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Circular Resonator Based Compact UltraWideband Bandpass and Notched Filters with Rejection of 5-6 GHz Band Thirumalaivasan K, Nakkeeran R, and Oudaya coumar S Department of Electronics and Communication Engineering Pondicherry Engineering College, Puducherry-605014, India thirumalaivasank@pec.edu, rnakeeran@pec.edu, oudaya.mtechece@pec.edu Abstract— In this paper, a circular ultra wideband (UWB) bandpass filter and notch filter using microstrip with wide passband, low insertion and return loss are presented. The proposed bandpass filter covers the UWB indoor mask range from 3.1GHz to 10.6GHz. The filter has a circular plate resonator with interdigital coupling has been designed to act as bandpass filter with passband of 8.25 GHz. The notch filter is proposed using four open stub structure in the bandpass structure. The notch filter is derived from the bandpass filer, the notch filter is designed to introduce notch in the frequency range from (5-6) GHz. The designed filters are successfully simulated by electromagnetic simulator, IE3D. The filters exhibit low insertion loss over the desired passband, and a good out-of-band performance.

fractional bandwidth of larger than 20%. According to Shannon’s capacity theorem, this large bandwidth provides a very high capacity. Thus, high processing gain can be achieved that allows the access of a large number of users to the system. The impulse radio UWB is a carrier-less (i.e., baseband) radio technology and accordingly, in this radio technique no mixer is needed.

Therefore, the implementation of such a system is simple, which means that low cost transmitters/receivers can be achieved when compared to the conventional radio frequency (RF) carrier systems [4-5]. Because UWB systems operate in a very large bandwidth, they need to share the spectrum with other users as well as with the existing communication systems and consequently, interferences may occur [6].

Because of the rapid growth in broadband systems, the requirements for filter design have become stricter. So the broadband filters with compact size and superior stop band performance are designed [7]. The UWB bandpass and notch filters proposed are based on the Roger's RT/Duroid 5880 substrate with a dielectric constant of 2.2 and thickness of 3.125 mm. They are characterized and optimally designed using the electromagnetic (EM) simulator IE3D, which is part of the Zeland software package [8].

The paper is organized as follows: In Section II the UWB bandpass filters design using circular resonator structure. Section III dealt with UWB notch filter using four open stubs. Simulation results and analysis are presented in Section IV. Section V concludes the paper.

Keywords — Ultra wideband filter, multiple-mode resonator, microstrip coupling structure, notched filter.

I.

INTRODUCTION

In 1998, the Federal Communications Commission (FCC) recognized the significance of UWB technology and initiated the regulatory review process of the technology. Consequently, in February 2002 the FCC report appeared, in which UWB technology was authorized for the commercial uses with different applications, operating frequency bands as well as the transmitted power spectral densities [1]. European Commission for Post and Telecommunication (CEPT) has released a decision on the 24th March 2006 which allows operation of unlicensed UWB devices. UWB technology will support a lot of new applications with benefits for public safety and creating new business opportunities for distributors, vendors and manufacturers [2]. UWB technology will allow an increased usage of spectrum resources by sharing spectrum with low interferences to narrow band systems.

UWB technology is especially suited for radio location because of its huge bandwidth which provides a fine accuracy in ranging. UWB provides low-power, lowcost communication and positioning in one technology.

These features allow a new range of applications, including logistics, security applications, medical applications as well as military applications [3]. UWB communication is based on the transmission of very short pulses with relatively low energy. UWB technique has a fine time resolution which makes it a technology appropriate for accurate ranging. UWB radio signal occupies a bandwidth of more than 500 MHz or a

II.

A compact UWB band pass filter with wide passband of 8.25 GHz is proposed. The geometry of filter structure is shown in Fig.1. Interdigital coupled lines are employed to achieve strong coupling [9]. UWB filter consisted of circular MMR at the center section and two identical coupled-lines located at the left and right section.

Fig.1. Circular UWB bandpass filter

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CIRCULAR UWB FILTER

Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

IV.

In addition, the UWB bandpass filter exhibit very good selectivity in order to meet the FCC spectrum mask.

In turn UWB BPF provides good in-band and out-ofband performance. Furthermore, the circular resonator can easily realize a tight coupling with the feed-lines, resulting in more resonant-peaks in the UWB passband to realize a wide bandwidth. The interdigital feed-lines used here can enhance the coupling degree between the circular resonator and the feed-lines. This coupling can be adjusted to control the bandwidth. Thereby, the circular resonator and the symmetrical interdigital feed-lines can work together to make up the desired UWB passband properly [10-12].

III.

RESULTS AND DISCUSSIONS

Simulation was accomplished using IE3D, which is an electromagnetic wave simulator. The simulated S parameter of the proposed bandpass filter is shown in Fig.3. It is clear from the response that the proposed filter has better insertion loss of -2 dB and the low return loss of about -37 dB. The 3 dB fractional bandwidth computed from the response is about 123%. The proposed UWB notch filter has two transmission bands.

The first passband from 2.2 GHz to 5.2 GHz has -1 dB insertion loss and - 30 dB return loss. The second passband within 5.8 GHz and 10.4 GHz has –3 dB insertion loss and - 25 dB return loss.

UWB NOTCHED FILTER

An ultra-wideband notch filter with 5-6 GHz rejection band is proposed which is the modified version of circular filter. The multiple coupled line structure is incorporated with multiple-mode resonator to provide wide transmission band and enhance out-of band performance [13-16].

Fig.2. UWB notch filter with open stubs

Fig.3. Response of circular UWB bandpass filter

To inhibit the signals ranged from 5-6 GHz, four stepped-impedance open stubs are implemented on the MMR is shown in Fig 2. IEEE 802.11a operates in three distinct 100 MHz regions with different power limitations in the 5-6 GHz band. The lower band ranges from 5.15 to 5.25 GHz and it has power limitation of -3.01 dBm/MHz. the mid band is from 5.25 – 5.35 GHz and is limited by 3.98 dBm/MHz and the upper band is from 5.725- 5.825 GHz and is limited by 10 dBm/MHz. The interference is significant since the 802.11a signals are drastically higher at -3dBm/MHz in the lower band to 10 dBm/MHz in the upper band. For this reason, this paper proposes a notch filter to effectively reject the entire 5-6 GHz band of WLAN. Several techniques for providing transmission zero or rejection band microstrip structure have been demonstrated, such as Defect Ground Structure (DGS) [17], Photonic Band Gap (PBG) [18], split ring resonator (SRR) [19], spur-line structure [20], and slot resonator [21]. However, if narrow bandwidth rejection and reduction of fabrication complexity are concerned, the quarter wave length open stub is a good solution to achieve. So the high performance and compact UWB notch filter based on multiple coupled line structure and multiple mode resonators is demonstrated. The electrical coupled line length is close to 900 and the coupling gap is 0.3 mm for both structures.

The rejection is achieved between 5-6 GHz with better insertion loss of -40 dB. This filter can be integrated in UWB radio systems and efficiently enhance the interference immunity from WLAN. The simulated frequency responses of the wide bandpass filter are shown in Fig. 4.

Fig.4. Response of UWB notch filter

Flat group delay or linear phase is necessary to avoid distortion in the baseband signals. In the microwave domain, group delay equalizers are used to compensate for group delay variations mostly introduced by filters or amplifiers [22]. The group delay measurement for the UWB bandpass and notch filter are simulated and shown 260

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Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

in Fig. 5and Fig. 6. Group delay variation of the bandpass filter is about 0.3ns and for notch filter the group delay is measured about 0.45 ns.

Fig.7 shows the simulation result of phase of S21 for UWB bandpass filter whereas Fig.8 shows the simulation result of phase of S21 for UWB notch filter. Linear phase is a property of a filter, where the phase response of the filter is a linear function of frequency, excluding the possibility of wraps at Âą 1800 and linear phase filter will

Fig.7. Phase measurement of UWB bandpass filter

Fig.5. Group delay measurement of UWB bandpass filter

Fig.8. Group delay measurement of UWB notch filter

The UWB bandpass and notch filter with 5-6 GHz rejection band performance parameters like insertion loss, return loss, fractional bandwidth, passband of the filters, Group Delay, Phase and dimensions are collectively tabulated in Table I TABLE I SIMULATED FILTER PARAMETERS Fig.6. Group delay measurement of UWB notch filter

have constant group delay. Plot is shown that the phase of S21 throughout the passband of presented filter is acceptably linear for UWB applications.

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FILTER PARAMETERS

BANDPASS

Insertion loss (dB) Return loss (dB) Passband (GHz) Fractional bandwidth (%)

-2 - 37 8.25 123

Group Delay (ns) Phase at passband Size (mm3)

about 0.3 linear 4x39.2x1.6

NOTCH FILTER -1.20 & -1.4 -30 & -25 3 & 4.6 133.33 and 152.72 about 0.45 linear 6x39.2x1.6

Proc. of Int. Conf. on Control, Communication and Power Engineering 2010

V.

CONCLUSIONS

A circular resonator based UWB bandpass filter and notch filter using microstrip with wide passband, low insertion loss and return loss are demonstrated in this paper. The bandpass filter with circular plate has the passband of 8.25 GHz with insertion loss of -2 dB, return loss of -37 dB and -10dB fractional bandwidth of 123 %.

In order to achieve 5-6 GHz notch, four open stubs are included in the circular resonator. The notch filter has two passbands of 3 GHz & 4.6 GHz, each passband has insertion loss of -1.20 & -1.4 dB, return loss of -30 & -25 dB and -10dB fractional bandwidth of 133.33 % &152.72 %. The group delay obtained for bandpass filter is about 0.3 ns and for notch filter it is about 0.45 ns. The dimension of the designed bandpass and notch filters are 4 x 39.2 x 1.6 mm3 & 6 x 39.2 x 1.6mm3 respectively.

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