages and detai ls of the present inven¬ tion wi ll be explained by means of the following description of embodiments and accompanying drawings, wherein Fig. 1 shows a first embodiment of the inventive antenna system using a parabolic reflector, Fig. 2 shows detai ls of the support structure used. Fig. 3 shows a second embodiment using a spherical Luneburg-type lens and an endfire helical primary feed. Fig. 4 shows a third embodiment using a hemi-spher ca l Luneburg-type lens and a backfire helical primary feed. Fig. 1 shows a first embodiment of the invention using a parabolic reflector 10 at which a tubular structure 11 is arranged, which is shown in detai l in fig. 2. Fig. 2 shows the tubular structure 11 housing electronic means 13, like a low noise converter, with electronic compo¬ nents on a lower printed circuit board 13a and on a upper printed circuit board 13b, which are preferably arranged back-to-back. A primary feed 14, which is realized in this embodiment as a backfire helical antenna, is enclosed in a plastic radome 17 and connected via a line 15 to the electron¬ ic means 13. The tubular structure consists of a metal tubular support 16, which houses the electronic means 13 and which includes also a metal plate 16a. This plate 16a is arranged between the printed circuit boards 13a and 13b, which are fastened with several screws 12a und nuts 12b. Critical electronic components, which e.g. can be influenced easily by outer radiation or which transmit radiation, are protected by a housing 18, which is soldered to the upper printed circuit board 13b. In this embodiment the critical electronic components are part of an oscillator and its fre¬ quency can be changed by an adjustment arrangement 19, which is provided in the upper part of the housing 18. The input signal from the primary feed 14 is amplified, f l¬ tered and/or converted by the electronic means 13 and an according output signal is led via an output connector 20 to further not shown devices. To adjust the position of the primary feed 14 in dependence on the concentration means used, in this embodiment the ref¬ lector 10, an adjustable mounting 21 is provided. This can be realized as a simple screw thread adjustment or as any other well known adjustment device. Preferably the primary feed 14 s fixed to a carrier 30, which can be linked to the tubular support 16 and includes means for an electrical contact between the primary feed 14 and the electronic means 13. The carrier 30 can be exchanged very easi ly so that several kinds of primary feeds can be installed. Fig. 3 and fig. 4 show further embodiments using Luneburg- type lenses. Means with the same function as in the first embodiment, described with the aid of fig. 1 and fig. 2, have got the same reference numbers and wi ll be described only as far as it is necessary for the understanding of the present i nvent on. Fig. 3 shows in principle a second embodiment of this invent¬ ion. A spherical Luneburg lens 22 refracts an incoming beam 23 at a focal point 24. The tubular structure 11 is arranged outside the Luneburg lens in such a way that the primary feed 14, which is real¬ ized as an endfire helical antenna, is located near the focal point 24. The tubular structure 11 is fastened at means for supporting 25, which are just indicated. In this embodiment nearly any type of feed is possible: feed horns, polyrod feeds, patch antenna feeds, Vivaldi antenna feeds, etc. Fig. 4 shows in principle a third embodiment using a hemi-sp- herical Luneburg lens 26, which is attached to a metal-plate 27. This plate 27 reflects the incoming beam 23 and the hemi¬ spherical Luneburg lens 26 refracts it at the focal point 24. The tubular structure 11 is arranged inside the hemi-spheri- cal Luneburg lens in such a way that the primary feed 14, which is realized as a backfire helical antenna, is located near the focal point 24. The tubular structure 11 is fastened at the metal-plate 27. As well in the second embodiment as in the third embodiment the refraction-index of the lens used 22, 26 may be varied so that the corresponding focal point 24 is located inside or outside of the lens-surface. Thereby the strength of the received signal can be improved. On the other hand the position of the primary feed 14 may be varied, whereby the signal strength can be improved. It may be mentioned that with the embodiments described with the aid of fig. 1 and fig. 4 the variation of feed type is limited by the necessity for the feed to be situated at the end of the support, but receiving the radiation focussed by the concentration means 10, 22 respectively. Other examples for appropriate feeds are a primary dipole antenna, a ring-fo¬ cus feed, and a "short-backfire" antenna. Due to reasons of clearness the adjustable mounting 21 is not indicated in fig. 3 and fig. 4. It should be mentioned that such a mean can be provided to adjust the position of the feed 14 in relation to the position of the focal point 24. In versions of the antenna systems according to fig. 3 and fig. 4, which may be used for the reception of several micro¬ wave beams, several primary feeds may be provided. These feeds are located at or near the focal points of the beams to be received and one or more of the said primary feeds are supported by a common hollow structure and/or by seperate ones, which house corresponding electronic means. In a version of the said embodiments the means for concentra¬ tion may include or may be bui lt of a grating which diffracts incoming radiowaves. As primary feed antenna may be taken any of the said ones . The present invention presents a radiowave, especially a microwave antenna system, which includes means for the concen¬ tration of said means, like a parabolic reflector or a Luneburg-type lens. A primary feed, which receives the concentrated microwaves, is supported by a tubular structure. This tubular structure houses electronic means, such as a low noise converter (LNC). For the embodiments of fig. 1 and fig. 4 the primary feed helix must operate in a backfire mode. In these cases the invention is very advantageous, as the elimination or reduc¬ tion of the feeder line to a great extent results in improved performance and lower costs. The compact electronic means in the support allow fewer mechanical parts, a lighter weight, and reduced cost relative to the prior art. The embodiment according to fig. 3 is more compact, mechanica¬ lly simpler, and lighter than conventional designs. By the arrangement according to the invention, the length of a needed feeder line can be reduced, or such a line can even be avoided. Thereby time and money for the assembly can be saved, and the performance is improved. Also the mechanical parts are cheaper, simpler, and lighter. And space needed for the installation is reduced, as no converting means are be¬ hind a reflector. - S - Further versions of the said embodiments may include at least one of the following variations: - the primary feed 14 is connected to the electronic means by a simple coaxial construction using a dielectric support pressed into place and carrying a centre conduc¬ tor sprung to accept the centre conductor of the feed. In this way feeds may be easily exchanged to suit diffei— ent satellites, and a test connector may be connected as required. Typical feed types are the helical feed and microstrip feeds; - the electronic means may be realised such as a low noise amplifier (LNA), a band pass filter (BPF), and a mono¬ lithic microwave integrated circuit (MMIC ) may be locat¬ ed on one circuit board and power supply components are located on another circuit board. By using a MMIC the number (ca. 50) of discrete components can be reduced and thereby the size of electronic means can be reduced; - the LNA can use two high electron mobility transistors ( HEMT) to achieve a very low noise figure; - the BPF can be realised as parallel coupled microstrip line filter and can be rotated through some degrees, e.g. 30 degrees, to minimise length; - the components used may be of the surface mount ( leadless ) type to minimise size. Additionally it may be mentioned that the use of the inven¬ tion together with a lens, like homogeneous-type lens, Luneburg-type lens or so, for receiving signals from differ¬ ent sources, as satellites, has the advantage that said sourc¬ es may be close together. When using a lens with offset focal point at a distance of 2 times radius of lens ( this is consid¬ ered as optimum when considering size/weight of lens, direc¬ tivity/size of feed and dimensions of LNC), signals from satellites as close together as 3 degrees can be received. For use with lens type antennas the invention is of optimal shape for mounting radially to the lens. For multiple source applications (e.g. multiple satellites in geostationary or¬ bit) the compact, radially mounted nature enables multiple versions of the invention to be located at closely spaced foca I poi nts.

Claims: C l a i m s Antenna system for the reception of radiowaves with a radiowave concentration means ( 10; 22; 26 ) , which concen¬ trates by reflection, refraction and/or by diffraction radiowave beams in at least one focal point ( 14), with a primary feed (14) located at said focal point (14) and electronic means (13), which convert, filter and/or amplify signals correspond ng to said received radiowaves, characterized in that said primary feed (14) is supported by a hollow structure (11 ) which houses said electronic means (13). Antenna system according to claim 1, character zed in that said concentration means are achieved as a radiow¬ ave reflector (10) and the support structure (11) is mounted in a hoLe of said reflector (10). Antenna system according to claim 1 or 2, characterized in that parts of the electronic means (13) are integrat¬ ed and realized as part of a hybrid or integrated cii— cuit, e.g. a Monolithic Microwave Integrated Circuit (MMIC). Antenna system according to one of the claims 1 to 3, characterized in that an adjustment mechanism (21) is provided to enable the primary feed position to be changed to suit concentration means ( 10, 22, 26) in dependence on their characterist cs. Antenna system according to one of the claims 1 to 4, characterized in that the primary feed is shaped as a helical co I .

Inventors: FREMANTEAU PATRICE, FUJIMOTO MASAHIRO, HARRISON DAVID, HOWSON CHRISTOPHER, FREMANTEAU, PATRICE, FUJIMOTO, MASAHIRO, HARRISON, DAVID, HOWSON, CHRISTOPHER
Applicants: THOMSON CONSUMER ELECTRONICS, THOMSON CONSUMER ELECTRONICS S.A.
Application year: 1992
Main classification: H01Q19
IPC codes: H01Q1, H01Q11, H01Q19