More Practical Filters and Couplers: A Collection from Applied Microwave & Wireless
With additional articles on filter and coupler design, this collection focuses on tunable structures and couplers.
TABLE OF CONTENTS More Practical Filters and Couplers: A Collection from Applied Microwave & Wireless
Design of a Simple Tunable/Switchable Band-Pass Filter
Adaptive and multimode wireless equipment can benefit from filters that can vary their center frequency and bandwidth
By K.Jeganathan
Overview
From APPLIED MICROWAVE & WIRELESS, VOL. 12, NO. 3, MARCH 2000
As the frequency spectrum gets crowded, with an increasing number of communication devices operating in a particular band, the role of the filter is becoming more and more critical. Since multimode portable terminals and tunable transceivers are starting to appear in the market, the importance of tunable filters is gaining momentum in the area of mobile communications. What is needed is a simple, cheap and small solution. Tunable filters greatly simplify the transceiver design and play a major role, especially in the area of wideband and multimode transceivers. This article reviews some of the fundamentals of the LC-tuned resonator circuit and its implementation as a tunable or switchable band-pass filter and provides a feasible solution for the above applications in the UHF and VHF band.
LC Resonator
The simplest band-pass filter is a series or parallel LC tuned circuit. Figure 1a shows the resonant circuit that is connected to a source of resistance of R s. Using the voltage division rule, it can be shown that
where
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X t= X L X C/( X L+ X C)
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X C=1/ jwc
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X L= jwl
Figure 1a: The resonant circuit connected to a source of resistance of R s.
After some mathematical manipulation, we will arrive at
Figure 1b shows the corresponding...
Copyright Noble Publishing Corporation 2002 under license agreement with Books24x7
