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 in- verted-F antenna and a monopole antenna sharing a common antenna ground. A first antenna port may be coupled to an inverted-F antenna reso- nating 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 cou- pled 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 fre- quency 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 an- tenna at the same time requiring 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 minimum total length of the antenna trace is determined by the quarter wave length of the lowest frequency band. The higher frequency band preferably should be at least around 1.3 times higher than the lower frequency band and can be around twice as high or higher than the lower frequency band. At least a sub- stantial section of the metal antenna trace can be provided on a printed cir- cuit board, PCB, or on a flexfilm. In various embodiments, the section on the PCB is extended with a metal wire electrically connected to the PCB metal trace if needed. The metal wire can be straight, bent curved or meandered.

[0004] In a first aspect the multiband antenna structure comprises an ex- tended 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 fre- quency 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 sig nals 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 in- ductor 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 various embodiments, there is also provided a second combined notch filter comprising a second stop filter section designed to attenuate sig nals of low frequency band, and a second resonance match section designed to provide resonance for signals of a high frequency band. By using different combinations of said first combined notch filter and said second combined notch filter and arranging them at predetermined positions along the ex- tended metal trace it is possible to connect two or more transceivers operat- ing at different frequencies simultaneously.

[0007] 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.

[0008] 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 embodi- ments, one end of the antenna structure is connected to an antenna ground to form an F-antenna.

[0009] It should be noted that said first combined notch filter and said sec- ond combined notch filter are indeed combining a band stop function with a band match function. Thus, signals of a first frequency band around a first frequency will be blocked or efficiently attenuated while signals of a second frequency band around a second frequency will be matched so the filter will be transparent for this second frequency band.

[0010] 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

[0011] The accompanying drawings, which are incorporated in and consti- tute 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 basic embodiment of the dis- closed multiband antenna structure with a single feeding port,

Fig. 2 is a schematic circuit diagram of a second embodiment of the dis- closed multiband antenna structure with double feeding ports,

Fig. 3 is a schematic circuit diagram of a first combined band notch filter, referred to as a Hi band stop/Low band match filter,

Fig. 4 is a schematic circuit diagram of a second combined band notch fil- ter, referred to as a Low band stop/Hi band match 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 fil- ter, Fig. 7 is a schematic circuit diagram of a third embodiment of the dis- closed multiband antenna structure with double feeding ports,

Fig. 8 is a schematic circuit diagram of a third embodiment of the dis- closed multiband antenna structure with a single feeding port and Fig. 9 is a schematic circuit diagram of a third embodiment of the dis- closed multiband antenna structure with triple feeding ports.

DETAILED DESCRIPTION

[0012] 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 com- bined band notch filter 20. The length of the high frequency section 19 corre- sponds to a quarter wave length of a high frequency band F1 and is the an- tenna 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.

[0013] 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 res- onance match filter. The combined band notch filter 20 will attenuate signals having a frequency at the high frequency band F1. Thus, only the high fre- quency 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 pro- vided by a first attenuation capacitor C2 and a first double function inductor L1 connected in parallel with the first attenuation capacitor C2 forming to- gether the first stop filter section 22. The C2 connected in parallel with first double function inductor L1 can be depicted L1//C2. [0014] 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 induc- tor L1 connected in series with a first matching capacitor C1. Preferably, the frequency of the high frequency band F1 is considerably higher than the fre- quency of the low frequency band F2, such as 1.3 times higher. A very good function will be obtained if 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 feed- ing point 26 is connected along the extended metal trace 12 to the high fre- quency section 19. Other embodiments with multiple feeding point or ports will be described below.

[0015] A first double port antenna is shown in Fig. 2. This antenna can be referred to as a dual band dual port F antenna or an FinF antenna. The ex- tended metal trace 12 also in this case has a length corresponding to a quar- ter wave length of the low frequency band F2. A signal of the higher fre- quency 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 sec- ond 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 fre- quency section 19 constitute the metal trace 12 and is the antenna for the low frequency band F2.

[0016] The attenuation of low frequencies in the second combined band notch filter 30 is provided by a first double function capacitor C3 and a sec- ond 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 cir- cuit for the low frequency F2. As a result, the impact of the low frequency sig nal on the high frequency transmitting and receiving (TRX) port 28 will be re- duced 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 sec- tion 34 that comprises a first matching inductor L2 in series with the first dou- ble function capacitor C3 and will have a low return loss for the F1 (high fre- quency) 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.

[0017] As an example, the frequency of the low frequency band F2 is 868MFIz 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 accom- modate a 2.4GFIz Bluetooth (BLE) high frequency band because the quarter wave length of 2.4GFIz 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.

[0018] Fig. 3 shows the first combined band notch filter 20. It can also be re- ferred to as a HIGH STOP/LOW MATCFI 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 MATCFI /LOW STOP filter and can be used in different embodiments of antenna structures as will be described below.

[0019] 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.

[0020] In an alternative embodiment as shown in Fig. 7, the multiband an- tenna 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 be- tween the first end 14 and the second end 16 at a distance from the high fre- quency 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 ex- tending 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 ex- tended 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.

[0021] In the alternative embodiment of a second double port antenna struc- ture 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 be- tween the high frequency transmitting and receiving port 28 and the high fre- quency section 19 of the metal trace 12, so as to block or decrease the im- pact 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. [0022] 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 fre- quency 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.

[0023] The embodiment of a multiband antenna structure 10 shown in Fig. 9 comprises an extended metal trace 12 extending between a first end 14 and a second end 16. This antenna structure can be referred to as a QinFinF an- tenna. A first transceiver 52 operating at a high frequency band F1 is con- nected to a high frequency section 19 of the extended metal trace 12 through a first LS/FIM filter 54 of the second combined notch filter 30 type having LOW STOP/HIGH MATCH properties. The high frequency section 19 ex- tends between the first end 14 and a first HS/LM filter 56 of the first combined notch filter type and has a length corresponding to a quarter of a wave length of the F1 frequency band.

[0024] The full length of the extended metal trace 12 corresponds to a quar- ter of a wave length of a low frequency F2 signal and will be an F2 antenna used for radiating radio signals from a second transceiver 58 operating at the low frequency F2 band.

[0025] A third transceiver 60 operating at a second high frequency band F3 is connected to a second high frequency section 19’ of the extended metal trace 12 at a second high frequency transmitting and receiving port 66. A second LS/HM filter 62 of the second combined notch filter 30 type having LOW STOP/HIGH MATCH properties is connected between the second high frequency transmitting and receiving port 66 and the second high frequency section 19’. The second high frequency section 19’ extends between the sec- ond end 16 and a second HS/LM filter 64 of the first combined notch filter type and has a length corresponding to a quarter of a wave length of the high frequency band F3. Both the combined HS/LM filters 56 and 64 are transpar- ent for the F2 frequency while the combined LS/HM filters 54 and 62 act as stop filters for the F2 frequency making the whole antenna structure act as an F-antenna for the F2 signal.

[0026] Purely as an example, the F1 signal can be a Bluetooth band at 2400MHz, the F2 signal can be an Industrial, Scientific and Medical radio band (ISM) at for instance 880MHz, and the F3 signal can be a GPS signal at 1575 MHz. In the configuration of the antenna structure 10 shown in Fig. 9, F1 >F2, and F3>F2. The frequencies in the disclosed antenna structure can be several different frequencies. Each of the ports/transceivers has their own set of frequency bands. As a further example there can be one port for the lowest frequency such as an ISM 800 loT application of 800-900MHz. Then another port can have two frequency bands as for example a WLAN system that has 2 frequency bands at 2.4GHz and 5GHz at the same port. Sections of the main antenna structure can then be filtered of to get the right resonat- ing lengths for each of the frequency bands. Then at another port there might be a BLE, BT, ZigBee or other system on 2.4GHz in the other end of the an- tenna structure. Or there can be a GPS section integrated in the antenna on the 1555-1610MHz band.

[0027] There can be a multitude of systems with different frequency bands included in one antenna structure where the lowest frequency might but not necessarily sets the length of the antenna structure. All thinkable RF systems can be combined in the disclosed antenna structure in order to use the best position for an antenna on a printed circuit board or on a flexfilm with an addi- tional metal wire in the most efficient way.

[0028] 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 are possible in accordance with this in- vention. The HIGH STOP/LOW MATCH filters 20 and LOW STOP/HIGH MATCH filters 30 can be used to divide the antenna trace into separate sec- tions of different lengths corresponding to a selected frequency or frequency band. Furthermore, HIGH STOP/LOW MATCH filters 20 and LOW

STOP/HIGH MATCH filters 30 can be used for connecting a plurality of trans- ceivers to the different sections of the antenna trace. Each transceiver can be operating at a frequency band corresponding to a quarter of a wave length of the length of the separate section it is connected to.

[0029] 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 consider- ation 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.