EP1560287B1

EP1560287B1 - Multi-frequency antenna

Info

Publication number: EP1560287B1
Application number: EP04002213.9A
Authority: EP
Inventors: Jui-Hung Hsu
Original assignee: HTC Corp
Current assignee: HTC Corp
Priority date: 2004-02-02
Filing date: 2004-02-02
Publication date: 2013-04-17
Anticipated expiration: 2024-02-02
Also published as: EP1560287A1

Description

This application claims the benefit of Taiwan application Serial No. 092119341, filed on July 15, 2003 .

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates in general to a type of antenna, and more particularly to a type antenna that has multiple operational frequencies.

Description of the Related Art

The electronic industry is having its prosperity nowadays; different types of portable electronic devices are also very popular. Taking the personal digital assistant (PDA) as an example, in addition to the decreasing size of the products, the ability to do wireless transmission is also a research focus that engineers try their very best in order to obtain an competitive edge over their competitors.
In a wireless system, the antenna is the window for signal transmission and it directly influences the transmission quality of the wireless signals. Its significance is self-evident. Among the different structures of antenna, the microstrip antenna is a mature technology that (1) has simple structure. (2) has small size, and (3) can easily be integrated into circuit boards. Those properties allow microstrip antennas to play an important role in personal communicational systems. However, despite of its advantageous features, in order to realize its full potential, other objective conditions such as low dielectric constant, large current distribution, and low in the antenna_'s material need to be met. The overall quality of the antenna is closely related to these conditions.
In addition to low return loss, consideration for bandwidth is also an important factor for a good design of an antenna. In^.the past, designers usually increased the size of the antenna or decreased the dielectric constant of the substrate in order to achieve greater bandwidth. These old methods resulted in waste of available room in circuit boards and they are no longer viable choices due to the requirement for increasing components density in portable devices nowadays.
With respect to the prior art attention is drawn to international patent publication WO 01/20714 A1 from which a planar antenna is known, said antenna including first and second conductive plates, which are disposed approximately parallel to one another and are electrically coupled one to the other, the first plate including first and second electrical elements separated by a slot therebetween, the slot having first and second linear portions, such that the first linear portion is disposed between the first and second electrical elements, and the second linear portion is substantially perpendicular to and intersects with the first linear portion. Further, publication of European patent application EP 1 079 462 A2 relates to the structure of a dual-band planar antenna. The radiating element in a planar antenna has a slot consisting of two portions of different widths. One end of the wider portion of the slot is close to the feed point of the radiating element. The narrower portion of the slot starts from a point in the wider portion and extends to the edge of the radiating element. The portions of the slot are advantageously straight. The order of magnitude of the ratio of the widths of the portions is three. An advantage of the technical teaching disclosed in EP 1 079 462 A2 is that the bandwidths of a dual-band planar antenna are larger than those of prior-art structures of the same size.
Still further, the technical teaching disclosed in the U.S. patent published as US-A-6,166,694 overcomes the deficiencies in the art by providing a miniature, built-in dual band antenna which is suitable for use in future compact mobile terminals. According to exemplary embodiments disclosed in US-A-6,166,694 , a built-in antenna is provided which includes two spiral conductor arms which are of different lengths and capable of being tuned to different frequency bands. The spiral arms are mounted on the mobile terminal's printed circuit board via a substrate. Matching of the antenna is performed by a matching bridge which is positioned between a feeding pin and grounded post. By adjusting the length of the matching bridge, the matching of the antenna can be changed. In an alternative embodiment disclosed in US-A-6,166,694 , a loading resistor is attached to the matching bridge in order to enhance the bandwidth of the antenna.
From WO 02/05382 A an antenna arrangement for a portable radio communication device is known, comprising a first and a second antenna element, and a conductive shield connectable to a ground plane device, said first and second antenna elements are located on opposite sides of the shield, wherein said first and second antenna elements are of different types.
From US 2002/089454 A1 an antenna transducer, and an associated method, for a mobile station operable in a cellular communication system is known. The mobile station also includes GPS receive circuitry for receiving and operating upon GPS (global positioning system) signals. The antenna transducer includes a primary antenna transducer portion for transducing signals generated to effectuate a communication service in the cellular communication system. And, the antenna transducer includes a second antenna transducer portion for transducing GPS signals transmitted to the mobile station. The primary and second antenna transducer portions are disposed upon a common substrate, and the second antenna transducer portion exhibits circular polarization characteristics.
From US 2003/160728 A1 a small antenna device is known having a wide frequency band suitable for being built in mobile communications apparatus. This antenna device includes a planar radiating element (radiating plate) and a grounding plate provided in parallel to and facing the radiating plate. A feeding line is disposed at approximately the end center of the radiating plate, and supplies high-frequency signals. A shorting portion shorts the radiating plate and grounding plate at near the feeding line. A slit is provided at an end face of the radiating plate approximately opposing the feeding line to form two resonators. A coupling level between two resonators is optimized by adjusting the shape or dimensions of this slit, or loading a reactance element or conductive plate on this slit.
WO01/17063 provides a miniature, built-in multi-band antenna which is suitable for use in compact mobile terminals. According to exemplary embodiments, a semi built-in printed antenna is provided which includes patch elements of different sizes and capable of being tuned to different frequency bands. To broaden bandwidth, one of the patches is at least extended beyond the ground plane.
From the article by FU-REN HSIAO ET AL: "A dual-band planar inverted-F patch antenna with a branch-line slit", MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, JOHN WILEY, NEY YORK, NY, US; vol. 32, no. 4, 20 Ferbuary 2002 (2002-02-20), pages 310-312, XP002246573 ISSN: 0895-2477, DOI: DOI:10:1002/MOP.10163 it is known to embed a branch-line slit in the radiating patch of a planar inverted-F patch antenna, to obtain novel 900 and 1800 MHz dual-band operation. The embedded branch-line slit has two branch slits (one long folded slit and one short bent slit) protruding from the main slit which has an open and at the patch boundary. The main slit and the long folded branch slit together strongly meander the excited patch surface currents starting from the feed to the portion of the patch encircled by the folding branch slit, which leads to a significant reduction in the required dimensions for the proposed antenna.

SUMMARY OF THE INVENTION

The present invention relates to a multi-frequency antenna as defined in claim 1. Further, the present invention relates to a portable electronic device as defined in claim 4.
Preferred embodiments of the present invention are disclosed in the dependent claims.
It is therefore an object of the invention to provide a multi-frequency antenna that has the ability to operate in multiple frequencies and has better performance by increasing the bandwidth through better utilization of the available room.
The invention achieves the above-identified object by providing a multi-frequency antenna. The multi-frequency antenna includes an antenna body, a patch antenna, and a ground plane. The antenna body has first and second radiation arms, as well as a feed-in terminal and a ground terminal both disposed in one side of the antenna body for the purpose of signal feeding and grounding. The first and second radiation arms are arranged in a symmetrically inward spiral structure. Two current paths with different lengths are created along the two radiation arms from the feed-in terminal, thereby enabling the antenna to operate at two frequencies. Furthermore, a patch antenna can be disposed beside the antenna body to allow the antenna to have more operational frequencies. In practice, the length of the patch antenna can be designed according to the bandwidth used by Bluetooth signals in order to meet the requirement of Bluetooth communication. The ground plane is located beneath the antenna body and the patch antenna for the purpose of grounding of the antenna's signals. In implementation, a section of the ground plane, which is above the endfire direction, can be hollowed in order to increase antenna's bandwidth. The hollowed section can also be used to dispose other components in order to increase the component density.
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The following description is made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating a multi-frequency antenna.
FIG. 1B illustrates a symmetrically inward spiral structure.
FIG. 2 illustrates a patch antenna.
FIG. 3A depicts the arrangement of the antenna body, the patch antenna, and the ground plane of the multi-frequency antenna.
FIG. 3B shows that the ground plane is partially hollowed.
FIG. 4 charts the measurement result of the return loss of the antenna body 100.
FIG. 5 charts the measurement result of the return loss of the patch antenna 200.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1A, relating to a reference example, the antenna body 100 has a first radiation arm ARM1 and a second radiation arm ARM2. The antenna body 100 is also equipped with a feed-in terminal FD and a ground terminal GND for feed-in of signals and grounding of signals respectively. According to the structure of the antenna, two major current paths are formed; current path L1 starts from feed-in terminal FD and goes through the radiation arm ARM1; current path L2 starts from feed-in terminal FD and goes through the radiation arm ARM2. In particular, the current path L1 is shorter than the current path L2. When the signal is fed into the antenna body 100, the antenna has a higher operational frequency f_H if resonance occurs across the current path L1. If resonance occurs across the current path L2, the antenna has a lower operational frequency f_L. Thus, the antenna body 100 is operable at two frequencies. By adequate adjustment of the current paths, the operational frequency f_L can be set within the GSM (Global System for Mobile Communication) bandwidth (824-960 MHz), and the operational frequency f_H can be set within the PCS (Personal Communication System) bandwidth (1710-1900 MHz). Therefore, the requirement for the dual-frequency operation modes with central frequencies of 900 MHz and 1800 MHz, for example, can be achieved.
In order to decrease the size of the antenna, the radiation arms ARM1 and ARM2 of the antenna body 100 is designed in the form of a symmetrically inward spiral structure, as depicted in FIG. 1B. Symmetrically inward spiral structure means that the current paths created by the two radiation arms both spiral inwardly; the radiation arm ARM1 extends dextrorotarily, and the radiation arm ARM2 extends levorotarily. Because both extensions of the radiation arms go inwardly from the feed-in point to a center region of the antenna radiator, the lengths of the current paths can be increased in the limited space and therefore the size of the antenna can be effectively reduced.
Additionally, in order to allow the antenna to have more operational frequencies, a patch antenna can be disposed next to the antenna body to obtain more flexibility for the application of the antenna. Referring to FIG. 2, a patch antenna 200 has a feed-in terminal FD', and a ground terminal GND'. The current path L3 created from the feed-in terminal FD' allows the patch antenna 200 to have a third operational frequency f that is different to both the operational frequencies f_H and f_L. In practice, the length of the current path L3 can be designed for the bandwidth of blue tooth signal by setting f to 2.45 GHz in order to meet the requirement for Bluetooth communication.
FIG. 3A depicts the arrangement of the antenna body 100, the patch antenna 200, and ground plane GPLN of the multi-frequency antenna. As shown in FIG. 3A, the antenna body 100 and the patch antenna 200 are disposed nearly. For example, the antenna body 100 and the patch antenna 200 are disposed at a distance of about 1 to 7 mm in order to be coupled to PCS bandwidth. Further, the ground plane GPLN, indicated by the dashed line, is electrically coupled to the ground terminals GND and GND', is beneath the antenna body 100 and the patch antenna 200. When the antenna is working, the electric field radiates from the antenna in the endfire direction E. In order to increase the bandwidth of the antenna, a section of the ground plane GPLN can be hollowed, or cut off, as depicted in FIG. 3B, for example. After hollowing the part of the ground plane GPLN with respect to the endfire direction, as shown in FIG. 3B, (the hollowed section is shown as the area enclosed by the dashed line), the area of the actual ground plane GPLN' is less than that of the original ground plane GPLN, whereby the antenna bandwidth can be increased. Moreover, the space saved by the hollowed section can be used to dispose other components, such as slots for interface cards, to better utilize the available room in a circuit board and increase the component density.
FIG. 4 charts the measurement result of the return loss of the antenna body 100. If the operational bandwidth is defined by the voltage standing wave ratio (VSWR) having a value less than 3, the antenna body 100 certainly satisfies the design requirements of both GSM bandwidth and DCS (Digital Communication System) bandwidth, especially for high frequency. FIG. 5 charts the measurement result of the return loss of the patch antenna 200. If the operational bandwidth is defined by S11 having a value less than - 10dB, the characteristics of the patch antenna 200 meet the requirement for Bluetooth signaling according to the frequency range set in the Bluetooth standard.
The multi-frequency antenna proposed by the invention has at least the following advantages.
The symmetrically inward spiral structure adopted in the antenna body effectively reduces the size of the antenna.
The design of hollowing the section of the ground plane increases the bandwidth of the antenna and the hollowed section can be used to provide space for other components in order to increase the component density.
While the invention has been described by way of example and in terms of a preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.

Claims

A multi-frequency antenna with a first operational frequency and a second operational frequency for a portable electronic device, the multi-frequency antenna comprising:
a ground plane (GPLN') and an antenna radiator (100) disposed parallel to the ground plane and having a feed-in terminal (FD), a ground terminal (GND) electrically coupled to the ground plane (GPLN'), and a first and a second radiation arms (ARM1, ARM2) both arranged in a spiral form and coupled to each other at said feed-in terminal and form a first current path (L1) and a second current path (L2) which realize the first and second operational frequencies respectively, wherein the multi-frequency antenna is characterized in that the antenna radiator (100) has a symmetric structure relative to a central line of the antenna radiator (100),

said feed-in terminal (FD) is disposed offset from the centre line at a one side thereof,

said first arm (ARM1) is arranged on said one side of the centre line and spins inwardly from the feed-in terminal (FD) to a centre region of the antenna radiator (100),

said second arm (ARM2) extends from the feed-in terminal (FD) to the other side of said centre line opposite said one side, and spins inwardly on said other side of the centre line symmetrically to said first arm (ARM1), and

that the ground plane (GPLN') has a cut-off section beneath the endfire direction (E) of the antenna such that the first and second arms (ARM1, ARM2) partially extend beyond the ground plane (GPLN') in the endfire direction (E).
The multi-frequency antenna according to claim 1, wherein the first operational frequency belongs to GSM bandwidth, and the second operational frequency belongs to DCS bandwidth.
The multi-frequency antenna according to claim 1, wherein the first operational frequency belongs to GSM bandwidth, and the second operational frequency belongs to DCS bandwidth.
A portable electronic device with a first operational frequency, a second operational frequency, and a third operational frequency, the portable electronic device comprising:
a multi-frequency antenna according to claim 1; and

a patch antenna (200), separately disposed in a side of the multi-frequency antenna, having a third current path to realize the third operational frequency.
The portable electronic device according to claim 4, the first operational frequency belongs to GSM bandwidth, the second operational frequency belongs to DCS bandwidth, and the third operational frequency is 2.45 GHz.
The portable electronic device according to claim 4, wherein the antenna radiator (100) and the patch antenna (200) are disposed at a distance of about 1 to 7 mm.
The portable electronic device according to claim 6, wherein the first current path has a length which sets the first operational frequency within GSM bandwidth, the second current path has a length which sets the second operational frequency within PCS bandwidth.
The portable electronic device according to claim 6, wherein the third current path (L3) sets the third operational frequency meeting the requirement of Bluctooth communication.
The portable electronic device according to claim 4, wherein the first current path (L1) sets the first operational frequency within GSM bandwidth, and the second current path (L2) sets the second operational frequency within DCS bandwidth.
The portable electronic device according to claim 4, wherein the third current path (L3) sets the third operational frequency meeting the requirement of Bluetooth communication.
The portable electronic device according to claim 10, wherein the first operational frequency belongs to GSM bandwidth, the second operational frequency belongs to DCS bandwidth, and the third operational frequency is 2.45 GHz.