**3. UWB-bandpass filters with embedded slot**

This section proposes new UWB-bandpass filters using slotted linear tapered-line resonators (SLTR) and slotted step-impedance resonator (SSIR) structures driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded slot structure in the input and output feed line can create a notched band.

UWB-Bandpass Filters with Improved Stopband Performance 305

**3.1. Embedded slot feed characteristics** 

8.543 mm, *w* = 0.8 mm, and g = 0.2 mm.

proposed structure as shown in Fig.13 (b).

varying L (b) varying W

The embedded slot at the feed line has been proposed in order to form a notch band. The RT/Duroid 3003 substrate has been used in this study. Fig.12 (a) shows the part of embedded slot feed and its frequency responses of *S21* when varying the length L of the embedded slot from 5 to 10 mm. It can be found that a center frequency of notched frequency can be adjusted from 9 GHz down to 5 GHz. When increasing the width W of the embedded slot while keeping the center frequency to be the same, the bandwidth of notched band is increased as shown in Fig. 12 (b). The summary of geometry parameters for the embedded slot structure when varying the width W of the embedded slot from 0.6 to 1.6 mm and varying the length L of the embedded slot from 8.593 to 8.393 mm is shown in Table.1. It can be clearly seen that at 3 dB bandwidth of the notched band is increased from 220 to 810 MHz. Therefore, by tuning the length and width of the embedded slot, center frequencies and bandwidth of notched band can be easily adjusted. Embedded slot is thus suitable for use in the UWB-bandpass filter when a notched band is required. To creat the notched band at 5.6 GHz, the dimensions of the proposed embedded slot feed include *l* =

To verify the notched mechanism, the current distributions of embedded structure at 5.6 GHz notch frequency are shown in Fig.13. We can notice that in Fig. 13 (a) the current distribution passes through the conventional feed line but it cannot pass through the

**Figure 12.** *S21* magnitude responses of the embedded slot structure with a slot of 0.2 mm when: (a)

(a) (b)

**Figure 11.** Comparisons of measured and simulated responses of the filters: (a) single-SLTR, (b) single-SLTR with three slots, (c) single-SSIR, (d) two-SLTR, (e) two-SLTR with three slots and (f) two-SSIR

#### **3.1. Embedded slot feed characteristics**

304 Ultra Wideband – Current Status and Future Trends

**Figure 11.** Comparisons of measured and simulated responses of the filters: (a) single-SLTR, (b) single-SLTR with three slots, (c) single-SSIR, (d) two-SLTR, (e) two-SLTR with three slots and (f) two-SSIR

(e) (f)

(a) (b)

(c) (d)

The embedded slot at the feed line has been proposed in order to form a notch band. The RT/Duroid 3003 substrate has been used in this study. Fig.12 (a) shows the part of embedded slot feed and its frequency responses of *S21* when varying the length L of the embedded slot from 5 to 10 mm. It can be found that a center frequency of notched frequency can be adjusted from 9 GHz down to 5 GHz. When increasing the width W of the embedded slot while keeping the center frequency to be the same, the bandwidth of notched band is increased as shown in Fig. 12 (b). The summary of geometry parameters for the embedded slot structure when varying the width W of the embedded slot from 0.6 to 1.6 mm and varying the length L of the embedded slot from 8.593 to 8.393 mm is shown in Table.1. It can be clearly seen that at 3 dB bandwidth of the notched band is increased from 220 to 810 MHz. Therefore, by tuning the length and width of the embedded slot, center frequencies and bandwidth of notched band can be easily adjusted. Embedded slot is thus suitable for use in the UWB-bandpass filter when a notched band is required. To creat the notched band at 5.6 GHz, the dimensions of the proposed embedded slot feed include *l* = 8.543 mm, *w* = 0.8 mm, and g = 0.2 mm.

To verify the notched mechanism, the current distributions of embedded structure at 5.6 GHz notch frequency are shown in Fig.13. We can notice that in Fig. 13 (a) the current distribution passes through the conventional feed line but it cannot pass through the proposed structure as shown in Fig.13 (b).

**Figure 12.** *S21* magnitude responses of the embedded slot structure with a slot of 0.2 mm when: (a) varying L (b) varying W

UWB-Bandpass Filters with Improved Stopband Performance 307

*w1*

**Figure 14.** The proposed filters for notched band: (a) single-SLTR, (b) two-SLTR, (c) single-SSIR and (d) single-SSIR with dual-notched band. The dimensions are as follows: *l1*=16*.*0mm, *l2*=6*.*45mm, *l3*=11*.*0mm, *l4*=3*.*47mm, *l5*=8.543mm, *l6*=6.5mm, *l7*=4.5mm, *l8*=5.54mm, *w1* = 4*.*0mm, *w2* = 0*.*5mm, *w3* = 0*.*8mm, *w4* =

(d)

*g1 l7 l7*

(a)

*l1 l2 l3 l2 l1*

*l6*

*l3*

*g1 g1*

*w5 w5*

*g1*

*l4*

*l4g1 l4 l4g1*

*g1 l3 l2 l1*

*g1 l3 l2 l1*

*w3*

*g1 l8*

*g1*

*g1*

*w w4 <sup>2</sup>*

*g1*

*l4 g1 l4 l4g1*

*g1 l5 l4*

*w w4 <sup>2</sup>*

*g1*

*l4 g1 l4 l4g1*

*g1 l5 l4*

*l1 l2*

*l1 l2*

*g1*

*l5*

*g1*

*l5*

*w5 w5*

*g1 g1*

*l1 l2 l3 l2 l1*

*g1 g1*

*w1 w1*

*w5 w5*

*w w4 <sup>2</sup>*

(b)

(c)

*w1 w1*

*w2*

*w4*

*g1 l7 l7*

*w1 w1*

*w2*

*w4*

Fig.15 (a) shows photograph of the fabricated single-SLTR for notched band. Fig. 16 (a) shows a comparison of measured and simulated responses of the single-SLTR filter with a notched band. The measured results are agreed very well with the simulation predictions,

5*.*5mm, *w5* = 4*.*5mm and *g1* = 0*.*2mm

*w3*

*w1*

*w3*

*w3*

*w3*

**3.3. Experimental verification** 

**Figure 13.** Current distribution at 5.6 GHz of embedded structure: (a) a conventional feed line and (b) the proposed embedded structure


**Table 1.** Geometry parameters for the embedded slot structure

### **3.2. Filter designs and measured results**

#### *3.2.1. SLTR filter with three slots and embedded slot*

The UWB-bandpass filters using slotted linear tapered-line resonators (SLTR) with three slots are proposed. The filters consists of the interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded slot structure in the input feed line can create a notched band. Fig.14 (a) shows the SLTR with three slots and one embedded slot at the input feed for notched band. The two-cascaded SLTR with three slots and one embedded slot at input feed is also shown in Fig. 14 (b). All dimensions of the UWB-bandpass filters have been shown.

#### *3.2.2. SSIR filter with embedded slot*

Fig.14 (c) shows the SSIR with one embedded slot at the input feed for notched band. The SSIR with embedded slot at input and output feed for dual-notched is also shown in Fig.14(d). This section proposes UWB-bandpass filters using slotted step-impedance resonator (SSIR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded slot structure in the feed line can create a notched band.

(a)

(b)

(d)

**Figure 14.** The proposed filters for notched band: (a) single-SLTR, (b) two-SLTR, (c) single-SSIR and (d) single-SSIR with dual-notched band. The dimensions are as follows: *l1*=16*.*0mm, *l2*=6*.*45mm, *l3*=11*.*0mm, *l4*=3*.*47mm, *l5*=8.543mm, *l6*=6.5mm, *l7*=4.5mm, *l8*=5.54mm, *w1* = 4*.*0mm, *w2* = 0*.*5mm, *w3* = 0*.*8mm, *w4* = 5*.*5mm, *w5* = 4*.*5mm and *g1* = 0*.*2mm

#### **3.3. Experimental verification**

306 Ultra Wideband – Current Status and Future Trends

the proposed embedded structure

**Table 1.** Geometry parameters for the embedded slot structure

*3.2.1. SLTR filter with three slots and embedded slot* 

**3.2. Filter designs and measured results** 

of the UWB-bandpass filters have been shown.

*3.2.2. SSIR filter with embedded slot* 

can create a notched band.

**Figure 13.** Current distribution at 5.6 GHz of embedded structure: (a) a conventional feed line and (b)

W(mm) L(mm) BW(MHz)<-3 dB 0.6 8.593 220 0.8 8.543 250 1.0 8.493 360 1.2 8.483 470 1.4 8.423 720 1.6 8.393 810

The UWB-bandpass filters using slotted linear tapered-line resonators (SLTR) with three slots are proposed. The filters consists of the interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded slot structure in the input feed line can create a notched band. Fig.14 (a) shows the SLTR with three slots and one embedded slot at the input feed for notched band. The two-cascaded SLTR with three slots and one embedded slot at input feed is also shown in Fig. 14 (b). All dimensions

Fig.14 (c) shows the SSIR with one embedded slot at the input feed for notched band. The SSIR with embedded slot at input and output feed for dual-notched is also shown in Fig.14(d). This section proposes UWB-bandpass filters using slotted step-impedance resonator (SSIR) driven by interdigital coupled lines at both ends of the resonators for improving the stopband performances. Also, using embedded slot structure in the feed line

Fig.15 (a) shows photograph of the fabricated single-SLTR for notched band. Fig. 16 (a) shows a comparison of measured and simulated responses of the single-SLTR filter with a notched band. The measured results are agreed very well with the simulation predictions,

confirming that the proposed SLTR filter with a notch is capable of narrow notched band, 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 over desired UWB passband, respectively. Fig. 15 (b) shows photograph of the fabricated two-SLTR filter. Fig. 16 (c) shows a comparison of measured and simulated responses of the two-SLTR filter, which a good agreement has been obtained for passband and sharp rejection skirt in upper stop band. The measured return and insertion losses of the two-SLTR filter are found to be higher than 2 dB and lower than 10 dB at the notched frequencies about 5.6 GHz which the bandwidth of notched band are about 276 MHz. Fig. 15 (c) and (d) show photograph of the fabricated SSIR filter with single and dual-notched band. Fig. 16 (c) and (d) show a comparison of measured and simulated responses of the SSIR filters with single and dual-notched band at the notched frequencies about 5.6 GHz and 8.3 GHz which the bandwidth of notched band are about 276 MHz and 300 MHz, respectively. The proposed filters show improved upper stopband performance with high insertion loss. The upper stopband with the insertion loss lower than 15 dB occupies an enlarged range of 12 to 18 GHz. As we can see that the proposed filter exhibits notched and dual- notched band, a wide upper stopband with values of *S21* lower than 30 dB at 15 GHz, 10 dB at about 18 GHz. These superior upper stopband performances are caused by the stopband characteristics of the proposed slotted resonator structure and narrow notched band by embedded slot structure. The group delay of fourth filters slightly varies between 0.2 and 0.3 ns in the passband.

UWB-Bandpass Filters with Improved Stopband Performance 309

**Figure 16.** Comparisons of measured and simulated responses of the filters: (a) single-SLTR, (b) two-

(c) (d)

(a) (b)

By modifying the UWB-bandpass filters with embedded slot, the embedded slot can be reduce size using embedded fold-slot. It usies slotted linear tapered-line resonator (SLTR) and slotted step-impedance resonator (SSIR) driven by interdigital coupled lines at both

The embedded fold-slot at the input feed has been proposed in order to form a notch band. The RT/Duroid 3003 substrate has been used in this study. Therefore, by tuning the length and width of the embedded slot from previous section, center frequencies and bandwidth of notched band can be easily adjusted. Embedded fold-slot is thus suitable for use in the

SLTR, (c) single-SSIR and (d) single-SSIR with dual-notched band

**4. UWB-bandpass filters with embedded fold-slot**

ends of the resonator to improve the stopband performances.

**4.1. Embedded fold-slot feed characteristics** 

**Figure 15.** Photographs of fabricated UWB filters for notched band: (a) single-SLTR, (b) two-SLTR, (c) single-SSIR and (d) single-SSIR with dual-notched band

**Figure 16.** Comparisons of measured and simulated responses of the filters: (a) single-SLTR, (b) two-SLTR, (c) single-SSIR and (d) single-SSIR with dual-notched band

### **4. UWB-bandpass filters with embedded fold-slot**

By modifying the UWB-bandpass filters with embedded slot, the embedded slot can be reduce size using embedded fold-slot. It usies slotted linear tapered-line resonator (SLTR) and slotted step-impedance resonator (SSIR) driven by interdigital coupled lines at both ends of the resonator to improve the stopband performances.

#### **4.1. Embedded fold-slot feed characteristics**

308 Ultra Wideband – Current Status and Future Trends

passband.

confirming that the proposed SLTR filter with a notch is capable of narrow notched band, 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 over desired UWB passband, respectively. Fig. 15 (b) shows photograph of the fabricated two-SLTR filter. Fig. 16 (c) shows a comparison of measured and simulated responses of the two-SLTR filter, which a good agreement has been obtained for passband and sharp rejection skirt in upper stop band. The measured return and insertion losses of the two-SLTR filter are found to be higher than 2 dB and lower than 10 dB at the notched frequencies about 5.6 GHz which the bandwidth of notched band are about 276 MHz. Fig. 15 (c) and (d) show photograph of the fabricated SSIR filter with single and dual-notched band. Fig. 16 (c) and (d) show a comparison of measured and simulated responses of the SSIR filters with single and dual-notched band at the notched frequencies about 5.6 GHz and 8.3 GHz which the bandwidth of notched band are about 276 MHz and 300 MHz, respectively. The proposed filters show improved upper stopband performance with high insertion loss. The upper stopband with the insertion loss lower than 15 dB occupies an enlarged range of 12 to 18 GHz. As we can see that the proposed filter exhibits notched and dual- notched band, a wide upper stopband with values of *S21* lower than 30 dB at 15 GHz, 10 dB at about 18 GHz. These superior upper stopband performances are caused by the stopband characteristics of the proposed slotted resonator structure and narrow notched band by embedded slot structure. The group delay of fourth filters slightly varies between 0.2 and 0.3 ns in the

**Figure 15.** Photographs of fabricated UWB filters for notched band: (a) single-SLTR, (b) two-SLTR,

(c) (d)

(a) (b)

(c) single-SSIR and (d) single-SSIR with dual-notched band

The embedded fold-slot at the input feed has been proposed in order to form a notch band. The RT/Duroid 3003 substrate has been used in this study. Therefore, by tuning the length and width of the embedded slot from previous section, center frequencies and bandwidth of notched band can be easily adjusted. Embedded fold-slot is thus suitable for use in the

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

UWB-Bandpass Filters with Improved Stopband Performance 311

*w2 w2 w2*

*g1*

*w1*

*l3 g1 l1 l2*

**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,

(d)

(a)

*w1 w1*

*w4 w4*

*l4 g1 l4*

*w1 w1*

*w3*

*g1 l3 l2 l1*

*g1 l3 l2 l1 g1*

*w2 w3*

*g1*

*l1 l2*

*l1 l2*

*l1 l2 g1 l6*

*w3*

*l3*

*g1*

(b)

*w2 w2*

*w3*

*w w3 <sup>2</sup>*

*g1 g1 l6*

*l7 l8*

*g1*

*g1 g1 l5 l5 l5 l5*

*w1 w2*

(c)

*g1 g1 l3*

*l4 l4 l4 g1 l4*

*l1 l2 l3 l2 l1*

*w1 w2 w3 w1*

*l7 l7 l8 l7*

*l9*

*l11*

*<sup>w</sup> l9 l10 <sup>7</sup>*

*g1*

*l9*

*w6*

*w5*

*w2*=0*.*5mm, *w3*=5*.*5mm, *w4*=4*.*5mm, *w5*=0*.*5mm, *w6*=2*.*1mm, *w7*=0*.*52mm and *g1*=0*.*2mm

*w1*

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