DESC:TECHNICAL FIELD
[0001] The present invention relates generally to antennas for handheld devices. The invention, more particularly, relates to a multiband conformal antenna for handheld devices.
BACKGROUND
[0002] Internal antennas are an essential component found in most modern radio devices, such as mobile computers, mobile phones, smartphones, personal digital assistants (PDAs), or other personal communication devices (PCD). It is a big challenge to design an embedded conformal antenna in the limited space of the mobile phone to cover all the bands for e.g., Long-Term Evolution (LTE)/ Global System for Mobile Communications (GSM)/ Universal Mobile Telecommunications Service (UMTS)bands and have a smaller form factor in size.
[0003] One such antenna type which could be used for hand-held devices as well as operating in multiband environment is an Inverted F-Antenna. Inverted F-Antennas have a limited space coverage which operates Long Term Evolution (LTE)/ Global System for Mobile Communications (GSM)/ Universal Mobile Telecommunications Service (UMTS)bands. The inverted-F antenna isa variant of the monopole, wherein the top section has been folded down so as to be parallel with the ground plane. This is typically done to reduce the size of the antenna while maintaining a resonant trace length. However, the Inverted-F antennae have narrow bandwidths. A wider bandwidth can be achieved by lengthening the antenna, which however, increases the radiation resistance of the antenna.
[0004] United States Patent No.: US 9.406,998 B2 (Korva et al.) discloses a planar inverted-F antenna (PIFA) configured to operate in a high-frequency band, and a matched monopole configured to operate in a low-frequency band, that are used within a handheld mobile device (e.g., cellular telephone). Planar inverted-F antenna (PIFA) is a variation of linear inverted-F antenna, wherein the wire radiator element is replaced by a plate to expand the antenna operating bandwidth. As the operating frequency decreases, the PIFA antenna size increases in order to maintain operating efficiency. Therefore, a multi-band PIFA, operating in both upper and lower bands, requires a larger Volume and height in order to meet the lower-band frequency requirements typical of mobile communications. To reduce the size of mobile devices operating at these lower frequencies, ordinary monopole antennas are commonly used instead of a PIFA.

[0005] The document “Internal Small-Size PIFA for LTE/GSM/UMTS Operation in the Mobile Phone” 978-1-4244-4968-2/10/ discloses a small-size coupled-fed printed PIFA to cover all the eight operating bands of the LTE/GSM/UMTS (698-960/1710-2690 MHz) in the mobile phone.

[0006] The document “Small-size printed coupled-fed antenna for eight-band LTE/GSM/UMTS wireless wide area network operation in an internal mobile handset” IET Microw. Antennas Propag., 2013, Vol. 7, Iss. 6, pp. 399–407 discloses a small-size printed antenna for eight-band long-term evolution (LTE)/GSM/UMTS wireless wide area network operation in an internal mobile handset application.

[0007] Both the aforesaid documents mention a PIFA structure mainly having a radiating strip, an inductive shorting strip and a coupling feed. By incorporating the planar printed coupling feed technique, using a coupling strip to capacitively excite the radiating strip through a small gap and by incorporating the long inductive shorting strip to further improve the impedance matching for desired frequencies. But such a configuration leads to complexity in the structure and designs are constrained in terms of narrow band width characteristics, size, and requirement of effective ground region in the design.

[0008] The document “Ceramic Based Small LTE MIMO Handset Antenna,” Yu-Jiun Ren, IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 61, NO. 2, FEBRUARY 2013 discloses using ceramic materials for making antennas that are widely used in single or at maximum dual band systems. A ceramic based electrically small coupled-fed internal antenna without any loaded lumped component is disclosed. The type of configuration disclosed in the document leads to complexity in the structure as well as integrity. Ceramic based antennas suffer from narrow band width characteristic and needs a three-dimensional space for integration as well. Hence due to their narrow band width characteristics, they cannot not be used to multi band systems such as 3G and 4G wireless communications.

[0009] The document “Planar Compact LTE/WWAN Monopole Antenna For Tablet Computer Application, International Journal of Advanced Research in Science Engineering and Technology (IJARSET)”Vol. 3, Issue 2, February 2016, and United States Patent Publication No.: US 2010/0253581 A1, Pub. Date: Oct. 7, 2010 discloses a planar compact monopole antenna. The antenna comprises an inverted-L driven monopole and dual parasitic shorted strips. The inverted-L monopole strip as a quarter-wavelength resonant structure and a shorter parasitic shorted strip to generate the fundamental resonant modes.

[0010] The prior-art documents described above disclose effective ground region in the design profile. Further, fabrication and integration of such structures (PIFA and Ground plane-based designs) becomes critical for many handheld based device applications. In the prior-art documents, inductive shorting strips were used in the design for making the antenna size compact. This results in the degradation of the antenna radiation efficiency factor and Voltage Standing Wave Ratio (VSWR) range as well.

[0011] There is still a need of an invention which solves the above defined problems anda need to provide a compact, flexible, reliable antenna with improved Voltage Standing Wave Ratio (VSWR) and ground less design for integrating with the handheld devices.
SUMMARY OF THE INVENTION
[0012] An aspect of the invention includes a multiband antenna. The multiband antenna comprises a pair of elongated radiating strips, a parasitic radiating strip, a coupling strip aligned adjacent to the parasitic radiating strip with a predetermined gap between the parasitic radiating strip and the coupling strip. The pair of elongated radiating strips, parasitic radiating strip, and coupling strip are rectangular strips meandered along the length and breadth of the substrate to operate as monopole type antennas operate as high Q resonators operating at simultaneous fundamental and higher order resonances. The coupling strip has two ends where one end comprises of a coupling feed and the other end comprises of a termination circuit. The multiband antenna is configured to operate in penta-band frequency range, wherein the range is selected from: 824MHz – 896MHz, 1790MHz – 1990MHz, 2110MHz – 2170MHz, 2300MHz – 2400MHz and 2500MHz – 2690MHz.
[0013] To cover the lower wide band frequency of 824MHz-896 MHz, the pair of elongated radiating strips operate at a fundamental resonance frequency of 750 MHz-960 MHz. The elongated radiating strips use a self-filtering mechanism to reject unwanted frequencies in the lower wide band.
[0014] To cover the higher wide band frequency of 1790-2690 MHz, the parasitic radiating strip and coupling feed resonates at a harmonic frequency of 1710MHz and the coupling feed resonates at a frequency of 2690MHz. The elongated radiating strips use a self-filtering mechanism to reject unwanted frequencies in the wide upper band frequencies. The coupling feed is also configured for impedance matching simultaneously at multi frequencies.
[0015] The parasitic radiating strip and coupling feed operate as twin pad feeding structure enabling solder less mechanical contact with electronic components external to the antenna. The multiband antenna is uniplanar and free of ground plane.
[0016] Accordingly, a multiband antenna that is compact in size, that covers multiple cellular and wireless LAN bands (at least five), that is conformal in structure is described below.
BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
[0017] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and modules.
[0018] Figure 1 illustrates an exemplary Top view/ Plan View of the antenna, in accordance with an exemplary embodiment of the present invention.
[0019] Figure 2 illustrates an exemplary Bottom View of the antenna of Figure 1, in accordance with an exemplary embodiment of the present invention.
[0020] Figure3 illustrates an exemplary Side View of the antenna of Figure 1, in accordance with an exemplary embodiment of the present invention.
[0021] Figure 4 illustrates a graph showing the measured return loss in the standard testing environment of the antenna of Figure 1.
DETAILED DESCRIPTION
[0022] The various embodiments of the present invention describe about multi band conformal antenna for handheld devices. It further provides an improved multi band conformal antenna for handheld devices.
[0023] In the following description, for purpose of explanation, specific details are set forth in order to provide an understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, some of which are described below, may be incorporated into a number of systems.
[0024] However, the systemis not limited to the specific embodiments described herein. Further, structures and devices shown in the figures are illustrative of exemplary embodiments of the present invention and are meant to avoid obscuring of the present invention.
[0025] It should be noted that the description merely illustrates the principles of the present invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present invention. Furthermore, all examples recited herein are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
[0026] Figure 1 shows an exemplary Top view/ Plan View of the multiband antenna (100), according to an exemplary implementation of the present invention. The dimensions of the antenna are 40mmx17mm x 0.127mm. The antenna is a simple radiating structure with a pair of elongated radiating strips (101b, 101c), parasitic radiating strip (101a) and a coupling strip (102) printed on a substrate. The parasitic radiating strip (101a) and a coupling strip (102) are aligned adjacent to each other with a predetermined gap (103a) between them, are also printed on the substrate. In one exemplary embodiment, the gap is of size of 0.6mm. A simplified printed coupling-feed technique is used, where one end of the coupling strip (102) comprises of a coupling feed (102a) and the other end comprises of a termination circuit (102b),whereby coupling feed (102a) capacitively excites the radiating strip through a predetermined gap(103a).A standard printed circuit board printing process is used in printing the elongated radiating strips (101b, 101c), parasitic radiating strip (101a) and the coupling strip (102).Each of these elongated radiating strips (101b, 101c) are printed in rectangular shape, meandered along the length and breadth of the substrate (100a) that enables these elongated radiating strips (101b, 101c), radiating strip (101a) and the coupling strip (102) to operate as monopole resonators. In one exemplary embodiment, the width of the elongated radiating strips (101b, 101c) is 0.4 mm.

[0027] The substrate (100a) on which the elongated radiating strips, radiating strip and coupling strips are printed is poly(4,4'-oxydiphenylene-pyromellitimide) commonly known as Kapton material. The Kapton material has a dielectric constant of 3.5 and offers lot of flexibility to make it conformal to surface of handheld phone. By printing of the antenna (100) on only one side of the Kapton substrate(100a), makes the antenna uni-planar.

[0028] The monopole resonators (elongated radiating strips (101b, 101c), radiating strip (101a) and the coupling strip (102)) function as linear high Q resonators that have simultaneous fundamental and higher order resonances. These high Q resonators operate in penta-band frequency range, wherein the range is selected from: 824MHz – 896MHz, 1790MHz – 1990MHz, 2110MHz – 2170MHz, 2300MHz – 2400MHz and 2500MHz – 2690MHz.The manner in which the high Q resonators function in the higher and lower bands of frequency is explained below.
[0029] A first strip (101b) and a second strip (101c) of the pair of elongated radiating strips exhibit dual-resonant behavior. By the dual resonant behavior of the radiating strips (101b, 101c) coverage of frequency in wide lower band is achieved. To achieve the wide lower band coverage, the first strip (101b) of the pair of elongated radiating strips resonates at a fundamental resonance frequency of 750MHz and a second strip (101c) of the pair of elongated radiating strips resonates at a fundamental resonance frequency of 960MHz. Due to inductance between the elongated radiating strips and the resonant frequencies of elongated radiating strips, the elongated radiating strips come closer to each other. Then, a dual-resonant behavior is achieved to result in a wide lower band to cover the desired frequency range of 750~960 MHz thereby enabling frequency rejection in 750~960 MHz band.

[0030] By using a simplified printed coupling-feed technique, the coupling strip (102a) capacitively excites the parasitic radiating strip (101a) through the predetermined gap (103a). The coupling feed (102a) and the inducted parasitic radiating strip(101a) operate in a wide upper band to cover the desired frequency range of 1710~2690 MHz To achieve the wide upper band coverage, the parasitic radiating strip (101a) resonates at a harmonic frequency of 1710MHz and the coupling feed (102a) resonates at a harmonic frequency of 2690MHz.

[0031] The parasitic radiating strip (102a) and the coupling feed (102b) function as an electrically long coupled line with termination circuit (102b) that matches frequency ranges. The termination circuit (102b) enables achieving wide higher band matching as well as self-filtering mechanism to reject unwanted frequencies. The parasitic radiating strip (102a) and the coupling feed (102b) are inductive and capacitively coupled with each other, resulting in very good return loss. Accordingly, the unwanted frequency in between lower band (750-960MHz) and higher band (1710 MHz ~ 2690 MHz) are removed.

[0032] The parasitic radiating strip (101a) and coupling feed (102a) operate as twin pad feeding structure enabling solder less mechanical contact with electronic components external to the multiband antenna. Since the high Q resonators are uniplanar, there is no ground plane required to remove ground voltage from antenna.
[0033] Figure 2 discloses exemplary Bottom View of the multiband antenna (200). The substrate (200a) is shown without any printed circuits on them. The circuit is printed only one side (as shown in Figure 1) of the substrate (200a)using standard PCB printing process.

[0034] Figure 3 illustrates an exemplary Side View of the antenna. In Figure 3, the antenna is shown having reference numeral 300 and 300a is the substrate on which the said Antenna is printed using standard PCB printing process.
[0035] Figure 4 illustrates a graph showing the measured return loss in the standard testing environment of the antenna, where the graph depicts Incident Power in x axis measured in Decibels (dB) and Reflected Power shown in Frequency shown in MegaHertz (MHz) in y axis. The measured return loss characteristics has been illustrated for the Lower band 750-960MHz as well as for the higher band 1710-2690 MHz in Figure 4. For 750 MHz, the measured return loss is -5.62 dB, for 960 MHz the measured return loss is -11.52 dB, for 1710 MHz the measured return loss is -9.23 dB and for 2690 MHz the measured return loss is -15.24 dB.
[0036] Therefore, the antenna as disclosed herein is compact in size, covers multiple cellular and wireless LAN bands (at least five), conformal in structure. The antenna does not need any separate ground. The antenna can easily be plugged into multiband transceiver PCB as it does not require any separate ground. Thus, the antenna being free of ground plane, is amenable for embedding in plastic lid of phones, laptops using Laser Direct Structuring Technology (LDS).
[0037] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:
1. A multiband antenna (100), comprising:
a pair of elongated radiating strips (101b, 101c) printed on a substrate;
a parasitic radiating strip (101a) printed on the substrate; and
a coupling strip (102) printed on the substrate and aligned adjacent to the parasitic radiating strip with a predetermined gap (103) therebetween.

2. The multiband antenna (100) as claimed in claim 1, wherein the multiband antenna is printed on one side of the substrate.

3. The multiband antenna (100) as claimed in claim 1,wherein the pair of elongated radiating strips (101b, 101c), parasitic radiating strip (101a), and coupling strip (102) are rectangular strips meandered along the length and breadth of the substrate to operate as monopole resonators.

4. The multiband antenna (100) as claimed in claim 1, wherein the one end of the coupling strip (102) comprises of a coupling feed (102a) and the other end comprises of a termination circuit (102b).

5. The multiband antenna (100) as claimed in claim 3, wherein the monopole resonators are linear high Q resonators having simultaneous fundamental and higher order resonances.

6. The multiband antenna (100) as claimed in claim 4, wherein the high Q resonators operate in penta-band frequency range, wherein the range is selected from: 824MegaHertz (MHz) – 896MegaHertz (MHz), 1790MegaHertz (MHz) – 1990MegaHertz (MHz), 2110MegaHertz (MHz) – 2170MegaHertz (MHz), 2300MegaHertz (MHz) – 2400MegaHertz (MHz) and 2500MegaHertz (MHz) – 2690MegaHertz (MHz).

7. The multiband antenna (100) as claimed in claim 1, wherein a first strip (101b) of the pair of elongated radiating strips resonates at a fundamental resonance frequency of 750MHz and a second strip (101c) of the pair of elongated radiating strips resonates at a fundamental resonance frequency of 960MHz.

8. The multiband antenna (100) as claimed in claim 4, wherein the parasitic radiating strip(101a) resonates at a harmonic frequency of 1710MHz and the coupling feed (102a) resonates at a frequency of 2690MHz.

9. The multiband antenna (100) as claimed in claim 4, wherein the coupling feed (102a) is configured for impedance matching simultaneously at multi frequencies.

10. The multiband antenna (100) as claimed in claim 5, wherein the high Q resonators are uniplanar and free of ground plane.

11. The multiband antenna (100) as claimed in claim 5, wherein the high Q resonators have self-filtering mechanism to reject unwanted frequencies.

12. The multiband antenna (100) as claimed in claim 1, wherein the parasitic radiating strip (101a) and coupling feed (102a) operate as twin pad feeding structure enabling solder less mechanical contact with electronic components external to the antenna.