5. Microwave UWB bandpass filter with notch band

As illustrated in Figure 2, the UWB band has dramatic high FBW and surprisingly 7.5 GHz absolute bandwidth; therefore, the UWB has got great potential in many applications. However, a variety of undesired radio signal interferences and noise exist in the UWB frequency spectrum covering 3.1–10.6 GHz. Such as WiMAX (3.5 GHz), WLAN (5.2 GHz, 5.8 GHz), C-band satellite signals (5.975–6.745 GHz, 6.725–7.025 GHz), and RFID (6.8 GHz). As shown in Figure 2, some interference is introduced to the UWB communication system due to these narrowband signals. Thus, several notches are required to filter out the unwanted radio interference signals in UWB communication systems. In general, the methods of introducing a notch band in the UWB bandpass filter is of same essence, which is the electromagnetic energy of a certain frequency absorbed in the UWB band, so that signals with this frequency has been shorted out and averted to transmit from input to the output port. The design of the UWB notch filter has the following two

Figure 20. Top view of the UWB bandpass filter with notch band.

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

#### Figure 22.

EM simulation results versus circuit simulation results versus measurement results of presented UWB notch band 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 perfor-

As illustrated in Figure 2, the UWB band has dramatic high FBW and surprisingly 7.5 GHz absolute bandwidth; therefore, the UWB has got great potential in many applications. However, a variety of undesired radio signal interferences and noise exist in the UWB frequency spectrum covering 3.1–10.6 GHz. Such as WiMAX (3.5 GHz), WLAN (5.2 GHz, 5.8 GHz), C-band satellite signals

(5.975–6.745 GHz, 6.725–7.025 GHz), and RFID (6.8 GHz). As shown in Figure 2, some interference is introduced to the UWB communication system due to these narrowband signals. Thus, several notches are required to filter out the unwanted radio interference signals in UWB communication systems. In general, the methods of introducing a notch band in the UWB bandpass filter is of same essence, which is the electromagnetic energy of a certain frequency absorbed in the UWB band, so that signals with this frequency has been shorted out and averted to transmit from input to the output port. The design of the UWB notch filter has the following two

5. Microwave UWB bandpass filter with notch band

Simulation and measurement results of presented UWB bandpass filter.

mance and multi-transmission zeros.

UWB Technology - Circuits and Systems

Figure 19.

Figure 20.

92

Top view of the UWB bandpass filter with notch band.

introduced to realize low-pass transmission characteristics with improved out-offband performance. Embedded open-circuited stubs are utilized to generate a pair of notch band, which is located at 5.75 and 8.05 GHz, as depicted in Figure 21. The developed filter is analyzed by using EM simulator CST microwave and fabricated on TACONIC substrate of dielectric constant 2.2. Excellent agreement can be observed which proves that the proposed UWB bandpass filter is of UWB with dual-notch band characteristics and wide stopband, as illustrated in Figure 22.

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