Dual-band digital audio broadcasting antenna

Abstract

 The present invention relates to a dual-band digital audio broadcasting antenna comprising a first meandered monopole antenna element (1) designed for a frequency band from about 174 MHz to about 240 MHz (Band III frequency band), and a second monopole antenna element (2) designed for a frequency band from about 1452 MHz to about 1492 MHz (L-Band frequency band), which are formed by thin metal traces provided on the top surface of a carrier (5). The electrical length of the first meandered antenna element (1) is equivalent to quarter of wavelength of the Band III frequency band, and the electrical length of the second monopole antenna element (2) is equivalent to quarter of wavelength of the L-Band frequency band.

Description

[0001] The present invention relates in general to a dual-band digital audio broadcasting system (dual-band DAB system), and in particular to a dual-band digital audio broadcasting antenna (dual-band DAB antenna) which is intended to be used in a dual-band DAB system and which is designed to be fitted on an automobile, for example, and in particular on the front glass of an automobile ("on-glass" antenna).

[0002] The dual-band DAB system comprising a dual-band DAB antenna usually operates at two frequency bands, the so-called "Band III" frequency band at frequencies from about 174 MHz to about 240 MHz, and the L-Band frequency band from about 1452 MHz to about 1492 MHz. The dual-band DAB antenna, when used on a glass carrier, such as the front glass of an automobile, must not have a uniform and solid structure but rather thin metal trace lines of small width with gaps and empty spaces between them, in order to achieve a kind of "see-through" effect, in order not to obstruct the view of the driver of the automobile.

[0003] A dual-band DAB film antenna of this type is described in JP 2000-295023 from Harada IND CO LTD, for example. The dual-band DAB film antenna disclosed in this document comprises two monopole antenna elements, wherein the longer monopole antenna element designed for the "Band III" frequency band is bent to form a U-shaped monopole antenna element for slightly reducing the size of the "Band III" monopole element. Further, the prior art "Band III" monopole antenna element does not include an RF inductor, making the size and length of this U-shaped antenna element very large. Finally, this known antenna does not provide the possibility to re-arrange the antenna structure in order to achieve a one or dual terminal connection to the corresponding electric circuit, with the result that the antenna design and especially the electronic circuit design is restricted.

[0004] It is a main object of the present invention to provide a dual-band DAB system comprising a dual-band DAB antenna having a reduced size and length, without effecting the performance of the DAB antenna.

[0005] It is a further object of the present invention to provide such a dual-band DAB system and a dual-band DAB antenna using additional electronic components for further reducing the length of the longer "Band III" monopole antenna element.

[0006] Furthermore, it is an object of the present invention to provide such a dual-band DAB system and a dual band DAB antenna providing several ways to connect the DAB antenna to an electric radio frequency circuit.

[0007] These and other objects are achieved by a dual-band DAB antenna system and a dual-band DAB antenna comprising two monopole antenna elements having a different structure, i.e. a first meandered monopole antenna element designed for the Band III frequency band, and a second straight monopole antenna element designed for the higher frequency of the L-Band frequency band.

[0008] Because of the meandered structure of the first Band III monopole antenna element, a substantial reduction of the size and length of the dual-band DAB antenna can be achieved.

[0009] In a preferred embodiment, the Band III monopole antenna element can be series connected to an RF inductor element. In particular, one terminal of the RF inductor element is connected to the Band III monopole antenna element and the other terminal of the RF inductor element is connected via the antenna feed point to the electronic radio frequency circuit.

[0010] For the above reasons, this dual-band DAB antenna can provide a dual-band characteristic for dual-band DAB system in a very small and compact size, due to its unique structure and the optional provision of an RF inductor to the Band III monopole antenna element.

[0011] According to a first aspect of the invention, the first meandered monopole antenna element (Band III monopole antenna element) and the second monopole antenna element (L-Band monopole antenna element) are connected to form one antenna feeding point for connection to the electronic radio frequency circuit. However, according to a second aspect of the invention, the DAB antenna structure can also be designed to have two feeding points, i.e. the first and second monopole antenna elements are separated and can independently connected to the electronic radio frequency circuit. Thus, the antenna of this invention can either be designed to have one or two input terminals (feeding terminals), making the electronic circuit design more flexible and cost effective. Further, both arrangements allow the provision of an RF inductor connected to the first meandered Band III monopole antenna element.

[0012] In both arrangements, the first and second monopole antenna elements are made of narrow metal traces with very small thickness. These metal traces are fitted on the top of a hard substrate or on the top of a very thin and transparent plastic layer (also referred as a carrier). Said carrier comprises on its topside the metal trace elements and on its bottom side a self-adhesive glue. The complete unit is the "on-glass" antenna, which just glues on the glass window of a car. Further, by using a special plastic foil as the transparent plastic layer, a high degree of transparency for usage on a glass of a car can be achieved.

[0013] Furthermore, this antenna is using only one side of the plastic foil or the hard substrate material making it very easy to mass-produce. In general, the simple structure of the whole DAB antenna unit allows a cost effective mass production.

[0014] Embodiments of the present invention will now be described in connection with the drawings, in which:

Figure 1 shows a first embodiment of a dual-band DAB antenna having one antenna feeding terminal, where Figure 1a shows the DAB antenna comprising a Band III monopole antenna element provided with an RF inductor, and Figure 1b shows the DAB antenna without an RF inductor;

Figure 2 shows a cross-sectional view of the dual-band DAB antenna showing the metal traces, the plastic layer and adhesive glue;

Figure 3 shows a second embodiment of a dual-band DAB antenna having separate feeding terminals, where Figure 3a shows the DAB antenna comprising a Band III monopole antenna element provided with an RF inductor, and Figure 3b shows the DAB antenna without an RF inductor;

Figure 4 shows a block diagram of the receiving DAB system for the DAB antenna of Figure 1 having one antenna feeding terminal;

Figure 5 shows a block diagram of the receiving DAB system for the dual-band DAB antenna of Figure 3 having two antenna feeding terminals;

Figure 6 shows the VSWR (voltage standing wave ratio) response of the DAB antennas of Figures 1 and 3; and

Figure 7 shows several radiation patterns at different frequency points.

[0015] Reference is first made to Figures 1a and 1b. Both figures show the first embodiment of the dual-band DAB antenna of the invention, wherein Figure 1a shows the DAB antenna being provided with an RF inductor, and Figure 1b shows the same DAB antenna, but without an RF inductor (explained below). Both DAB antennas of Figures 1a and 1b comprise two main monopole antenna elements 1 and 2, and one common feeding terminal 4 adapted for connection to an electronic radio frequency circuit (shown in Figure 4). The first monopole antenna element 1 has a meandered monopole structure designed for the Band III frequency band, i.e. frequencies from about 174 MHz to about 240 MHz, and the second monopole antenna element 2 has a substantially straight monopole antenna structure designed for the higher frequency of the L-Band frequency band, i.e. frequencies from about 1452 MHz to about 1492 MHz.

[0016] Both monopole antenna elements 1 and 2 are connected together to form one common antenna feeding terminal 4 which will be connected to an electronic RF circuit 7 (Figure 4).

[0017] The first meandered monopole antenna element 1, the second monopole antenna element 2, and the common feeding terminal 4 are narrow metal traces with very small thickness formed on the top surface of a hard substrate or a very thin and transparent plastic layer 5 (also referred as "carrier" or "carrier foil").

[0018] The first monopole antenna element 1 of the DAB antenna of Figures 1a, 1b is designed to have a meandered structure in order to minimize the physical size of the antenna. The electrical length of this meandered antenna element 1 should be equivalent to quarter of wavelength of the Band III frequency band (about 174 MHz to about 240 MHz). The width of the trace line and the gap between the meander lines determine the impedance characteristic of the antenna and its frequency band resonance, i.e., the length of this meandered antenna element 1 determines the frequency band resonance. Figure 6 shows the VSWR (voltage standing wave ratio) response of such a DAB antenna.

[0019] The second monopole antenna element 2 in Figures 1a and 1b has also a length of a quarter of wavelength, designed to operate at the higher frequency band of the L-Band (about 1452 MHz to about 1492 MHz). The structure of the second monopole antenna element 2 is a straight metal trace except at the top where the metal trace is bent to minimize its overall size. At the top of the second monopole antenna element 2, the current distribution and the power flow is minimum. For this reason, it is possible to bend the second monopole antenna element 2 without significantly affecting the performance of this antenna element. The width of the trace determines the frequency resonance and input impedance characteristic.

[0020] The distance between the first monopole antenna element 1 and the second monopole antenna element 2 in the first and second embodiment is also of importance since both antenna elements 1, 2 must be strategically placed apart in order to achieve a dual-band characteristic, without any unwanted resonances to occur. Therefore, both monopole antenna elements 1, 2 are connected to the feeding terminal 4 in order to have to main resonances at the Band III and the L-band at the feeding terminal 4.

[0021] The carrier 5 for both monopole antenna elements 1, 2 and related components can be hard substrate material, e.g. FR4, or a transparent flexible plastic foil designed to support the metal traces. The bottom side or surface of said carrier 5 is provided with self-adhesive glue 6, especially for automotive glass usage. The degree of transparency of the carrier 5 must be very good, and the adhesive peeling strength must be quite high. Its operation temperature range must be large and must be UV and chemical resistant. The plastic foil or hard substrate material (generally referred as carrier 5) have also some dielectric characteristic with a dielectric constant ranging from 2,5 to 4. This dielectric characteristic is also influencing the performance of the DAB antenna and should be taken into account in the design process.

[0022] The adhesive special glue 6 must provide good contact between the carrier 5 and glass for a wide range of temperatures. It must also withstand UV radiation from the sun and must have some chemical resistance.

[0023] All the elements, i.e. the first meandered monopole antenna element 1, the second monopole antenna element 2, and the common feeding terminal 4, are provided on the top surface of the carrier 5, and the self-adhesive glue 6 is provided on the bottom surface of the carrier 5 as shown in the cross-sectional view of Figure 2.

[0024] As already mentioned above, both DAB antennas of the first embodiment, as shown in Figures 1a and 1b, have a similar structure. However, the DAB antenna of Figure 1a is provided with an RF inductor 3 making it possible to further reduce the size and length of the DAB antenna. In particular, the meandered monopole antenna element 1 is connected to the RF inductor element 3 in series, i.e. between the meandered antenna element 1 and the common feeding terminal 4.

[0025] The RF inductor 3 as provided in Figure 1a is used to compensate the electrical length of the meandered monopole antenna element 1. Thus, in combination with the RF inductor, the meandered monopole antenna element 1 can be much shorter than a quarter of wavelength. The higher this RF inductor 3 is in value, the shorter the monopole antenna element 1 can be. The usage of the RF inductor 3 is not always needed, as can be seen from Figure 1b. This RF inductor 3 can be either inserted within the antenna element 1, when the carrier 5 is hard enough to support it or can be fitted inside a related electronic radio frequency circuit when a thin transparent and flexible plastic foil is used as the carrier 5.

[0026] Figures 3a and 3b show a second embodiment of the dual-band DAB antenna having a basic antenna structure similar to that of the DAB antennas shown in Figures 1a and 1b. However, the dual-band DAB antennas of Figures 4a and 4b are designed to have two feeding terminals 4a and 4b. Thus, both monopole antenna elements 1, 2 are adapted to allow separate connection to a related electronic radio frequency circuit (shown in Figure 5). Similar to Figures 1a and 1b, the structure of the DAB antenna of Figure 4a includes an RF inductor 3, and the DAB antenna of Figure 4b does not have an RF inductor.

[0027] The DAB antenna as described above is adapted for connection to an electronic radio frequency circuit 7 to form an active DAB antenna.

[0028] Figure 4 shows an example of such an electronic RF circuit 7 for connecting the DAB antennas of Figures 1a and 1b having a single feeding terminal 4, whereas Figure 5 shows an electronic RF circuit 7' for connecting the DAB antennas of Figures 3a and 3b.

[0029] The electronic RF circuit 7 comprises an RF filter or diplexer 8, an RF low noise amplifier (LNA) 9, a Bias-T element 10 to provide the DC power to the circuit, and an RF coaxial cable 11 which can be connected to the DAB tuner/receiver 12.

[0030] As depicted in Figure 4, the electronic RF circuit 7 includes a diplexer or RF filter 8 in case the antenna has one feeding terminal 4 (see Figures 1a and 1b), whereas the electronic RF circuit 7' of Figure 5 comprises band-pass filters 8' at each frequency band (i.e. Band III and L-Band) in case the DAB antenna has two feeding terminals (see Figures 3a and 3b).

[0031] In both RF circuits 7, 7', these filters 8, 8' are used to pass through the in-band signals (wanted signals) and to reject the remaining unwanted signals which are present on the air and to compress even lower the noise floor level.

[0032] Further, the RF circuit 7 of Figure 4 has a low noise amplifier (LNA) 9 which is used after filtering (filter 8) to amplify the wanted signals. The noise contribution of this amplifier 9 must be as small as possible in order to compress the noise even further and to amplify the main carrier signal mostly. This is very important especially for digital communication where the bit error rate depends on the signal-to-noise ratio, which must be high. By using this amplifier 9, the noise figure of the complete system can be reduced for a more error free reception.

[0033] As depicted in Figure 5, the electronic RF circuit 7' for the DAB antenna having two feeding terminals 4a, 4b is provided with two separate low noise amplifiers 9', which are connected to the corresponding Band III filter and L-Band filter, respectively.

[0034] In both RF circuits 7, 7', the low noise amplifier(s) 9, 9' are connected to a bias-T 10 for supplying DC (direct current) power in order for the amplifier 9, 9' to work. The DC power supplied from the bias-T gives DC to the circuit and passes RF power at the output.

[0035] Further, in both RF circuits 7, 7' of Figures 4 and 5, an RF coaxial cable 11, 11' is used to connect the active antenna with the DAB tuner/receiver box 12, 12' and to bring DC power to the electronic circuit. This cable 11, 11' should be selected to have minimum power loss.

[0036] The DAB tuner/receiver box 12, 12' (demodulator) is used to receive the wanted signals and extrapolate the digital information from these wanted signals. It also supplies DC power to the electronic circuit through the cable 11, 11' and the bias-T 10, 10'. This DAB box 12, 12' is usually inserted inside the car.

[0037] Figure 7 shows several radiation patterns at different frequency points of 174 MHz, 240 MHz, 1425 MHz and 1492 MHz.

[0038] It should be noted that the complete electronic circuit can be housed within a plastic box, with some water and moisture resistance, to prevent corrosion or damage of the circuit from steam, heat and dust.

Claims

1. Dual-band digital audio broadcasting antenna comprising a first meandered monopole antenna element (1) designed for a frequency band from about 174 MHz to about 240 MHz (Band III frequency band), and a second monopole antenna element (2) designed for a frequency band from about 1452 MHz to about 1492 MHz (L-Band frequency band).

2. Dual-band digital audio broadcasting antenna according to claim 1, characterized in that a first meandered monopole antenna element (1) and the second monopole antenna element (2) are formed by thin metal traces provided on the top surface of a carrier (5).

3. Dual-band digital audio broadcasting antenna according to claim 1 or claim 2, characterized in that the first meandered monopole antenna element (1) is formed by thin metal trace lines of small width with gaps and empty spaces between them provided on the top surface of a carrier (5), wherein the electrical length of the first meandered antenna element (1) is equivalent to quarter of wavelength of a frequency band from about 174 MHz to about 240 MHz.

4. Dual-band digital audio broadcasting antenna according to any of the claims 1 to 3, characterized in that the structure of the second monopole antenna element (2) is a straight metal trace except at the top where the metal trace is bent to minimize its overall size, wherein the electrical length of the second monopole antenna element (2) is equivalent to quarter of wavelength of a frequency band from about 1452 MHz to about 1492 MHz.

5. Dual-band digital audio broadcasting antenna according to any of the claims 2 to 4, characterized in that the metal traces of the first and second monopole antenna elements (1, 2) are provided on the top surface of a hard substrate (5).

6. Dual-band digital audio broadcasting antenna according to any of the claims 2 to 4, characterized in that the metal traces are provided on the top surface of a thin and transparent plastic layer (5).

7. Dual-band digital audio broadcasting antenna according to any of the claims 2 to 6, characterized in that said carrier (5) is provided with a self-adhesive glue (6) on its bottom surface for attaching the carrier (5) on a glass surface of an automobile.

8. Dual-band digital audio broadcasting antenna according to any of the claims 2 to 7, characterized in that said carrier (5) is made of plastic foil or hard substrate material having a dielectric constant ranging from 2,5 to 4.

9. Dual-band digital audio broadcasting antenna according to any of the preceding claims, characterized in that the first monopole antenna element (1) and the second monopole antenna element (2) are connected to form a single antenna feeding terminal (4) for connection to an electronic radio frequency circuit (7).

10. Dual-band digital audio broadcasting antenna according to any of the preceding claims, characterized in that the first monopole antenna element (1) and the second monopole antenna element (2) are constructed to have two separate feeding terminals (4a, 4b), one terminal (4b) for the first monopole antenna element (1), and one terminal (4a) for the second monopole antenna element (2), for connection to an electronic radio frequency circuit (7).

11. Dual-band digital audio broadcasting antenna according to any of the preceding claims, characterized in that the first meandered monopole antenna element (1) is series connected to an RF inductor element (3).

12. Dual-band digital audio broadcasting antenna according to any of the claims 9 to 10, characterized in that the first monopole antenna element (1) is series connected to an RF inductor element (3), wherein one terminal of the RF inductor element (3) is connected to the first meandered monopole antenna element (1) and the other terminal of the RF inductor element (3) is connected to the antenna feeding terminal (4; 4b).

13. Dual-band digital audio broadcasting antenna according to any of the preceding claims, characterized in that the antenna is connected to an electronic radio frequency circuit (7; 7').

14. Dual-band digital audio broadcasting system comprising a dual-band digital audio broadcasting antenna according to any of the claims 1 to 13.

Drawing