A MULTIBAND ANTENNA

Abstract

 A multiband antenna structure comprising an extended metal trace with a first end and a second end. A first combined band notch filter is arranged between said first end and said second end. A high frequency section of the extended metal trace extending between one end and the first combined band notch filter has a first length corresponding to a quarter of a wave length of a first high frequency band, F1, and a full length of the extended metal trace extending between the first end and the second end corresponds to a quarter of a wave length of a second low frequency band F2. Said first combined band notch filter comprises a first stop filter section designed to attenuate signals of said first high frequency band, and a first resonance match section designed to provide resonance for signals of said second low frequency band.

Description

TECHNICAL FIELD

[0001] Multiband antennas are used to support wireless communications in multiple wireless communications bands.

PRIOR ART

[0002] US9559433 discloses an antenna structure forming a dual arm inverted-F antenna and a monopole antenna sharing a common antenna ground. A first antenna port may be coupled to an inverted-F antenna resonating element at a first location and a second antenna port may be coupled to the inverted-F antenna resonating element at a second location. A third antenna port may be coupled to the monopole antenna. Tunable circuitry can be used to tune the antenna structures. An adjustable capacitor may be coupled to the first port to tune the inverted-F antenna. An additional adjustable capacitor may be coupled to the third port to tune the monopole antenna.

SUMMARY OF THE INVENTION

[0003] A basic multiband antenna structure as disclosed comprises at least an extended dual band metal antenna trace for at least two different frequency bands, one lower frequency band and one higher frequency band. The antenna structure can be matched for both a high and a low band at the same time, thus combining at least two different bands in to one single antenna at the same time taking no longer trace length or space than the low band antenna itself would demand. Both antennas can be supplied through a single feeding point or port or through separate ports. The total length of the antenna trace is decided by the quarter wave length of the lowest frequency band. The higher frequency band preferably is at least twice as high as the lower frequency band. At least a substantial section of the metal antenna trace can be provided on a printed circuit board, PCB. In various embodiments, the section on the PCB is extended with a metal wire electrically connected to the PCB metal trace. The metal wire can be straight, bent or curved.

[0004] In a first aspect the multiband antenna structure comprises an extended metal trace with a first end and a second end. a first combined band notch filter arranged between said first end and said second end, wherein a high frequency section of the extended metal trace extending between one end and the first combined band notch filter has a first length corresponding to a quarter of a wave length of a first high frequency band, F1, and a full length of the extended metal trace extending between the first end and the second end corresponds to a quarter of a wave length of a second low frequency band F2. Said first combined band notch filter comprises a first stop filter section designed to attenuate signals of said first high frequency band, and a first resonance match section designed to provide resonance for signals of said second low frequency band.

[0005] In various embodiments the first resonant matching section of the disclosed multiband antenna structure comprises a first matching capacitor C1 forming a series resonant circuit together with a first double function inductor L1. Said stop filter section comprises a parallel resonant circuit with said first double function inductor L1 and a first attenuating capacitor C2.

[0006] In further embodiments the disclosed multiband antenna structure the first end is connected to an antenna ground, and a feeding point of the antenna is connected to the high frequency section of the extended metal trace.

[0007] Antenna structures using two ports for two different radio systems operating at different frequencies will provide an isolation effect which makes it possible to run both radio systems simultaneously without disturbing each other or decreasing the sensitivity of the radio systems. In various embodiments, one end of the antenna structure is connected to an antenna ground to form an F-antenna.

[0008] Additional advantages will be set forth in part in the description which follows or may be learned by practice. The advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments and together with the description, serve to explain the principles of the methods and systems. In the drawings,

Fig. 1

is a schematic circuit diagram of a first embodiment of the disclosed multiband antenna structure with a single feeding port,

Fig. 2

is a schematic circuit diagram of a second embodiment of the disclosed multiband antenna structure with double feeding ports,

Fig. 3

is a schematic circuit diagram of a first combined band notch filter,

Fig. 4

is a schematic circuit diagram of a second combined band notch filter,

Fig. 5

is schematic filter diagram of the first combined band notch filter,

Fig. 6

is schematic filter diagram of the second combined band notch filter,

Fig. 7

is a schematic circuit diagram of a third embodiment of the disclosed multiband antenna structure with double feeding ports, and

Fig. 8

is a schematic circuit diagram of a third embodiment of the disclosed multiband antenna structure with a single feeding port.

DETAILED DESCRIPTION

[0010] A basic multiband antenna structure 10 as shown in Fig. 1 comprises an extended metal trace 12 extending between a first end 14 and a second end 16. The first end 14 is connected to an antenna ground 18. The full length of the extended metal trace 12 corresponds to a quarter wave length of a low frequency band F2. A first combined band notch filter 20 is provided between said first end 14 and said second end 16. A high frequency section 19 of the extended metal trace 12 extends between one end and first combined band notch filter 20. The length of the high frequency section 19 corresponds to a quarter wave length of a high frequency band F1 and is the antenna for the high frequency band F1. Thus, the multiband antenna structure 10 combines a high frequency band F1 antenna and low frequency band F2 antenna.

[0011] The first combined notch filter 20 comprises a first stop filter section 22 designed to attenuate signals of said first high frequency band, and a first resonance match section 24 designed to provide resonance for signals of said second low frequency band. The first stop filter section 22 is a parallel resonance stop filter, and the first resonance match section 24 is a serial resonance match filter. The combined band notch filter 20 will attenuate signals having a frequency at the high frequency band F1. Thus, only the high frequency section 19 of the extended metal trace 12 will be used as an antenna for the high frequency band F1. The attenuation of high frequencies is provided by a first attenuation capacitor C2 and a first double function inductor L1 connected in parallel with the first attenuation capacitor C2 forming together the first stop filter section 22. The C2 connected in parallel with first double function inductor L1 can be depicted L1//C2.

[0012] The combined band notch filter 20 will be substantially transparent to frequencies in the low frequency band F2 as a result of the first resonance match section 24 comprising a combination of the first double function inductor L1 connected in series with a first matching capacitor C1. Preferably, the frequency of the high frequency band F1 is at least twice the frequency of the low frequency band F2, or F1 ≥ 2F2. The combination of the first attenuation capacitor C2 connected in parallel with first double function inductor L1 and first matching capacitor C1 connected in series with L1 and C2 can be depicted L1//C2 + C1. The antenna structure shown in Fig. 1 is provided with a dual band port or feeding point 26 which can be used for both transmitting and receiving. The dual band port or feeding point 26 is connected along the extended metal trace 12 to the high frequency section 19. Other embodiments with multiple feeding point or ports will be described below.

[0013] A first double port antenna is shown in Fig. 2. This antenna can be referred to as a dual band dual port F antenna. The extended metal trace 12 also in this case has a length corresponding to a quarter wave length of the low frequency band F2. A signal of the higher frequency band F1 in this embodiment is fed from a high frequency transmitting and receiving (TRX) port 28. The high frequency transmitting and receiving (TRX) port 28 connects to a high frequency section of the extended metal trace 12 through a second combined band notch filter 30 comprising a second stop filter section 32 for attenuating the low frequency band F2. A low frequency transmitting and receiving (TRX) port 36 is used for low frequency band F2 signals and connects to a low frequency section 21 of the extended metal trace 12. The low frequency section 21 together with the high frequency section 19 constitute the metal trace 12 and is the antenna for the low frequency band F2.

[0014] The attenuation of low frequencies in the second combined band notch filter 30 is provided by a first double function capacitor C3 and a second attenuating inductor L3 connected in parallel with the first double function capacitor C3 forming together the second stop filter section 32. Capacitor C3 in parallel with inductor L3 (C3//L3) provides a blocking parallel resonant circuit for the low frequency F2. As a result, the impact of the low frequency signal on the high frequency transmitting and receiving (TRX) port 28 will be reduced or eliminated. Instead, the low frequency signal will follow the path to the antenna ground 18 unaffected by the high frequency port 28. The second combined band notch filter 30 also comprises a second resonant match section 34 that comprises a first matching inductor L2 in series with the first double function capacitor C3 and will have a low return loss for the F1 (high frequency) signals. In this example filter components of second combined band notch filter can be: L2=0.6 nH, C3=5.1 pF and L3=6.8 nH.

[0015] As an example, the frequency of the low frequency band F2 is 868MHz and the length of the quarter wave trace then is 86 mm, which will be the total length of the antenna trace. The antenna trace will also accommodate a 2.4GHz Bluetooth (BLE) high frequency band because the quarter wave length of 2.4GHz is 30mm. An antenna trace with the length 30mm of the first section 19 will fit well in the total 86mm length. In this example filter components of the first combined band notch filter can be: C1=6.2 pF, C2=0.8 pF and L1=4.7 nH.

[0016] Fig. 3 shows the first combined band notch filter 20. It can also be referred to as a HIGH STOP/LOW MATCH filter and can be used in different embodiments of antenna structures as will be described below. Fig. 4 shows the second combined band notch filter 30. It can also be referred to as a HIGH MATCH /LOW STOP filter and can be used in different embodiments of antenna structures as will be described below.

[0017] The band notch filters have a level of efficiency in attenuating one frequency band while creating transparency for another frequency band. The frequency diagram shown in Fig. 5 indicates this for the HIGH STOP/LOW MATCH filter 20. A stop attenuation S21 of the 2.4GHz - 2.5GHz band as shown with a continuous line is over 25dB. A Return loss S11 as shown with a dashed line in the stop notch filter for the 868MHz signal is below -25dB. The frequency diagram shown in Fig. 6 indicates this for the LOW STOP/HIGH MATCH filter 30. The stop attenuation S21 of the 868MHz stop band as shown with a continuous line is over 25dB. The Return loss S11 as shown with a dashed line in the stop notch filter for the 2.4-2.5GHz signal is below -25dB.

[0018] In an alternative embodiment as shown in Fig. 7, the multiband antenna structure 10 is a two-band antenna with the low frequency transmitting and receiving port 36 provided at the first end 14 of the extended metal trace 12 and the high frequency transmitting and receiving port 28 provided at the second end 16 through the LOW STOP/HIGH MATCH filter 30. A first HIGH STOP/LOW MATCH filter 20 is provided in the extended metal trace 12 between the first end 14 and the second end 16 at a distance from the high frequency transmitting and receiving port 28 corresponding to a quarter wave length of the high frequency band F1. For a 2.4-2.5 GHz signal this distance is approximately 30 mm. Thus, a section of the extended metal trace 12 extending between the second end 16 and the first HIGH STOP/LOW MATCH filter 20 will be a high frequency band F1 antenna. The full length of the extended metal trace 12 extending between the first end 14 and the second end 16 will be a low frequency band F2 antenna. For a 868 MHz signal this distance is approximately 86 mm.

[0019] In the alternative embodiment of a second double port antenna structure as shown in Fig. 7, feeding of the antenna structure is made from two ends. The low frequency band signal F2 will use the full length of the metal trace 12. A LOW STOP/HIGH MATCH filter 30 preferably is provided between the high frequency transmitting and receiving port 28 and the high frequency section 19 of the metal trace 12, so as to block or decrease the impact of the low frequency band signal F2 on a radio transceiver connected to the the high frequency transmitting and receiving port 28. The LOW STOP/HIGH MATCH filter 30 will be transparent for the high frequency band signal F1 thanks to the first matching inductor L2 that will resonance with the first double function capacitor C3 in the LOW STOP/HIGH MATCH filter 30 to form transparent a serial resonance for the high frequency transmitting and receiving port 28. The first double function capacitor C3 will at the same time block and enhance the blocking of the low frequency band signal F2.

[0020] The embodiment of a multiband antenna structure 10 shown in Fig. 8 comprises an extended metal trace 12 extending between a first end 14 and a second end 16. The first end 14 is connected to the dual band feeding port 26. The full length of the extended metal trace 12 corresponds to a quarter wave length of a low frequency band F2. A first combined band notch filter 20 is provided between said first end 14 and said second end 16. A high frequency section 19 of the extended metal trace 12 extends between the dual band feeding port 26 and the first combined band notch filter 20. The length of the high frequency section 19 corresponds to a quarter wave length of a high frequency band F1 and is the antenna for the high frequency band F1. Thus, the multiband antenna structure 10 combines a high frequency band F1 antenna and low frequency band F2 antenna.

[0021] A plurality of different multiband antenna structures comprising other combinations of feeding points and HIGH STOP/LOW MATCH filters 20 and LOW STOP/HIGH MATCH filters 30 is possible in accordance with this invention.

[0022] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the inventive concept. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. It is intended that the specification and examples be considered as exemplary only, and that the claims be construed as encompassing all equivalents of the present invention which are apparent to those skilled in the art to which the invention pertains.

Claims

1. A multiband antenna structure comprising an extended metal trace (12) with a first end (14) and a second end (16), characterized by

a first combined band notch filter (20) arranged between said first end (14) and said second end (16),

wherein a high frequency section (19) of the extended metal trace (12) extending between one end and the first combined band notch filter (20) has a first length corresponding to a quarter of a wave length of a first high frequency band, F1, and a full length of the extended metal trace extending between the first end (14) and the second end (16) corresponds to a quarter of a wave length of a second low frequency band F2,

wherein said first combined band notch filter (20) comprises a first stop filter section (22) designed to attenuate signals of said first high frequency band, and a first resonance match section (24) designed to provide resonance for signals of said second low frequency band.

2. The multiband antenna structure as claimed in claim 1,

wherein said first resonance match section comprises a first matching capacitor C1 forming a series resonant circuit together with a first double function inductor L1, and

wherein said first stop filter section comprises a parallel resonant circuit with said first double function inductor L1 and a first attenuating capacitor C2.

3. The multiband antenna structure as claimed in claim 1, wherein the first end is connected to an antenna ground, and a feeding point of the antenna is connected to the high frequency section of the extended metal trace.

5. The multiband antenna structure as claimed in claim 1, wherein a second combined notch filter (30) is provided between a first high frequency band, F1, transmitting port (28) and the high frequency section of the extended metal trace (12), said second combined notch filter (30) comprising a second stop filter section (32) for attenuating the low frequency band F2, and a second resonant match section (34),

wherein said second stop filter section (32) comprises a first double function capacitor C3 and a second attenuating inductor L3 connected in parallel with the first double function capacitor C3, and

wherein said second resonant match section (34) comprises a first matching inductor L2 in series with the first double function capacitor C3.

Drawing