FI118749B - Column Antenna - Google Patents

Description

118749

slot antenna

The invention relates to an antenna for portable radio devices, which includes a radiating slot in the ground plane of the radio device. The invention also relates to a radio device having an antenna according thereto.

5 The space available for the design of portable radio antennas is an important factor. Without a size limitation, a good quality antenna is relatively easy to make. However, in portable devices, the antenna is preferably placed inside the covers of the device, whereby the size of the device has always reduced the movement of the antenna. This means an increase in the complexity of design. This is also affected by the fact that the antenna often has to operate in two or more frequency bands.

In practice, the antenna that goes inside a compact device with a satisfactory performance is most easily obtained as a planar structure; The antenna includes a radiating plane and a ground plane parallel to this. These planes are usually interconnected at so-15 pivotal points by a short-circuit conductor to form a PIFA (planar inverted F antenna) structure. The size of the ground plane naturally affects the characteristics of the antenna. As with the monopoly bishop, the ground plane of an ideal planar antenna is very wide. As the ground plane decreases, the antenna performance decreases as the antenna resonances weaken and due to the ground plane's own resonances. . ···. This also makes it easier to resonate in the other conductive parts of the device.

The performance degradation is manifested by a decrease in bandwidth and antenna gain. For dual-band antennas, this disadvantage is of course much greater in the lower band • · * ·, which is mostly in the 0.9 GHz band. PIFAn also has the disadvantage of being poorly suited to flat radios because converging * 25 levels and ground .

In the present invention, the antenna is based on the ground plane radiation. , into a twist. Such a gap is known per se. For example, the application publication * * *: *:: Fl 20021668 discloses an antenna structure having a radial gap in the ground plane. The Ky-: ...: antenna structure is shown in Figure 1. It has a radio circuit board 105, the upper surface 30 of which is mainly conductive. This conductive surface acts as the antenna ground [···. At one end of the circuit board, there is an antenna radiating plane 120, which is joined by an antenna feed conductor 131 and a short-circuit conductor 132. From its short-circuit point, the radiating plane ja-·. The ground plane 110 has two parallel slots extending from its · · 35 edges. The first slot 115 passes adjacent the short circuit S of the antenna 2 118749 and the second slot 116 such that the antenna feed point F on the surface of the circuit board 105 is between the first and second slots. The second slot can be dimensioned so as to generate vibration in the upper operating band of the antenna, whereby the slot then improves matching.

The slot radiator of Figure 1 is only a PIFA auxiliary radiator in the upper operating band of the antenna. The lower operating band is based on PIFA's lower resonance. Thus, the radiant level of PIFA is necessary, so that the above disadvantages of PIFA are also affected. No valid operating band based on ridge resonance can be obtained in the 0.9 GHz range.

The object of the invention is to reduce the above-mentioned disadvantages associated with the prior art. The slot antenna according to the invention is characterized in what is set forth in independent claim 1. The radio device according to the invention is characterized in that which is set out in independent claim 7. Certain preferred embodiments of the invention are set forth in other claims.

The basic idea of the invention is as follows: The functional basic part of the antenna of a small radio device is a ground slot at the other end which is open at one end. The gap is located so that a relatively narrow strip of ground is left between it and the edge of the ground plane. An elongate auxiliary element is raised at the end of this paint strip, adjacent to the open end of the slot, which rises slightly from the ground plane and is then oriented. ···. 20 ten slots per closed end. The auxiliary element increases the electric length of the gap so that the basic resonance frequency of the gap falls within the lower operating band of the dual band antenna. The gap thus acts as a radiator in the lower operating band • ♦ · [·. The antenna is fed at a preferred location near the slot: the closed end. In addition, the auxiliary element is dimensioned such that, when feeding the antenna · at 25 higher bandwidth frequencies, the auxiliary element wakes up its own vibration, thereby acting as a radiator in the upper operating band.

. . An advantage of the invention is that the lower operating band of the dual band antenna can be: implemented with a relatively small space consuming structure. This is because the * * * uses a ground plane gap radiator and the auxiliary element required, for example, is considerably smaller in area compared to the PIFA radiant plane. lower ground level. A further advantage of the invention is that, in the antenna according to the invention, the space between the auxiliary element and the ground plane can be utilized by placing there the other components of the diol device. A further advantage of the invention is that the antenna according to the invention can be positioned at a SAR (Specific Absorption Rate) more advantageously than known antennas. A further advantage of the invention is that the adaptation of the antenna according to the invention does not require separate adaptation components.

The invention will now be described in detail. Reference is made to the accompanying drawings, in which Figure 5 shows an example of a known ground plane slot emitter, Figure 2 shows an example of an antenna according to the invention, Figure 3 shows an example of an antenna feed and ground system according to the invention, 5 illustrates an antenna of the invention in a radio device, Fig. 6 shows another example of an antenna of the invention in a radio device, 15 illustrates an example of the band characteristics of an antenna according to the invention, Fig. 8 illustrates an antenna efficiency structure.

* ·· * # * • ♦ • · »» ·. *. ': Figure 1 was already described in the prior art description.

Figure 2 shows an example of an antenna according to the invention. The illustration shows the radio • ·: the circuit board 205 of the device, the upper surface of which is mainly conductive. This conductive surface acts as the signal ground of the radio device, i.e. ground plane 210. At one end of the circuit board there is a ground plane non-conducting slot 220. This leaves the edge of the ground plane, i.e.:. it opens to the edge of the ground plane. The slot 220 extends parallel to the end of the ground plane and the other end, i.e. the closed end, extends relatively near the opposite long side of the ground plane when viewed from the open end of the slot. Between the gap and the end of the ground plane there is a relatively narrow ground plane region 212, referred to herein as the paint strip. The term "relative" over some distance in this specification and in the claims refers to a distance which is at least an order of magnitude smaller than the wavelength corresponding to the maximum operating frequency of the antenna.

• · · • ·· · ·

In the slit 220, vibration can be induced by applying electromagnetic energy 4118749 to the slit at a specific frequency. In this case, the gap acts as a radiator, thus emitting energy to the environment. Figure 2 shows the dashed radiator feed point FP, which in this example is close to the closed end of the gap, is indicated by a dashed line. However, the properties of such a gap radiator, such as efficiency, are not yet satisfactory. In addition, its characteristic frequency in a pocket-sized device is difficult to obtain sufficiently low to require an operating band below one gigahertz. The opening of the gap to the edge of the ground plane makes it a quarter-wave resonator. This helps to achieve lower natural frequencies as compared to half- wave resonators, but not enough.

For the above reasons, the antenna structure according to the invention further comprises a conductive auxiliary element 230. This is, for example, a piece of rigid sheet metal having an elongated first portion and a substantially perpendicular second portion. The auxiliary element is galvanically attached at one end of the second portion to the end of the paint strip 212 adjacent to the open end of the slot 220 such that the first portion of the auxiliary element 15 is above the paint strip 212. It may also extend transversely to the gap 220. In its longitudinal direction, the first portion extends around the closed end of the slot. Its distance from the ground plane, i.e. the height of the antenna corresponding to the second part of the auxiliary element, is relatively small, for example 5 mm.

The auxiliary element 230 naturally influences the characteristics of the antenna. Slot Substitutes -: “* · * The field at its characteristic frequency is a parallel resonance column. The auxiliary element increases both the inductance and the capacitance in the partial circuit, whereby the specific frequency of the structure is reduced. The same thing can be expressed so that the auxiliary element increases the electrical length of the gap. The auxiliary element can be dimensioned so that the antenna characteristic

• I I

The frequency of j'Y 25 occurs, for example, in the GSM850 or GSM900 (Global System for

Mobile communications) even if the physical length * '·· * of the radiating gap is less than 4 cm. A further feature of the antenna's operation is that the auxiliary element can be induced to vibrate at its own characteristic frequency. The specific frequency · of the auxiliary element can be traced, for example, in the frequency range of the GSM1800 or GSM1900 rigid system, whereby the antenna has two usable operating bands. The lower operating band \ t is based on the ground plane slot extended by the auxiliary element and the upper operating band is based on the auxiliary element.

• · * * * · »

Fig. 3 shows an example of an antenna according to the invention and grounding. Partial view (a) shows the circuit board 305 of the radio device as seen from above and the sub-picture '· 35 (b) as seen from below. On the upper surface of the circuit board there is a radial gap 320 of the antenna in the ground plane 310, as in Fig. 2. Partial view (a) also shows the auxiliary element 330 in broken band. The antenna is electromagnetically fed by a supply conductor 340. The supply conductor is a conductor strip located on the underside of the circuit board 305. This extends from the antenna port substantially perpendicular to the radiating slot line at the feed point FP near the closed end of the slot. The signal ground GND is located on the underside of the circuit board at a certain distance 5 from the slot 320, so the ground is neither at the slot nor quite close.

The impedance of the antenna structure measured from the antenna port is affected by e.g. the location of the feed point FP and the length of the free portion of the feed line 340. By appropriately selecting these, the antenna can be fitted without separate adapter components. The feed conductor can also be extended for fitting through the printed circuit board to its upper surface and connected 10 therein to the edge of the radiating slot on the side of the paint strip 312.

Figure 4 shows two examples of tuning of an antenna according to the invention. One way is to make the radiating gap meandering. In the example image, slot 420 forms a meander pattern. Another way is to design the auxiliary element. In the example of the figure, the first portion 15 above the paint strip 412 of the auxiliary element 430 is cut off a portion of the CUT. The third way is to change the height h of the auxiliary element, i.e. the distance of the first leg from the ground. The designation Ah in the figure indicates such a change.

Figure 5 shows an example of the location of an antenna according to the invention in a radio device. The RD1 radio unit in the example is a foldable mobile unit with a hinge HG. * ··. 20, a first pivot part TP1 and a second pivot part TP2. The radio device is shown in a reduced longitudinal section. The first pivoting part includes e.g. the device has a keyboard and a microphone, and the other swivel section has a * * / / mm. device display and speaker EP. The second pivoting part is thus the part held by the user:.:. In this example, the antenna 500 is located at the opposite end of the • hinged HG from the hinge. The radiating slot and the auxiliary element are located on the outside of the circuit board 505 of the first pivoting member when viewed under normal use by the user. Such a location means relatively:. low SAR value with the EP speaker attached to the user's ear.

··· · ♦ * ·

Figure 6 shows another example of the location of an antenna according to the invention in a radio apparatus. Also, in this example, the radio device RD2 is mechanically two-part, so that the parts can now be solubilized with respect to each other. Thus, the device has a first solver and a second slider SP2. The radio device is shown in reduced longitudinal section. The first slider includes e.g. the device has a V * i keypad and a microphone, and the other slider has e.g. device display and speaker EP.

35 The second slider is thus the part which is held by the operator's ear. In this example, the antenna 600 is located at the end of the first slider, which is further from the second slider, with the radio unit in its extended position. The radiating gap * and the auxiliary element are located on the outer side of the first slider circuit board 605 in normal use as viewed from the user. Such a position represents 5 relatively low SARs with the speaker EP near the user's ear.

Figure 7 shows an example of the band characteristics of an antenna according to the invention. It has a graph 71 which shows the change in return attenuation RL as a function of frequency when the antenna is in idle state. The antenna has two clear operating bands. The lower operating band is in the 850 MHz band and has a width of about 90 to 10 MHz with a cutoff value of -5 dB as the cut-off frequency criterion. This bandwidth is remarkably large. The upper operating band is in the 1.9 GHz range and has a bandwidth of approximately 70 MHz with a cutoff value of -5 dB as the cut-off criterion. In the middle of the operating bands, the back attenuation is about 15 dB, which indicates a good fit.

Figure 8 shows an example of the efficiency of an antenna according to the invention. Fig. 81 shows a change in the efficiency of a dual band antenna corresponding to the reverse attenuation curve of Fig. 7 as a function of frequency when the antenna is in idle state. In the lower operating band, the efficiency varies on both sides of 0.6. In the middle of the upper operating band, the efficiency is about 0.85 and then decreases to about 20 when going to the edge of the band. By way of comparison, Fig. 8 also shows the efficiency curve 82 of the PIFA having the lower operating bands. The efficiency of the PIFA in the lower operating band is approximately the same as that of the antenna of the invention. In the higher operating band, PIFA is superior to the antenna according to the invention with an average efficiency of more than 0.8. However, there is a noticeable difference in height of the Anj * V 25 sneakers. The tested antenna according to the invention is 5 mm high and the PIFA • 1 · 1 / reference object is 9 mm high. The circuit board with ground plane is the same in both ***** antennas.

: a: |: Figure 9 shows an example of the effect of the user's head on the antenna efficiency. The graph 91 relates to the same antenna according to the invention as the graph 81, and the graphs 92 relate to the same PIFA as the graph 82. Thus, in this case, the antennas are in a normal operating position adjacent to the user's head. It is observed that the efficiency ratios fall very clearly, however, with the antenna according to the invention, less than PIFAI. In the lower operating band, the antenna of the invention ····: *** has an average efficiency of 0.13, but only 0.08 for PIFA. At the higher operating band, the efficiency of the antenna according to the invention is on average 0.11, but on PIFA only 0.075.

7 118749

The prefixes "bottom" and "top" in this specification and claims refer to the position of the antenna structure in which the circuit board of the radio device is horizontal and the radiating slot of the antenna is on its upper surface. Of course, the device can be used in any position.

Some antenna structures according to the invention have been described above. The shapes of the antenna parts may, of course, differ from those shown in the figures. For example, the auxiliary bag may be a slot for increasing bandwidth, and there may be more than one auxiliary element itself. The radiating gap and the paint strip it separates may also be parallel to the long side of the circuit board of the radio device. The circuit board of the radio device may be a multi-10 sandwich board, whereby the antenna feed conductor may be located in some intermediate layer thereof. The inventive idea can be applied in various ways within the limits set by the independent claim 1.

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Claims (8)

An antenna of the radio device, which radio device comprises a circuit board (205; 305), the upper surface of which is mostly conductive ground plane (210; 310), and the antenna comprises in the ground plane a radiating slot (220; 320) which opens at the edge of the ground plane 10 characterized in that the slot is the main radiator of the antenna, between the gap and the edge of the ground plane lies a relatively narrow ground strip (212; 312) and that the antenna further comprises a conductive elongated auxiliary element (230; 330) for increasing the electrical length of the slot and for improving the radiation characteristics, which auxiliary element is coupled to the outer end of said ground strip, next to the open end of the gap 15 (220; 320) and directed towards the closed end above the ground strip. Antenna according to claim 1, characterized in that said auxiliary element is further arranged to resonate at a specified frequency, to form another, upper functional band, in the antenna. Antenna according to Claim 1, characterized in that its supply line 20 is a conductor strip of said circuit board, which conductor extends substantially at a [...]] direction perpendicular to the line of the radiating gap at the input point, which is close to the closed end of the gap. • · • · • * Antenna according to claim 1, characterized in that there is at least one curvature for tuning the antenna in the radiant gap. «M An antenna according to claim 1, characterized in that the auxiliary element has a configuration (CUT) for tuning the antenna. • · ' Antenna according to claim 1, characterized in that the height of the auxiliary element; * ·, · height from the surface of the circuit board is max. 5 mm. • · Radio device, comprising a circuit board whose upper surface is mostly conductive ground plane and the antenna of which radio device comprises in the ground plane a radiant slot which opens at the edge of the ground plane, characterized in that the slot is the main radiator of the antenna. the slot and edge of the ground plane remain a relatively narrow ground strip and the antenna of the radio device further comprises a conductive elongated auxiliary element for enlarging the electrical length of the slot and for enhancing radiation properties, which auxiliary element is coupled at the outer end of said ground strip, adjacent to the open end of the slot directed towards the gap closed 5 above the ground strip. The radio device (RD1; RD2) according to claim 7, which radio device comprises a first (TP1; SP1) and a second (TP2; SP2) portion which can be moved relative to each other, which second portion of the device's normal use situation is a portion which is poured onto the user's ear, characterized in that said circuit board refers to the circuit board (505; 605) of the first portion (TP1; SP1) and said antenna (500; 600) is in use situation located on the outer surface of the circuit board. seen from the user. * · «• · • · ·· 1 9 · • · · ··· • · · · · · 1 • t • · • · · •» · ** »· • m * · · • Φ · ·· 1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · • n