Adviser :Hon Kuan Reporter : Wen-Lang Chen Date : 12/01/2008

A UWB FILTER USING MIXED OPEN STUBS TO SUPPRESS HARMONIC

RESPONSE

OUTLINE

• INTRODUCTION

• FILTER DESIGN

• EXPERIMENTAL RESULTS AND DISCUSSION

• CONCLUSION

INTRODUCTION

Fig. 2. Theoretical responses of the simplified bandpass filter. (a) Narrowband frequency. (b) Wideband frequency.

Fig. 1. Schematic diagram of the proposed ultra-wide-stopband microstrip bandpass filter.

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 56, NO. 6,

JUNE 2008

INTRODUCTION

Fig. 1. Configurations of BSFs using (a) open stubs, (b) spurline, and (c) combination of open stubs and spurline.

Fig. 2. Simulated and measured insertion loss of BSFs. M represents measurements, and S represents simulation.

IEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 15, NO. 4, APRIL 2005

The proposed filter is formed on the RT/Duroid 5880 with εr = 2.2 and ｈ= 0.508mm.Simulation resultslow band =3.3G~5.28GHzHigh band =6.37G~9.63GHz

FILTER DESIGN

spurious response

Figure 1. The simulated frequency resopnse without bandstop.

Figure 2. Configurations of (a) embedded of open-stub (b) conventional open-stub (c) the proposed structure (d) Comparison of the simulated frequency response for the three structures.

(d)

Figure 3. The simulated frequency response by using different widths of open-stubs.

Method 1 Method 2

Proposed structure(mixed open stubs)

FILTER DESIGN

With a bandstop filter, the simulated frequency response can well suppress spurious response from 10 to 20 GHz and provide a rejection level 20 dB below.

Figure 4. (a)Layouts of the UWB filter with bandstop filter. (b) The comparison of the simulated frequency resopnse with bandstop and without bandstop.

(a)

(b)

FILTER DESIGN

EXPERIMENTAL RESULTS AND DISCUSSION

Figure 5. (a) Picture, (b) simulated and measured frequency response of the UWB filter.

The UWB filter at lower passband has good measured results, including a center frequency f0 of 4.35 GHz, low insertion loss of -1.9 + 0.4 dB, wide bandwidth of 3.5–5.2 GHz (FBW 39%). The UWB filter at higher passband also shows good measured results, including a center frequency f0 of 8.1 GHz, low insertion loss of -2 + 0.5 dB, wide bandwidth of 6.5–9.7 GHz (FBW = 40%). The measured upper stopband is significantly widened up to 20GHz with an attenuation level higher than 23 dB. The measured locations of transmission zeros appear at 2.6, 5.9 and 12.7 GHz .

CONCLUSION In order to improve the stopband performance, a wide bandstop filter using mixed open stubs cascaded with UWB bandpass filter for the harmonic suppression has been proposed.

The proposed BSF shows a deeper rejection and wider stopband than the conventional open-stub BSF without increasing the circuit size.

By increasing the widths of shunt open stubs, the more widen stopband range will be achieved.

The proposed bandpass filter shows 23 dB rejection during the frequency range from 10GHz to 20GHz.

Thanks for your attention!