1. Field of the Invention
The present invention relates to a direct current (DC) block with a band-notch characteristic using a DGS. More particularly, the present invention relates to a DC block with a band-notch characteristic using a defected ground structure (DGS) to superiorly block a certain frequency band in the UWB.
2. Description of the Related Art
In general, the ultra wideband (UWB) communications can perform high-speed data transmission in a very wide frequency band with a very low power. The frequency band used for the UWB communications is 3.1˜10.6 GHz, and 5.15˜5.825 GHz of that range is used for HIPERLAN/2 or Institute of Electrical and Electronics Engineers (IEEE) 802.11a, wireless local area network (WLAN) standards. The power used in the WLAN band is 70 dB higher than that in the UWB. Accordingly, a UWB communication signal in a WLAN frequency band can be subjected to interference so that methods of removing signals of the WLAN frequency band among the UWB communication signals have been suggested.
A primary method applies a band stop filter (BSF) at the end of the radio frequency (RF) communications system. However, as a result of using the BSF, the communications system decreases in efficiency and increases in size.
Meanwhile, an active circuit is usually a circuit including a nonlinear element such as the field effect transistor (FET), bipolar junction transistor (BJT) and diode. There are active circuits such as an amplifier, oscillator, mixer, frequency doubler and phase shifter.
In order to use the active circuit in the RF communications system, a DC block which keeps a signal line transmitting signals in the system and the active circuit from being directly connected with each other is needed.
The DC block keeps a DC power from flowing in an RF signal line and having influence on RF signals, and conventionally, a capacitor has been mainly used for the DC block. However, if the capacitor is used in the super high frequency and ultra wideband system such as the UWB system, self-resonance or undesired parasitic components may sometimes occur. Accordingly, features of the capacitor are not guaranteed, efficiency of the capacitor decreases and the cost increases.
To solve the problems, a DC block using micro strip lines has been suggested. The DC block is formed with a pair of micro strip lines parallel to each other, and both ends of each micro strip line are electrically cut off so that it can function as a DC open circuit.
A configuration has been suggested to use as a low pass filter (LPF) by applying a DGS to the DC block using the micro strip lines.
Usually, the DGS is a structure with an etched defect pattern on a ground surface of a transmission line, so that a slow wave of small loss and a stop band in a certain frequency band can be formed. In addition, the DGS effectively increases the capacitance and inductance of the transmission line and has features of the LPF with one pole. Accordingly, the DGS is conventionally used as the LPF or the band pass filter (BPF).
As described above, when the DGS is used in the DC block, if the DGS is used as the LPF or BPF, the DGS can also be used as the BSF. However, until now such application has not been tried, and the DGS has to be modified in order to use the DC block with the DGS as the BSF. Accordingly, a method of forming a band-notch of a desired bandwidth in a desired frequency band has to be studied by applying the DC block with the modified DGS to the RF system.