A Y-ANTENNA

Abstract: The disclosure relates to a Y-antenna which includes an elongate Y-shaped metal portion and a bottom plate (16) of metal which is mounted beneath and substantially at right angles to the vertical shank (14) of the Y and is galvanically connected to this shank. The Y-shaped metal structure includes two preferably parallel notches (26, 24) quarter wave resonant on different frequencies and preferably open at one short end and which are electromagnetically coupled to one another. The two parallel notches are disposed in the V-shaped shanks (10, 12) of the Y and, in one preferred embodiment, have a common side which consists of the upper edge of the vertical portion (14) of the Y. In one preferred embodiment, only one of the notches is directly fed with energy. The antenna gain and the bandwidth of the antenna can be increased with the aid of an extra metal screen in the form of a shank which is galvanically connected to the short-circuited short end of the directly fed V-shank, whereafter the extra shank is bent so that it covers approximately 70 % of the upwardly directed longitudinal aperture of the V-shanks. A further increase of the bandwidth can be obtained in that the upper edges of the shanks (10 and 12) are provided with rectangular sheet flarings (27 and 28).

Description: A Y- ANTENNA The present invention relates to a low, open notch antenna, designared a Y-antenna, preferably intended as a mobile telephone antenna for motor vehicles, or alternatively for portable pocket telephones or personal pagers. The antenna comprises a Y-shaped sheet structure with two open notches quarter wave resonant, at different frequencies, electromag¬ netically coupled to one another and fed preferably by means of one feed unit at a common feed point. The antenna further includes a rectangular base plate of metal symmetrically mounted benearh and at right angles to the vertical shank of the Y, and galvanically connected thereto. In certain cases when the antenna is placed on a large sheet metal area as is the case in private cars, the base plate can be secured to the sheet metal of the car by means of a reten¬ tive double-adhesive tape via which the antenna will moreover be capacitatively coupled to the subjacent sheet metal of the vehicle. In other cases when the antenna is mounted on a por¬ table pocked telephone or a personal pager, the base plate is designed so that it is possible, by filter effect, to obtain if necessary a relatively large coupling impedance between the antenna and the apparatus chassis. Antennae for motor vehicles normally consist of a quarter wave long onopole antenna or a colinear Franklin antenna normally approx. three quarter waves high and, as far as portable tele¬ phones are concerned, the quarter wave or half wave long an¬ tennae are the most generally prevalent. Antennae with an open slot, so-called notch antennae (fig 1) are known in the art and described by Cary and Johnson. However, it should be observed that, for example, a notch an¬ tenna (fig 1) described by Cary and Johnson does not give an omnidirectional radiation pattern, but a pattern of the car- dioid type in the yz plane, which signifies maximum radiation in the direction of the positive x axis and zero radiation in the opposite direction. In this case, the notch antenna con¬ sists of a notch in a large sheet metal, as is apparent from fig 1. If the sheet is cut considerably so that the remaining sheet around the notch, for example the distance between notch and edge, is of the order of magnitude of between 3 and 4 hund- redths of a wavelength of that frequency where the open notch has its quarter wave resonance, and if this considerably cut notch sheet is placed at right angles above, and ideally in contact with, an earth plane sheet, there will be obtained an as good as oπmi irectional antenna or, in other words, there will be obtained that antenna which is shown in fig 2 and whose radiation properties also substantially correspond to a quarter wave high monopole antenna when this, in a correspon¬ ding manner, is placed above an earth plane. The height of the notch antenna can be limited to less than a tenth of a wavelength (0.10 lambda) which is to be compared with the height of a monopole antenna which, at resonance, is just beneath a quarter wavelength (0.25 lambda). The above described version of the notch antenna, which corresponds to the antenna embodiment according to fig 2, is known in the art. For many applications where an antenna of slight extent in the vertical direction and good omnidirec¬ tional radiation properties is desired, the above-described version of the notch antenna offers a satisfactory solution to the antenna problem as far as these properties are con¬ cerned, but it is a solution which, in many cases, can never¬ theless not come into question because of the unsatisfactory band width properties of the antenna design and construction. The present invention has for its object to realise an an¬ tenna possessing superior omnidirectional radiation proper¬ ties which, in addition to being of slight extent in the vertical direction, also offers a greater band width capa¬ bility than the prior art notch antenna described above. The present invention realises a mechanically simple and low omnidirectionally radiating and vertically polarized antenna of substantially the same omnidirectional radiation proper¬ ties and polarization as well as length and vertical dimen¬ sions as a prior art embodiment of the notch antenna (fig 2), in addition to which the antenna according to the present invention, apart from being low and short, displays a con¬ siderably improved band width which entails 7 to 8 % or more, which greatly exceeds the band width which the corresponding prior art antenna shown in fig 2 can offer. This situation is based int. al. on the fact that the antenna according to the present invention includes two parallel notches of different lengths. The above and other objects have been attained according to the present invention by means of a low Y-shaped metal struc¬ ture whose height can be restricted to less than a tenth of a wavelength of the central frequency in the working range of the antenna, and in which the Y-shaped structure is designed in such a manner that it includes two quarter wave resonant, preferably parallel notches which are open at one short end and are electromagnetically coupled to one another. According to one preferred embodiment, the two notches have a common side which consists of the upper edge of the vertical portion 14 of the Y. The open parallel notches 24 and 26 are each disposed in their V-shaped shank 10 and 12 of the Y, the angle between the V-shaped shanks being of the order of magnitude of 2 x 30-60°. In the preferred embodiment, only one notch - preferably the low frequency i.e. the longer notch - is fed. This entails that the one notch is directly fed and the other is fed by mutual electromagnetic field connection so that the field fed notch enters into function when the frequency of the transferred field energy approches the resonance frequency of the notch, at the same time as it then distances itself from the resonance frequency of the directly fed notch. As far as the electromechanical design is concerned, it should be observed that the Y-shaped metal structure is galvanically connected to a base plate 16 made of metal whicn, for example, can constitute a part of an earth piane or function as a coupling element to an adjacent earth plane cr, in other words, constitute a part of a counterweight to the Y-shaped antenna structure. The base plate is designed and coupled to the antenna carrier on which the antenna is to be placed in such a manner that the radiated energy on transmission and thereby maximum sensitivity on receiving are obtained and this, as far as possible, in a plane which is imagined as extending at right angles out from the vertical Y-shank 14, and that the out¬ going radiation and sensitivity, respectively are equal or have slight variations in each bearing direction in this plane. By employing a slightly more complex design of the invention, the antenna gain in the above-mentioned plane, like the band width of the antenna can be increased by a few percent. This is achieved by reducing the radiation out from the V-aperture of the Y-structure, which is realised with the aid of an extra metal screen 22 which is galvanically connected to the shortcircuited short end of the directly fed V-shank, where¬ after the extra shank extends just outside the plane through the longitudinal aperture 'of the V-shank where it is bent so that this covers approx. 70% thereof. The edges of this extra shank follow along the longitudinal sides of the V-shanks to more than half of their length and at a distance which pre¬ ferably is less than one hundredth of a wavelength within the frequency band of the antenna. Further increase of the band width to above 10% i.e. 10-11% or more is achieved by introducing edge disruptions to the upper horizontal edges of the shanks 10 and 12. In one pre¬ ferred embodiment, these disruptions are applied as a tooth¬ ing of these edges preferably m the form cf rectangular flaπngs 27 and 28 of the shank plates 10 and 12, the free corners of the rectangles having been cut at 45°, fig 8. As a result of this edge toothing, the Q values of the two notch resonances are reduced and, thereby, each notch gives a greater band width. Influence of the resonances of the notch resonances is determined by the height, length and position of the sheet teeth along the upper edges of the shanks 10 and 12. The sheet teeth are preferably placed so that they are in the middle of the upper edges of the shanks 10 and 12. The length of the teeth is, in one preferred embodiment, approx. l/8th of a wavelength at the opposing notch resonance fre¬ quency and their height corresponds to one to two hundredths of a wavelength of the central frequency in the working range of the antenna. The dimensions of the teeth are trimmed so that the both notches' broadened frequency bands overlap one another. The feed impedance of the antenna can, in such instance, be well adapted to the impedance of the feed cable without large variations over the entire working frequency range of the antenna and this entails also that only small variations in the radiation properties of the antenna can be obtained over the same frequency band. The further objects of the present invention and the advan¬ tages afforded by the invention will be more readily under¬ stood by reference to the following description and the accompanying drawings which show one preferred embodiment of the Y-antenna according to the invention. Fig 1 shows a notch antenna. Fig 2 shows a particular embodiment of the notch antenna. Fig 3 (a-c) show by way of example one embodiment of the present invention. Fig 4 (a-b) show one example of a further embodiment of the present invention. Fig D (a-c), rig 6 (a-c) and fig 7 (a-c) show examples of component parts included in the antenna of the pre¬ sent invention. Fig 8 shows a modified embodiment of the invented antenna. Fig 9 and fig 10 show examples of component parts included in the antenna of the present invention. The Y-antenna according to the present invention comprises a Y-shaped sheet structure 14 with two open notches 24 and 26 quarter wave resonant at different frequencies, each disposed in their V-shaped shanks and 10 and 12, respectively, of the Y, where the angle between these shanks is preferably 60° (fig 3 a-c). In the illustrated embodiment of the Y-antenna, only the longer, lower frequency notch 26 is supplied with energy, which, thus, will thereby by directly fed while the second notch 24 is fed by mutual electromagnetic field connection between the notches. The feed unit consists, in the preferred embodiment, of a so-called semi-rigid coaxial cable 18. The more complex embodiment of the present invention includes an extra metal shank 22 which is shown in fig 4a and/or alternatively rectangular flarmgs along the upper edges of the shanks 10 and 12, as shown m fig 8a. Since the notches are of different lengths and thereby diffe¬ rent resonance frequencies, they can function each in their of two adjacent frequency ranges. The directly fed notch functions in the frequency range of the second notch as a link in a transmission chain on transmission of energy to the second notch. If the intention is that the Y-antenna is to encompass a wide, unbroken frequency band, the notch lengths and the position of the feed point 18-20 are trimmed until the adjacent frequency ranges obtain a well adapted overlap region which entails good impedance adaptation and good radiation properties within the total frequency band. The angle between the two shanks 10 and 12 of the V, like the notch width, belong to those parameters which influence the coupling between the notches and should therefore be included in a fine tuning of the Y-antenna. The antenna is suitably mounted on a planar metal plate 16. In a carrier wave fre¬ quency of approx. 890 MHz, the antenna can suitably have the following data: Antenna length 85,0 mm Antenna height 23,0 mm Notch length (26) 75,0 mm Notch length (24) 85,0 mm Notch height (26) 2,7 mm Notch height (24) 2,7 mm Shank height (10) 25,0 mm Shank length (10) 85,0 mm Shank height (12) 25,0 mm Shank length (12) 85,0 mm Shank width (10) 12,3 mm Shank width (12) 12,3 mm Base plate (16) length 85,0 mm Base plate (16) width 30,0 mm Extra shank total length 75,0 mm Shank edge tooth length (27) 32,0 mm Shank edge tooth height (27) 5,0 mm Shank edge tooth length (28) 40,0 mm Shank edge tooth height (28) 5,0 mm Different alterations and modifications of the invention are possible without these falling outside the scope of the pre¬ sent invention such as this is defined in the Claims. For example, the dimensions of the antenna can be changed so that it suits other frequencies, eg. frequencies around 450 MHz or 1700 MHz.

Claims: C L A I M S 1. A Y-antenna including an elongate Y-shaped metal part and a bottom plate of metal mounted beneath and substantially at right angles to the vertical shank of the Y, and galvanically connected to this shank, c h a r a c t e r i z e d in that the Y-shaped metal structure includes two preferably parallel notches (26, 24) quarter wave resonant on different frequen¬ cies and open at one short end; and that the two notches are each disposed in its V-shaped shank (10, 12) of the Y and have a common side which consists of the upper edge of the vertical portions (14) of the Y. 2. The Y-antenna as claimed in Claim 1, c h a r a c t e ¬ r i z e d in that only the low frequency notch is coupled to feed unit (18), entailing that the other notch is fed by mutual electromagnetic field connection. 3. The Y-antenna as claimed in Claim 2, c h a r a c t e ¬ r i z e d in that an extra metal shank (22) is galvanically connected to the short-curcuited short end of the directly fed V-shank (10), whereafter the extra shank, shortly outside the plane through the short sides of the short-circuited V-shanks, continues until it reaches just above the longi¬ tudinal aperture of the V-shanks where it is bent so that it covers approx. 70% of the longitudinal aperture of the V-shanks. 4. The Y-antenna as claimed in any one of the preceding Claims, c h a r a c t e r i z e d in that the upper edges of the sheet shanks (10 and 12) are provided with rectangular flarings (27 and 28).

Inventors: CASSEL JAN, CASSEL, JAN
Applicants: CASSEL JAN, CASSEL, JAN
Application year: 1993
Main classification: H01Q13
IPC codes: H01Q1, H01Q5, H01Q13