HK1036156B - Dual band diversity antenna having parasitic radiating element - Google Patents

Description

Dual band diversity antenna with passive radiating element

Technical Field

The present invention relates generally to antennas, and more particularly to diversity antennas for use in communication devices.

Background

Antennas for personal communication devices, such as radiotelephones, may not function properly when in close proximity to a user when in operation, or when the user is moving while the device is in operation. The close proximity of the antenna to an object or the movement of the user during operation of the radiotelephone can result in a reduction in signal quality or a fluctuation in signal strength, which is known as multipath fading. Diversity antennas have been designed which work in combination with the main antenna of a radiotelephone to improve signal reception.

Many popular handheld wireless telephones are being miniaturized. Indeed, many contemporary models are only 11-12 centimeters long. Unfortunately, as the size of the radiotelephone is reduced, its internal space is correspondingly reduced. The reduction in internal space makes it difficult to achieve the bandwidth and gain requirements necessary for radiotelephone operation with existing diversity antennas, since their size can be reduced accordingly.

Fortunately, a diversity antenna can be considered that can resonate in multiple frequency bands. For example, the japanese Personal Digital Cellular (PDC) system uses two "receive" frequency bands and two "transmit" frequency bands. Therefore, a diversity antenna in a radiotelephone for use in the japanese PDC system should preferably be able to resonate in each of the two receive bands. Unfortunately, the ability to provide diversity antennas with adequate gain over multiple frequency bands is currently limited due to size limitations imposed by radiotelephone miniaturization.

Summary of The Invention

It is therefore an object of the present invention to provide a diversity antenna which is capable of resonating over multiple frequency bands and having sufficient gain for use in personal communication devices such as radiotelephones.

It is a further object of the present invention to provide a reduced size diversity antenna that can resonate over multiple frequency bands with sufficient gain and can be mounted in a small interior space of a small radiotelephone.

These and other objects of the present invention are provided by a planar diversity antenna for a communication device such as a radiotelephone having two radiating elements secured to opposite sides of a dielectric substrate and passively coupled to jointly resonate in two adjacent frequency bands. One radiating element is referred to as a "feed" radiating element, which has a meandering conductive path thereon, as well as an RF feed point and ground point. The second radiating element is referred to as a "passive" radiating element having a meandering conductive path thereon. The passive radiating element is spaced from, and is generally in a parallel relationship with, both the "feed" radiating element and the ground plane.

When a planar diversity antenna according to the invention is used in a radio telephone, the shield covering the RF circuitry can be used as a ground plane. The planar antenna element is secured within the housing of the radiotelephone such that the parasitic radiating element is in spaced parallel relationship with the outer planar surface of the shield, and an aperture in the outer surface of the shield permits an electrically live feed element to extend from the RF circuit through the shield aperture and electrically connect to a feed point on the conductive path of the feed radiating element. A ground feed element electrically connects the ground post on the feed radiating element conductive path to the grounded shield.

The feed and passive radiating elements may have meandering conductive paths of different electrical and physical lengths. The dual-band resonances of the feed and passive radiating elements radiate jointly. Exemplary adjacent frequency bands include between 0.810 and 0.828GHz and between 0.870 and 0.885 GHz.

Diversity antennas according to the present invention may be advantageous because their configuration enables them to conform to the small space constraints of current radiotelephones and other communication devices, while providing modest gain and bandwidth characteristics. The dual-band functionality of a diversity antenna incorporating aspects of the present invention may be particularly advantageous in many countries, such as japan, that use multiple frequency bands to transmit and receive radiotelephone communications. The invention can be suitably used as a diversity antenna for a dual-band antenna telephone.

Brief Description of Drawings

Fig. 1 illustrates a planar inverted F Antenna (plannar invested F Antenna) for use in a radiotelephone.

Fig. 2A-2C illustrate a dual band diversity antenna having a fed radiating element and a parasitic radiating element in accordance with the present invention.

Fig. 3 is an exemplary resonance curve obtained by a dual band diversity antenna incorporating aspects of the present invention.

Figure 4 illustrates a dual band diversity antenna according to the present invention attached to a radiotelephone radome.

Detailed description of the invention

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; furthermore, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference symbols in the various drawings indicate like elements.

As is known to those skilled in the art, an antenna is a device used to transmit and/or receive electrical signals. A transmitting antenna generally includes a feed element that induces radiation to an aperture or reflective surface to radiate an electromagnetic field. A receiving antenna typically includes an aperture or surface that focuses the incoming radiation field onto a collecting feed to produce an electrical signal proportional to the incoming radiation. The power radiated from or received by an antenna depends on the aperture area of the antenna and is described in terms of gain. The radiation pattern of an antenna is typically depicted in polar coordinates. The voltage standing wave ratio (VSWP) is related to the impedance matching of the antenna feed point to the feed line or transmission line. To radiate RF energy with minimal loss, or to transfer received RF energy to a receiver with minimal loss, the impedance of the antenna should match the impedance of the transmission line or feed.

Radiotelephones typically employ a primary antenna that is operatively electrically connected to a transceiver associated with signal processing circuitry disposed on an internal printed circuit board. To maximize the power transferred between the antenna and the transceiver, the transceiver and antenna are preferably interconnected such that the respective impedances are substantially "matched", i.e., electrically tuned at the circuit feed to filter out or compensate for unwanted antenna impedance components to provide a 50 ohm (or desired) impedance value.

As those skilled in the art will appreciate, a diversity antenna may be used in combination with a main antenna within the radiotelephone to prevent call attenuation due to fluctuations in signal strength. Signal strength may vary due to user movement between cells of a cellular telephone network, user movement between buildings, interference from stationary objects, and the like. Diversity antennas are designed to pick up signals that the main antenna cannot pick up through space, pattern, and bandwidth or gain diversity. Diversity antennas may also be used to compensate for RayLeigh (RayLeigh) fading, which may include very sudden fading or loss of signal strength due to multipath phase cancellation.

One type of diversity antenna known in the art is a Planar Inverted F Antenna (PIFA) and is illustrated in fig. 1. The illustrated PIFA10 includes a radiating element 12 that is in spaced apart relation to a ground plane 14. The radiating element is also grounded to the ground plane 14, as indicated by 16. A live RF connection 17 extends from underlying circuitry (not shown) through the ground plane 14 to the radiating element 12 at 18. The PIFA is tuned to the desired frequency by adjusting the following parameters that affect gain and bandwidth: varying the length L of the radiating element 12; changing the gap H between the radiating element 12 and the ground plane 14; and varying the distance D between the grounded and live RF connections. The size of the ground plane is also an important tuning parameter. Other parameters familiar to those skilled in the art may be adjusted for tuning the PIFA, but are not discussed further herein.

Referring now to fig. 2A-2C, a dual band diversity antenna 20 is illustrated in accordance with a preferred embodiment of the present invention. The antenna 20 includes a dielectric substrate 22, such as a fiberglass circuit board, having first and second opposed surfaces 22a and 22 b. A particularly preferred material for the substrate is FR4 board, which is familiar to those skilled in the art of circuit boards. But different dielectric materials may be used for the substrate 22.

For the illustrated embodiment, the dielectric substrate 22 preferably has a dielectric constant between 4.4 and 4.8. It should be understood that dielectric substrates having different dielectric constants may be used without departing from the spirit and scope of the present invention.

The diversity antenna according to the invention is particularly suitable for the debate between rayleigh (line of sight and main reflection) and rayleigh (Ricean) (multiple reflection) attenuation. The present invention allows the diversity antenna to reside in a small mobile radiotelephone and assist when the main antenna enters a large attenuation region.

The dimensions of the dielectric substrate 22 may be highly dependent on the spatial limits of the radiotelephone or other communication device in which the diversity antenna 20 is included. Typically, the dielectric substrate 22 has a thickness T between 1.0 and 1.5 millimeters (mm); the width W is between 11 and 22 mm; and the length L is between 21 and 23 mm.

A layer of copper or other conductive material is secured to the first and second substrate surfaces 22a and 22b and is designated 24a and 24b, respectively. One preferred conductive material is copper tape because portions of it can be easily removed when tuning the antenna. Typically, the thickness of the conductive layers 24a, 24b on each respective substrate surface 22a, 22b is within 0.5 Ounces (OZ) (about 14 grams) and 1.0OZ (about 28 grams) of copper.

As shown in fig. 2B, a ground terminal 27 and a live RF feed point 28 are electrically connected to conductive layer 24 a. The locations of the ground clip 27 and the live RF feed point 28 on the conductive layer 24a of the first surface of the substrate are selected according to the desired input impedance. As shown in fig. 2C, a coaxial contact 29 extends through, but is not electrically connected to, the substrate second surface conductive layer 24 b. As will be described below, the ground lug 27 and the live RF feed point 28 are electrically connected by a coaxial connector 29 to circuitry (not shown) located in the underlying radiotelephone.

The conductive layer 24b affixed to the substrate second surface 22b is a passive conductive layer; i.e. it is not electrically connected to the other parts of the antenna 20. As those skilled in the art will appreciate, passive electromagnetic elements couple and "feed off" near field currents (i.e., current flowing on a conductive surface is present in the "field" of the current-induced electromagnetic field near the conductive surface). Passive antennas are not antennas that are directly excited by an RF source, but are antennas that are excited by energy radiated by another source. The presence of the passive element may alter the resonant characteristics of the antenna in close proximity, thereby allowing the antenna to resonate in more than one frequency band.

As will be described below, the first and second substrate surfaces 22a, 22b and the respective conductive layers 24a, 24b thereon each function as a respective radiating element as shown at 30a and 30 b. Radiating element 30a is referred to as a "fed" radiating element, while radiating element 30b is referred to as a "passive" radiating element. As will be described below, the feeding and passive radiating elements 30a, 30b allow the antenna 20 to be tuned to resonate in at least two frequency bands.

Referring to fig. 2B and 2C, portions 26a, 26B of each conductive layer 24a, 24B, respectively, have been removed to produce a curved conductive pattern, indicated at 32a and 32B, respectively, for radiating RF energy. As will be appreciated by those skilled in the art, the length of each of the curved conductive patterns 32a, 32b is a tuning parameter. The feed radiating element 30a and the parasitic radiating element 30b cause the antenna 20 to resonate in at least two frequency bands. The passive radiating element 30b is excited by the magnetic field generated by the fed radiating element 30 a. The feed radiating element 30a and the passive radiating element 30b are preferably configured to produce two different resonant frequencies. Thereby, the bandwidth of the antenna can be increased compared to an antenna having only a single radiating element.

Referring now to fig. 3, an exemplary resonance curve 40 resulting from a dual band diversity antenna according to the present invention is illustrated. The VSWR is plotted along the "Y" axis and is indicated by 42. The frequency is plotted along the "X" axis and is indicated by 44. As represented by the illustrated resonance curve 40, the fed radiating element 30a and the passive radiating element 30b are configured to resonate in two closely spaced receive bands (band 1) and (band 2). Band 1 extends from frequency f1 to frequency f2, while band 2 extends from frequency f3 to frequency f 4. Band 1 and band 2 are closely spaced and have a VSWR of less than 2: 1 to facilitate impedance matching. The resonance curve 40 indicates where (in terms of frequency) the match between the antenna and the receiver circuit will be at a loss of 0.5dB or less. The dual band diversity antenna shown is made nearly 1/4-1/4 wave retractable antenna with gain in both bands. As understood by those skilled in the art, the resonance curve 40 is adjustable by "tuning" the antenna 20. Tuning includes adjusting and selecting various parameters of the dual band diversity antenna as described below.

Referring to fig. 4, housing portions 60a, 60b are illustrated in an assembled view, for example, in upper and lower housing portions 60a, 60b of a radiotelephone communications device, as will be understood by those skilled in the art, configured to enclose circuit board 54 and diversity antenna 20. The antenna 20 is placed over the shield 52 and in spaced relation to the shield 52. The shield 52 overlies the circuit board 54 and provides electromagnetic interference shielding for various microelectronic components (not shown) that are secured to the circuit board. The shield 52 has a flat outer surface 53 which serves as a ground plane for the antenna 20.

In the illustrated embodiment, the coaxial connector 29 provides a passageway for the live feed element 33 to extend from the circuit board 54 through the shield aperture 31 and electrically connect with the feed point 28. The depicted coaxial connector 29 also provides a path for the ground feed element 35 to electrically connect the ground post 27 to the ground shield 52. as will be appreciated by those skilled in the art, the live feed element 33 connects the live RF feed point 28 to the receiver input and output terminals (not shown) preferably through an RF switch (receive only) (not shown) on the underlying circuit board 54 which disconnects the main and diversity antennas from the receiver.

The passive radiating element 30b of the antenna 20 is generally maintained in a parallel spaced relationship with the outer surface 53 of the shield 52. Foam 55 or other similar non-conductive material is preferably placed between the passive radiating element 30b and the outer surface 53 of the shield 52 and serves as a means to reduce the effects of oscillation and vibration.

Tuning parameters for the illustrated diversity antenna 20 include, but are not limited to: the length L of the antenna 20; thickness D1 of dielectric substrate 22; distance D2 between shield 52 and antenna 20; distance D3 between live RF feed point 28 and ground post 27; and the length of the curved conductive pattern of both the fed radiating element 30a and the passive radiating element 30 b. The length of the dielectric substrate 22 and the meandering conductive pattern define the "electrical length" necessary to radiate a resonant structure. The separation of the ground plane, feed and feed is a retrofit to a conventional antenna.

The foregoing is illustrative of the present invention and is not to be construed as limiting thereof. Although a few exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. All such modifications are therefore considered to be within the scope of the invention as defined in the claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. It is therefore to be understood that the foregoing is illustrative of the present invention and is not to be construed as limited to the specific embodiments disclosed, and that modifications to the disclosed embodiments, as well as other embodiments, are intended to be included within the scope of the appended claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims (16)

1. An antenna (20), comprising:

a dielectric substrate (22) including opposing first and second faces (22a, 22 b);

a first radiating element (30a) disposed on said dielectric substrate first face (22a), said first radiating element (30a) including a first meandering conductive path (24a) having an RF feed point (28) and a ground terminal (27);

a second radiating element (30b) disposed on said dielectric substrate second face (22b) and capacitively coupled to said first radiating element (30a), said second radiating element (30b) including a second meandering conductive path (24b), wherein said first meandering conductive path and said second meandering conductive path have different lengths, and wherein said first radiating element and said second radiating element jointly resonate in at least two different frequency bands;

a live feed element (33) extending through said dielectric substrate (22) and electrically connected to said RF feed point (28); and

a ground feed element (35) extending through said dielectric substrate (22) and electrically connected to said ground post (27), wherein the ground feed element (35) is in electrical contact with a different second radiating element (30 b).

2. The antenna (20) of claim 1 wherein said dielectric substrate (22) has a dielectric constant between 4.4 and 4.8.

3. The antenna (20) of claim 1 wherein said first and second radiating elements (30a, 30b) jointly resonate in adjacent frequency bands.

4. An antenna (20) according to claim 3 wherein said adjacent frequency bands are between 0.810 and 0.828GHz and between 0.870 and 0.885GHz respectively.

5. An antenna assembly for a communication device, said antenna assembly comprising:

a ground plane (53) having a via;

a planar antenna (20) in adjacently parallel spaced relation to said ground plane (53), wherein said antenna (20) comprises:

a dielectric substrate (22) including opposing first and second faces (22a, 22 b);

a first radiating element (30a) disposed on said substrate first side (22a)

Said first radiating element (30a) comprises a first radiating element having an RF feed point (28) and

a first meandering conductive path (24a) to a ground point (27); and

a second radiating element (30b) disposed on said substrate second face (22b) and capacitively coupled to said first radiating element (30a), said second radiating element

(30b) Comprising a second meandering conductive path (24b), wherein said first and second meandering

The curved conductive paths (24a, 24b) have different lengths, and wherein the first radiation

The element and the second radiating element jointly resonate in at least two different frequency bands;

a live feed element (33) extending through said ground plane aperture and electrically connected to said RF feed point (28) through said dielectric substrate (22), wherein said live feed element does not contact said second radiating element; and

a ground feed element (35) extending from said ground plane (53) and electrically connected to said ground point (27) through said dielectric substrate (22).

6. The antenna component of claim 5, wherein said dielectric substrate (22) has a dielectric constant between 4.4 and 4.8.

7. The antenna component according to claim 5, wherein said first and second radiating elements (30a, 30b) jointly resonate in adjacent frequency bands.

8. The antenna component of claim 7, wherein said adjacent frequency bands are between 0.810 and 0.828GHz and within 0.870 and 0.885GHz, respectively.

9. A wireless telephone device comprising:

a housing (60a, 60 b);

a circuit board (54) disposed in said housing (60a, 60b) and having a face and electronic components mounted thereon;

a shield (52) overlying and secured to a portion of the face of said circuit board (54), said shield (52) having a flat outer surface (53) with a through-hole formed therein;

a planar antenna (20) covering said shield outer surface (53) and comprising:

a dielectric substrate (22) including opposing first and second faces (22a, 22 b);

a first radiating element (30a) disposed on said substrate first face (22a), said first radiating element (30a) including a first meandering conductive path (24a) having an RF feed point (28) and a ground point (27); and

a second radiating element (30b) disposed on said substrate second face (22b) and capacitively coupled to said first radiating element (30a), said second radiating element (30b) including a second meandering conductive path (24b), and wherein said first and second radiating elements jointly resonate within at least two frequency bands;

wherein said planar antenna (20) is secured within said housing (60a, 60b) such that said second radiating element (30b) is in spaced parallel relationship with said shield outer surface (53);

a live feed element (33) extending from said circuit board (54) through said shield aperture and electrically connecting said RF feed point (28); and

a ground feed element (35) extending from said shield (52) and electrically connected to said ground point (27).

10. A radiotelephone apparatus according to claim 9 further comprising means (55) for reducing vibration, said means (55) being disposed between said second radiating element (30b) and said shield outer surface (53).

11. A radiotelephone apparatus according to claim 9 wherein said first and second meandering electrically conductive paths (24a, 24b) have different lengths.

12. A radiotelephone apparatus according to claim 9 wherein said dielectric substrate (22) has a dielectric constant between 4.4 and 4.8.

13. A radiotelephone apparatus according to claim 9 wherein said live feed element (33) extends through said dielectric substrate (22).

14. A radiotelephone apparatus according to claim 9 wherein said ground feed element (35) extends through said dielectric substrate (22).

15. A radiotelephone apparatus according to claim 9 wherein said first and second radiating elements (30a, 30b) jointly resonate in adjacent frequency bands.

16. The radiotelephone apparatus of claim 15 wherein said adjacent frequency bands are between 0.810 and 0.828GHz and between 0.870 and 0.885 GHz.