An antenna used in a base station including a repeater for a wireless communication system can have various forms and structures. Recently, a dual polarization antenna structure of 2T2R (2Tx/2Rx) MIMO scheme has been widely employed in wireless communication antennas by applying a polarization diversity scheme. In this case, the signals of the respective transmission & reception paths generally employ a structure for isolating transmitted and received signals using duplexers.
FIG. 1 is a schematic block diagram of a prior art base station apparatus of a mobile communication system. FIG. 1 shows an antenna system 10 having a 2T2R MIMO structure used in a typical mobile communication base station, and first and second duplexers 20 and 21 provided to each transmission & reception path. The antenna system 10 includes a first antenna (Ant0) 100 for transmitting and receiving signals for a first path P0 and a second antenna (Ant1) 101 for transmitting and receiving signals for a second path P1 in a 2T2R structure. The first and second antennas 100 and 101 are arranged to generate polarized waves orthogonal to each other.
In addition, first and second duplexers 20 and 21 respectively connected to the first and second antennas 100 and 101 of the antenna system 10 to separate or combine the transmitted and received signals of the first and second paths P0 and P1 are provided. The first duplexer 20 is connected to a first transmission & reception unit (P0 transmission & reception unit) 30, and the second duplexer 21 is connected to a second transmission & reception unit (P1 transmission & reception unit) 31. The first transmission & reception unit 30 processes signals transmitted and received on the first path, and the second transmission & reception unit 31 processes signals transmitted and received on the second path PI.
The first duplexer 20 has a structure in which a transmission filter (Tx0) 204 and a reception filter (Rx0) 206, which process a transmitted signal and a received signal for the first path P0, respectively, are connected using a T-junction 202. The second duplexer 21 has a structure in which a transmission filter (Tx1) 214 and a reception filter (Rx1) 216, which process a transmitted signal and a received signal for the second path P1, are connected using a T-junction 212.
Here, isolation between the transmitted signal and the received signal on the first path P0 is determined by the first duplexer 20 including the transmission filter 204 and the reception filter 206 connected by the T-junction 202. That is, isolation between the transmitting terminal and the receiving terminal of the first duplexer 20 is the transmission and reception isolation on the first path P0. Similarly, isolation of the transmitted signal and the received signal on the second path P1 corresponds to the isolation produced in implementing the second duplexer 21 including the transmission filter 214 and the reception filter 216 connected by the T-junction 212.
Therefore, as a method to increase isolation between the transmitted signal and the received signal, only improving filtering characteristics (for example, skirt characteristic) in the first and second duplexers 20 and 21 is substantially considered. In general, a technique of increasing the number of stages of each of the transmission filter and the reception filter or increasing the number of notches at a frequency to be isolated is generally employed. However, such a solution has problems of increasing the size of filters and difficulty in manufacture and production of filters.
Further, in order to meet the demand for faster processing and improved quality in the mobile communication market, each base station is being evolved into a small (or micro) cell, and an antenna system and base station equipment are being developed in an integrated manner. Accordingly, there is growing demand for a more compact and lightweight duplexer including the transmission filter and the reception filter described above. It has been a very difficult challenge to increase isolation between the transmitted signal and the received signal in consideration of the size and weight of the duplexer as described above.
Therefore, the present disclosure has been made in an effort to effectively resolve the aforementioned problems, and it is an object of the present disclosure to provide a device configured to increase isolation between the transmitted signal and received signal on a transmission & reception path or maintaining or satisfying a certain required level of isolation while reducing the size and weight of a duplexer configured to process the transmitted and received signals.