Manufacturing costs of apparatuses in general and mass products in particular should be as low as possible. The less there are parts in a structure and work stages in manufacturing the parts, the lower the costs. Furthermore, in portable radio devices, the mechanical stability of a structure is emphasized. For example, in a high-frequency antenna, even a slight mechanical change may render the whole device unusable. The less there are parts in a structure and the sturdier and better protected the parts, the better the stability and, hence, the reliability of the structure. So, a low count of parts helps both minimize the manufacturing costs and improve the reliability of a device.
As far as antennas are concerned, protruding antennas, largely used in mobile stations, for instance, are susceptible to damage, and with the necessary additional parts they significantly add to the manufacturing costs. Internal antennas in mobile stations are usually planar antennas because these have good electrical characteristics with respect to the antenna size. FIGS. 1a and 1b illustrate an example of such known planar antennas. This structure is disclosed in publication WO 01/08255. FIG. 1a is a perspective of the antenna and FIG. 1b shows a lateral view of the same structure. FIG. 1a shows, within the covering 150 of a radio device, a printed circuit board 110, depicted here in vertical position, and on one side of the circuit board a conductive layer providing a ground plane GND for the antenna. A central part in the structure is the antenna element 120, which is in single piece and comprises the radiating plane 121 proper, a first bent portion 122, a second bent portion 123, and a third bent portion 124. Connected to the rectangular radiating plane 121 at a point F of its vertical center line is a feed conductor 101 of the antenna. The antenna element extends, after a bend, from the upper edge of the radiating plane up to the ground plane, perpendicularly thereto. The first bent portion 122 thus formed functions as a short-circuit conductor having the length of that particular edge of the radiating plane, and the antenna is a so-called planar inverted-F antenna, or PIFA. The antenna element also extends from the edge opposite to the short-circuited edge towards the ground plane, after a bend. The middle section of the second bent portion 123 thus formed extends near the ground plane. In the middle section there is a rectangular bend inside the structure. Between the resulting third bent portion 124 and the ground plane, which are parallel, there is a significant capacitance, further increased by a dielectric plate 105 disposed therebetween. In addition to certain electrical characteristics, non-substantial here, an advantage of the structure is that the radiating plane is supported to the ground plane through the bent portions of the antenna element without separate supporting parts. The antenna element is fabricated by stamping an appropriately shaped piece from a rigid conductive sheet and bending it. In addition, antenna fabrication includes, as separate work stages, the attachment of the feed conductor 101 to the radiating plane and said dielectric plate 105 to the antenna element, as well as the attachment of the resulting assembly to the printed circuit board.
From publication WO 01/33665 it is known a structure which is similar to the one described above but which additionally has a parasitic antenna element to increase the number of operating bands, for example. The publication concerns, apart from the structure, also the manufacturing method thereof, which includes as a separate stage the connecting of the feed conductor to the antenna element. In this case, too, both antenna elements are made by stamping and bending a conductive sheet.