SYSTEM

[Technical Field]

The present invention generally relates to a Base Station (BS) antenna for a mobile communication system. More particularly, the present invention relates to a BS antenna useful for a Time Division Duplex (TDD) mobile communication BS system.

[Background Art]

In general, a mobile communication BS system amplifies an intended signal at a high-power amplifier of a BS, provides the transmission signal to an antenna via a power-supply cable, and radiates the transmission signal through the antenna. The antenna receives a signal and transmits the received signal to a Low Noise Amplifier (LNA) of the BS through the power-supply cable. Then the LNA amplifies a weak received signal. For the purpose of providing a service, the antenna is installed at a high place such as a building roof or a tower and a BTS is installed on the ground within the building or under the tower. Therefore, a very long signal transmission line is established between the BTS and the antenna.

Due to the long signal transmission line between the BTS and the antenna, much of a transmission signal and a received signal are lost during transmission along the signal transmission line. Especially when the distance between the BS system and the antenna is tens of meters, 3dB or more of an input signal is found to be lost in link budget calculation. The signal loss reduces coverage due to the decrease of transmit power and degrades reception sensitivity by Noise Figure (NF) degradation.

Owing to the recent technological development of a transmission power amplifier and cost saving, the decrease of transmit power can be overcome by increasing the output power of the power amplifier. The decreased reception sensitivity can be improved by increasing the transmit power of a Mobile Station (MS), but entailing a reduced lifetime of a battery. In this context, methods for improving a reception NF without imposing constraints on MSs have been studied. For this purpose, usually, a Tower Mounted Amplifier (TMA) 2 is installed in the vicinity of an antenna 1 and connected to the antenna 1 to thereby compensate for NF degradation caused by signal loss on a power-supply cable. An exemplary associated technology is disclosed in Korea Patent Application No. 2004-16163 entitled "Tower Top Amplifier Being Mount/Demount Directed to Antenna", invented by Duk-yong Kim, et. al. and filed by the same applicant on March 10, 2005.

The method for improving a reception NF by use of the BS antenna 1 and the TMA 2 has limitations in overcoming NF degradation caused by signal loss in a power-supply circuit within the BS antenna 1. Moreover, since the TMA 2 amplifies a signal received from each radiation element by a single amplifier, defects in the amplifier leads to a bypass operation, degrading the NF considerably. In the case of a TDD switch for separating transmission from reception, it should perform in correspondence with high transmit power.

[Detailed Description of the Invention] [Technical Problems to be Solved]

An object of the present invention is to address at least the problems and to provide a BS antenna for minimizing loss caused by an internal power-supply circuit and signal separation in a mobile communication system.

Another object of the present invention is to provide a BS antenna for preparing for the risk of deadly degradation of reception performance by maintaining a reception level to be relatively stable in a mobile communication system.

A further object of the present invention is to provide a BS antenna using a TDD switch with a performance corresponding to low power, for separating transmission from reception in a mobile communication system.

[Means to Solve Problems]

To achieve the above objects of the present invention, there is provided a BS antenna having received signal amplifiers. Each of the received signal amplifiers is installed for at least one radiation element in a radiation element part of the BS antenna, filters a downlink signal received from the radiation element according to a predetermined reception band, amplifies the filtered signal, and outputs the amplified signal.

[Favorable Effects]

As described above, a BS antenna for a mobile communication system according to the present invention brings the following effects. Firstly, an NF associated with an internal power supply circuit of an antenna can be minimized by connecting amplifiers directly to respective radiation elements in a distributed manner. Because a received signal is amplified by a plurality of amplifiers, not a single one, a rapid decrease in reception level can be prevented despite an error in any of the amplifiers. Secondly, an RF signal and a control signal synthesized by A BTS are separated once within the antenna, thus decreasing loss. Fourthly, since a TDD switch for separating transmission from reception switches a transmission signal distributed on a radiation element basis, the switch can perform in correspondence with low power. Fifthly, a relatively low-power transistor having a low 1-db Compression Point (CP) can be used for an amplifier. Sixthly, isolation specification required for the TDD switch can be relieved. Seventhly, use of a plurality of low-power amplifiers decreases the probability of amplifier breakage caused by an external interference signal.

[Brief Description of the Drawings]

FIG. 1 illustrates an exemplary conventional BS antenna system having a TMA;

FIG. 2 is a block diagram of an overall BS antenna in a mobile communication system according to an embodiment of the present invention;

FIG. 3 is an exemplary detailed block diagram of a received signal amplifier illustrated in FIG. 2;

FIG. 4 is another exemplary detailed block diagram of a received signal amplifier illustrated in FIG. 2;

FIG. 5 illustrates simulation results of the BS antenna according to the present invention and the conventional BS antenna in terms of signal loss; FIG. 6 is a perspective view of the overall BS antenna in the mobile communication system according to the embodiment of the present invention;

FIG. 7 is a detailed exploded perspective view of important parts of the BS antenna illustrated in FIG. 6;

FIG. 8 is an exterior perspective view of a received signal amplification/distribution module illustrated in FIG. 6; and

FIG. 9 is a detailed perspective view of a lower cap illustrated in FIG. 6.

[Best Modes for Carrying Out the Invention]

Preferred embodiments of the present invention will be described in detail with the attached drawings. The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of exemplary embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention.

FIG. 2 is a block diagram of an overall BS antenna in a mobile communication system according to an embodiment of the present invention. Referring to FIG. 2, basically, the BS antenna of the present invention does without the conventional TMA and is connected directly to a BTS.

The BS antenna includes a signal separator 10 having a bias-T, for separating an RF signal, a control signal for antenna control, and a DC power received from the BTS and a division/phase shift module 60 for primarily dividing the RF signal separated by the signal separator 10 at 1 :N (1 :4 in the illustrated case of FIG. 2) through a divider 62 and shifting the phase of each divided signal according to a phase control signal through a phase shifter 64.

The BS antenna of the present invention further includes received signal amplification/division modules 70. Each of the received signal amplification/division module 70 has a received signal amplifier 72 for receiving a signal from the division/phase shift module 60, transmitting the received uplink transmission signal to radiation elements 80 according to a transmission/reception switching control signal (a TDD synchronization signal, TDD Sync), filtering a downlink signal received from the radiation elements 80 according to a predetermined reception band, and amplifying the filtered signal, and a radiation element front-end divider 74 for secondarily dividing a signal received from the received signal amplifier 72 at 1 :M (at 1 :2 in the illustrated case of FIG. 2), and outputting the divided signals to the radiation elements 80. It is to be understood herein that a final division ratio set by the division ratio 1 :N of the divider 62 in the division/phase shift module 60 and the division ratio 1 :M of the radiation element front-end dividers 74 of the received signal amplification/division modules 70 is determined according to the number of radiation elements of the antenna.

The antenna of the present invention further includes an RF coupler 40 for generating a signal coupled with the RF signal on an RF signal line between the signal separator 10 and the division/phase shift module 60, an RF detector 50 for detecting the RF signal from the coupled signal received from the RF coupler 40, and a DC/DC converter 30 for receiving the DC power from the signal separator 10 and providing the DC power as an operation power to an LNA of each received signal amplification/distribution module 70.

The antenna of the present invention further includes a Main Control Module (MCM) for receiving the control signal and the DC power from the signal separator 10 and the RF signal from the RF detector 50, outputting the phase control signal to the phase shifter 64 of the division/phase shift module 60 according to the control signal, DC power, and RF signal, and outputting the TDD Sync signal to the received signal amplification/division modules 70 according to the control signal, DC power, and RF signal.

A big difference between the conventional technology and the BS antenna of the present invention having the above-described configuration is the existence of the received signal amplification/division modules 70 installed in the vicinity of the radiation elements 80, for amplifying almost immediately signals received from the radiation elements 80 without loss on a transmission line. In this manner, the antenna of the present invention distributes received signal amplifiers to respective radiation elements and connects them directly to the radiation elements. Thus, loss in the internal power supply circuit of the antenna is minimized. Also, since a received signal is divided for a plurality of amplifiers and amplified by them, a rapid drop of a reception level is prevented in spite of an error in any of the amplifiers. Since transmission signals divided on a radiation device basis are switched, a switch can be used, which performs in correspondence with low power and isolation specification required for the switch can be relieved.

FIG. 3 is an exemplary detailed block diagram of the received signal amplifier of a received signal amplification/division module illustrated in FIG. 2. Referring to FIG. 3, a received signal amplifier 72 includes a first switch 733 for switching to a transmission/reception path according to the TDD Sync signal, a second switch 724 connected to radiation elements 80, for switching to the transmission/reception path according to the TDD Sync signal, a Band Pass Filter (BPF) 726 for receiving a signal from the second switch 724 during reception and passing only frequencies within a predetermined reception band, and an LNA 728 for low-noise amplifying the output of the BPF 726.

During RF transmission, the first and second switches 722 and 724 switch to the transmission path according to the Time Sync signal, so that a transmission signal is provided to the radiation elements 80 through the first and second switches 722 and 724.

During RF reception, the first and second switches 722 and 724 switch to the reception path according to the Time Sync signal. The BPF 726 passes a predetermined reception frequency band of signals received from the radiation elements 80 and the LNA 728 low-noise-amplifies the filtered signal and the first switch 722 switches the low-noise-amplified signal down to the BTS.

As described above, because signals received through the radiation elements 80 are amplified by the nearby LNA 728, the antenna of the present invention minimizes signal loss. Compared to the conventional technology, the received signal is amplified before it is added with noise on an internal transmission line of the antenna in the present invention. Therefore, the amplification efficiency of a valid signal is further increased. Due to the absence of any particular device on the transmission path, loss can be minimized during signal transmission.

FIG. 4 is another exemplary detailed block diagram of a received signal amplifier illustrated in FIG. 2. Referring to FIG. 4, a received signal amplifier 72' is similar in configuration to that illustrated in FIG. 3, except that the former does not have the BPF 726 for filtering a received signal and instead, it has a transmission/reception BPF 727 between the second switch 724 and the radiation elements 80. As a transmission signal passes through the BPS 727, spurious emission is improved.

FIG. 5 illustrates simulation results of the BS antenna according to the present invention and a conventional BS antenna in terms of NF. FIG. 5(a) illustrates NF simulation results of a conventional antenna, for example, the BS antenna illustrated in FIG. 1 and FIG. 5(b) illustrates NF simulation results of the BS antenna of the present invention.

Typically, a mobile communication BS antenna is elongated as a plurality of radiation elements are arranged vertically in the nature of service. The resulting increase in the length of a power-supply circuit that provides a signal to each radiation element causes power loss. A recent widespread BS antenna supporting electric downtilt, Electric Downtilt Antenna (EDNA) generally has an efficiency of about 70% and suffers from an about 30% NF degradation, i.e. 1.5-dB NF degradation caused by signal loss in the power- supply circuit. It is also noted that the TMA adds an about 2-dB NF degradation. On the other hand, FIG. 5B reveals that the present invention has a total antenna NF of 1.84dB, which is a 1.66OdB improvement. The reason for calculating the NF of the TDD modules to be 1.8dB is that an insertion loss caused by a jumper cable between the antenna and the TMA can be improved by 0.2dB.

FIG. 6 is a perspective view of the overall BS antenna in the mobile communication system according to the embodiment of the present invention and FIG. 7 is a detailed exploded perspective view of important parts of the BS antenna illustrated in FIG. 6. FIGs. 6 and 7 illustrate an exemplary mechanical configuration of the BS antenna of the present invention, especially an internal mechanical configuration of the antenna with respect to the rear surface of a reflection plate 110 (for convenience' sake, a surface with radiation elements mounted thereon is referred to a front surface). Like reference numerals denote the same components in FIGs. 2 and 6.

Referring to FIGs. 6 and 7, the antenna according to the present invention is mechanically configured so that a ray dome 170 having a top and bottom capped with upper and lower caps 180 and 90, respectively forms the exterior of the antenna and various devices including radiation elements (not shown) are installed within the ray dome 170. The plurality of received signal amplification/division modules 70 are installed on the rear surface of the reflection plate 110, to be directly connected to (connectors of) the radiation elements according to the present invention.

The lower cap 190 connected to the BTS is provided with the signal separator 10, followed by the RF coupler 40 and the division/phase shift module 60 sequentially. The RF detector 50 is installed on an upper portion of the rear surface of the reflection plate 110 and the MCM module 100 is mounted in the upper cap 180.

In the vicinity of the signal separator 10 at a lower portion of the reflection plate 110, a rotation device 192 having a driving motor and a rotation gear is installed to rotate the reflection plate 110 left and right. The radiation direction of antenna beams is adjusted by rotating the reflection plate 110 along with the rotation of the rotation device 192.

Meanwhile, transmission lines taking the form of cables connect the signal separator 10, the RF coupler 40, the division/phase shift module 60, the RF detector 50, and the MCM module 100 in FIG. 6. For example, a transmission line 106 marked as a black solid line between the signal separator 10 and the MCM module 100 is used to transfer the control signal and the DC power separated by the signal separator 10.

In the antenna having the above mechanical configuration, the MCM module 100 is fixed to the reflection plate 110. As illustrated in FIG. 7, the MCM module 100 can be fixedly mounted to the reflection plate 110, while being fitted into a mounting guide structure 102. This MCM module 100 may have an independent housing, for easy repair and maintenance. In addition, a top end of the upper cap 180 is designed in the form of a cover to allow easy opening and closing so that the MCM module 100 can be installed or detached easily. Since the MCM module 100 is usually configured to have rather complex electronic circuits, it has a high probability of breakage relative to other internal components of the antenna. Accordingly, the above installation and detachment structure of the MCM module 100 allows easy MCM replacement, leading to easy repair and maintenance of the whole antenna. Especially when the MCM module 100 is removed from the antenna, the received signal amplification/division modules 70 are bypassed and there is no problem in the basic antenna function, that is, transmission and reception. Thus, no interruptions occur to a mobile communication service.

The present invention is also characterized in that a transmission line for transferring the phase control signal and the Time Sync signal from the MCM module 100 to the division/phase shift module 60 and each received signal amplification/division module 70 is provided basically through a multi-line board 130 formed using a Print Circuit Board (PCB), such as a multi-layer board. The multi-line board 130 can be attached to a side surface of the reflection plate directly or through a board guide panel 120 according to an embodiment of the present invention. A final connection between the multi-line board 130 and the MCM module 100 is enabled by a multi-line cable 104 such as a flat cable (ribbon cable) having a multi-line connector such as an Insulation Displacement Connector (IDC) at an end, or a Flexible PCB (FPCB). This configuration further renders the installation and removal of the MCM module 100 easy. Needless to say, the transmission line 106 for providing the control signal and the DC power from the signal separator 10 to the MCM module 100 also has connectors in the form of jacks. Since transmission lines for transferring control signals from the MCM module 100 are formed through the multi-line board 130, transmission line complexity is reduced, fabrication and operation are easy, and design freedom is increased, compared to formation of individual transmission lines.

With the fixed installation of the MCM module 100 to the reflection plate 110, the MCM module 100 rotates with the reflection plate 110 when the reflection plate 110 rotates by the rotation device 192. Therefore, such damage as caused by twists of the transmission lines connected to the MCM module 100 is prevented. Use of a rotary joint and a slip ring as in a general structure may increase cost and impair reliability.

FIG. 8 is an exterior perspective view of a received signal amplification/distribution module 70 illustrated in FIG. 6. Referring to FIG. 8, the antenna front-end divider 74 of the received signal amplification/division module 70 is a single PCB attached to one side of the received signal amplifier 72. A transmission line pattern for a divider having a division ratio of 1 :2, for example, can be formed on the antenna front-end amplifier 74. The transmission line pattern is formed such that both ends of the transmission line pattern of divided parts are positioned in correspondence with the connectors of radiation elements connected to the antenna front-end divider 74 and the transmission line pattern of a combined part is formed within the attached received signal amplifier 72, for example, it is connected to connectors of the second switch (724 in FIG. 2) or the BPF (727 in FIG. 4). Since the length of the transmission line that may cause signal loss is minimized, the received signal amplification/division module 70 is optimal in terms of preventing signal loss.

FIG. 9 is a detailed perspective view of the lower cap illustrated in FIG. 6. Referring to FIG. 9, connectors 92 are formed on a lower surface of the lower cap 190, for connecting to a connection cable running to the BTS. Particularly, a square hole, for example, is formed on a portion of the lower surface of the lower cap 190 according to the present invention. The DC/DC converter 30 is detachably inserted into the square hole by use of a screw, for easy repair and maintenance, like the installation structure of the MCM module 100. The BS antenna for a mobile communication system according to the embodiment of the present invention can be configured and operated as described above. While the invention has been shown and described with reference to certain embodiments of the present invention thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention. For example, while a total of eight radiation elements are illustrated in FIG. 2, the present invention is applicable to an antenna with more radiation devices.

Also, while it has been described that the received signal amplifiers 72 are provided, each for two radiation elements connected it, each received signal amplifier can be given for one radiation element.

While each received signal amplifier 72 has one LNA in the above description, one more extract LNA can be added to each received signal amplifier so as to adaptively cope with LNA breakage. In this redundancy structure, a path connection to the extra LNA can be established by an additional switch and the MCM can monitor the performance of each LAN and provide a switching control signal to the additional switch.

Therefore, the scope of the present invention should be defined by the appended claims and all equivalents.

[Industrial Applicability]

The present invention is applied to a BS antenna in a mobile communication system.