Broadband coupling filter

#1. Field of the Invention

#The present invention relates to a broadband coupling filter, and more particularly, to a broadband coupling filter capable of generating a notch filtering effect.

#2. Description of the Prior Art

#FIG. 1A is a schematic diagram of a broadband coupling filter according to an embodiment of the present invention

#FIG. 1B to FIG. 1D are schematic diagrams of each layer of the broadband coupling filter in FIG. 1A.

#FIG. 2 and FIG. 3 are schematic diagrams of frequency responses of the broadband coupling filter in FIG. 1A.

#Please refer to FIG. 1A to FIG. 1D. FIG. 1A is a schematic diagram of a broadband coupling filter 10 according to an embodiment of the present invention, and FIG. 1B to FIG. 1D are schematic diagrams of each layer of the broadband coupling filter 10. The broadband coupling filter 10 uses partial structure of a power divider disclosed in U.S. patent application Ser. No. 12/634,692 (now U.S. Pat. No. 8,068,796, issued Nov. 29, 2011), and generates new effects. Therefore, the broadband coupling filter 10 can act as a feeding network of a smart antenna with little insertion loss, and can effectively suppress noises. In detail, the broadband coupling filter 10 includes a substrate 100, signal terminals P1, P2, P3, P4, a grounding plate GND_PLT, block transmission lines TML_B1, TML_B2 and a connection unit WR. The substrate 100 is a three-layer Printed Circuit Board (PCB), in which an upper layer (shown in FIG. 1B) includes the signal terminals P1, P2 and the block transmission line TML_B1 being printed, a middle layer (shown in FIG. 1C) includes the grounding plate GND_PLT being printed, and a lower layer (shown in FIG. 1C) includes the signal terminals P3, P4 and the block transmission line TML_B2 being printed. Furthermore, as can be seen from FIG. 1A to FIG. 1D, the grounding plate GND_PLT has a hole HL. The block transmission lines TML_B1 and TML_B2 have identical shapes, and are set above and below the hole HL respectively. Besides, the signal terminal P1 is utilized for receiving a signal, the signal terminal P2 is utilized for outputting a filtering result of the signal. The signal terminal P3 and the signal terminal P4 are connected via the connection unit WR.

#Since the block transmission lines TML_B1 and TML_B2 are not isolated by the grounding plate GND_PLT, signals are coupled between the block transmission lines TML_B1 and TML_B2. After the connection unit WR connects the signal terminals P3 and P4, there is a loading effect in a transmission path from the signal terminal P1 to the signal terminal P2. Therefore, by properly adjusting a length, material, or components of the connection unit WR, different effects can be generated in the transmission path from the signal terminal P1 to the signal terminal P2.

#For example, if the connection unit WR is realized by a metal conducting wire, a frequency response of the broadband coupling filter 10 can be represented by FIG. 2. In FIG. 2, a solid curve indicates ratios of energy transmitted and reflected to the signal terminal P1 indifferent frequencies, and a dot curve indicates ratios of energy transmitted (coupled) from the signal terminal P1 to the signal terminal P2 in different frequencies. As can be seen from FIG. 2, an insertion loss from the signal terminal P1 to the signal terminal P2 is very small.