UWB DR Filter Malaysia 2010(3)

8/6/2019 UWB DR Filter Malaysia 2010(3)

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European Journal of Scientific ResearchISSN 1450-216X Vol.46 No.4 (2010), pp.503-509 EuroJournals Publishing, Inc. 2010http://www.eurojournals.com/ejsr.htm

Ultra-Wideband Dielectric Resonator Bandpass Filter

Mohd F. Ain Associate Prof., Universiti Sains Malaysia

E-mail: [email protected]

Ahmad A. Sulaiman Research Student, PhD, Universiti Teknologi MARA, Malaysia


Zainal A. AhmadProfessor, Universiti Sains Malaysia


M.A. Othman Research Student, PhD, Universiti Sains Malaysia


Ali Othman Research Student, PhD, Universiti Teknologi MARA, Malaysia


Ihsan A. Zubir Research Student, Msc, Universiti Sains Malaysia


Abstract

This paper presents a novel design of a bandpass filter using combination of asimple transmission line and cylindrical dielectric resonator for X-Band application. Threedielectric resonators with same permittivity and diameter of 60 and 5 mm respectively areidentified to be contributed to an ultra-wideband bandwidth of the filter. This new approachincreases the coupling effect as well as minimizing the insertion loss in the passband.Experimental results from the simulation are closely agreed to the measured values. In

order to prove that the new approach contributes more advantages and viable at the desiredapplication band, the return and insertion losses of the filter were analyzed.

Keywords: Bandpass filter, Dielectric resonator, ultra-wideband

1. IntroductionA high performance resonator is an important element in many microwave circuits such as filters,amplifiers, couplers, and antennas for electronic and microwave communication systems. A variety of geometrical resonators have been reported by Virdee [1]. Dielectric resonator (DR) offers a lotadvantages in increasing the performance of RF and microwave devices which make it as an ideal


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505 Mohd F. Ain, Ahmad A. Sulaiman, Zainal A. Ahmad, M.A. Othman,Ali Othman and Ihsan A. Zubir

The main difference lies in the fact that the wavelength in dielectric materials is divided by the

square root of the dielectric constant, r

in a function of r o

g

=

, where o

is the free spacewavelength at the resonant frequency. Moreover, unlike resonant cavities, the reactive power storedduring resonance is not strictly confined inside the resonator. The leakage fields from the resonator can

be used for coupling or adjusting the frequency. The wavelength inside the DR,g

is also inverselyproportional to the square root of the dielectric The resonant frequency and radiation Q-factor can bevaried even dielectric constant of the materials are fixed due to the dielectric resonators able to offerflexibility in dimensions. It is amenable in integrating to existing technologies by exciting usingprobes, slots, microstrip lines, dielectric image guides or coplanar waveguide.

Figure 1: Geometry of the simulated and fabricated bandpass filter.

Dielectric

resonator

Input and outputports

Substrate

Strip line

Vacuum box

DR1 DR2DR1

(a) Simulated layout

(b) Fabricated layout

Fig. 1 shows the simulated and fabricated circuit layouts of the bandpass filter. The striptransmission line is made up from copper metal with electrical conductor of 5.8 e +7 S/m, whiledielectric resonator is a ceramic type made up from ZnSnTio with dielectric constant, r = 60 andtangent loss of 0.002. The base substrate is a Duriod type with r = 2.5 and tangent loss is about 0.002.The overall circuit length is 49 mm, while the location of dielectrics are DR1 = 14.5 mm, DR2 = 24.5mm and DR3 = 41.55 from the input port.

Since cylindrical shape of dielectric resonators have a flexible radius, r , height, h and dielectricconstant, due to various sizes can be bought from the market. The applications of these resonatorshave been used in filters and oscillators [7]. Such shape offers a wide degree of freedom in microwave


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Ultra-Wideband Dielectric Resonator Bandpass Filter 506

circuit designs since the ration of r/h could determine the Q-factor for a given dielectric. Thus a height,slender cylindrical DR can be made to resonate at the same frequency as a wide and thin DR. However,the Q-factors for these two resonators will be different. This characteristic offers a flexible degree forchoosing the most suitable aspect ratio to the best frequency and bandwidth. The high Q-factor andcompact size make it an ideal couple especially in microstrip technology.

3. Results and DiscussionWideband devices can be designed using two or more DRs. All DRs are operating in a same principle.Each DR will resonate for a same mode but with different frequency such that the combinationresponse is an additional result from the single response which able to increase the overall bandwidth.For example if DR 1 has a normalized resonant frequency of f 1 and bandwidth of BW 1, while DR 2 has anormalized resonant frequency of f 2 and bandwidth of BW 2, then the combination response could has abandwidth BW that is larger than the sum of BW 1 + BW 2, if f 1 and f 2 are properly chosen. If the Q-factors of the two resonators are approximately the same ( oQQQ

=21 ) and if the return loss of the

combined response is equal to or better than 10 dB over the bandwidth BW , then the required values forthe resonant frequencies of the individual DRs can be approximately equal to [2]:

oo Q f Q f 6

51,6

51 21 +

(1) Assuming the bandwidths of the two DRs are also similar ( o BW BW BW = 21 ), then the combined

bandwidth is approximately o BW BW 3 by ignoring any mutual interaction as well as any loadingeffects of the feed, that could either increase or decrease the bandwidth response. For example, if allDRs having a Q-factor of 7, the cutoff frequencies can be simplified as equation below [2]:

oohool f f f f f f 7273

3605

1,7271

3605

1 =

+==

=(2)

where f l and f h are the lower and upper cutoff frequencies, respectively. The combined response wouldhave a 10 dB return loss bandwidth of 30%. Fig. 2 shows the ultra-wideband of simulation and

measurement results from the filter for a comparison. Both of the graphs are almost having a samepattern. However insertion loss from measurement is higher than the simulation. The simulated resultshows a very good flat insertion loss in the passband frequencies. The return loss from the simulatedresult is higher than the measured value. These mean that the simulated results are better than themeasured values. In term of transition bands, the results from the simulation are steeper than themeasurement. It is also clearly shows that the bandwidth of the simulated result is wider than themeasurement.

Table 1 shows the summary of few parameters from simulated and measured responses forapparent critical points as a comparison. The best insertion loss of -0.86 dB is obtained from thesimulated result, while only -3.53 dB from the measured response. This is due to high dissipation effectof the material loss in microwave frequencies. However, the maximum return loss of measurementvalue in the pass band of the filter is about 4 dB better than the simulated result. The bandwidth of themeasured circuit is only 1.03 GHz compared to 1.28 GHz from the simulation result. The widebandwas obtained from both result are due to the implementation of few dielectric resonators on the design.

The combination of dielectric and microstrip line in designing a bandpass filter with suchstructure is a novel. The idea of designing this bandpass filter was due to the dielectric resonator canincrease Q-factor in a circuit response and able to maximize power transfer in dielectric resonatorantennas. Since antenna is a single port device and filter is a two ports device, the same advantages anddesign techniques have been used to achieve the objectives.


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Figure 2: Measured and simulated results.

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

9 9 .5 1 0 10. 5 11Frequency (GHz)

I n s e r t

i o n a n

d R e

t u r n

l o s s e s

( d B )

Mea sured S11

Mea sured S21

Simulated S11

Simulated S21

Table I: Comparison values of simulation and measurement

Items Simulation MeasurementInsertion loss -0.86 dB -3.53 dBReturn loss -15.54 dB -19.42 dBBandwidth 1.28 GHz 1.03 GHz

A more dominant parameter affecting the degree of coupling is the dielectric constant of theDR. For the higher values of dielectric constant, the stronger coupling will be. Nevertheless, themaximum amount of coupling is significantly reduced if the dielectric constant of the DR is low. Thiscan become a problematic if low dielectric constant values are applied to obtain a wideband operation.

In order to obtain a compact size of a design is using a DR that contain of a high dielectricconstant. However, the range of dielectric constants that can be used is limited, since there is a tradeoff between the compact circuit and the dielectric constant due to the high percentage of power beingtrapped in the surface waves of the microstrip substrate. Since surface waves are not generated in DRs,the radiation efficiency is not affected by the highest dielectric constant on the top. At the same time,the Q-factor is increases proportionally to the dielectric constant will reduce the bandwidth of the filter.By properly choosing the dielectric constant, the Q-factor can be reduced. The volume of the DR andQ-factor can be traded off depending on the particular design application. For a low profile design, acombination of high dielectric constant and large DR area can be used to obtain a reasonablebandwidth.

Figure 3: The effect of dielectric length of radius on return loss

Frequency (GHz)

L o s s e s

( d B )


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4. ConclusionA bandpass filter was designed to operate at center frequency of 10 GHz. The filter has advantages of very small ripple at the passband insertion loss and able to operate with a wide bandwidth. Thestructure of the filter is simple for ease fabrication process. The measurement values are closely agreedto the simulation results.

AcknowledgementAuthors would like to thank Universiti Teknologi Mara, and Universiti Sains Malaysia for supportingthe project.

References[1] Bal S. Virdee, Christos Grassopoulos, Folded Microstrip resonator, IEEE MTT-S Int.

Microwave Symp. Dig. ,vol. 3, pp. 2126-2164, June 2003[2] A. Petosa, Dielectric Resonator Antenna Handbook , Artech House, Bolton, 2007.

[3]

Matthei, G.L, Young, L, Jones, E.M.T., Microwave Filters, Impedance Matching Networks,and Coupling Structures, Artech House, MA, 1980.[4] Edwards, T.C., Foundations for Microstrip Circuit Design , Wiley and Sons, 2 nd Ed., 1991.[5] A.M. Street, A.P. Jenkins and D. Abbott, Filter design using CAD. I. Linear circuit

simulation, IEE Colloquium on Microwave CAD, (Ref. No: 1997/377), 1997.[6] D. M. Pozar, Microwave Engineering , Addison Wesley, MA, 1990.[7] Xiaoming, X. and R. Sloan,"Distributed coupling model of the dielectric resonator to microstrip

line." IEEE Microwave and Guided Wave Letters, vol. 9, pp. 348-350, Sept 1999.[8] Huang C.Y., J.Y. Wu and K.L Wong, Cross-slot-coupled microstrip antenna and dielectric

resonator antenna for circular polarization, IEEE Trans. on Antennas & Propagation, vol. 47,No. 4, pp. 605-609, Apr. 1999.

[9]

Collin, R.E, Foundations for Microwave Engineering , New York: McGraw Hill, 1966.

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UWB DR Filter Malaysia 2010(3)