FI120119B - The antenna structure - Google Patents

Description

i

The antenna structure

The invention relates in particular to an internal multi-band antenna structure for small radio devices.

The space available for the design of portable radio antennas is 5 important factors. 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 separate 10 frequency bands.

In practice, the antenna that goes inside a compact device with the most satisfactory characteristics can be obtained in the form of a planar structure: the antenna has a radiating plane and a parallel ground plane. These levels are usually interconnected by a short-circuit conductor to form a PIFA (Planar 15 Inverted F-Antenna) structure. However, as the distance between the radiating plane and the ground plane is reduced from its optimum value, PIFA properties such as bandwidth are reduced. This poses a problem in the relatively common radio devices nowadays. In addition, the decline in equipment has also meant a decrease in their ground level. As a result, PIFA performance deteriorates with antenna resonances.:. 20 and ground level resonances to useless frequencies. * ···. because of. For dual-band mobile antennas, the disadvantages occur with higher • · lower bandwidth in the 0.9 GHz range.

: · · · · ·: · The problem with the flatness of the radio can be reduced by making the antenna: *** ·· monopoly. Figure 1 shows an example of such an internal mo-25 antenna. The drawing shows the circuit board PCB of the radio device and the two radiating elements 120,130 of the antenna. The circuit board surface is for the most part conductive ground level GND. The radiating element 120 is the main radiator. It is located at the • •. when viewed from above the plate, it is almost completely outside, leaving the ground plane to the side of the radiator. When viewed from its feed point FP, the main radiator 120 is divided into two branches 121, 122 of different lengths to form two separate operating bands. The main radiator and its branches are for the most part in a plane parallel to the PCB of the circuit board. To extend the longer leg 121 and modify the radial pattern at its outer end, there is a portion toward the geometric plane of the circuit board, so that the antenna has a certain height. However, this height 35 remains less than the height required by the other parts of the radio device 2 together. An inductive component may be coupled to ground near the feed point FP to improve antenna matching. The second radiating element 130 is a parasitic element. It is connected from the ground point GP at one end of the element to the ground plane GND. Ground point GP and said feed point, viewed from above, are adjacent to a corner of the circuit board, side by side. The parasitic element 130 leaves the ground point parallel to the beginning of the main element, in this example a plane slightly lower than the main element, and then turns beneath the main element.

The lower operating band of the antenna is based on the resonance of the longer branch 121 of the main element and the upper operating band and the resonance of the parasitic element 130 of the shorter branch 122 of the main element. The frequencies of the latter two resonances are different but still close to each other so that a uniform and relatively wide upper operating band is obtained.

The monopole antennas described above will outperform PIFA in the same size space. The disadvantage, however, is that the lower operating band remains relatively narrow, so that it can easily be displaced slightly from the designed area, for example by external conductive materials. The ground plane size of a radio device is one factor affecting the lower bandwidth; if the ground plane size deviates from the optimum, the bandwidth will further decrease. A further disadvantage is that the resonances of the main element mutually influence each other, which signifies a decrease in the efficiency of the antenna and also in the bandwidths.

• · ·. ’···. The object of the invention is to reduce the above-mentioned disadvantages associated with the prior art.

• · y. '. An antenna structure according to the invention is characterized by what is set forth in the independent claim 1. Certain preferred embodiments of the invention are described in the other claims.

The basic idea of the invention is as follows: The radiating structure of the antenna comprises a first air-insulated first monopole emitter and a second monopoly emitter on a ceramic substrate. The former resonates in the lower operating band of the antenna and. ···. the latter in the upper operating band. An integral part of the antenna structure is also a matching circuit which, in addition to the matching, provides a second resonance for the first radiator. The ceramic substrate and the matching circuit are placed on a plastic body supporting the first radiator or on a small auxiliary plate attached thereto to form an integrated antenna module. The structure may further comprise a radiating parasitic element for widening the upper operating band.

• · 3

An advantage of the invention is that a relatively wide lower operating band is obtained for a small antenna. This is due to the double resonant low bandwidth radiator generated by the matching circuit of the invention. A further advantage of the invention is that 5 common feed points can be used for the lower and upper operating band radiators. This is because the matching circuit according to the invention acts as a filter which improves the separation between the radiators. A further advantage of the invention is that the effect of the ground level size of the radio device on the lower operating bandwidth is significantly less than in known monopoly antennas. A further advantage of the invention is that the entire antenna structure can be tested as a stand-alone module, whereby testing is no longer required when the module is installed in the radio device.

The invention will now be described in detail. Referring to the accompanying drawings, Fig. 1 shows an example of a known internal monopole antenna, Fig. 2 shows an example of an antenna structure according to the invention, Fig. 3a shows a top view of the antenna structure according to Fig. 2, Fig. Fig. 5 shows an example of the efficiency of the antenna structure according to the invention.

• · · · · · · · · · · ·

Figure 1 was already described in connection with the prior art description.

2 shows an example of an antenna structure according to the invention. Figure 2 is a perspective view showing only the general mechanical structure of the antenna. It shows · · · 25 the circuit board PCB of the radio device, the upper surface of which is to a large extent the conductive ground level GND. The antenna structure is located at the end of the circuit board outside this. The radiating structure comprises two monopole radiators. The first radiator 221: *** is a strip-like conductor element on the surface of the dielectric support body 205. The body 205 ··· ./ is attached to the PCB end of the PCB and has a vertical * in this example. . 30 A curved portion viewed from above that conforms to the shape of the end of the radio device for which the antenna is intended. The first radiator 221 is mounted on the outer surface of the curved portion of the body. The curved portion is relatively thin, and the material of the body 4 is selected such that the first radiator is almost air insulated. The second radiator 222 is a conductive coating on a ceramic substrate. Here, the ceramic substrate 210 is an oblong rectangular body disposed between the first radiator 221 and the circuit board, viewed from above, parallel to the PCB end of the circuit board. The body 205 includes a horizontal portion of its curved portion facing the circuit board. Ceramic substrate 210 with conductive coatings is attached either directly to the horizontal portion of the body, i.e. the "base", or to a small dielectric sub-plate which is again attached to the base. Parts of the antenna structure form an integrated antenna module 200, which can be tested separately and then mounted on a radio device.

The antenna structure according to the invention has at least two separate operating bands. The two operating bands are called the lower and upper operating bands. In Figure 2, the first radiator 221 resonates in the lower operating band and the second radiator 222 in the upper operating band. The radiators have a common feed point FP to be connected to the antenna port 15 of the radio device, which in this example is a projection extending over the PCB of the antenna structure. The electrical structure of the antenna is described in more detail below.

Figure 3a is an example of a top view of the antenna structure of Figure 2, and Figure 3b is a plan view of the PCB side. In Fig. 3a, the antenna structure support body 205, the dielectric sub-plate 215 on the "bottom" of the support body, the ceramic substrate 210 on the sub-plate, the first radiator 221 on the body are shown. the outer surface, the second radiator 222 located on the top surface of the substrate 210 and the auxiliary plate. antenna matching circuit. The matching circuit is an integral part of the • · '.' 1 'antenna structure according to the invention. It includes capacitive elements C1 and C2 and inductive elements L1 and L2, all of which are discrete lump components in this example. Their connection is illustrated in Figure 4. The second radiator 222 is significantly narrower than the rest of the inlet • • * ··· *. This narrow portion increases the inductance in the radiator feed circuit and can be considered as belonging to the antenna fit »· v .; load circuit.

The first and second radiators have a common ground point G1 and a common feed point FP, galvanically coupled to the feed point F2 of the second radiator 222 in the antenna structure. The first radiator receives its supply through the matching circuit to its input · * · .. point F1. The ground point G1 and the feed point FP are located at the projections of the auxiliary plate 215. ·. i la which extends over the circuit board PCB of the radio device. The ground point G1 is coupled through the auxiliary plate passage to the ground plane GND of the radio device, and the feed point FP is connected through the auxiliary plate passage to the antenna port of the radio device.

5

Further, the exemplary structure includes a parasitic radiator 230 shown in Fig. 3a, which is a conductive strip on the surface of auxiliary plate 215 between the substrate 210 and the outer, curved portion of the body 205. At its other end, the parasitic radiator 230 is connected to the ground plane GND via the second ground point G2 on the auxiliary plate. The resonance frequency of the Pa-5 racite radiator is arranged in the upper operating band of the antenna to widen it.

Figure 3b shows the components of the matching circuit, such as capacitor C2, mounted on auxiliary board 215. Further, the detail of the conductor strip on the side surface of the substrate 210 which connects the second radiator 222 to its feed point F2 below the substrate is also shown in detail.

Fig. 4 is a circuit diagram showing an example of a matching circuit for an antenna structure according to the invention. The matching circuit 240 corresponds to the structure shown in Figure 3a. There is a first capacitor C1 between the common feeder point FP and the ground point G1 for the radiators. The feed point is coupled to the second radiator 222 via an inductance dance L 'corresponding to the inductance of the aforementioned narrow conductor strip in the conductive coating of the ceramic substrate. At the lower end of the inductance L 'one can imagine the entry point of the second radiator in Fig. 4. Also connected to the supply point FP is a series resonant circuit having a first capacitor C2 and then a second coil L2 when leaving the supply point. The other end of the incident resonant circuit is coupled through a first coil L1 to a ground point G1 and directly to a first radiator ice 221.

• · · ·

Thus, the first coil L1 is located between the entry point of the first radiator and the ground point and adjusts the impedance of the first radiator. The impedance of the second emitter ···: again is matched by the first capacitor C1.

··· · ·····························································································································NING order order 25: The first radiator 221 has a double resonance instead of a single basic resonant. The frequencies of these resonances can be arranged in close proximity to one another so that the lower operating band becomes relatively wide.

··· ** ·· * The matching circuit also forms the first port and the first port represented by the second radiator 30 inlet and ground point G1 of the bandpass filter: • **; between the radiator feed point and the second port represented by ground point G1. An- • · ·. ·. the lower operating band of the tennis is in the pass band of the filter, and the attenuation from the first gate to the second port is significantly high in the hair of the upper operating band. This means an improvement in the separation between the radiators so that a common feed point FP can be used for the radiators in the antenna structure.

6

Figure 5 shows an example of band characteristics of an antenna structure according to the invention. The graph shows the change of the reflection coefficient S11 as a function of frequency. It is measured from an antenna structure with the dimensions of the ceramic substrate 18x3x1.5 mm3 and the size of the whole antenna module 40x8x6 mm3 width 8 mm kos-5 denoting the outer edge of the module from the edge of the ground plane. The substrate used has a relative dielectric coefficient of 35. The lower the reflection coefficient, the better the antenna is fitted and the better it functions as a radiator and radiation receiver. For example, if the cut-off frequency criterion is a reflection coefficient value of -5 dB, the lower operating band of the antenna is about 810 to 1030 MHz with a band-10 width of about 220 MHz (24%). The lower operating band extends well over the marked frequency band W1, which includes both the 824-894 MHz band of the Global System for Mobile telecommunications (GSM) system and the 880-960 MHz band of the European GSM (Extended GSM) system. The remarkably large width of the lower operating band has been achieved by the fact that two resonances r1 and r2 are arranged in the frequency range in question with the matching circuit according to the invention so that they do not severely interfere with each other. The first resonance r1 and the second resonance r2 are the resonances of the whole formed by the first radiator 221 and the matching circuit, in particular its resonant circuit.

The upper operating band of the antenna is, according to the above criterion, about 1.70-2.17 GHz with a bandwidth of about 470 MHz (24%). The upper operating band covers the frequency band W2 shown in the figure, which includes the GSM1800 frequency band O 1710-1880 MHz, the GSM1900 system band 1850-1990 MHz and the WCDMA (Wideband Code Division Multiple Access) band 19 25-2170 MHz. The upper operating band is also based on two resonances r3, ··· · r4. The lower of these, the third resonance r3, is the second of the ceramic substrate! ···. the resonance of the radiator 222, and the fourth resonance r4 is the resonance of the parasitic radiator 230.

• · v .; Figure 6 shows an example of the efficiency of the antenna structure according to the invention.

• · «30 The graph shows the change in efficiency as a function of frequency with the antenna. j \ in free mode. In the lower operating band, the efficiency varies from -3.8. ···. dB to -2.5 dB. In the higher operating band, the efficiency varies between -3.7 • - · T dB and -2.7 dB. The operating bands considered herein are the following frequency ranges: 1 ··· W1 and W2. One factor affecting efficiency is the size of the ground plane of the radio unit · .1 ·· 35. The above results have been obtained with a ground plane of 40x100 mm2.

7

The prefixes "horizontal", "vertical", "bottom" and "top" and the attribute "top" refer to the position of the antenna structure in which the circuit board of the radio device and the bottom of the antenna structure are horizontal and the frame substrate is above the bottom. Of course, the operating position of the device can be any.

An antenna structure according to the invention has been described above. Of course, the shape and position of the structural parts may differ from those shown. For example, a parasitic radiator may also be located on the surface of a dielectric body. The auxiliary plate may be omitted, whereby the substrate and the matching circuit are directly over the bottom of the frame. In the matching circuit 10, both the capacitive member C1 and C2 can also be implemented with only adjacent conductive strips on a dielectric substrate. Likewise, at least of the inductive elements, the smaller L1 can also be realized with a narrow conductor strip of dielectric substrate only. With the discrete coil, there may be in series a low inductance strip which is used as a tuning member by machining it in the test step 15, for example with a laser. The narrow conductor strip accommodating the second radiator, which in the example of Figures 3a and 3b is on the surface of the substrate, may also be substantially on said auxiliary plate. The inventive idea can be applied in various ways within the limits set by the independent claim 1.

M »· · · · · · · · · · · · · · · · · · · · · · · · · · · · ··· M · M M M M M M M · • M M M M M M M M M M M M ·· 1 · · · · · ··· · ·

Claims (11)

An antenna structure for realizing the internal antenna of the radio device having a lower · · ··· * and an upper functional band, which antenna structure comprises monopoly type first radiator (221), which resonates on the lower functional band and a monopoly type 25 second radiator (222), which resonates on the upper function band, as well as adaptation components for adjusting the impedance of the beam, characterized by. . ·. it comprises a ceramic substrate (210), the conductive coating of which is the second radiation. clean (222), since the first radiator (221) is an almost air-insulated conductive element supported by a dielectric frame (205), said radiators have a common ground point (G1), which is coupled in the ground plane of the radio device (GND) and a: in common input point (FP) which is galvanically coupled in the input point (F2) by the second radiator, and adaptation components form an adaptation circuit (240) comprising a first inductive means (L1). ), coupled between the grounding point and the first radiator input point (F1), for adapting the first radiator, a first capacitive means (C1), coupled between the common input point (FP) and the grounding point (G1), for adapting the second radiator, and a series resonant circuit coupled between the input point (F1) of the first radiator 5 and the second radiator input point (F2), to realize the second resonance of the first radiator for propagation of lower function the band and simultaneously for forming a bandpass filter between the pore formed by the second radiator's input point (F2) and the grounding point (G1) and the port formed by the first radiator's input point (F1) and the grounding point, to improve decoupling between the jets. An antenna structure according to claim 1, characterized in that it further comprises a parasitic radiator (230) coupled to the ground plane at one end, the resonant frequency of which is on the upper functional band for its expansion. An antenna structure according to claim 1, characterized in that said resonant circuit comprises a capacitive means (C2) and an inductive means (L2) connected in series. Antenna structure according to claim 3, characterized in that at least one of said capacitive means (C1, C2) and inductive means (L1, L2) is a discrete component. • · · "il 20 An antenna structure according to claim 3, characterized in that at least one of said capacitive means (C1, C2) is realized with conductive bands on a di · · 1 ·: electrical support. An antenna structure according to claim 3, characterized in that at least one of the said inductive means (L1, L2) is realized with a conductive band on a dielectric substrate. Antenna structure according to claim 1, characterized in that the first · ♦ · radiator (221) is a conductive band on the outer surface of said frame (205), which conductive band is substantially vertical in width, with other words perpendicular to the front. ·· ♦! leaning to the ground plane. • · ··· Antenna structure according to claim 1, characterized in that it further comprises a dielectric auxiliary disk (215) supported in said frame (205), and the ceramic substrate (210), the adaptation circuit (240) and said input point ( FP) and the grounding point (G1) are on this auxiliary disk. 11 Antenna structure according to claim 1, characterized in that the second radiator (222) is substantially narrower at its input end than in its other portions, for increasing the inductance (1) in the input circuit of the second radiator, to further advance improve the adaptation of the second radiator. Antenna structure according to claim 8, characterized in that on said auxiliary clamp (215) there is an additional parasite radiator (230) and a separate second grounding point (G2), through which one end of the parasite radiator is connected in the ground plane (GND). . Antenna structure according to claim 1, characterized in that it forms an integrated antenna module (200). · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 1 · • ♦ · · · · · ·