Figure 9.

Simulated and measurement frequency responses of presented UWB.

By using the numerical calculation method mentioned in Figure 4, the design graphs for implementing UWB bandpass filter are sketched in Figure 11. For example, by properly choosing the values of θ2, the excited four resonant frequencies can be easily adjusted to the desired UWB specifications. Therefore, the first four resonant modes are located at 2.86, 5.58, 8.56, and 10.21 GHz, and the dimension parameters are optimized by IE3D as follows: L<sup>1</sup> = 8, L<sup>2</sup> = 1.6, L<sup>3</sup> = 1.6 L<sup>4</sup> = 1.4, L<sup>5</sup> = 1.2, L<sup>6</sup> = 3, L<sup>7</sup> = 2.5, L<sup>8</sup> = 1, L<sup>9</sup> = 4, L<sup>10</sup> = 3.6, L<sup>11</sup> = 8, W<sup>1</sup> = 0.2, W<sup>2</sup> = 0.3, W<sup>3</sup> = 0.6, W<sup>4</sup> = 0.2, and W<sup>5</sup> = 0.3. It can be observed in Figure 12 that simulation results are in good agreement with measurement results, which shows UWB bandpass characteristics with small and flat group delay in the passband.

### 4.3 UWB bandpass filters with multilayer structure

In order to design bandpass filter with UWB performance while occupied compact size, dual-layered structure is proposed in [56]. The UWB filter is constructed by substrate integrate waveguide (SIW) ridge resonator, and the bandwidth of the UWB filter can be easily tuned by properly changing the width of rod in ridge resonator. The scheme diagram is sketched in Figure 13.

of the presented SLMMR, classical odd-even-mode method can be introduced to analyze the resonant modes of UWB filter. With even-mode excitation and oddmode excitation, the input admittance can be, respectively, written as follows:

jY<sup>1</sup> tan θ<sup>1</sup> � jY<sup>2</sup> cot θ<sup>2</sup> þ jY<sup>3</sup> tan θ<sup>3</sup>

<sup>þ</sup> jYc tan <sup>θ</sup><sup>c</sup>

�jY<sup>1</sup> cot θ<sup>1</sup> � jY<sup>2</sup> cot θ<sup>2</sup> þ jY<sup>3</sup> tan θ<sup>3</sup>

Yc þ Y<sup>1</sup> cot θ<sup>1</sup> þ Y<sup>2</sup> cot θ<sup>2</sup> � jY<sup>3</sup> tan θ<sup>3</sup>

 <sup>þ</sup> jYc tan <sup>θ</sup><sup>c</sup> Yc þ �ð Þ Y<sup>1</sup> tan θ<sup>1</sup> þ Y<sup>2</sup> cot θ<sup>2</sup> � Y<sup>3</sup> tan θ<sup>3</sup> tan θ<sup>c</sup>

tan θ<sup>c</sup>

(19)

(20)

Yine ¼ Yc

Transmission coefficient |S21|versus weak coupling and strong coupling.

Physical layout of the quintuple-mode resonator.

UWB Technology - Circuits and Systems

Yino ¼ Yc

Figure 7.

Figure 8.

86

Figure 11.

Design graph for SLMMR, (a) normalized even-mode resonance frequencies versus θ2, (b) normalized oddmode resonance frequencies versus θ2.

Figure 12. Measured results versus simulated results of fabricated UWB filter.

As depicted in Figures 14 and 15, the bandwidth of UWB filter increases as the R<sup>s</sup> increases, and the coupling strength and the bandwidth are both decreased as R<sup>L</sup> lessens; thus, the bandwidth of UWB filter can be easily tuned by properly adjusting the R<sup>s</sup> and RL, and design parameters are finally chosen as W<sup>0</sup> = 0.4, L<sup>0</sup> = 4, W<sup>1</sup> = 0.55, L<sup>1</sup> = 4.85, W<sup>2</sup> = 0.85, L<sup>2</sup> = 5.1, W<sup>3</sup> = 1.4, L<sup>3</sup> = 4.9, W<sup>4</sup> = 2.25, L<sup>4</sup> = 4.74, W<sup>5</sup> = 3.15, and L<sup>5</sup> = 4.1. For the purpose of validating the design methodology, the dual-layer UWB bandpass filter is fabricated on the substrate of Rogers 6006 with relative permittivity if 6.15 and measured. The measurement results indicate that the proposed UWB filter is of extremely low insertion loss (<1 dB) and 47 dB stopband suppression up to 17.4 GHz with compact size, which can be observed in Figure 16.

Since the shorted coupled line structure is not a symmetrical structure, the ABCD matrix analysis method is employed to solve the input admittance of the proposed

> D B

2 6 4

� 1 B BC � AD B

> A B

Y ¼ Yupper þ Ylower (21)

<sup>5</sup> (22)

3 7

UWB bandpass filter, and the Y-matrix of this filter can be written as

Physical layout of the presented UWB filter. (a) Top band side view. (b) Front view.

Yupper ¼

where

89

Figure 14.

Different transmission characteristics versus varied Rs.

Figure 13.

Review on UWB Bandpass Filters

DOI: http://dx.doi.org/10.5772/intechopen.87204

#### 4.4 UWB bandpass filters with parallel-coupled lines

The parallel-coupled lines can also employ to design UWB bandpass filter with simple structure. In [47], shorted coupled line structure and λ/4 shorted stub are introduced to achieve UWB bandpass filter with compact size. The ideal transmission line model of proposed UWB bandpass filter is demonstrated in Figure 17.

Figure 13. Physical layout of the presented UWB filter. (a) Top band side view. (b) Front view.

Figure 14. Different transmission characteristics versus varied Rs.

Since the shorted coupled line structure is not a symmetrical structure, the ABCD matrix analysis method is employed to solve the input admittance of the proposed UWB bandpass filter, and the Y-matrix of this filter can be written as

$$Y = Y\_{upper} + Y\_{lower} \tag{21}$$

where

$$Y\_{upper} = \begin{bmatrix} \frac{D}{B} & \frac{BC - AD}{B} \\ -\frac{1}{B} & \frac{A}{B} \end{bmatrix} \tag{22}$$

As depicted in Figures 14 and 15, the bandwidth of UWB filter increases as the R<sup>s</sup>

The parallel-coupled lines can also employ to design UWB bandpass filter with simple structure. In [47], shorted coupled line structure and λ/4 shorted stub are introduced to achieve UWB bandpass filter with compact size. The ideal transmission line model of proposed UWB bandpass filter is demonstrated in Figure 17.

increases, and the coupling strength and the bandwidth are both decreased as R<sup>L</sup> lessens; thus, the bandwidth of UWB filter can be easily tuned by properly adjusting

Design graph for SLMMR, (a) normalized even-mode resonance frequencies versus θ2, (b) normalized odd-

the R<sup>s</sup> and RL, and design parameters are finally chosen as W<sup>0</sup> = 0.4, L<sup>0</sup> = 4, W<sup>1</sup> = 0.55, L<sup>1</sup> = 4.85, W<sup>2</sup> = 0.85, L<sup>2</sup> = 5.1, W<sup>3</sup> = 1.4, L<sup>3</sup> = 4.9, W<sup>4</sup> = 2.25, L<sup>4</sup> = 4.74, W<sup>5</sup> = 3.15, and L<sup>5</sup> = 4.1. For the purpose of validating the design methodology, the dual-layer UWB bandpass filter is fabricated on the substrate of Rogers 6006 with relative permittivity if 6.15 and measured. The measurement results indicate that the proposed UWB filter is of extremely low insertion loss (<1 dB) and 47 dB stopband suppression up to 17.4 GHz with compact size, which can be observed in Figure 16.

4.4 UWB bandpass filters with parallel-coupled lines

Measured results versus simulated results of fabricated UWB filter.

Figure 11.

Figure 12.

88

mode resonance frequencies versus θ2.

UWB Technology - Circuits and Systems

Figure 15. Variation of frequency responses against varied RL.

Figure 16. Measurement results and simulated results of fabricated UWB filter.

where the whole ABCD matrix can be derived by

$$
\begin{bmatrix} A & B \\ & \\ C & D \end{bmatrix} = M\_2 M\_3 M\_4 M\_5 M\_6 \tag{23}
$$

Mm ¼

Configuration of proposed UWB bandpass filter with shorted coupled lines.

where

Figure 18.

91

Final circuit layout with dimension parameters of presented filter.

Figure 17.

Review on UWB Bandpass Filters

DOI: http://dx.doi.org/10.5772/intechopen.87204

2 4

Ylower ¼ �<sup>j</sup> <sup>1</sup>

<sup>k</sup> <sup>¼</sup> ð Þ <sup>Z</sup>0<sup>e</sup> � <sup>Z</sup>0<sup>o</sup> ð Þ Z0<sup>e</sup> þ Z0<sup>o</sup>

1 0

1

cot θ<sup>1</sup>

k sin θ<sup>1</sup>

3

k sin θ<sup>1</sup>

cot θ<sup>1</sup>

<sup>Z</sup><sup>0</sup> <sup>¼</sup> ffiffiffiffiffiffiffiffiffiffiffiffiffiffi Z0oZ0<sup>e</sup>

5 ð Þ m ¼ 3; 5 (25)

p (27)

(26)

1 jZm tan θ<sup>m</sup>

qZ<sup>0</sup>

where

$$M\_n = \begin{bmatrix} \cos \theta\_n & jZ\_n \sin \theta\_n \\\\ j\left(\frac{1}{Z\_n}\right) \sin \theta\_n & \cos \theta\_n \end{bmatrix} \quad (n = 2, 4, 6) \tag{24}$$

Review on UWB Bandpass Filters DOI: http://dx.doi.org/10.5772/intechopen.87204

$$M\_m = \begin{bmatrix} 1 & 0\\ \frac{1}{jZ\_m \tan \theta\_m} & 1 \end{bmatrix} (m = 3, 5) \tag{25}$$

$$Y\_{lower} = -j\frac{1}{qZ\_0} \begin{bmatrix} \cot \theta\_1 & \frac{k}{\sin \theta\_1} \\ \frac{k}{\sin \theta\_1} & \cot \theta\_1 \end{bmatrix} \tag{26}$$

where

$$k = \frac{(Z\_{0\epsilon} - Z\_{0\epsilon})}{(Z\_{0\epsilon} + Z\_{0\epsilon})} Z\_0 = \sqrt{Z\_{0\epsilon} Z\_{0\epsilon}} \tag{27}$$

Figure 18. Final circuit layout with dimension parameters of presented filter.

where the whole ABCD matrix can be derived by

Measurement results and simulated results of fabricated UWB filter.

<sup>j</sup> <sup>1</sup> Zn � �

2 6 4

Mn ¼

where

90

Figure 16.

Figure 15.

Variation of frequency responses against varied RL.

UWB Technology - Circuits and Systems

A B C D

" #

cos θ<sup>n</sup> jZn sin θ<sup>n</sup>

sin θ<sup>n</sup> cos θ<sup>n</sup>

¼ M2M3M4M5M<sup>6</sup> (23)

<sup>5</sup> ð Þ <sup>n</sup> <sup>¼</sup> <sup>2</sup>; <sup>4</sup>; <sup>6</sup> (24)

3 7

Figure 19. Simulation and measurement results of presented UWB bandpass filter.

Thus, transmission coefficient can be derived. By properly changing the electrical lengths, UWB bandpass characteristics can be fulfilled, and the dimension parameters can be determined by using full-wave EM simulator, as demonstrated in Figure 18. Then simulation results and measurement results of fabricated UWB bandpass filter are shown in Figure 19, which shows excellent passband performance and multi-transmission zeros.

methods: first, introducing additional notch unit circuits and, second, introducing lateral signal interference. The notch unit can be realized by various configurations, which includes single-mode/multimode resonator, a defected ground structure resonator, a metamaterial resonator, etc. Ultimately, the purpose of introducing notch unit circuits is to construct an electromagnetic absorption that set a notch in the UWB. Obviously, the notch which is designed based on aforementioned method is independently controllable. Furthermore, the number of notches can be easily extended, such as dual-notch band UWB filter and triple-notch band UWB filter. To approach UWB bandpass characteristics with notch band, open-ended stubs can be applied to generate electromagnetic absorption [70]. The physical configuration is shown in Figure 20. Triple pairs of dumbbell defected ground structure are

EM simulation results versus circuit simulation results versus measurement results of presented UWB notch

The layout diagram of embedded open-circuited stubs and dual-notch band of proposed UWB filter.

Figure 21.

Review on UWB Bandpass Filters

DOI: http://dx.doi.org/10.5772/intechopen.87204

Figure 22.

93

band bandpass filter.
