EP1717902B1

EP1717902B1 - Planar monopole antennas

Info

Publication number: EP1717902B1
Application number: EP20060007137
Authority: EP
Inventors: Chih-Lung Chen; Chih-Kai Liu
Original assignee: Wistron Neweb Corp
Current assignee: Wistron Neweb Corp
Priority date: 2005-04-20
Filing date: 2006-04-04
Publication date: 2009-03-04
Anticipated expiration: 2026-04-04
Also published as: DE602006005413D1; CN1855625A; EP1717902A1

Description

BACKGROUND

The invention relates in general to planar monopole antennas and in particular to planar monopole antennas with sleeve structures.
Embedded antennas, such as chip antennas and planar antennas, are widely applied in wireless communication devices. A conventional type is a ceramic chip antenna produced by LTCC (Low Temperature Co-fired Ceramic) technology. Conventional planar antennas such as microstrip antennas, printed antennas and Planar Inverted F Antennas (PIFAs), are generally applied in GSM, DCS, UMTS, WLAN, and bluetooth wireless equipment such as mobile phones and wireless LAN adapters.
Referring to Fig. 1, a conventional planar monopole antenna primarily comprises a substrate S, a ground G, a radiator R and a cable W. The ground G and the radiator R are formed on a surface S1 of the substrate S, and the radiator R is longitudinal along axis Y.
The cable W, such as a coaxial cable, comprising a signal wire W1 and a ground wire W2 enclosing the signal wire W1. As shown in Fig. 1, the radiator R.comprises a feed end RF adjacent to the ground G. The feed end RF is connected to the signal wire W1, and the ground G is connected to the ground wire W2, respectively.
EP 1 469 554 A1 discloses a dual-access monopole antenna assembly including two sleeve portions and a monopole element therebetween. The two sleeve portions are electrically connected to the ground. At a distance from the sleeve portions, a secondary monopole antenna for the Bluetooth or IEEE 802.11b band is arranged.
US 6 559 809 B1 discloses a planar antenna having first and second conductors arranged at different sides of a substrate. The first and second conductors may overlap.
In "Modeling Antenna Close to the Human Body", 2000 IEEE Aerospace Conference Proceedings 18-25 March 2000, Big Sky, MT, USA, vol.5, 2000, pages 83-89, M.A. Stuchly et al. disclose a monopole antenna fed by a coaxial cable.
In "Dual-band strip-sleeve monopole for handheld telephones". Microwave and Optical Technology Letters, Wiley, USA, vol. 21, no. 2, April 20th, 1999, pages 79-82, M. Rahman et al. disclose a cubic antenna structure including a rectangular metal box.
US 6 392 599 B1 discloses a communication antenna having a radiator and two sleeve portions. However, no relationship of the lengths of these elements is defined.
With respect to typical frequency range of Digital Video Broadcasting (460-860MHz), the frequency coverage ratio of a conventional planar monopole antenna as shown in Fig. 1 is usually less than 30%, adversely affecting communication efficiency.

SUMMARY

The present invention provides a planar monopole antenna according to claim 1.
The present invention provides a planar monopole antenna including a substrate, a ground, a first sleeve portion, a second sleeve portion, a radiator and a cable connecting the radiator for communicating radio signals within a specific frequency range. The first sleeve portion is formed on the substrate and electrically connected to the ground, wherein the first sleeve portion projects from a side of the ground in a first direction with a first length. The second sleeve portion is formed on the substrate and electrically connected to the ground, wherein the second sleeve portion projects from the side of the ground in the first direction with a second length, and the side of the ground defines a third length from the first to the second sleeve portion. The first and second sleeve portions extend from the ends of the side of the ground. The longitudinal radiator is formed on the substrate and situated between the first and second sleeve portions, wherein the radiator comprises a main body and two L-shaped angle portions at the top end of and symmetrical with respect to the main body. Specifically, the angle portions substantially extend opposite to the first direction, wherein total length of the main body and each of the angle portions is substantially equal to the sum of the first, second, and third lengths.

DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective diagram of a conventional planar monopole antenna;
Fig. 2 is a perspective diagram of an example of a planar monopole antenna;
Fig. 3 is a perspective diagram illustrating VSWR between 400-900MHz of a conventional planar monopole antenna and an embodiment of a planar monopole antenna;
Fig. 4 is a perspective diagram of an embodiment of a planar monopole antenna; and
Fig. 5 is a perspective diagram of an embodiment of a planar monopole antenna with zigzag structures.

DETAILED DESCRIPTION

Referring to Fig. 2, an exemple of a planar monopole antenna for transmitting radio signals within a specific frequency range includes a substrate S, a ground G, a first sleeve G1, a second sleeve G2, a radiator R and a cable W. The ground G and the radiator R are formed on a surface S1 of the substrate S. As shown in Fig. 2, the radiator R is longitudinal along axis Y, comprising a feed end RF at the bottom thereof, adjacent to a side G' of the ground G. The cable W, such as a coaxial cable, comprises a signal wire W1 and a ground wire W2 enclosing the signal wire W1. The radiator R comprises a feed end RF adjacent to the ground G. The feed end RF is connected to the signal wire W1, and the ground G is connected to the ground wire W2, respectively.
In Fig. 2, the first and second sleeves G1 and G2 are parallel, formed on the surface S1, extending from the ends of the side G'. The first sleeve G1 has a first length L1, and the second sleeve G2 has a second length L2 along Y axis, respectively. The first length L1 is substantially equal to the second length L2. In some embodiments, the substrate S is FR4 (Flame Retardant Type 4), and the ground G, the first and second sleeves G1 and G2 are metal, integrally formed on the surface S1 by PCB fabrication.
As shown in Fig. 2, the side G' is perpendicular to Y axis, defining a third length L3 equal to the distance from the first sleeve G1 to the second sleeve G2. The radiator R has a fourth length L4 along Y axis, and the distance d from the radiator R to the first sleeve G1 is substantially equal to the distance d from the radiator R to the second sleeve G2. The fourth length L4 is designed substantially equal to 1/4 of the radio signal wavelength. Specifically, the fourth length L4 is also substantially equal to the sum of the first, second and third lengths L1, L2 and L3 (L4=L1+L2+L3). Thus, the radiator R, the first and second sleeves G1 and G2 can exhibit capacitive effect and facilitate broader bandwidth for wireless communication.
Fig. 3 illustrates Voltage Standing Wave Ratio (VSWR) between 400-900MHz of two planar monopole antennas. Dashed line 31 indicates VSWR between 400-900MHz of a conventional planar monopole antenna, and solid line 32 indicates VSWR between 400-900MHz of the planar monopole antenna as shown in Fig. 2 (L1=L2=65mm, L3=12mm, L4=140mm).
In general, a standard antenna requires an available VSWR less than 3. With respect to Fig. 3, the frequency coverage ratio of the conventional planar monopole is about 25% (the proportion of the frequency range under VSWR<3 indicated by dashed line 31 within 400-900MHz), and the frequency coverage ratio of the planar monopole antenna in Fig. 2 is about 90% (the proportion of the frequency range under VSWR<3 by solid line 32 within 400-900MHz). That is, the planar monopole antenna of the example can provide higher frequency coverage ratio and broader communication bandwidth than the conventional planar monopole antenna.
Referring to Fig. 4, an embodiment of a planar monopole antenna comprises a deformed radiator R' to reduce the extent of the antenna in direction Y and facilitate miniaturization.. The radiator R' has a main body R1 and a pair of L-shaped angle portions R2 and R3, both symmetrical with respect to the main body R1. Specifically, total length of the main body R1 and each of the angle portions R2 and R3 is substantially equal to the sum of the first, second and third lengths L1, L2 and L3, and substantially equal to 1/4 of the radio signal wavelength. Thus, the radiator R', the first and second sleeves G1 and G2 can provide capacitive effect and facilitate broader bandwidth for wireless communication.
As shown in Fig. 4, the main body R1 extends along Y axis, and the angle portions R2 and R3 symmetrically extend outward from an end of the main body R1. Specifically, the angle portions R2 and R3 extend opposite to Y axis. As the sum of first, second and third lengths L1, L2 and L3 are predetermined, the radiator R' can have a length L4', extending less in direction Y, reducing antenna dimension. The length L4' in direction Y in Fig. 4 is less than the length L4 shown in Fig. 2.
To save more space on the surface S1 of the substrate S, referring to Fig. 5, an embodiment of a planar monopole antenna comprises a pair of angle portions R2 and R3 with zigzag structures, to reduce the extent of the radiator R' in direction Y. Total length of the main body R1 and each of the angle portions R2 and R3 is substantially equal to the sum of the first, second and third lengths L1, L2 and L3, and substantially equal to 1/4 of the radio signal wavelength. Thus, the radiator R', the first and second sleeves G1 and G2 can provide capacitive effect and facilitate broader bandwidth for wireless communication. Comparing Fig. 2 with Figs. 4 and 5, when the total length of the first, second and third lengths L1, L2 and L3 is predetermined, the extent of the radiator R' in direction Y can be reduced to facilitate miniaturization, wherein L4''<L4'<L4.
Planar monopole antennas with symmetric sleeve structures are provided according to the embodiments. The sleeves can be printed on a substrate by PCB fabrication, exhibiting capacitive effect with the radiator, thereby facilitating broader bandwidth for wireless communication. Moreover, the extent of the radiator can be reduced in various structures to facilitate miniaturization. The invention can provide broader bandwidth than conventional planar monopole antennas for wireless communication, suited for various types of DVB devices, such as digital TVs.
While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). within the scope of the appended claims.

Claims

A planar monopole antenna for communicating a radio signal, comprising:
a substrate (S);

a ground (G);

a first sleeve portion (G1), formed on the substrate (S) and electrically connected to the ground (G), wherein the first sleeve portion (G1) projects from a side of the ground (G) in a first direction (Y) with a first length (L1);

a second sleeve portion (G2), formed on the substrate (S) and electrically connected to the ground (G), wherein the second sleeve portion (G2) projects from the side of the ground (G) in the first direction (Y) with a second length (L2), and the side of the ground defines a third length (L3) from the first sleeve portion (G1) to the second sleeve portion (G2);
wherein the first and second sleeve portions (G1; G2) extend from the ends of the side of the ground (G); the planar monopole antenna further comprising:

a radiator (R), formed on the substrate (S) and situated between the first and second sleeve portions, the radiator (R) comprising a longitudinal main body (R1) and two L-shaped angle portions (R2; R3) connected to opposite sides of the top end of the main body (R1), wherein the two L-shaped angle portions (R2; R3) are symmetrical with respect to the main body (R1) and mainly extending opposite to the first direction (Y), and the sum of the lengths of the main body (R1) and either one of the two L-shaped angle portions (R2; R3) is substantially equal to the sum of the first, second, and third lengths (L1; L2; L3); and

a cable (W), connecting the radiator (R) for communicating the radio signal.
The planar monopole antenna as claimed in claim 1, wherein each of the angle portions (R2; R3) comprises a zigzag structure.
The planar monopole antenna as claimed in claim 1, wherein the ground (G), the radiator (R), the first and second sleeve portions (G1; G2) are formed on a surface of the substrate (S).
The planar monopole antenna as claimed in claim 1, wherein the distance from the radiator (R) to the first sleeve portion (G1) is substantially equal to the distance from the radiator (R) to the second sleeve portion (G2).
The planar monopole antenna as claimed in claim 1, wherein the first and second sleeve portions (G1; G2) are substantially perpendicular to the side of the ground (G).
The planar monopole antenna as claimed in claim 1, wherein the fourth length is substantially 1/4 of the radio signal wavelength.
The planar monopole antenna as claimed in claim 1, wherein the first length (L1) is substantially equal to the second length (L2).
The planar monopole antenna as claimed in claim 1, wherein the substrate (S) is FR4.
The planar monopole antenna as claimed in claim 8, wherein the ground (G), the radiator (R), the first and second sleeve portions (G1; G2) are printed on a surface of the substrate (S) by PCB fabrication.
The planar monopole antenna as claimed in claim 1, wherein the radiator (R) comprises a feed end (RF) adjacent to the side of the ground (G), and the cable (W) comprises a ground wire (W2) connecting the ground (G) and a signal wire (W1) connecting the feed end (RF).