Dual-Mode Dual-Band Filter

IEEE MICROW A VE AND WIRELESS COMPONENTS LETTERS,VOL.20,NO.2,FEBRUARY 201073

Dual-Mode Dual-Band Filter With Band Notch Structures

Youngje Sung

Abstract—A novel approach for designing dual-mode dual-band bandpass ?lters is proposed and experimentally studied.By em-bedding a pair of slits in the square patch,the dual-band response is realized and one transmission zero is introduced between the two passbands.Two degenerate modes are achieved by loading with a small square perturbation,which can be placed at the diagonal line.There are three transmission zeros.The slits control the ?rst and third transmission zeros.On the other hand,the right crossed slots control the ?rst and the second transmission zeros.Index Terms—Dual-mode dual-band ?lter.

I.I NTRODUCTION

R

ECENT development in wireless communication sys-tems has created a need for RF circuits with a dual-band operation.Various con?gurations have been proposed for realizing a dual-band ?lter [1]–[4].In [1],a dual-band was implemented as a combination of two individual ?lters with two speci?c single passbands.By cascading a wideband passband ?lter and a stopband ?lter,a dual-band bandpass ?lter (BPF)was achieved [2],but these solutions suffer from high insertion loss and large overall size.The stepped impedance resonator (SIR)has been used in dual-band design [3],[4].In this case,the second resonance property is dominated by the impedance

ratio

of the SIR.Dual-mode ?lters have been widely used in wireless commu-nications systems because of their advantages in applications requiring high quality microwave s with features such as small size and low loss.As is well known,there are several commonly used dual-mode microstrip resonators including the circular ring [5],square loop [6],and square patch [7].

In this letter,a dual-mode dual-band with a pair of slits is pro-posed.The dual-band property derives from the slits applied to the square and the dual-mode property in the two passbands that is induced by a perturbation positioned at the center of the diag-onal line.The right angle crossed slots control the ?rst resonance and lower the resonant frequency,which makes the square patch resonator compact.On the other hand,the right angle crossed slots only slightly perturb the second resonance and keep the second resonant frequency unchanged [7].

Manuscript received May 28,2009;revised October 18,2009.First published January 26,2010;current version published February 10,2010.

The author is with the Department of Electronics Engineering,Kyonggi Uni-versity,Suwon 443-760,Korea (e-mail:yjsung@kgu.ac.kr).

Color versions of one or more of the ?gures in this letter are available online at 7161e50d581b6bd97f19ea8a.

Digital Object Identi?er

10.1109/LMWC.2009.2038434

Fig.1.Con?guration of the proposed dual-band dual-mode ?lter.

II.C ONFIGURATION

The basic con?guration investigated in this letter is shown in Fig.1.The ?lter proposed here is fabricated on a commer-cially available substrate

with

and .The width of the feed line is chosen to be 1.2mm,which cor-responds to the characteristic impedance of

50.The ?lter is fed by a microstrip line by gap coupling where the gap for the feed structure is denoted

by .It is found from the simulated

results that the dimensions

(

and )of the T-shaped feed structure can be adjusted for good impedance matching.Simu-lation is carried out using HFSS.

The outer side length of the proposed ?lter is denoted

by ;it has slits—with the length and width

of

and ,respec-tively—that are located in front of the I/O

port,apart from its edge.The slot situated at the center is a combination of the right cross slots with the

length and

width [7]and the square slots

that are located

at

from the I/O port.The side length of the square slot is denoted by .While a structure without slits was already reported in [8],the proposed ?lter failed to realize

dual-mode property at the second resonant

frequency

even though it was designed for dual-mode dual-band application.Fig.2presents the simulated results that compare the values

of

for square patch ?lters with and without slits,respec-tively.The solid line represents

the

property of a conven-tional square patch ?lter with the side length of 16mm;the

dotted line stands for

the

property of a square patch ?lter to which a pair of slits are added.A conventional square patch ?lter exhibits single resonance property,while one with slits,as demonstrated in Fig.2,forms a transmission zero around 2.7GHz,separating single passband into two bands.By prop-erly setting the length of the slit to be 10mm (approximately a quarter-wavelength at 2.7GHz),the slit resonates,acting as a notch and trapping some of the power that was transmitted

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74IEEE MICROWA VE AND WIRELESS COMPONENTS LETTERS,VOL.20,NO.2,FEBRUARY

2010Fig.2.Simulated results (S )comparing the properties of square patch ?lters

with and without slits.

from input port to output port [9].The slot located at the center,

whose length in one side

is ,leads each of the bands to have

dual-mode property.Accordingly,the proposed ?lter has dual-

band dual-mode property.

III.D UAL -M ODE D UAL -B AND B ANDPASS F ILTER

Fig.3shows the simulated results of the proposed ?lter with

different

sizes

of the slits.The length of the square in one side is set at 16mm;the

length

and

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