2013 First International Conference on Artificial Intelligence, Modelling & Simulation Conversion of UHF Composite Low Pass Filter Into Microstrip Line Form Liew Hui Fang Syed Idris Syed Hassan Mohd Fareq Abd. Malek School of Microelectronic School of Electrical System School of Electrical System Engineering Engineering Engineering Universiti Malaysia Perlis Universiti Malaysia Perlis Universiti Malaysia Perlis Pauh Putra Campus Pauh Putra Campus Pauh Putra Campus 02600 Arau, Perlis 02600 Arau, Perlis 02600 Arau, Perlis MALAYSIA MALAYSIA MALAYSIA Email:[email protected] Email: [email protected] Email: [email protected] Yufridin Wahab Norshafinash Saudin School of Microelectronic Engineering School of Electrical System Engineering Universiti Malaysia Perlis Universiti Malaysia Perlis Pauh Putra Campus Pauh Putra Campus 02600 Arau, Perlis 02600 Arau, Perlis MALAYSIA MALAYSIA Email: [email protected] Email:[email protected] Abstract— This paper presents the design of a compact, good selectivity near the passband since they have no composite, low-pass filter circuit into microstrip line form attenuation poles [2,9]. So, both types of low-pass filters using a new, transforming method. The composite, low-pass always have the problem of converting the lumped circuit filter operating in the UHF range were designed and prototype into microstrip when the order number, N, implemented on an FR4 substrate. The circuits were increases, making the circuit larger or more complex. simulated and developed using Advanced Design Software (ADS) for both lumped element and microstrip filters. A Elliptic–function filters have attenuation poles near their correction factor was considered due to fringing inductance passband, making them attractive for highly-selective and capacitance. The ADS simulation results showed that applications [2,4]. The disadvantages of elliptic design the response of the microstrip line circuit of the composite, and implantation are very complicated, and have a ripple low-pass filter with fringing correction factor was well at both in passband and stopband section as well. And the agreement with its lumped circuit. This showed that the new passband elliptic filter consists of highly non-linear transforming method enabled to the lumped element circuit response especially near with band-edge [2,8-9]. into a microstrip line to solve the complex design of The composite low-pass filter is less complex and composite filters. having a sharp roll –off. It was designed by applying the Keywords — microstrip line filter; constant-k filter; m- image parameter method [1-2]. The image parameter [6] derived; microwave communication; composite low pass filter was initiated by defining the image impendence and voltage function for arbitrary reciprocals of a two-port I. INTRODUCTION network because these designed results are required for the cutoff frequency and attenuation characteristics. Microstrip filters always find an important place in During the design of the composite, low-pass filter, two many RF microwave applications. They are most widely of the important factors that must be taken into preferred for selecting or confining the microwave signals consideration are the constant-k filter section and the m- within specified spectral ranges. The challenges on the derived section. microwave filters with requirements such as improved Ashwani Kumar etal [3,4] designed a microstrip line performance, miniature size, lighter weight, and lower composite filter using the defected ground structure(DGS) cost are ever increasing with the emerging applications of method .Its shunt connected series LC circuits are wireless communications. transformed with either quarter-wave short circuiting When the order of the filter increases, the method of stubs or quarter-wave open circuiting stub[4,7]. The calculating the dimensions becomes complicated, and it is performance of DGS composite filter was verified by adequate to specify that the response occurs at minimum comparing lumped elements, microstrip line and DGS stopband and passband attenuation. The most Butterworth measurement results. Overall, the result of DGS based and chebyshev require a high-order design to ensure a 978-1-4799-3251-1/13 $31.00 © 2013 IEEE 385391 DOI 10.1109/AIMS.2013.79 Matching High-f Matching low pass filter achieved good stability and more shaper Sharp section cutoff section cut off response than that of microstrip line and the DGS. cutoff It is also having large rejection bandwidth. The m=0.6 constant m- m=0.6 1 k derived 1 performances of composite filter are improved by using Z Zo o 2 T m<0.6 2 defected ground structure. But the disadvantages of DGS is complex circuitry, high power consumption and image Z Z frequency problems. ZiT iT iT Stephane Pinel etal [5] state the compact planar and Figure. 1. Block diagram of circuit components in the composite filter vialess composite filter are designed by using the image [1, 6] parameter method and semiconductor component approaches which operate at C-V band. The lumped A. Constant-k T-section element vialess composite filter are fabricated by using liquid crystal polymer substrate, which consists of The nominal characteristic impedance of constant–k characteristic low cost solution RF, high performance, section is made a constant value for the assigned ultra compact, and millimeter wave application. The frequency, which is given in [1, 2, 3]. overall folded layout of composite filter occupies an ultra The values of L and C for constant K can be calculated compact area and optimized by using full wave simulation by using the following formula. IE3D. The combination of stepped impedance filter and ZL /2 folded stepped impedance resonator performed by lumped co (1) elements schematic filter. And the measurement result exhibit rejection of attenuation pole which is greater than /2 ZC co (2) -40dB.The design was only present lumped element at final layout optimization. Fine tune was performed for the overall structure in order to miniaturize the circuit and L/2 L/2 to avoid the impact of excessive stub length [5]. Mostly all works showed that image parameter method using in designing of lumped elements of C composite filter have not been mentioned clearly the ways of transforming the circuit into mictrosip line. So, a new approach of transforming lumped circuit into microtsrip Figure 2. Low-pass, constant-k filter section in T-network [2] line is presented correction factor due to fringing is introducing so that accurate dimension can be determined An m-derived, low-pass, T-section is shown in Figure 3. without changing the properties of the composite filter. When a new simple and direct approach method is mL/2 mL/2 applied, it can solve the combination complexity of 4 important sections, that is constant-k, matching section, mC m-drive and bisected- π section, of transforming lumped 1 m2 elements. L 4m HEORY OF OMPOSITE LOW PASS ILTER II. T C - F Figure 3. m-derived T-section [2] DESIGN The design of composite filter involved the input and The inductance and capacitance values can be calculated output impedance fixed as 50 ohm, and the required using [1, 2]. C" mC cutoff frequency response sets as 2.5GHz. The (3) development of composite low pass filter consideration the condition is compulsory to combining the constant-K 1 m2 in cascade and m-derived sharp roll off and matching L' L (4) section at input and output. Figure1show that the 4m important section combination of network constituted in Series component composite filter circuit. mL L" (5) 2 where L and C have the same values as the k-constant section. 386392 B. Matching Section By combining in cascade, the constant–k section, the m-derived of sharp-cutoff section, and the m-derived matching section, we can produce a filter with the desired attenuation and matching properties. The sharp-cutoff section with m < 0.6 places an attenuation pole near the cutoff frequency to provide a sharp attenuation reaponse, and the constant-k section provides the high attenuation further into the stopbands. The bisected π- section with m=0.6 are palced at the ends of the filter to match the Figure 6. Model for series inductor with fringing capacitors Similarly the capacitance, C with fringing its inductance norminal source and load impendance, Zo, to the internal image impendance, , of the constant-K section and the is modeled as a T-network as shown in Fig. 7 m-derived section.The matching networks are using the m = 0.6 bisected –π section, as shown in Figure 4 [1-2]. mL/2 mL/2 mC/2 mC/2 Z Zo o 2 1 m L 1 m2 L 2m 2m Figure 7. Model for shunt capacitor with fringing inductors For inductance, L, the length of the microstrip with Z iT characteristic impedance ZOL = 100 ohm can be calculated Figure 4. Bisected π- matching section [2] using Equation (6): C L S III. MICROSTRIP LINE DESIGN TECHNIQUES d 1D T d L sin D T (6) 2 E Z U The microstrip inductor and capacitor always oL produce fringing, which must be taken into account and And its fringing capacitor can be calculated as: must be corrected. Four conditions have been studied i.e., C S 1 D d T C fL tanD T (7) 1) the filter is converted directly without correction, 2) the Z E U resonance LC circuit is achieved with a quarter wave stub oL d short to ground, and 3) the resonance LC circuit is For capacitor, C, the length of the microstrip with achieved with a quarter wave stub without ground.4) the characteristic impedance ZOC = 20 ohm can be calculated filter is converted directly with correction The typical using Equation (8): composite filter in lumped components is shown in Fig 5. d 1 d sin CZ (8) C 2 oC And the fringing inductance can be calculated as; Z Cd S L oC tanD L T fC D T (9) E d U where c (10) d f r Figure 5.