*4.2.1. SLTR filter with embedded fold-slot*

The UWB-bandpass filters using slotted linear tapered-line resonators (SLTR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances and using embedded fold-slot structure in the input feed line can create a notched band are proposed. Fig.18 (a) and 18 (b) show the SLTR and SLTR filters with three slots, using embedded fold-slot at the input feed for notched band. The two-cascaded SLTR with embedded fold-slot at input feed is also shown in Fig. 18 (c). All dimensions of the UWB-bandpass filters have been shown.

## *4.2.2. SSIR filter with embedded fold-slot*

Fig. 18 (d) shows the SSIR with embedded fold-slot at the input feed for notched band.

This section proposes a new UWB-bandpass filter with simple structures using slotted stepimpedance resonator (SSIR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded fold-slot in the input feed line can create a notched band.

**Figure 17.** Current distribution at 5.6 GHz of embedded structure: (a) the embedded structure, (b) the proposed embedded fold-slot structure

**Figure 18.** The proposed filters for notched band: (a) single-SLTR, (b) single-SLTR with three slot (c) two-SLTR, and (d) two-SSIR. The dimensions are as follows: *l1*=10*.*0mm, *l2*=6*.*45mm, *l3*=11*.*0mm, *l4*=5*.*4mm, *l5*=3.47mm, *l6*=6.5mm, *l7*=4.5mm, *l8*=2.0mm, *l9*=2.12mm, *l10*=1.47mm, *l11*=5.94mm, *w1*=4*.*0mm, *w2*=0*.*5mm, *w3*=5*.*5mm, *w4*=4*.*5mm, *w5*=0*.*5mm, *w6*=2*.*1mm, *w7*=0*.*52mm and *g1*=0*.*2mm

**Figure 19.** Embedded fold-slot feed

**4.2. Filter designs and measured results** 

*4.2.1. SLTR filter with embedded fold-slot* 

UWB-bandpass filters have been shown.

*4.2.2. SSIR filter with embedded fold-slot* 

input feed line can create a notched band.

(b) the proposed embedded fold-slot structure

embedded slot feed line and the embedded fold-slot feed line.

UWB- bandpass filter when a notched band is required. To creat the notched band at 5.6 GHz, the dimensions of the proposed embedded fold-slot feed include *l11* = 5.94 mm, *w5* = 0.8 mm, and g*<sup>1</sup>* = 0.2 mm. To verify the notched mechanism, the current distributions of embedded fold-slot structure at 5.6 GHz notch frequency are shown in Fig. 17. We can notice that in Fig. 17 (a) and (b) the current distribution cannot passes through the

The UWB-bandpass filters using slotted linear tapered-line resonators (SLTR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances and using embedded fold-slot structure in the input feed line can create a notched band are proposed. Fig.18 (a) and 18 (b) show the SLTR and SLTR filters with three slots, using embedded fold-slot at the input feed for notched band. The two-cascaded SLTR with embedded fold-slot at input feed is also shown in Fig. 18 (c). All dimensions of the

Fig. 18 (d) shows the SSIR with embedded fold-slot at the input feed for notched band.

**Figure 17.** Current distribution at 5.6 GHz of embedded structure: (a) the embedded structure,

This section proposes a new UWB-bandpass filter with simple structures using slotted stepimpedance resonator (SSIR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded fold-slot in the

UWB-Bandpass Filters with Improved Stopband Performance 313

Fig. 20 shows the photograph of the fabricated SLTR and SSIR filters for notched band. Fig. 21 shows a comparison of measured and simulated responses of the SLTR and SSIR filters with a notched band. The measured and simulated results have shown good agreement with a notch is capable of narrowing notched band, having good insertion losses within the passband and also widening the upper stopband. The measured return and insertion losses are found to be lower than 10 dB and higher than 2 dB, respectively over desired UWBpassband. The notched frequency of about 5.6 GHz has a bandwidth of about 276 MHz. The proposed filters show narrow notched band and improved upper stopband performance with high insertion loss. The upper stopband with the insertion loss lower than 10 dB occupies an enlarged range of 14 to 18 GHz. The group delay of both filters slightly varies between 0.2 to 0.3 ns in the passband. These superior stopband performances are caused by the stopband characteristics of the proposed slotted resonator structure, and narrow

In this chapter, the novel SLTR and SSIR UWB-bandpass filters with improved upper stopband performances have been presented and implemented. By properly forming SLTR and SSIR together with two interdigital coupled lines at both ends, the proposed filters are designed and constructed. The single-SLTR and SSIR filters show their performances in suppression of spurious responses. Also, two-SLTR and two-SSIR filters are designed and fabricated to show that they improve the passband and upper stopband performances with sharpened rejection skirts outside the passband and widened upper stopband. When comparing with SLTRs, we find that the SSIR structures are easier to design and fabricate and they also have better stopband characteristics. In addition, the SLTR and SSIR filters using embedded slot and embedded fold-slot with notched band, reduce size and improved upper stopband performances have been presented and implemented. The proposed filters demonstrate their capability in narrow notched band with the embedded slot, embedded fold-slot feed and suppression of spurious responses with slotted resonators. Also, the fabricated filters prove that they can create notched band and improve upper stopband

performances with sharpened rejection and widen the upper stopbands.

*Department of Special Investigation (DSI), Thailand*  Sarawuth Chaimool and Prayoot Akkaraekthalin

*King Mongkut's University of Technology, North Bangkok, Thailand* 

**4.3. Experimental verification** 

**5. Conclusion** 

**Author details** 

Mongkol Meeloon

notched band is caused by embedded fold-slot structure.

**Figure 20.** Photographs of fabricated UWB-filters for notched band: (a) single-SLTR, (b) two-SLTR, (c) two-SLTR and (d) two-SSIR

**Figure 21.** Comparisons of measured and simulated responses of the filters: (a) single-SLTR, (b) single-SLTR with three slots, (c) two-SLTR, (d) two –SSIR
