GB2428895A

GB2428895A - Compact antenna and antenna array arrangements

Info

Publication number: GB2428895A
Application number: GB0611001A
Authority: GB
Inventors: Stephen Smith; Saad Alhossin
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-07-25
Filing date: 2006-06-01
Publication date: 2007-02-07
Anticipated expiration: 2026-06-01
Also published as: GB0515191D0; GB0611001D0; GB2428895B

Abstract

An antenna comprises at least three linear conductor elements 5, 6, 7 arranged in a series. The middle element 6 is a first length and the elements 5, 7 on either side are a second length, which is different from that of the first length. Two feeding points 1 - 4 are located at the gaps between the middle and side elements. The phase of the signal provided at each feed point may be changed by 0{ to 180{. The number of gaps and feed points may be two or more. A signal power divider 22 may be used to supply the signals to the feed points 1 - 4. The antenna elements 5 - 7 may be formed by linear wires or plates or by printed elements on a circuit board which may include quarter wavelength balun elements 19, 20. Also disclosed is an antenna comprising at least two linked spiral conductor elements of the same length where there is a feed point at the centre of each spiral. The above antenna arrangements may provide compact dual band antennas which may be used in compact antenna array formations. The distance between feed points may be varied to match the feed impedance to an input impedance of between 35 L and 150 L . The number of feed points and their spacing and the feed signal phase may be adjusted to influence the frequency, gain and magnetic signal pattern radiated by the antenna.

Description

I

Abualeiz Antenna Des cripti on This invention relates to the Magnetic antennas, Small antenna array, Dual band antennas, circular polarization antennas and base station antennas, and more particularly to phased magnetic antennas for wireless communication devices and systems.

Magnetic antennas were developed a long time ago, being used since the eighteenth centuiy.

Magnetic antennas can be constructed with a wire loop antenna or a radiating slot antenna.

Antennas that have both the magnetic and electric fields are not common. The magnetic antenna can be used as a single or in an array such as access gates and radar systems respectively. However, one of the most important things in antenna array design is to reduce the coupling between the elements of the army, but this causes a power loss and increases the array size. Some antenna applications and designs have to use a limited spacing between the elements in range between 0 and 0.5) to minimize the side sidelobes. However, the directivity in this range is quite small compared to the directivity in the other ranges. Therefore, the element spacing chosen should not be too small if the directivity is to be more important than sidelobes.

Magnetic antennas can be, but are not limited to, a part of hand devices, smart cards, or portable computers. Thus, the magnetic antenna must be of very small dimensions with enough efficiency. In past applications, RFIDtags and contact-less smart cards cannot be functional if they are not within a range of the ioop antenna that enables the chip (RFID-tags or contact-less smart card) to transmit the stored data to a reader. This range is limited by angle and distance. For example, the maximum coupling occurs when the chip is positioned in the front of the loop antenna that the reader is using. In this case, the loop area is perpendicular to the radiation direction that comes from the source.

Tn this invention a procedure for pmducing a magnetic and an electric field radiation from a linear wire, is proposed. The power that is removed by adjusting the space between elements (coupling power) is used to improve the electromagnetic power and reduce the total size of an antenna array system. This new method could be used to control the coupling direction in the application of Near Field Communication (NFC), Radio Frequency Identification (RFID) and applications that are using strong magnetic fields to produce a tough coupling. This invention has a low manufacturing cost and it could be made using different techniques; for example, from a linear wire Fig.l, a folded wide flat wedge Fig's.2A and 2B, a printed board Fig's.3A and 3B, or a spiral antenna Fig. 12.

A description of the invention will now follow:

An antenna consists of three conductor elements. Two of them are at the same length while the third has a length of two times the length of the first two elements, but not always. The conductor elements are positioned in a line. The two small conductors are in the sides while the other is in the middle between them. Two or more feeding points that are located at the sides or between the middle element feed the antenna. There are two different connections, reverse and forward, at phase shift 0 and 180 respectively.

It is possible to use a balun at the feeding points to make balance with sources. For 111-IF and VHF, the balun of the quarter lambda is used, while the printed dipole at high frequency uses a wideband printed balun. The number of feeding points is not limited to two only, it could be more.

The following figures show the invention where 1 and 2 are the connection points for the first feeder, 3 and 4 are the connection points for the second feeder, and 5, 6 and 7 are the three conductors elements, since the conductors 5 and 7 have the same length, while the conductor 6 has twice the length of 5. Points 1, 2, 3 and 4 are also called the first point of the third element, the second point of the second element, the first point of the second element and the second point of the first element, respectively. In order to connect the antenna to the transmission line, the antenna needs to use a baluns 8, 9, 10 and 11 or 19 and 20 for the folded wide flat wedge design or printed antenna design respectively. The feeding points 12, 13, 14 and 15 use a printed line 18 and ground 17 for the folded strip antenna in figure 2A and figure 2B, while the feeding points 21 and 23 are connected to a power divider 22 since the ground 17 is connected to 19 and 20. The printed antenna is fed at 24 using a dielectric layer 16, where the elements 19 and 20 are the section of wideband baluns and are connected to ground area 17.

Fig. 1 is a perspective diagrammatic view of general form of the wire conductor incorporating the principle of the present invention.

Fig.2-A shows the 3D-view example of the present invention when, it is in forward connection of the folded strip conductor using a quarter lambda balun.

Fig.2-B illustrates the 3D-view example of the present invention when, it is in reverse connection of the folded strip conductor using a quarter lambda balun.

Fig.3-A shows the 3D-view example of the present invention when, it is in forward connection of printed board conductor using a printed wideband balun.

Fig.3-B shows the 3D-view example of the present invention when, it is in reverse connection of printed board conductor using a printed wideband balun Figures 4 to ii show the simulation results when the antenna is in the reverse connection at center frequency 48%F=2.4 G1-lz: Fig.4 is a graph of the far field gain pattern for single element.

Fig.5 is a chart of the smith chart impedance for single element.

Fig.6 is a graph of the frequency versus gain for single element.

Fig.7 is a graph showing the magnetic field via positions (1 volt for each feeder).

Fig.8 shows the magnetic field via the frequency (1 volt for each feeder).

Fig.9 is a graph of electric field via positions (1 volt for each feeder).

Fig. 10 shows the electric field via the frequency (1 volt for each feeder).

Fig. 11 shows the frequency versus voltage standing wave ratio.

Fig. 12 is a perspective diagrammatic view of the general form of the spiral conductor incorporating the principle of the present invention for microwave and satellite applications.

Figures 13 to 16 show the simulation results of Abualeiz spiral antenna at design frequency 5 GHz: Fig. 13 is a graph of the retune losses for single element at matching impedance 300 L =.

Fig.14 shows the input impedance for single element that is matched at 300.

Fig. 15 is a graph of the total gain for single element.

Fig. 16 shows the axial ratio for single element.

Figures 17 to 20 show diagrams that explain the percentage size that can be saved by using the invention: Fig. 17 shows geomeiry of the total size of the common used broadside array (GI and G2) and Abualeiz array (G3) at maximum gain 5 97 dBi (reduction of 75 % of the total size at Gain 5.92 dBi).

Fig. 18 shows geometzy of the total size of the common used broadside array (G4 and G5) and Abualeiz array (G6) at maximum gain 7.85 dBi (reduclion of 72 % of the total size at Gain 7.73 dBi).

Fig. 19 shows geometry of the total size of the common used broadside array (G7 and G8) and Abualeiz array (G9) at maximum gain 8.29 dBi (reduction of 71 % of the total size at Gain 8.29 dBi).

Fig.20 shows geometry of the total size of the common used broadside array (Gb, Gil, G12 and G13) and Abualeiz array (G14) at maximum gain 9. 14 dBi (reduction of 87.4 % of the total size at Gain 9.14 dBi).

Fig.2 1 is a graph of the far field gain pattern for two elements array that is shown in Fig. 17.

Fig.22 is a chart of the Smith chart impedance for two elements array that is shown in Fig. 17.

Fig.23 is a graph of the frequency versus gain for two elements array that is shown in Fig. 17.

Fig.24 is a graph of electric field via positions for the array system of two elements that is shown in Fig. 17 (1 volt for each feeder).

Fig.25 shows the electric field via the frequency of two elements array that is shown in Fig. 17 (1 volt for each feeder).

Fig.26 is a graph of magnelic field via positions for the array system of two elements that is shown in Fig. 17 (1 volt for each feeder).

Fig.27 shows the magnetic field via the frequency of two elements array that is shown in Fig. 17 (1 volt for each feeder).

Claims

Claims 1. A single small antenna comprising three linear conductor

elements having two different lengths, the first which is being the length of the middle element, and the second of which being length of the sides elements, two feeding points positioned at the gaps between the middle element and the two side elements, each feed point can be changed in phase between 00 to 180 , the three linear conductor elements are arranged in series with each other, this antenna has two different frequencies F and 48% F at reverse (phase 180 ) and forward (phase 0 ) connection respectively, the number of feeding points and gaps is not limited to two only but it could be more.
2. A single small antenna comprising two spiral conductor elements having same lengths, two feeding points positioned at the centre of each spiral, each feed point can be changed in phase between 0 to 180 , the number of spiral conductors and feeding points are not limited to two only but it could be more.
3. A single small antenna according to claim I wherein: antenna reverse connection happens when the second edge of the first element and the first edge of the third element connect to the feeding point while the first and the second edges of the second elements connect to the ground.
4. A single small antenna according to claim 3 wherein: reverse connection makes the antenna work at the lowest frequency (48% F) with phase shift 180 between feeding points.
5. A single small antenna according to claim I wherein: antenna forward connection happens when the second edge of the first element and the second edge of the third element connect to the feeding point while the first edge of the second element and the first edge of the third element connect to ground.
6. A single small antenna according to claim 5 wherein: forward connection makes the antenna work at the highest frequency (F) when feeding points are in phase.
7. A single small antenna according to claim I and claim 2 wherein: the antenna is considered as a single element when the feeding points connect with a power divider.
8. A single small antenna according to claim I wherein: conductors are a linear wire using a quarter-lambda balun or any kind of baluns.
9. A single small antenna according to claim 2 wherein: the spiral conductors using a quarter- lambda balun or any kind of baluns
10. A single small anlenna according to claim 1 wherein: conductors are plates using a quarter- lambda balun or any kind of baluns.
11 A single small antenna according to claim I and claim 2 wherein: the antenna is a printed antenna using a wideband balun or any kind ofbahms.
12. A single small antenna according to claim 1 and claim 2 wherein: conductors are flibricated from copper or aluminium.
13. A single small antenna according to claim I wherein: the length of the middle element is twice that of the other side element.
14. A single small antenna according to claim 1 and claim 2 wherein: the phase of feeding points varies between 00 andl 80
15. A single small antenna according to claim 1 wherein: it is the first linear wire-antenna that

radiates a magnetic field.
16. A single small antenna according to claim 14 wherein: it produces a magnetic field variable with the changing in phase.
17. An array of 2-small antenna comprising 2-elements of small antenna positioned in parallel to each other at 0.1 25A, the total array size is 25% of the size of 2-elements of /2A-dipole parallel array at same gain.
18. An array antenna according to claim I and claim 17 wherein changing the phase between feeding points is used to contml the magnetic field pattent
19. An array antenna according to claim 1 and claim 17 wherein: using a reflector or increasing the number of elements cause an increase in magnetic field gain.
20. An array antenna according to claim 2 wherein: using a reflector or increasing the number of spiral elements cause an increase in magnetic field gain.
21. An array of N-small antenna comprising N-elements of small antenna positioned in parallel to each other, the total array size can be reduced to up to 9 % of the size of an array of M- elements that gives same gain
22. An array antenna according to claim 1 and claim 2 wherein: changing the distance between feeding points is used to match the input impedance for values between 35 Q to 150 Q.
23. The theory of the Abualeiz antenna is based on the following statements: if a wire antenna is fed by more than one feed point separated by uniform or non-uniform distance, in phase or with difference phases, the resonance Iiquency will drop to more than 50% dependent on the number of feeder points and their positions: using more than one feeder produces capacitance and inductance together, this leads to a drop in resonance frequency and works as a multi band filter: the coupling between the two side feeders is full: the coupling mechanism between two individual proposed antennas is not the same as that which happens between two dipoles, and it can be used for antenna reduction size if a different phase is considered