The present invention relates to a microstrip sector antenna comprising a conductive microstrip structure of interconnected radiating elements underneath of which the first dielectric layer and a conductive grounded layer are disposed, and the second solid dielectric layer isolated from said conductive microstrip structure and disposed above the conductive grounded layer.

Various constructions of microstrip sector antennas having different arrangements of -radiating elements and different widths of radiating main lobes are known from the prior art. The width of the main lobe is commonly defined as a value of an angle between the points of the main lobe of antenna radiation for which electromagnetic field intensity decreases to the level of -3 dB relative to the maximum value regarded as a value of reference. This angle is also called a half power beam width (HPBW).

The most popular type of microstrip sector antennas are antennas of HPBW values of 60, 90 or 120 degrees. Fig. 8 illustrates an exemplary characteristic of a microstrip antenna known from the prior art and falling into series of types HPBW 60°. As shown, effective HPBW value for such an antenna amounts about 63 degrees.

Design of an appropriate structure of radiating elements allowing for constructing a microstrip sector antenna having excellent working parameters requires both a high amount of creative effort as well as thorough technical knowledge. Relatively the simplest in design are HPBW 90° antennas in which a microstrip radiating structure is composed of a single column of most commonly identical radiating patches having most often polygonal or circular shape. In a case of antennas featuring greater HPBW values a microstrip structure is generally much more complicated.

One of known methods of designing HPBW 120° antennas involves redesigning HPBW 90° antennas and includes among others a multiplication of a number of columns of radiating elements, taking into account the impact of such a multiplication on electromagnetic antenna parameters. Although such a process is simpler than designing HPBW 120° antenna from scratch, it also requires from the skilled technician a substantial amount of creative work and experimental burden since a topology of such a microstrip structure is intrinsicate.

This issue has also been discussed in a Polish patent application P. 384512 where in order to broaden an antenna lobe an additional continuous dielectric layer extending over the microstrip structure in a distance of between 0.04 and 0.4 of the antenna wavelength has been introduced. According to this solution the additional dielectric layer overlaps the whole microstrip structure and allows constructing a sector antenna having HPBW value of 120 degrees with a microstrip structure designed for a HPBW 90° antenna. Designing such antennas involves a sequence of iterative steps of simulations, where in each step parameters of the additional dielectric layer (such as an exact distance between the layer and a microstrip structure; thickness, dielectric constant, dielectric loss angle, etc. of a dielectric layer) are modified until required electromagnetic parameters of an antenna are obtained.

Unfortunately a dielectric layer overlapping the whole microstrip structure substantially influences electrical parameters thereof. It is therefore necessary to modify and/or redesign the microstrip structure each time dielectric layer parameters are changed. This in turn makes a designing process a time-consuming activity.

The object of the present invention was to provide a sector microstrip antenna allowing for obtaining increased half power beam width values of the main lobe of directional characteristic of antenna radiation using a microstrip structure designed for an antenna of a smaller beam width value, and additionally an antenna featuring simpler designing process.

According to the invention there is provided a microstrip sector antenna of the kind mentioned in the outset, wherein said second solid dielectric layer comprises at least one gap, wherein the orthogonal projection of the gap at the plane of the microstrip structure overlaps at least a part of the microstrip structure.

In a preferred embodiment of the antenna, said second solid dielectric layer is disposed above the conductive microstrip structure in a distance within a range of from 0.04 to 0.4 wavelength of the antenna, and said gap is disposed at least partially above at least a part of the microstrip structure. Additionally it is advantageous when said second solid dielectric layer comprises at least two lateral radiating patches arranged on both sides of the conductive radiating structure outside the outline thereof and said gap is open and formed between said lateral patches. The lateral dielectric patches are preferably arranged coplanarly and their inner edges are substantially parallel relative to each other and to the longitudinal central axis of the conductive radiating structure.

Preferably said lateral dielectric patches have rectangular shape.

In a preferred embodiment said microstrip structure is substantially symmetrical with regard to the longitudinal central axis thereof and said lateral dielectric patches have symmetric shape and are arranged symmetrically with regard to the longitudinal central axis of said microstrip structure.

In case where said microstrip structure of radiating elements and feed lines is asymmetrical with regard to the longitudinal central axis thereof, it is advantageous if the lateral patch disposed at this side of said microstrip structure where in relation to said longitudinal central axis major part of the feed lines is arranged has bigger area than the area of the lateral patch disposed at the opposite side of the structure; or alternatively if it is arranged is closer to the radiating structure than the lateral patch disposed at the opposite side of the structure. The lateral dielectric patches preferably project at both ends of the longitudinal axes thereof outside the conductive radiating structure, preferably on distance at least equal to the width of the lateral patch.

Moreover the thickness of said lateral dielectric patch varies in a stepped or continuous manner in a direction perpendicular to the longitudinal axis of said radiating structure.

Further in a preferred embodiment of the antenna according to the present invention said lateral radiating patches are connected with each other by means of at least two dielectric coupling patches, preferably transverse coupling patches. Alternatively said second solid dielectric layer has a form of a single plate in which a closed gap is formed.

The additional solid dielectric layer according to the invention enables for obtaining considerable increase of a ^" half power beam width value in a simple manner and using common materials.

It has also been unexpectedly discovered by the inventor that a gap formed in such an additional solid dielectric layer that uncovers at least a part of a radiating structure (whether from below or from above) on the direction of the main part of the antenna radiation lobe, results in decreasing the influence of a modification of geometrical and/or electrical parameters of the additional ^" "solid dielectric layer on electrical parameters of the microstrip structure. Taking into account that modifications of electrical parameters of the microstrip structure enforce the necessity for redesigning the arrangement of the structure during antenna designing process, according to the present invention a considerable simplification of this process has been achieved. In particularly advantageous embodiments of the invention the gap uncovers the whole area of the structure and does not influence on the electrical parameters of the microstrip structure at all thus the necessity of any modification of the microstrip structure during a process of antenna designing is completely avoided.

Therefore the invention enables to design a given microstrip structure having satisfying parameters only once. In a further design process only the changes of an antenna power characteristic introduced solely by the modifications of an additional solid dielectric layer should be analyzed not paying attention to possible changes of electrical parameters of a microstrip structure which either do not occur at all or are substantially limited. The antenna wavelength (λο) should be according to the present invention understood as a length of an electromagnetic wave in a free space for the operational frequency (fo) of an antenna. For example for an antenna of an operational frequency of 5.5 GHz, the wavelength amounts approximately 55 mm.

The invention is illustrated below with reference to the preferred embodiments thereof and with reference to the attached drawings on which: Fig. 1 shows the first embodiment of ah antenna according to the present invention respectively in a schematic perspective view (Fig. 1A), a front view (Fig. 1 B) and a top view (Fig: 1C),

Fig. 2 shows the second embodiment of an antenna according to the present invention respectively in a schematic perspective view (Fig. 2A), a front view (Fig. 2B) and a top view (Fig. 2C),

Fig. 3 shows the third embodiment of an antenna according to the present invention respectively in a schematic perspective view (Fig. 3A), a front view (Fig. 3B) and a top view (Fig. 3C),

Fig. 4 shows the fourth embodiment of an antenna according to the present invention respectively in a schematic perspective view (Fig. 4A), a front view (Fig! ^' 4B) and a top view (Fig. 4C),

Fig. 5 shows the fifth embodiment of an antenna according to the present invention in a front view,

Fig. 6 shows the sixth embodiment of an antenna according to the present invention in a front view,

fig. 7 shows the seventh embodiment of an antenna according to the present invention in a front view,

fig. 8 shows a characteristic of electromagnetic field intensity of radiation of an exemplary antenna known from the prior art of a construction similar to the construction of the antenna from Fig. 2 but without the second solid dielectric layer, and

fig. 9 shows a characteristic of electromagnetic field intensity of radiation of an exemplary antenna according to the present invention of a construction shown in Fig. 2.

Fig. 1 presents first embodiment of a microstrip antenna 1 according to the present invention. The main radiating arrangement of the antenna 1 comprises a conductive microstrip structure 2 placed on a rectangular dielectric plate 3 made of epoxy-glass laminate, underneath of which a rectangular metal grounded plate 4 parallel to the microstrip structure 2 is disposed.

The dielectric plate 3 may be an epoxy-glass laminate such as for example laminate FR4 featuring dielectric loss angle δ of 0.02 and dielectric constant ε _Γ of 4.3 provided by Isola GmbH, teflon-ceramic laminate such as produced by Rogers Corporation, or any other material having properties suitable for a given operational range of an antenna. The dielectric plate 3 on which the microstrip structure 2 is etched is obviously only the support element for the structure 2. The microstrip structure 2 may also be created by cutting it out from a cooper-metal sheet and may constitute a self- supporting element.

In this embodiment, the microstrip structure 2 is symmetric and comprises six identical cpllinear rhomboidal radiating elements 5 connected in an appropriate way with conductive paths 6. The shapes, dimensions of individual radiating elements, spatial arrangement thereof and configuration of conductive paths interconnecting the elements is tailored to the desired operational parameters of an antenna.

The grounded plate 4 is separated from the microstrip structure 2 by means of the first dielectric layer 7 having thickness d and comprising an air layer and dielectric plate layer 3. A socket 8 and a metal pin 9 are fastened to the conductive microstrip structure 2 wherein the pin 9 galvanically connects the structure 2 with the grounded plate 4. A feed cable (not shown) for connecting the antenna with sending/receiving devices may be connected to the socket 8.

Above the surface of the microstrip structure 2 in a distance D an additional second solid dielectric layer 10 having the thickness G and in a form of rectangular plate 11 is disposed. An epoxy-glass plate having the length L equal to the length of the dielectric plate 3 with the microstrip structure 2 may be used for this purpose.

In the central area of the plate 11 , over the microstrip structure 2 a longitudinal gap 12 has been formed.

Since the gap 12 exposes a part of the radiating structure 2 along a direction of the main part of the radiating beam, the process of designing an antenna becomes simpler as functional relation between these elements (microstrip structure d and dielectric layer 10) is not so strict. In other words a modification of parameters of the additional dielectric layer 10 does not imply the same extent of alteration of electrical parameters of the microstrip structure 2. It is worth noting that in order to obtain such a reduction of influence between the dielectric layer 10 and the radiating structure 2 according to the present invention it is unnecessary to use any specific shape or localization of the gap 12. It is possible to employ any gap which is at least partially disposed above at least a part of the radiating structure 2.

In a particularly preferred embodiments of the present invention, the gap is an envelope curve of a microstrip structure so that no part of the additional second solid dielectric layer 10 overlaps an element of a microstrip structure 2, as shown in Fig. 3, or preferably it may be an open gap 12 having a width A that separates the additional solid dielectric layer 10 into two individual lateral dielectric patches 13 as illustrated in Figs. 2, 3, 5 and 6.

In all drawings, numerical references of functionally corresponding elements remain the same for all presented embodiments.

Fig. 2 shows the second preferred embodiment of an antenna according to the present invention, similar to the embodiment of Fig. 1 but with the additional second solid dielectric layer comprised of two lateral dielectric patches 13 of identical width S arranged coplanarly on both sides of the longitudinal open gap 12 extending over the whole microstrip structure 2. Thanks to that the additional solid dielectric layer overlaps neither the radiating elements 5 nor the conductive paths of the structure 2. The inner edges of the lateral patches 13 are located above the outer longitudinal edges of a rectangular outline of the microstrip structure 2 wherein the lateral patches 13 are arranged symmetrically with regard to the central axis 14 of the microstrip structure 2. Underneath the surface of the first dielectric layer 3 and the second solid dielectric layer 10 the conductive metal grounded plate 4 is disposed. Fig. 3 presents the third embodiment of an antenna according to the present invention having an asymmetrical microstrip structure 2 comprising a symmetric row of rhomboidal radiating elements 5 connected by feed paths 6 arranged asymmetrically relative to the row of elements 5.

According to the present invention the symmetry of a microstrip structure d should be determined in relation to the longitudinal central axis 14 of the entire structure 2 continuous as shown in Fig. 5 for two preferred embodiments of an antenna according to the present invention depicted in combined side view.

An alternative manner for modification of antenna radiation characteristic broadened to a sufficient degree involves an inclination of the lateral patches of the second solid dielectric layer at an angle a relative to the plane of the microstrip structure. For example such an inclination may be symmetrical for a symmetric microstrip structure 2, as shown in Fig. 6 or asymmetrical for an asymmetric structure 2.

Fig. 7 shows the seventh embodiment of a sector antenna 1 according to the present invention. In this example the additional second solid dielectric layer 10 in a form of two relatively massive cuboid blocks 17 is disposed directly on the conductive grounded layer 4 and the entire layer 10 is located below the first solid dielectric layer 3 with the radiating structure 2. Therefore in this case the distance D between the microstrip structure 2 and the additional dielectric layer is negative.

Fig. 9 shows a fragment of a power directional characteristic for the antenna according to the present invention in a plane perpendicular to the longitudinal axis of the microstrip structure. The Y axis corresponds to the values of electromagnetic field intensity of the antenna radiation while the X axis corresponds to the values of the angle (theta) between the point of maximal value of electromagnetic field intensity. The characteristic has been determined the antenna of construction demonstrated on Fig. 2 having the following constructional parameters: the height H between the second dielectric layer and the microstrip structure amounts 15 mm, the width S of the dielectric patch amounts 34 mm, the thickness G of the patch amounts 1 mm, the width A of the gap between the patches amounts 26 mm, dielectric constant ε, of the second solid dielectric layer material amounts 7.5. As shown the antenna provided with the additional second solid dielectric layer according to the present invention features HPBW value of 105 degrees. In comparison with the characteristic shown in Fig. 8, the influence of the additional second dielectric layer on the width of the main radiation lobe of an antenna is clearly visible and results in substantial increase of the HPBW value of 42°. Recapitulating the above discussion of the presented embodiments of the invention it should be noted that in the antennas according to the invention the additional height of placing of the opposite lateral dielectric patches and/or the distance: froni the microstrip structure and/or the inclination angle and/or the thickness of the opposite lateral dielectric patches.

Finally it shall be obvious that a single lateral patch from the presented preferred embodiments of the present invention may be substituted with set of a number of appropriately configured patches.

The skilled technician is also aware that a precise choice of the distance (D) of the second solid dielectric layer 10, its thickness (G), dielectric constant (ε _Γ ), dielectric loss angle (δ) and the other parameters of the arrangement and their mutual relationships depend on the antenna wavelength (λ ₀ ) and the desired degree of increasing a half power beam width (HPBW).

Although the drawings do not present some constructional details of an antenna according to the present invention, such as for example constructional details of fastening of the second solid dielectric layer 10, it is obvious that any appropriate fastening construction may be used that does not affect antenna electromagnetic characteristics. The second solid dielectric layer 10 may for example be stuck to a dielectric plate 3 or to an antenna housing not shown in the drawings, for example by means of suitable two-sided adhesive tape, thus providing proper distance (D) of a layer 10 from a microstrip structure 2. The embodiments above should not be, by any means, considered as exhaustive and/or limiting the invention, the spirit of which is characterised in the appended claims.