high pass filter

BY ANIRBAN BHOWAL

RAHUL JAISWAL SHARAD KUMAR

QUASILUMPED ELEMENT

• Microstrip line short section and stubs whose physical length is smaller than λg/4 are used for microwave realization of lumped parameters in microstrip filter structures.

• These are termed as quasilumped elements.

• They can be also termed as lumped elements if their physical length is smaller than λg/8.

High impedance short line sections

If l < λg/8 then,

Low impedance short line sections

If l < λg/8 then,

• A transmission line of characteristic impedance Zu has a ABCD matrix given by:

Interconversion formula

Quasilumped high pass filters

• Highpass filters constructed from quasilumped elements may be desirable for many applications, provided that these elements can achieve good approximation of desired lumped elements over the entire operating frequency band.

• If the size of any quasilumped element becomes comparable with the wavelength of an operating frequency, it no longer behaves as a lumped element.

• The simplest form of a highpass filter may just consist of a series capacitor,which is often found in applications for direct current or dc block.

Continued…

• Highpass filter can be easily designed based on a lumped-element lowpass prototype such as one shown in figure, where gi denote the element values normalized by a terminating impedance Zo and obtained at a lowpass cutoff frequency Ωc.If we apply the frequency mapping

Where Ω , ω=angular frequency variables for low pass and high pass filter respectively ωc=cutoff frequency of high pass filter Ωc= cutoff frequnecy of low pass filter

Transformation from low pass prototype into high pass filter

Fig. (a) represents a low pass prototype filter and fig. (b) represents high pass filter transformed from low pass prototype

• Series inductive element in the lowpass prototype filter is transformed to a series capacitive element in the highpass filter, with a capacitance

• And shunt capacitive element in the lowpass prototype is transformed to a shunt inductive element in the highpass filter, with an inductance

EXAMPLE

• GIVEN DATA:- • Cutoff frequency:- 1.5GHz • Passband ripple:- 0.1dB • Source/load impedance:- 50 ohms • A Lowpass prototype with chebyshev response is

chosen. Element values are go= g4 =1 g1 =g3 = 1.0316 g2 = 1.1474 Ωc=1

Calculated values

Design parameters

• Dielectric constant=2.2 (RT/D 5880)

• Substrate thickness=1.57mm

• Cutoff frequency =1.5Ghz