**4. Triangular loop-loaded band-notched UWB filter**

#### **4.1. Dual-stub-loaded slot-line MMR**

resonator is loaded to the slot-line, and a notch band for WLAN is produced, as shown in **Figure 10**. The dual-mode resonator is folded in order to improve the slow-wave effect for miniaturization. A substrate of 28 mm × 18 mm with a relative dielectric constant of ε<sup>r</sup> = 3.5 and a thickness of h = 0.8 mm is used in the design. Finally obtained parameters of the filter shown in **Figure 1** are *W*<sup>0</sup> = 1.80 mm, *L*<sup>1</sup> = 3.80 mm, *L*<sup>2</sup> = 4.70 mm, *W*<sup>1</sup> = 1.50 mm, *L*<sup>3</sup> = 8.00 mm, *W*<sup>2</sup> = 0.30 mm, *L*<sup>4</sup> = 17.40 mm, *W*<sup>3</sup> = 0.60 mm, *L*<sup>5</sup> = 3.70 mm, *W*<sup>4</sup> = 0.50 mm, *L*<sup>6</sup> = 3.80 mm, *W*<sup>5</sup> = 0.30 mm, *L*<sup>7</sup> = 2.50 mm, *W*<sup>6</sup> = 0.30 mm, *L*<sup>8</sup> = 3.50 mm, and *r* = 0.55 mm. Measurements are

**Figure 10.** Configurations of the proposed band-notched UWB BPF using dual-mode microstrip resonator-loaded three-

**Figure 9.** The transmission characteristic of the simplified resonator with varied parameters. (a) L and (b) S.

A comparison between the simulated and measured results is shown in **Figure 11**, where the solid lines and the dashed lines indicate the EM-simulated results and measured results, respectively. Simulated results show that the 3-dB bandwidth of the filter covers from 3.1 to 5.15 GHz and from 5.35 to 10.6 GHz, while the measured ones show that the 3-dB bandwidth covers from 3.2 to 5.15GHz and from 5.35 to 10.6GHz. Simulated and measured insertion losses of each passband are about 2 dB; return losses are −12 dB/−18 dB and − 18 dB/−10 dB. Return loss in the notch band is greater than 15 dB. Except for the deviation that may be caused by

the fabrication, the simulated results agree well with the measured results.

performed by using vector network analyzer AV3926.

stub-loaded slot-line MMR. (a) Top view and (b) bottom view.

50 UWB Technology and its Applications

Two stubs are symmetrically loaded to slot-line, which forms a dual-stub-loaded slot-line MMR, as shown in **Figure 12(a)**. Because the proposed slot-line MMR is a symmetrical structure, even-odd mode theory can be applied to analyze its resonant characteristics. **Figure 12(b)** and **(c)** gives equivalent circuits of the slot-line MMR.

Under odd-mode excitation, the symmetrical plane can be seemed as short-circuited, and its resonant condition can be derived as

$$Z\_{\mathfrak{g}} \tan \theta\_{\mathfrak{g}} \tan \theta\_{\mathfrak{c}} + Z\_{\mathfrak{g}} \tan \theta\_{\mathfrak{g}} \tan \theta\_{\mathfrak{A}} + Z\_{\mathfrak{A}} \tan \theta\_{\mathfrak{A}} \tan \theta\_{\mathfrak{c}} = 0 \tag{2}$$

where *Z*A and *Z*B and *θ*A, *θ*B, and *θ*C are the characteristic impedance and electrical length of the dual-stub-loaded MMR, respectively.

Under even-mode excitation, the symmetrical plane can be seemed as open-circuited, and its resonant condition can be summarized as

$$Z\_{\rm A} \tan \theta\_{\rm A} + Z\_{\rm B} \tan \theta\_{\rm B} = Z\_{\rm B} \tan \theta\_{\rm A} \tan \theta\_{\rm B} \tan \theta\_{\rm C} \tag{3}$$

Resonant modes of the resonator can be controlled and allocated according to the requirements by changing the parameters of the resonator.

To have a clear knowledge of slot-line resonator, resonant characteristics of the dual-stubloaded slot-line resonator are performed by invoking the 3D EM simulator. Resonant modes

**Figure 12.** (a) Dual-stub-loaded slot-line MMR and its equivalent circuits: (b) odd mode and (c) even mode.

of slot-line resonator against *S*, *L*<sup>1</sup> , and *L*<sup>2</sup> are plotted in **Figure 13**, where *f* 1 , *f* 2 , and *f* 3 indicate the first, second, and third resonant modes of resonator, respectively. When *S* increases from 0.2 to 2.2 mm, *f* 3 decreases from 9.6 to 8.2 GHz, while *f* 1 and *f* 2 shift slightly. When *L*<sup>1</sup> increases from 23 to 25 mm, both *f* 1 and *f* 2 , together with *f* 3 decrease steadily. When *L*<sup>2</sup> increases from 1 to 6 mm, *f* 2 drops from 8.2 to 6.5 GHz, *f* 3 drops from 13.5 to 8 GHz, and *f* 1 keeps unchanged. Obviously, three resonant modes of the resonator can be designed intuitively and well set in the UWB passband.

#### **4.2. Ultra-wideband BPF using dual-stub-loaded slot-line MMR**

Layout of a proposed UWB BPF is depicted in **Figure 14**, which is constructed by a slot-line resonator and two microstrip feed lines. On the bottom layer, a dual-stub-loaded slot-line resonator is formed firstly, where two identical stubs are symmetrically loaded to a uniform slot-line resonator. **Figure 15** illustrates the frequency responses of the slot-line UWB BPF with different lengths of feed line (L4) under all the other sizes fixed. When the slot-line resonator is fed under weak coupling case with *L*<sup>4</sup> = 4.8 mm, three resonant modes with peak S21 magnitudes are observed at about 4.08, 6.41, and 9.5 GHz, respectively. As *L*<sup>4</sup> increases to 10 mm, the S21 magnitude realizes an almost flat frequency response over a UWB passband. After its sizes are slightly adjusted, an UWB frequency response is satisfactorily realized. Under the use of this hybrid microstrip/slot-line structure, the desired strong coupling between feed lines and MMR can be easily achieved by properly selecting the relative position between them.

**4.3. Realization of notch band**

(a) *S* (*L*<sup>1</sup> = 23 mm, *L*<sup>2</sup> = 3 mm), (b) *L*<sup>1</sup>

Considering the fact that the above-achieved UWB passband range may interfere with the existing wireless systems such as wireless local area network (WLAN), a notch band may be

**Figure 14.** Schematic of the UWB BPF using dual-stub-loaded slot-line MMR. (a) Top layer and (b) bottom layer.

**Figure 13.** Resonant modes of dual-stub-loaded slot-line resonator with fixed *W*<sup>1</sup> = 2.0 mm, *W*<sup>2</sup> = 0.3 mm, and varied

(*S* = 0.6 mm, *L*<sup>1</sup> = 23 mm).

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(*S* = 0.6 mm, *L*<sup>2</sup> = 3 mm), and (c) *L*<sup>2</sup>

Slot-Line UWB Bandpass Filters and Band-Notched UWB Filters http://dx.doi.org/10.5772/intechopen.80004 53

**Figure 13.** Resonant modes of dual-stub-loaded slot-line resonator with fixed *W*<sup>1</sup> = 2.0 mm, *W*<sup>2</sup> = 0.3 mm, and varied (a) *S* (*L*<sup>1</sup> = 23 mm, *L*<sup>2</sup> = 3 mm), (b) *L*<sup>1</sup> (*S* = 0.6 mm, *L*<sup>2</sup> = 3 mm), and (c) *L*<sup>2</sup> (*S* = 0.6 mm, *L*<sup>1</sup> = 23 mm).

**Figure 14.** Schematic of the UWB BPF using dual-stub-loaded slot-line MMR. (a) Top layer and (b) bottom layer.

#### **4.3. Realization of notch band**

of slot-line resonator against *S*, *L*<sup>1</sup>

3

from 23 to 25 mm, both *f*

52 UWB Technology and its Applications

2

the UWB passband.

between them.

0.2 to 2.2 mm, *f*

to 6 mm, *f*

, and *L*<sup>2</sup>

, together with *f*

**Figure 12.** (a) Dual-stub-loaded slot-line MMR and its equivalent circuits: (b) odd mode and (c) even mode.

3

S21 magnitudes are observed at about 4.08, 6.41, and 9.5 GHz, respectively. As *L*<sup>4</sup>

decreases from 9.6 to 8.2 GHz, while *f*

**4.2. Ultra-wideband BPF using dual-stub-loaded slot-line MMR**

1 and *f* 2

drops from 8.2 to 6.5 GHz, *f*

the first, second, and third resonant modes of resonator, respectively. When *S* increases from

Obviously, three resonant modes of the resonator can be designed intuitively and well set in

Layout of a proposed UWB BPF is depicted in **Figure 14**, which is constructed by a slot-line resonator and two microstrip feed lines. On the bottom layer, a dual-stub-loaded slot-line resonator is formed firstly, where two identical stubs are symmetrically loaded to a uniform slot-line resonator. **Figure 15** illustrates the frequency responses of the slot-line UWB BPF with different lengths of feed line (L4) under all the other sizes fixed. When the slot-line resonator is fed under weak coupling case with *L*<sup>4</sup> = 4.8 mm, three resonant modes with peak

to 10 mm, the S21 magnitude realizes an almost flat frequency response over a UWB passband. After its sizes are slightly adjusted, an UWB frequency response is satisfactorily realized. Under the use of this hybrid microstrip/slot-line structure, the desired strong coupling between feed lines and MMR can be easily achieved by properly selecting the relative position

3

are plotted in **Figure 13**, where *f*

drops from 13.5 to 8 GHz, and *f*

decrease steadily. When *L*<sup>2</sup>

1 and *f* 2 1 , *f* 2 , and *f* 3

1

shift slightly. When *L*<sup>1</sup>

indicate

increases

increases

increases from 1

keeps unchanged.

Considering the fact that the above-achieved UWB passband range may interfere with the existing wireless systems such as wireless local area network (WLAN), a notch band may be highly demanded in various practical applications. For this purpose, a microstrip dual-mode triangular loop resonator is formed on the top layer of a dielectric substrate and loaded to the dual-stub-loaded slot-line MMR.

**Figure 16** depicts the geometry, equivalent circuit model, and simulated frequency response of a slot-line loaded with back-sided microstrip triangular loop resonator, respectively. **Figure 16(a)** shows a simplified circuit geometry of the structure, where the white portion indicates the slot-line and the black ones are microstrip feed lines and a dual-mode triangular loop resonator with perturbations. Its equivalent circuit model is given in **Figure 16(b)**. Coupling between dual-mode resonator and source/load can be intuitively neglected because its value is quite small. **Figure 16(c)** plots the simulated results derived from the equivalent circuit model, where the solid and dashed lines indicate the simulated reflection and transmission coefficients, respectively. Two transmission zeros in the notch band are created by the resonant modes of the microstrip resonator.

Next, two small patches are symmetrically added as the perturbation element to the lower angles of the triangular loop resonator. These perturbations can accomplish the further separation of the two degenerate modes, creating the dual-mode behavior of the resonator. Resonant modes of the triangular loop resonator are coupled to the slot-line, providing a bypass for the adjacent signal of its resonance, and a notch band is thus created. **Figure 17(a)** shows the transmission characteristics of the resonator versus *L*<sup>5</sup> , that is, the perimeter of a triangular loop resonator. As *L*<sup>5</sup> increases from 31 to 37 mm, the central frequency of notch band falls off from 6.25 to 5.39 GHz, and its absolute bandwidth decreases from 1.49 to 1.37 GHz. Obviously, the perimeter of triangular loop resonator can directly determine the position of the notch band. **Figure 17(b)** illustrates the influence on the frequency response from varied *W*5 and width of two patches. As *W*<sup>5</sup> increases from 0.2 to 1.0 mm, the notch bandwidth goes up from 1.52 to 1.79 GHz. These exhibited characteristics can be used to determine the central frequency and bandwidth of the created notch band; thus the notch band of the UWB BPF can be fully controlled.

**Figure 15.** Frequency responses of transmission coefficient of the proposed UWB BPF with different feeding line lengths (*L*4 ).

**4.4. Filter implementation and results**

 and (b) *W*<sup>5</sup> .

(c) simulated results.

slot-line against (a) *L*<sup>5</sup>

Based on the filter structure and analysis approach described above, a UWB BPF with a controllable notch band is designed and fabricated on a substrate with a dielectric constant of

**Figure 17.** Frequency-dependent transmission coefficient of the proposed dual-mode triangular loop resonator-loaded

**Figure 16.** A microstrip triangular loop resonator-loaded slot-line. (a) Diagram, (b) equivalent circuit model, and

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**Figure 16.** A microstrip triangular loop resonator-loaded slot-line. (a) Diagram, (b) equivalent circuit model, and (c) simulated results.

**Figure 17.** Frequency-dependent transmission coefficient of the proposed dual-mode triangular loop resonator-loaded slot-line against (a) *L*<sup>5</sup> and (b) *W*<sup>5</sup> .

#### **4.4. Filter implementation and results**

highly demanded in various practical applications. For this purpose, a microstrip dual-mode triangular loop resonator is formed on the top layer of a dielectric substrate and loaded to the

**Figure 16** depicts the geometry, equivalent circuit model, and simulated frequency response of a slot-line loaded with back-sided microstrip triangular loop resonator, respectively. **Figure 16(a)** shows a simplified circuit geometry of the structure, where the white portion indicates the slot-line and the black ones are microstrip feed lines and a dual-mode triangular loop resonator with perturbations. Its equivalent circuit model is given in **Figure 16(b)**. Coupling between dual-mode resonator and source/load can be intuitively neglected because its value is quite small. **Figure 16(c)** plots the simulated results derived from the equivalent circuit model, where the solid and dashed lines indicate the simulated reflection and transmission coefficients, respectively. Two transmission zeros in the notch band are created by the

Next, two small patches are symmetrically added as the perturbation element to the lower angles of the triangular loop resonator. These perturbations can accomplish the further separation of the two degenerate modes, creating the dual-mode behavior of the resonator. Resonant modes of the triangular loop resonator are coupled to the slot-line, providing a bypass for the adjacent signal of its resonance, and a notch band is thus created. **Figure 17(a)**

falls off from 6.25 to 5.39 GHz, and its absolute bandwidth decreases from 1.49 to 1.37 GHz. Obviously, the perimeter of triangular loop resonator can directly determine the position of the notch band. **Figure 17(b)** illustrates the influence on the frequency response from varied

up from 1.52 to 1.79 GHz. These exhibited characteristics can be used to determine the central frequency and bandwidth of the created notch band; thus the notch band of the UWB BPF can

**Figure 15.** Frequency responses of transmission coefficient of the proposed UWB BPF with different feeding line lengths

, that is, the perimeter of a tri-

increases from 31 to 37 mm, the central frequency of notch band

increases from 0.2 to 1.0 mm, the notch bandwidth goes

dual-stub-loaded slot-line MMR.

54 UWB Technology and its Applications

resonant modes of the microstrip resonator.

angular loop resonator. As *L*<sup>5</sup>

be fully controlled.

and width of two patches. As *W*<sup>5</sup>

*W*5

(*L*4 ).

shows the transmission characteristics of the resonator versus *L*<sup>5</sup>

Based on the filter structure and analysis approach described above, a UWB BPF with a controllable notch band is designed and fabricated on a substrate with a dielectric constant of ε<sup>r</sup> = 3.5, loss tangent of 0.0018, and thickness of h = 0.8 mm. The layout of proposed UWB BPF with a notch band is depicted in **Figure 18**. As mentioned above, a dual-stub-loaded slot-line resonator is etched on the ground plane, and on the top layer, two folded microstrip feed lines and a microstrip triangular loop resonator are constructed. All the dimensions of the filter shown in **Figure 18** are *W*<sup>0</sup> = 1.8 mm, *L*<sup>1</sup> = 23.0 mm, *W*<sup>1</sup> = 2.0 mm, *L*<sup>2</sup> = 3.0 mm, *W*<sup>2</sup> = 0.3 mm, *L*<sup>3</sup> = 2.0 mm, *W*<sup>3</sup> = 0.8 mm, *L*<sup>4</sup> = 11.5 mm, *W*<sup>4</sup> = 0.6 mm, *L*<sup>5</sup> = 36 mm, *W*<sup>5</sup> = 0.3 mm, and *S* = 0.6 mm.

respectively. In general, the measured results agree well with the simulated results except the loss in the high-frequency band that may be caused by the dielectric loss and fabrication tolerance. Meanwhile, simulated and measured results indicate that the group delay within

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Slot-line UWB BPFs and band-notched UWB filters are presented. UWB BPFs are implemented by using microstrip feed slot-line MMR. To acquire a notch band in the UWB passbands, microstrip resonators are loaded to the slot-line. Circuit model for microstrip resonatorloaded slot-line is given and analyzed. The design methodology has been finally verified by the measured results. Band-notched UBW BPFs are hot spots in a few years; there are some

[1] Federal Communications Commission. Revision of part 15 of the commission's rules regarding ultra-wideband transmission systems. Tech. Rep., ET-Docket 98-153, FCC02-48.

[2] Zhu L, Sun S, Menzel W. Ultra-wideband (UWB) bandpass filters using multiple-mode resonator. IEEE Microwave and Wireless Components Letters. 2005;**15**(11):796-798 [3] Gao SS, Yang XS, Wang JP, Xiao SQ, Wang BZ. Compact ultra-wideband (UWB) bandpass filter using modified stepped impedance resonator. Journal of Electromagnetic

[4] Wu HW, Chen YW, Chen YF. New ultra-wideband (UWB) bandpass filter using trianglering multi-mode stub-loaded resonator. Microelectronics Journal. 2012;**43**(11):857-862 [5] Zhu L, Wang H. Ultra-wideband bandpass filter on aperture-backed microstrip line.

[6] Shi X, Xi X, Liu J, Yang H. Novel ultra-wideband (UWB) bandpass filter using multiple-

trends in this field, such as multiple notched band and tunable notched band.

the passbands is varied between 0.3 and 0.7 ns.

Address all correspondence to: xuehuiguan@gmail.com

East China Jiaotong University, Nanchang, PR China

Waves & Applications. 2008;**22**(22):541-548

Electronics Letters. 2005;**11**(18):1015-1016

mode resonator. IEICE Electronics Express. 2016;**13**(11)

**5. Conclusions**

**Author details**

Xuehui Guan

**References**

Apr 2002

Simulated and measured transmission and reflection coefficients of the constructed filter are plotted in **Figure 19**. Simulated results show that the 3-dB passband of the filter covers the ranges of 2.83–4.78 GHz and 6.29–10.33 GHz, respectively, while measured ones show that the 3-dB passband covers the ranges of 2.49–4.91 and 6.29–9.2 GHz. Measured minimum insertion losses of the first and second passband are 1.1 and 1.5 dB, respectively. Measured maximum return losses in the first and second passband are 13.2 and 13.5 dB, respectively. Simulated and measured maximum insertion loss in the notch band is 25 and 35 dB,

**Figure 18.** Schematic of the proposed band-notched UWB BPF with dual-mode triangular loop resonator-loaded dualstub slot-line MMR. (a) Top layer and (b) bottom layer.

**Figure 19.** Simulated and measured frequency responses of the designed band-notched UWB BPF.

respectively. In general, the measured results agree well with the simulated results except the loss in the high-frequency band that may be caused by the dielectric loss and fabrication tolerance. Meanwhile, simulated and measured results indicate that the group delay within the passbands is varied between 0.3 and 0.7 ns.
