Highpass and Bandstop Filters In this chapter, we will discuss some typical microstrip highpass and bandstop filters. These include quasilumped element and optimum distributed highpass filters, narrow-band and wide-band bandstop filters, as well as filters for RF chokes. Design equations, tables, and examples are presented for easy reference. | Microstrip Filters for RF Microwave Applications. Jia-Sheng Hong M. J. Lancaster Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-38877-7 Hardback 0-471-22161-9 Electronic CHAPTER 6 Highpass and Bandstop Filters In this chapter we will discuss some typical microstrip highpass and bandstop filters. These include quasilumped element and optimum distributed highpass filters narrow-band and wide-band bandstop filters as well as filters for RF chokes. Design equations tables and examples are presented for easy reference. HIGHPASS FILTERS Quasilumped Highpass 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. Care should be taken when designing this type of filter because as 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. For more selective highpass filters more elements are required. This type of highpass filter can be easily designed based on a lumped-element lowpass prototype such as one shown in Figure a where gi denote the element values normalized by a terminating impedance Z0 and obtained at a lowpass cutoff frequency i T. Following the discussions in the Chapter 3 if we apply the frequency mapping vil. n - w where Í1 and w are the angular frequency variables of the lowpass and highpass filters respectively and wc is the cutoff frequency of the highpass filter. Any series in- 161 162 HIGHPASS AND BANDSTOP FILTERS a C C3 Cn Zo Zn 1 b FIGURE a A lowpass prototype filter. b Highpass filter transformed from the lowpass prototype. ductive element in the lowpass prototype filter is transformed to a series capacitive element in the .
