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Microstrip Filters for RF/Microwave Applications, 2nd Edition by Jia-Sheng Hong

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CHAPTER TWELVE

Ultra-Wideband (UWB) Filters

Ultra-wideband (UWB) technology is being reinvented with many promising modern applications [1,2]. Ultra-wideband or broad-band microwave filters are essential components for these applications, such as UWB wireless and radar systems. The rapid growth in this field has prompted the development of various types of UWB filters [3–76]. In this chapter, typical types of UWB filters are described. This includes UWB filters comprised of short-circuit stubs, those using coupled single- or multimode resonators, or quasilumped elements, those based on cascaded high- and lowpass filters, and those with single- or multiple-notched bands.

12.1 UWB FILTERS WITH SHORT-CIRCUITED STUBS

12.1.1 Design of Stub UWB Filters

The optimum distributed highpass filter, which consists of short-circuited stubs, as introduced in Chapter 6, can be designed as an UWB bandpass filter [9]. Consider a filter design to have a passband covering the entire FCC-defined UWB band from 3.1 to 10.6 GHz [1]. Referring to Figure 6.3b, we can let the low cutoff frequency fc = fc1 = 3.1 GHz and the high cutoff frequency (π/θc - 1)/fc = fc2 = 10.6 GHz. Thus, the electrical length θc, referenced at the low cutoff frequency, can be found to be

(12.1) Numbered Display Equation

Table 12.1 tabulates some typical element values of the transmission line circuit in Figure 6.3a, where n is the number of short-circuited ...

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