Polarization diversity antenna system

A polarization diversity antenna system includes antenna elements having first to fourth slotlines bent at right angles so that the second slotline is provided adjacent to the first slotline, the third slotline is diagonally opposite to the first slotline and provided adjacent to the second slotline, and the fourth slotline is provided adjacent to the third slotline and diagonally opposite to the second slotline, and a switching network in which coupling units are formed between ends of the horizontal slotlines and between ends of the vertical slotlines that are close to intersections of the vertical and horizontal slotlines to determine polarization.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2005-0104995 filed on Nov. 3, 2005 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polarization diversity in an antenna system and, more particularly, to a polarization diversity antenna which has a simple structure and a small size.

2. Description of the Related Art

In the antenna field, polarization means a polarity direction of an E field with respect to a propagation direction of an electromagnetic wave. Every antenna has polarization of its own, and matching of polarization directions of transmitting and receiving antennas is an important consideration. The polarization can be classified into linear polarization and circular polarization.

Polarization diversity is a technology for improving frequency efficiency in mobile communications using different frequencies of adjacent cell base stations. In this technology, two frequency signals are cross-polarized using a single antenna.

That is to say, two frequency signals which do not interfere with each other and have an orthogonal phase are mixed to be used for the single antenna. In this manner, the same frequency can be reused in the neighboring cell, thus enhancing user capacity.

In related art, a dual-polarization antenna or a mechanically rotating feed line is used to realize the above-mentioned polarization diversity.

However, the former is problematic in that a structure for achieving polarization diversity is very complicated and a large amount of power is consumed, and the latter is problematic in that reliability is reduced due to mechanical breakdown.

U.S. Pat. No. 5,977,929 discloses a structure of a polarization diversity antenna which is shown inFIG. 1.

Referring toFIG. 1, a crossed-dipole antenna includes four antenna elements12,14,16, and18, and a switching circuit40.

The switching circuit40controls operation of the antenna elements12,14,16, and18so as to provide vertical linear polarization and horizontal linear polarization, and acts as a radio frequency (RF) switching element having a plurality of PIN diodes.

Further, the switching circuit40has a voltage source42for providing direct current (DC) voltage to the switching circuit40, a pair of DC blocking capacitors C1and C2, and inductors L1, L2, and L3blocking a radio frequency signal.

The capacitor C1is connected to a positive RF signal input terminal44and the capacitor C2is connected to a negative RF signal input terminal46to block the DC voltage from the RF signal input terminals44and46.

Capacitors C1and C2may have the same value.

In addition, the inductor L1is connected to the voltage source42to block an RF signal from the voltage source42, and the inductor L3is connected to a ground to block the RF signal from ground.

If positive bias voltage is applied through the voltage source42to the switching circuit40, PIN diodes D2and D3are turned on and PIN diodes D1and D4are turned off. Therefore, the RF signal flows through the PIN diodes D2and D3of the switching circuit40as indicated by arrows48inFIG. 1.

Hence, the antenna element14is coupled with the antenna element16and the antenna element12is coupled with the antenna element18, so that the positive bias DC voltage applied to the switching circuit40forms horizontal linear polarization moving from a left side to a right side inFIG. 1.

On the other hand, if negative bias voltage is applied through the voltage source42to the switching circuit40, the PIN diodes D1and D4are turned on and the PIN diodes D2and D3are turned off. Therefore, the RF signal flows through the PIN diodes D1and D4of the switching circuit40as indicated by arrows50inFIG. 1.

Accordingly, the antenna element12is coupled with the antenna element14and the antenna element16is coupled with the antenna element18, so that negative bias DC voltage applied to the switching circuit40forms vertical linear polarization moving from a lower side to an upper side inFIG. 1.

A terminal of the inductor L2is connected to anodes of the PIN diodes D1and D3, and another terminal is connected to cathodes of the PIN diodes D2and D4. When a bias current is transmitted through the inductor L2, the inductor L2prevents the RF signal from flowing.

+Vrf which is applied to the terminal44and −Vrf which is applied to the terminal46denote an RF driving signal for the switching circuit40. In connection with this, −Vrf has a phase difference of 180° with respect to +Vrf.

The diversity antenna shown inFIG. 1has a simpler and more efficient structure in comparison with a former antenna.

However, in the diversity antenna, it is necessary to use a bidirectional bias signal to control a switching circuit. This is not a desirable solution since most RF devices have a single unipolar power source. Furthermore, there is a problem in that the antenna cannot be operated without bias voltage.

SUMMARY OF THE INVENTION

According to aspects of the present invention there is provided a polarization diversity antenna system that is simplified, small, and low cost.

Aspects of the present invention are not limited to those mentioned above, and other aspects of the present invention will be understood by those skilled in the art through the following description.

Aspects of the present invention provide a polarization diversity antenna system which may include antenna elements including first to fourth slotlines bent at right angles so that the second slotline is provided adjacent to the first slotline, the third slotline is diagonally opposite to the first slotline and adjacent to the second slotline, and the fourth slotline is provided adjacent to the third slotline and diagonally opposite to the second slotline, and a switching network in which coupling units are formed between ends of the horizontal slotlines and between ends of the vertical slotlines that are close to intersections of the vertical and horizontal slotlines to determine polarization.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 2illustrates a structure of a polarization diversity antenna system according to an exemplary embodiment of the invention.

With reference toFIG. 2, a polarization diversity antenna system200includes antenna elements210,220,230, and240, and a switching network250.

In connection with this, the antenna elements210,220,230, and240are formed of half wavelength slotlines, and the slotline constituting each antenna element is bent at a right angle.

Furthermore, the switching network250is a unit for coupling the antenna elements210,220,230, and240, and the coupling unit may be exemplified by a PIN diode.

The PIN diodes are provided on ends of the horizontally extending slotlines, and on ends of the vertically extending slotlines that are close to the intersection of the vertically and horizontally extending slotlines. InFIG. 2, the former diodes are designated by252and256, and the latter diodes are designated by254and258.

Capacitors260and262are formed on other ends of the vertical slotlines to be short circuited for an RF signal and to be an open circuit for a low frequency bias current.FIG. 3illustrates an RF equivalent circuit for the polarization diversity antenna system shown inFIG. 2.

FIG. 4illustrates the RF equivalent circuit when polarization is formed in a horizontal direction according to the exemplary embodiment of the invention.

If bias voltage of zero volts is applied to the switching network250, all the PIN diodes are closed. That is to say, the switches are disconnected as shown inFIG. 3.

An open circuit in the ends of the horizontal slotlines is transformed into a short circuit over a quarter wavelength at the intersection of the slotlines as shown inFIG. 4.

Accordingly, in-phase linear polarization is formed in a horizontal direction.

Also, the vertical slotlines are closed for the RF signal at the ends thereof, and act as a quarter wavelength short circuited stub. The vertical slotlines are opposite in phase to each other and do not radiate.

FIG. 5illustrates the RF equivalent circuit when polarization is formed in a vertical direction according to the exemplary embodiment of the invention.

If positive bias voltage is applied to the switching network250, all the PIN diodes are opened.

That is to say, the switches are connected as inFIG. 3, and in-phase linear polarization is formed in a vertical direction.

In this case, the vertical slotlines are short circuited at the intersection of the slotlines by the PIN diodes.

The horizontal slotlines are connected at the ends thereof by the PIN diodes, and act as the quarter wavelength short circuited stub. Furthermore, the horizontal slotlines are opposite in phase to each other and do not radiate.

A bias signal transmitted through a feed line as shown inFIG. 2, but may be divided by a decoupling inductor (L).

FIG. 6illustrates a structure of a polarization diversity antenna system according to another exemplary embodiment of the invention.

Referring toFIG. 6, in a polarization diversity antenna system600, antenna elements620and640are printed on a bottom side of a dielectric substrate, and remaining antenna elements610and630are printed on a top side of the dielectric substrate.

Additionally, instead of the capacitors provided on the ends of the vertical slotlines as shown inFIG. 2, open ended quarter wavelength microstrip stubs are formed.

The microstrip stubs form a short circuit for an RF signal, and an open circuit for a low frequency bias current.

A bias signal transmitted through a feed line as shown inFIG. 6, but may be divided by a decoupling inductor (L).

With respect to the invention,FIGS. 2 and 6mainly illustrate linear polarization, but the structure shown inFIGS. 2 and 6may be transformed so as to provide circular polarization.

Although the present invention has been described in connection with the exemplary embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and changes may be made thereto without departing from the scope and spirit of the invention. Therefore, it should be understood that the above embodiments are not limitative, but illustrative in all aspects.

The invention is advantageous in that a small polarization diversity antenna system having a simple structure is provided.

Furthermore, the invention is advantageous in that a switching network is controlled by unipolar bias voltage.