Patent Application
20090237183
1. Technical Field
The present disclosure generally relates to filters, and more particularly to a low-pass filter.
2. Description of Related Art
Conventionally, when a wireless network device operates at high power, harmonic components of high frequency are generated due to the nonlinear properties of the active components of the device, causing electromagnetic interference (EMI).
To address this, a filter is often used to suppress the harmonic components. Some manufacturers use a waveguide element, such as a microstrip, formed on a printed circuit board of the device.
Features of an ideal filter are signal attenuation of zero within a pass band, becoming infinite within a stop band, and transition as sharp as possible from the pass band to the stop band, providing the shortest possible distance between a transmission zero point and the stop band. In addition, increased transmission zero points improve performance of the filter in suppression of harmonic noise.
Referring to
Therefore, a need exists in the industry to overcome the described limitations.
The low-pass filter 10 includes an input portion 100, an output portion 120 aligned with the input portion 100, a high impedance transmission portion 140, a pair of rectangular low impedance transmission members 160, a first connecting portion 182, a second connecting portion 184, a third connecting portion 186, and a fourth connecting portion 188.
The input portion 100 inputs electromagnetic signals. The output portion 120 outputs the electromagnetic signals. The input portion 100 and the output portion 120 each have impedance values of approximately 50 ohms (Ω).
The high impedance transmission portion 140 electrically connects the input portion 100 to the output portion 120, transmitting electromagnetic signals therebetween. The high impedance transmission portion 140 is of varied shapes. The high impedance transmission portion 140 comprises a first end portion 142 electrically connected to the input portion 100, a second end portion 144 electrically connected to the output portion 120, and a bent portion 146 between and electrically connecting the first end portion 142 and the second end portion 144. That is, the high impedance transmission portion 140 extends varyingly from the input portion 100 to the output portion 120.
Here, the bent portion 146 is concertinaed. This configuration is also known as a comb-line structure. In this illustrated embodiment, the bent portion 146 is angular, or sharp-cornered. Alternatively, the bent portion 146 may be curved, with rounded corners or portions. Again, the bent portion 146 may be both angular and curved, that is, including a combination of angular corners or portions and curved corners or portions.
In this embodiment, the bent portion 146 reduces the area of the low-pass filter 10.
The low impedance transmission members 160 are located at opposite sides of the high impedance transmission portion 140. Each of the low impedance transmission members 160 comprises a first low impedance transmission portion 162 and a second low impedance transmission portion 164. A slot 170 is formed between the first low impedance transmission portion 162 and the second low impedance transmission portion 164. A width of the first low impedance transmission portion 162 is different from that of the second low impedance transmission portion 164.
The first low impedance transmission portion 162 comprises a third end portion 1620 and a first coupled line 1622. The second low impedance transmission portion 164 comprises a fourth end portion 1640 and a second coupled line 1642 coupled to the first coupled line 1622. The first connecting portion 182 or the second connecting portion 184 electrically connects the third end portion 1620 to the input portion 100 and the first end portion 142. The third connecting portion 184 or the fourth connecting portion 186 electrically connects the fourth end portion 1640 to the output portion 120 and the second end portion 144.
In this embodiment, the slot 170 is V-shaped. Alternatively, the slot 170 can be C-shaped, S-shaped, L-shaped, N-shaped, M-shaped, or W-shaped. That is, the second coupled line 1642 and the first coupled line 1622 have varied shapes, such that coupling capacitance between the first low impedance transmission portion 162 and the second low impedance transmission portion 164 varies.
In this embodiment, an overall length of the low-pass filter 10 is 5.82 mm, and an overall width of the low-pass filter 10 is 3.68 mm. An area of the low-pass filter 10 is 21.42 mm2, 30% less than exemplary low-pass filter 40.
In
S21=−10*Log [(Input Power)/(Output Power)].
When the electromagnetic signals pass the filter 10, a part of the input power is returned to a source of the electromagnetic signals, defined as a return power. Curve S11 indicates a relationship between the input power and the return power of the electromagnetic signals through the filter 10, and is represented by the formula:
S11=−10*Log [(Input Power)/(Return Power)].
For a filter, when the output power of the electromagnetic signal in a pass band frequency range approaches the input power of the electromagnetic signal, distortion of the electromagnetic signal is low and performance of the low-pass filter increased, there being an inverse relationship therebetween. As shown by curve S21 of
As shown in
While an embodiment of the present disclosure has been described, it should be understood that it has been presented by way of example only and not by way of limitation. Thus the breadth and scope of the present disclosure should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200810300620.1 | Mar 2008 | CN | national |
