Loop antenna assembly for telecommunication devices

[0002] This application claims the benefit of priority pursuant to 35 U.S.C §119(e)(1) from the provisional patent application filed pursuant to 35 USC §111(b): as Ser. No. 60/058,478 on Sep. 10, 1997.

[0003] This application is a continuation of PCT Ser. No. PCT/US98/18800, filed Sep. 10, 1998.

[0004] The present invention relates generally to an antenna assembly, and more particularly to a loop antenna assembly for a hand-held radio frequency transceiver, such as a cellular telephone or PCS device operating in the 800-900 or 1850-1990 MHz. frequency ranges, respectively.

[0005] There has been a recognized need for a compact antenna assembly for a hand-held radio frequency transceiver which offers increased performance in gain and front-to-back ratio at given input power levels. It is recognized that prior art monopole antennae, while providing good radiation characteristics and desirable drive point impedance, may be more subject to damage than a compact antenna protected within the interior of the transceiver housing.

[0006] Performance limitations of many other prior antennas for radio frequency transceivers have included limited signal range, limited directionality, significant radio frequency radiation output to the user, and significant multipath interference.

[0007] A compact loop directive antenna having improved front-to-back ratio and gain for given input power levels is provided by the present invention. Such a compact antenna would replace the popular monopole or whip-style antennas in current use and may be installed within the interior of the transceiver. The loop antenna assembly consists of a main loop antenna conductor disposed upon a dielectric substrate element. The main loop antenna conductor and dielectric element are maintained a predetermined distance away from a ground plane, which may be defined by a portion of the circuit board or other conductive member of the transceiver. The main loop antenna conductor can be formed as either a closed loop or open loop and may include a variety of feedpoint orientations to provide alternative polarizations of the transmitted signal. The ground plane may be defined by a portion of the printed circuit board of the device, a conductive part of the device housing, the battery pack of the device, or a separate conductive panel. Several purposes and objects of the disclosed apparatusses are described herein. One object of the present disclosure is to provide a compact antenna assembly with improved directionality and gain at given input power levels

[0008] Additional improvements and benefits of the antenna assembly of the present invention include: increased signal strength resulting in extended signal range and fewer dropped calls for a given power consumption rate; an increased battery life for a given output signal level; reduced radio frequency radiation incident to the user's body; a reduction in the physical size of a directional antenna for use on a wireless device; and, protection of the antenna structure from external damage.

[0009] Accordingly, it is a primary object of the present invention to provide an improved compact antenna assembly for communication devices with improved directionality, broadband input impedance, increased signal strength, and increased battery life.

[0010] Other benefits include a reduction in multipath interference and increased front-to-back ratio.

[0011] FIG. 1 is a perspective view of a communication device incorporating an antenna assembly according to the present invention;

[0012] FIG. 2 is a detailed perspective view of the antenna assembly of FIG. 1;

[0013] FIG. 3 is an elevational view of portion of the antenna assembly of FIG. 2, taken along lines 3—3;

[0014] FIG. 4 is an elevational view of the antenna assembly of FIG. 2, taken along lines 4—4;

[0015] FIG. 5 is a perspective view of a second embodiment of the antenna assembly according to the present invention;

[0016] FIG. 6 is an elevational view of the antenna assembly of FIG. 5, taken along lines 6—6;

[0017] FIG. 7 is a diagrammatic view of an antenna assembly according to the present invention, having a first feedpoint orientation;

[0018] FIG. 8 is a diagrammatic view of an antenna assembly according to the present invention, having a second feedpoint orientation;

[0019] FIG. 9 is a diagrammatic view of an antenna assembly according to the present invention, having a third feedpoint orientation; and

[0020] FIG. 10 is a perspective view of a third embodiment of the antenna assembly according to the present invention;

[0021] FIG. 1 illustrates a perspective view of a hand-held cellular telephone handset 10 and antenna assembly 12. Telephone handset 10 includes a front side 14 having speaker and microphone (not shown) and a rear side 16. Handset 10 is electrically powered by a battery or battery pack 18. Handset 10 includes one or more printed circuit boards 20 used to receive components and route signals between the multiple electronic components. Printed circuit board 20 in this embodiment also establishes a ground plane 32 for the antenna assembly 12. Alternative ground planes 32 may also be incorporated into the antenna assembly 12 as described hereinafter.

[0022] Antenna assembly 12 is revealed in FIG. 1 through a partial break-away of the handset 10 housing 11. The housing 11 may be made of an electrically nonconductive material. Antenna assembly 12 is positioned nearer to the top 24 than the bottom 26 of the handset 10 so that a user's hand will normally be away from the antenna assembly 12. Immunity to hand induced radiation losses is desirably improved by this placement of the antenna assembly 12 upon the handset 10.

[0023] FIG. 2 illustrates the antenna assembly 12 in perspective view. Antenna assembly 12 generally includes a loop conductor element 28, a dielectric substrate 30, and a ground plane 32. Loop conductor element 28 is generally square in shape; i.e., all four sides 34, 36, 38, 40 are of equal length. Top and bottom (horizontal) sides 36, 40 of loop conductor element 28 extend laterally across the dielectric substrate 30 to its periphery. The right and left sides 34, 38 (vertical) of the loop conductor element 28 are shorter than the dielectric side length, and thus portions 42 of the dielectric substrate 30 extend beyond the loop conductor element 28 generally adjacent the horizontal sides 36, 40. The circumference of the loop conductor element 28 is approximately one wavelength (1λ) of a frequency selected within the operating range of the handset 10.

[0024] Referring still to FIG. 2, the widths of the horizontal portions 36, 40 (w₄), and vertical portions 34, 38 (w₃) of the loop conductor 28 are approximately 0.12 and 0.06 inch, respectively, with a thickness, h₁, of approximately 0.005 inch for the 1850-1990 MHz. frequency range. The ratio between the top and bottom portion width, w₄, and the side portion width, w₃, is approximately 2:1. These dimensions, except h₁(thickness), would approximately double for operation in the 800-900 MHz. frequency range.

[0025] Illustrated in FIG. 3 is a cross-sectional view of the loop conductor element 28. The height dimension, h₁, of the loop conductor element 28 is approximately 0.005 inch. The width, w₁, of the loop conductor element 28 may range from 0.125 to 0.05 inch. Preferably for a width of 0.125 inch, the height should range between 0.001 to 0.020 inch. Preferably for a width of 0.05 inch, the height should range between 0.0005 and 0.032 inch.

[0026] Loop conductor 28 is illustrated herein as square-shaped when viewed from above, though alternative configurations such as circular, rectangular, or triangular shapes may also be practicable. Loop conductor 28 is formed by selectively etching away a conductive layer deposited upon a surface of the dielectric substrate 30. Alternatively, loop conductor 28 may be applied with known circuit printing techniques or may be a conductive wire affixed to the substrate 30 surface.

[0027] Still referring to FIG. 2, the dielectric substrate 30 is a layer of dielectric material selected to have a dielectric constant between 1 and 10. A further preferred range of the dielectric constant is approximately between 9 and 10. Dielectric substrate 30 is illustrated in the drawings as rectangular in form, though alternatively, substrate 30 may assume other shapes and configurations, i.e. circular, etc. Dielectric substrate 30 is substantially planar in configuration, and may be curved as in FIG. 10 or otherwise conformed to the internal shape of a portion of the handset. Dielectric substrate 30 thickness may range from approximately 0.03 to 0.5 inch. Dielectric substrate 30 has a thickness of 0.25 (¼) inch with a dielectric constant of 9.2 for the 1850-1990 MHz. frequency operating range.

[0028] Referring to FIG. 4, a distance, d₂, between the loop conductor element 28 and the ground plane 32 is within the range of approximately 0.05 and 0.30 times a desired wavelength (0.05λ-0.30λ). Dielectric substrate 30 and loop conductor element 28 are maintained a distance, d₁, away from the ground plane 32 by a support structure (not shown). For operation of the antenna assembly 12 at the 1850-1990 MHz. frequency range, the distance, d₁, is approximately 0.3-1.5 inches. Support structure may include a foam support between the dielectric substrate 30 and the ground plane 32.

[0029] Ground plane 32 of the antenna assembly is illustrated as a portion of the printed circuit board 20 of the handset 10. Alternatively, the ground plane 32 may be a conductive portion of the handset housing, the battery pack 18 or portion thereof, or even a separate conductive panel (not shown).

[0030] Referring again to FIG. 4, a parasitic element 42 in the form of conductive loop or linear dipole may be utilized to increase the antenna assembly 12 gain. Parasitic element 42 may be positioned away from the loop conductor element 28 a distance of approximately 0.05λ to 0.25λ. The loop parasitic element 42 is substantially parallely aligned with the loop conductor element 28 and the dielectric substrate 30. The linear dipole parasitic element 42 is also substantially parallel with vertical sides 34, 38 of loop conductor element 28.

[0031] Still referring to FIG. 4, the feed point connections 44, 46 of the antenna assembly 12 to the transmitter electronics are illustrated. A coax feedline 48 having a nominal 50 ohm impedance is utilized. Center conductor 50 of coax line 48 is electrically connected at an end 44 of loop conductor element 28, while shield element 56 is electrically connected at the other end 46 of the loop conductor element 28. Coax line 48 passes through an aperture 58 in the dielectric substrate 30 to provide relatively short leads between the coax 48 and the feed point connections 44, 46. The aperture 58 is generally defined in the area between the opposed ends 44, 46 of the loop conductor 28.

[0032] FIGS. 5 and 6 illustrate a second embodiment of the present invention. These figures illustrate an antenna assembly 12 similar to that of FIG. 2, except for the addition of another dielectric substrate layer 60 disposed between the ground plane member 32 and the first dielectric substrate layer 30. The second dielectric substrate 60 is selected with a dielectric constant between 1 and 40 and has a thickness of up to 0.5 inch.

[0033] With reference to FIGS. 7, 8 and 9, various feed point orientations may be utilized in the antenna assembly 12. FIG. 7 depicts a feed point connection which results in vertical polarization of the transmitted radio signal. FIG. 8 depicts a feed point connection which results in a slant-linear polarization. FIG. 9 depicts a feed point connection which results in horizontal polarization of the transmitted radio signal

[0034] FIG. 10 illustrates another embodiment of the present invention. Unlike the planar nature of the first and second embodiments, this embodiment illustrates a curved or conformal antenna assembly. Dielectric substrate 30 and loop conductor element 28 have a generally concave cross section and are related in shape to an interior surface of the housing 11 of the communication device 10. As the dielectric substrate 30 and loop conductor element 28 are conformed to an internal surface of the handset 10, packaging requirements may be minimized.

[0035] The above described embodiments of the invention are merely descriptive of its principles and are not to be considered limiting. Further modifications of the invention herein disclosed will occur to those skilled in the respective arts and all such modifications are deemed to be within the scope of the invention as defined by the following claims. Such modifications may include, but are not limited to, alternations of the loop configuration, selection of materials, and additions of elements.