Essay On Low Pass Filter

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3.1 Low Pass Filter
A low pass filter is a filter that passes low-frequency signals but attenuates frequencies higher than the cutoff frequency we can say that low pass filter has only single cutoff frequency and one pass band.It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter, and a band-pass filter is a combination of a low-pass and a high-pass filter. In low pass filter Inductors block high-frequency signals and conduct low-frequency signals, while capacitors do the reverse. A filter in which the signal passes through an inductor, or in which a capacitor provides a path to ground, presents less attenuation to low-frequency signals than high frequency signals [12].

L L
C

Figure 3.1 basic Low Pass Filter
The concept of a low-pass filter exists in many different forms, including electronic circuits, digital algorithms for smoothing sets of data, blurring of images, acoustic barriers, and so on. Low-pass filters play the same role in signal processing that moving averages do in some other fields, such as finance; both tools provide a smoother form of a signal which removes the short-term oscillations, leaving only the long-term trend. The inductors and capacitors are the reactive elements of the filter. The number of elements determines the order of the filter.

3.2 Low Pass prototype Filter
The design of low p...

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...h/W)-0.5] =0.88 3.13
& λgl = 300/(1.5√ εrel) = 53.300 mm 3.14
L1 = L3 = (Zo/go) (Ωc/2πfc) g1 = 8.209 Х 10-9 henery 3.15
C2 = (go/Zo) (Ωc/2πfc) g2 = 3.652 Х 10-12 farad 3.16 l1 = l3 = (λgl /2π) Sin-1 (ωc L1 / ZOL) =28.599 mm 3.17 l2 = (λgc /2π) Sin-1 (ωc C2 Zoc) = 8.25 mm 3.18

Figure 3.4. (a) Stepped Impedance, L-C Ladder Type LPF

Plots for transmission coefficient and reflection coefficient of simulate results are shown in figure 3.4(b)

Figure 3.4. (b) Response of the stepped impedance, L-C ladder type LPF

3.5 Concluding Remarks

Result shows the response of the proposed stepped impedance, L-C ladder type low pass filter. The graph is plotted by taking gain (dB) on the Y-axis and frequency in GHz on the X-axis. From the graph, it is clear that the cut-off frequency is found to be 1 GHz.

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