*2.3.4. Two-SSIR filter*

Fig. 8(c) depicts schematics of the proposed two-SSIR bandpass filter. The dimensions of the resonators and the interdigital coupled lines are the same.

### **2.4. Experimental verification**

In this section, six UWB-bandpass filters are implemented on the RT/Duroid 3003 with a substrate thickness of 1.524 mm, and a dielectric constant of 3.0 at a central frequency of 6.85 GHz and a fractional bandwidth of 100%. Fig. 9 and Fig. 10 shows photographs of the fabricated SLTR and SSIR filters. Fig. 11 shows comparisons of measured and simulated responses of the SLTR and SSIR filters. In Fig. 11(a), (b) and (c), it can be found that the measured results agree very well with the simulation expectations, confirming that the proposed UWB-SLTR and SSIR bandpass filter is capable of reducing the insertion losses within the passband and also widening the upper stopband. The measured return and insertion losses are found to be higher than 14 dB and less than 2 dB over the UWBpassband, respectively. In Fig. 11(d), (e) and (f), two-SLTR and SSIR filter shows the improved upper stopband performance, with the return losses higher than 15 dB inside the passband. The lower and upper band skirts get sharpened to a great extent, while the upper stopband with the insertion losses above 15 dB occupies an enlarged range of 11.3–25 GHz. Also, the proposed two-SLTR filter with three slots has an improved upper stopband performance, as shown in Fig. 11 (e). A two- SSIR filter has improved the upper stopband performances, with the return losses higher than 15 dB outside the UWB-passband, and

**Figure 9.** Photographs of the fabricated single-filters: (a) single-SLTR, (b) single-SLTR with three slots, and (c) single-SSIR

resonators and the interdigital coupled lines are the same.

Fig. 8 depicts schematics of the bandpass filters with two linear tapered-line resonators connected in cascade. Fig. 8 (a) and (b) was the proposed SLTR filters with single- and threeslotted structures, respectively. All dimensions of the resonators and interdigital coupled

Fig. 8(c) depicts schematics of the proposed two-SSIR bandpass filter. The dimensions of the

In this section, six UWB-bandpass filters are implemented on the RT/Duroid 3003 with a substrate thickness of 1.524 mm, and a dielectric constant of 3.0 at a central frequency of 6.85 GHz and a fractional bandwidth of 100%. Fig. 9 and Fig. 10 shows photographs of the fabricated SLTR and SSIR filters. Fig. 11 shows comparisons of measured and simulated responses of the SLTR and SSIR filters. In Fig. 11(a), (b) and (c), it can be found that the measured results agree very well with the simulation expectations, confirming that the proposed UWB-SLTR and SSIR bandpass filter is capable of reducing the insertion losses within the passband and also widening the upper stopband. The measured return and insertion losses are found to be higher than 14 dB and less than 2 dB over the UWBpassband, respectively. In Fig. 11(d), (e) and (f), two-SLTR and SSIR filter shows the improved upper stopband performance, with the return losses higher than 15 dB inside the passband. The lower and upper band skirts get sharpened to a great extent, while the upper stopband with the insertion losses above 15 dB occupies an enlarged range of 11.3–25 GHz. Also, the proposed two-SLTR filter with three slots has an improved upper stopband performance, as shown in Fig. 11 (e). A two- SSIR filter has improved the upper stopband performances, with the return losses higher than 15 dB outside the UWB-passband, and

**Figure 9.** Photographs of the fabricated single-filters: (a) single-SLTR, (b) single-SLTR with three slots,

(a) (b) (c)

*2.3.3. Two-SLTR filter* 

lines have been shown.

*2.3.4. Two-SSIR filter* 

and (c) single-SSIR

**2.4. Experimental verification** 

**Figure 10.** Photographs of the fabricated two-filters: (a) two-SLTR, (b) two-SLTR with three slots, and (c) two-SSIR

insertion losses above 25 dB in a range of 19–25 GHz and above 47 dB at 24 GHz as shown in Fig. 11 (f). However, the measured passband insertion loss is higher than the simulation result due to the dimension of the conductor and further the conductivity slightly deviated from the design. The group delay of both filters slightly varies between 0.2 and 0.3 ns in the passband.
