Abstract
An apparatus comprises an antenna element operable in multiple frequency bands and configured to be connected to a ground plane and to a radiofrequency system to provide impedance matching at the multiple frequency bands, where the radiofrequency system comprising at least a matching network. A maximum length of the antenna element is shorter than L/12 but longer than L/22, where L is the free-space wavelength corresponding to a lowest frequency related to a lowest frequency region of operation of the antenna element. A contour of the antenna element has a complexity factor F12 less than 1.25.
Claims
1. An apparatus comprising: an antenna element operable in multiple frequency bands and configured to be connected to a ground plane and to a feed line through a radiofrequency system to provide impedance matching at the multiple frequency bands, the radiofrequency system comprising at least a matching network, wherein: a maximum length of the antenna element is shorter than L/12 but longer than L/22, where L is the free-space wavelength corresponding to a lowest frequency related to a lowest frequency region of operation of the antenna element; and a contour of the antenna element has a complexity factor F12 less than 1.25.
2. The apparatus of claim 1, wherein the complexity factor F12 is less than 1.1.
3. The apparatus of claim 1, wherein the at least one matching network comprises at least an active circuit component.
4. The apparatus of claim 1, wherein the at least one matching network comprises only passive circuit components.
5. The apparatus of claim 1, wherein the contour of the antenna element has a complexity factor F32 less than 1.5.
6. The apparatus of claim 5, wherein the complexity factor F32 is less than 1.25.
7. The apparatus of claim 5, wherein the complexity factor F32 is less than 1.1.
8. The apparatus of claim 5, wherein the complexity factor F12 less than 1.15 and the maximum length of the antenna element is between L/17 and L/22.
9. The apparatus of claim 8, wherein the maximum length of the antenna element is between L/17 and L/20.
10. The apparatus of claim 8, wherein the maximum length of the antenna element is L/18.7.
11. The apparatus of claim 1, wherein the multiple frequency bands are allocated in first and second frequency regions.
12. The apparatus of claim 11, wherein the first frequency region has an impedance bandwidth greater than 15%.
13. The apparatus of claim 11, wherein the first frequency region has an impedance bandwidth greater than 20%.
14. The apparatus of claim 11, wherein the first frequency region comprises the frequency range from 824 MHz to 960 MHz.
15. The apparatus of claim 11, wherein the first frequency region comprises the frequency range from 698 MHz to 960 MHz.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Further characteristics and advantages of the described system become apparent in view of the detailed description which follows with some examples given for purposes of illustration only and in no way meant as a definition of the limits of the system, referenced by the accompanying drawings.
(2) FIG. 1 discloses the achievable bandwidth of an embodiment comprising a rectangular antenna element as a function of its maximum length.
(3) FIG. 2 a wireless device comprising a rectangular antenna element (horizontal), connected to a conductive trace and to a matching network.
(4) FIG. 3 return-loss corresponding to the embodiment provided in FIG. 2. The radiating system is matched below −6 dB within the nearly entire 698-960 MHz and 1710-2690 MHz frequency ranges.
(5) FIG. 4 matching network for the radiofrequency system used for matching an embodiment like the one shown in FIG. 2.
(6) FIG. 5 a wireless device featuring an antenna element with a maximum size of 24 mm and two conducting layers with rectangular shape.
(7) FIG. 6 matching network for the radiofrequency system used for matching an embodiment like the one shown in FIG. 2.
DETAILED DESCRIPTION
(8) FIG. 1 displays the achievable bandwidth for 5 different cases of antenna element. Such antenna element is a rectangular element such as for instance element (201) comprised in the embodiment provided in FIG. 2. The achievable bandwidth is displayed for 5 different maximum lengths of the antenna element: 15 mm (101), 25 mm (102), 30 mm (103), 40 mm (105) and 60 mm (104). As seen there, the greater the length, the better the element can be matched in the challenging low frequency region (698-960 MHz). However, beyond a certain point, the improvement achieved in the low frequency region does not compensate for the degradation in bandwidth in the high frequency region. It has been found that a suitable range of maximum lengths for an antenna element like the one comprised in an embodiment as shown in FIG. 2 is within the 20-40 mm range, yet preferably within the 22-35 mm or even 22-30 mm range. In some embodiments, such a maximum length will be around 25 mm.
(9) An example of a wireless device is shown in embodiment 210, FIG. 2. The embodiment comprises an antenna element that includes a rectangular conductive element (201) substantially aligned with an edge of the PCB. A conducting trace (202) interconnects the rectangular element with a radiofrequency system including a matching network (203). The radiating system further includes a ground plane (204) which is typically printed on a layer of a printed circuit board (PCB). Underneath and surrounding the antenna element and conducting trace, there is a clearance area (205) without ground plane.
(10) As shown in FIG. 3, the radiating system in FIG. 2 is well matched in the desired frequency bands. Featuring a return loss below −6 dB within nearly the whole 698-960 MHz and 1710-2690 MHz frequency bands (curve 301), a single antenna component with a single port such as the specific case provided in FIG. 2 is able to cover the entire frequency range of cellular bands in a state of the art smartphone.
(11) FIG. 4 shows an example of a matching network suitable for the embodiment in FIG. 2. In this particular example, the matching network includes a combination of more than 3 circuit elements including inductors and capacitors. In particular, this example features 7 elements including four inductors and three capacitors.
(12) Another embodiment is shown in FIG. 5. A wireless device comprises a ground plane layer on a PCB (501). In this particular case, the dimensions of the ground plane are 130×60 mm2, which is a typical size for a smartphone wireless device. An antenna element (502) is arranged on a corner of a wireless device, and more concretely nearby a corner of the ground plane, with a longer edge on the element being aligned or substantially aligned with and edge of the PCB. The maximum length of the conducting surface of this particular antenna element is 24 mm. The conductive surface comprises two connected convex elements, a first nearly squared, rectangular element, and a second longer rectangular element. The conductive surface is printed on a dielectric support, such as for instance an FR4, Rogers®, or ceramic substrate. Both top and bottom sides of the conductive surface are connected between them by some connector such as for instance one, two or more vias. In some particular examples, the conductive surface is constructed with two sandwiched dielectric layers with top and bottom sides also interconnected by vias. An embodiment of the characteristics of the example provided in FIG. 5 features an input return loss below −6 dB in the whole 698-960 MHz and 1710-2690 MHz frequency bands.
(13) In this particular embodiment, the ground plane is extended on one side up to the edge of the PCB where the antenna element is aligned, so that the overall clearance area (505) is smaller compared to the one (205) included in the embodiment shown in FIG. 2. A matching network (503) is connected to a trace (506) which is connected to the nearly squared element comprised in the antenna element (502). A detail of a suitable matching network for this embodiment is shown for instance in FIG. 6. The matching network features more than 3 components, and in particular, 7 components, including a first series inductor connected to the element (502).
