DESIGN AND ANALYSIS OF RF MEMS SWITCHABLE LPF L. Sirisha Vinjavarapu* 1, P. Venumadhav 2

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1 ISSN IJESR/November 214/ Vol-4/Issue-11/ L. Sirisha Vinjavarapu et al./ International Journal of Engineering & Science Research ABSTRACT DESIGN AND ANALYSIS OF RF MEMS SWITCHABLE LPF L. Sirisha Vinjavarapu* 1, P. Venumadhav 2 1 M.Tech Student, PVP Siddhartha Institute of Technology, Vijayawada (A.P), India. 2 Asst. Prof, Dept. of ECE, PVP Siddhartha Institute of Technology, Vijayawada (A.P), India. This paper deals with a relatively new area of radio frequency (RF) technology based on microelectromechanical systems (MEMS). RF MEMS provides a class of new devices and components which display superior high frequency performance relative to conventional (usually semiconductor) devices, and which enable new system capabilities. In addition, MEMS devices are designed and fabricated by techniques similar to those of very large-scale integration, and can be manufactured by traditional batch-processing methods. In this paper, a novel approach for constructing a switchable low pass filter by using the radio the Radio Frequency (RF) Micro Electro Mechanical System (MEMS) technology. The tunability is achieved by unique MEMS tuning elements to perturb the electrical and magnetic fields surrounding the resonators. The use of such elements as a tuning mechanism results in a wide tuning range at a relatively low tuning voltage and fast tuning speed. The filter and the switches are designed at a frequency of 2 and 3 GHz. RF performance of switchable filter is carried out using Advanced Design System (ADS). Keywords: CPW, RF MEMS, LPF, Microstrip Transition. 1. INTRODUCTION The rapid development in wireless communication systems has led to an explosion of interest in improved design approaches for the radio frequencies and microwave areas [1]. The recurring demand for flexible, compact and low power wireless systems has generated the need for technological solutions that can dramatically reduce manufacturing cost, size, weight, improved performance and battery life [2]. Tunable systems are receiving an increasing attention since this is an elegant way to meet a great part of these requirements. Tunable systems can be developed using PIN diode, FET, Varactor diode, PLL synthesizer, RF MEMS technology to realize devices such as filters, switches, phase shifters and antennas. The importance of switchable and tunable filter is gaining momentum in the area of wireless communication. The present day switchable filter using a microstrip ring resonator loaded with two p-i-n diode has high loss performance and inter modulation distortion [3]. By replacing p-i-n diodes with varactor diode, an electronically tunable filter with isolation exceeding 2 db with 9% tuning bandwidth was demonstrated [4]. The use of MEMS technology for RF and Microwave application promises to solve several technological limitations that have plagued the high frequency electronics field for decades. MEMS switches can provide low loss, switching and tuning of microwave circuits with higher dynamic range, lower cost and greater flexibility than competing techniques [5]. In this paper, section 2 describes about the usage of Wilkinson power divider. RF MEMS switch, CPW microstrip transition and a LPF is focus on the section 3. The RF MEMS switchable LPF analysis and simulation results in section WILKINSON POWER DIVIDER Within the RF and microwave community, power dividers have served a prominent role for years. The main function of a power divider is to split a given input signal into two or more signals as needed by the circuit/system. A typical application for a power divider is to split a signal to feed multiple low power amplifiers, and then have the signals from the amplifiers recombine into a high power output signal. A signal is *Corresponding Author 825

2 either fed through an equal split power divider featuring a specific number of output ports, or a series of equal split power dividers. The phase difference between each signal being transmitted allows for electronic beam scanning, allowing the transmitted beam to be focused in different directions depending upon the phase difference. Fig 1 shows the ADS implementation of power divider. The power divider built using a single-sided copper clad RT Duroid 588 board from Rogers Corporation and hand cut copper tape traces to act as the microstrip conductor, while later iterations were constructed from milling double sided copper clad RT Duroid 588. The relative permittivity and loss tangent are 1.9 and.5 respectively. The calculated widths and lengths of the 5Ω and 7.7Ω lines are given below. Table 1: lengths and widths of the Wilkinson power divider W (width) (mm) L (length or radius) mm Angle (in degrees) 5Ω Ω Fig 1: ADS implantation of Power divider The simulated Wilkinson power divider is operated in the frequency range of with an operating bandwidth of 1.6 GHz, and a return loss at 2.8 GHz frequency is -32 db, the S- parameters are given in figures 2 and Fig 2: S11 parameter of the power divider db(s(3,1)) db(s(2,1)) Fig 3: The transmission parameters of the power divider Copyright 213 Published by IJESR. All rights reserved 826

3 3. RF MEMS SWITH AND LPF A RF switch should consist of a transmission line to carry the electromagnetic signal and an actuation mechanism for operating the switch. The transmission line should be comprised of an RF input, RF output, and segmented region for opening or closing the switch. In this paper, co-planar waveguides (CPW) were chosen for the transmission line. CPW is easily fabricated transmission line geometry because it can be created in a single, thin film deposition of a conductive material. For a series switch, the CPW must be segmented to enable an isolating switch state. To operate the switch, an actuated portion of transmission line must complete the segmented transmission line to allow the electrical signal to pass from the input to the output. For a shunt switch, the CPW transmission line is continuous and small portion of conductor is used to short circuit the electrical signal from the RF conductor to the ground plane. As with the series switch, the actuator enables contact between the RF conductor and ground with a small section of conductor. Both types of switches mentioned thus far use ohmic contact for completing the circuit paths. Alternatively, these contacts could utilize a capacitive contact in which a thin dielectric film is positioned between the two conductive regions. At elevated frequencies, the RF energy is capacitively coupled through the dielectric to the switch contact. Fig 4 and fig 5 are the RF MEMS switch is designed at two frequencies (2 and 3 GHz). The parameters are tabulated in the table 2. Fig 4: 2GHZ RF MEMS Switch Fig 5: 3GHZ RF MEMS Switch Table 2: RF MEMS SWITCH dimensions Freq CPW Centre Conductor width Ground width CPW length (L) 2 GHz.2mm GHz.2mm The simulated MEMS switch is operated in the frequency 2 and 3 GHz s with a return loss at 2 GHz frequency is db, 3 GHZ frequency is db. The S- parameters are given in figures Gap (S) Copyright 213 Published by IJESR. All rights reserved 827

4 freq= 2.GHz = Fig 6: Return loss parameter of 2 GHz Switch in ON State freq= 2.GHz = Fig 7: Insertion loss of 2GHz RF MEMS Switch in ON state freq= 2.GHz = Fig 8: Return loss parameter of 2 GHz Switch in Off State db(s(1,2)) freq= 2.GHz db(s(1,2))= Fig 9: Insertion loss of 2GHz RF MEMS Switch in OFF state -4 freq= 3.GHz = Fig 1: Return loss of 3GHz RF MEMS Switch in ON state Copyright 213 Published by IJESR. All rights reserved 828

5 . db(s(2,1)) freq= 3.GHz db(s(2,1))= Fig 11: Insertion loss of 3GHz RF MEMS Switch in ON State freq= 3.GHz =-7.885E Fig 12: Return loss of 3GHz RF MEMS Switch in OFF state db(s(2,1)) freq= 3.GHz db(s(2,1))= CPW to Microstrip Transition Fig 13: insertion loss of 3GHz RF MEMS Switch in OFF state The transition is designed at 2 and 3 GHz with the substrate thickness of.635 mm and dielectric constant of 1.9 [9]. whose layout window is shown in Fig. 5. The calculated step widths (s1, s2, s3) for the transition from CPW to microstrip are.55mm,.8 mm and.95 mm and length = 1mm respectively. The S parameter response for transition at 2GHz is shown in Fig 14. Table 3: CPW microstrip transition dimensions Freq CPW Centre Conductor width Ground width CPW length (L) Gap (S) 2 GHz.2mm GHz.2mm Fig 14: CPW to microstrip transition Copyright 213 Published by IJESR. All rights reserved 829

6 Fig 15: 2GHz CPW to microstrip transition -4 freq= 2.4GHz = Fig 16: S11 parameter of CPW to microstrip transition at 2 GHZ. -.2 db(s(1,2)) Fig 17: S12 parameter of CPW to microstrip transition at 2 GHZ Fig 18: 3GHz CPW to microstrip transition -4-5 freq= 3.GHz = Fig 19: S11 parameter of CPW to microstrip transition at 3 GHZ Copyright 213 Published by IJESR. All rights reserved 83

7 . -.2 db(s(1,2)) Fig 2: S12 parameter of CPW to microstrip transition at 2 GHZ Filter design The design of Low pass filter involves two main steps: one is to select an appropriate low pass prototype.the element values of the low pass prototype filters, which are usually normalized to make a source impedance g = 1 and the normalized frequency Ωc =1. are then transformed to the L C elements for the desired cutoff frequency and the desired source impedance, which is normally 5 ohms for microstrip filters [1-11]. The component values are tabulated in Table II. The next main step in the design of microstrip low pass filter is to find an appropriate microstrip realization that approximates lumped element filter. The element values for the low pass prototype with butterworth response at pass band ripple factor 3dB, characteristic impedance source/load = 5 ohms, are taken from normalized values gi i.e. g1,g2,g3,gn.the layout of stepped impedance low pass filter is shown in Fig.7.The S parameter response for 2 GHz low pass filter design is shown in fig. 8.The filter design steps are as follows: 1. Cutoff frequency = 2 and 3 GHz 2. Order of filter LA (w ) = 1 log1 {1+ ε (ω / ωc)2n } (1) ε={antilog1la/1}-1;l=3db (2) 3. Prototype values of filter g=1;gn+1=1 (3) gk =2sin{(2k-1)П/2N} (4) k = 1, 2 N 4. After impedance and frequency scaling : C K = CK / R ω c (5) L K = LK R /ω c (6) 5. For distributed design the electrical length: Capacitor section = Zl/R CK (7) Inductor section = LK R/ Zh (8) Table 4: filter dimensions Filter Section Impedance 2GHz-Width (mm) 2GHz- Length (mm) 3GHz-Width (mm) 3GHz-Length (mm) L1(C1) L2(L2) L3(C3) L4(L4) Source & Load Copyright 213 Published by IJESR. All rights reserved 831

8 Fig 21: Design of 2 GHz LPF in ADS software db(s(2,1)) -4-5 Fig 22: S parameters of 2 GHz filter Fig 23: design of 2 GHz LPF in ADS software -5 db(s(2,1)) RESULTS AND DISCUSSION Fig 24: S parameters values of 3 GHz filter The proposed Switchable Low Pass Filter shown in Fig.9. Low Pass Filter is designed using microstrip transmission lines. RF MEMS switches are used to achieve wider tunability and better RF performance. To maintain the overall characteristics impedance as 5 ohm, the total number of transitions used is n=3. Copyright 213 Published by IJESR. All rights reserved 832

9 Fig 25: Layout Model for RF MEMS switch RF Performance Fig 26: MEMS switchable LPF at 2GHz ON state and 3GHz switch OFF state RF performance of the switchable Low Pass Filter in the OFF and ON states of the switch are obtained using ADS EM simulator. Fig.1 and 11 shows the variation of scattering parameters for the Switchable Low Pass Filter in the ON and OFF states of the switch.when the switch is ON at 2 GHz and OFF at 3GHz, the simulation results in db insertion loss, db return loss and db isolation. Similarly when the switch is ON at 3GHz and OFF at 2GHz, the simulation results in db insertion loss, -6.9dB return loss and db isolation Fig 27: MEMS switchable LPF at 2GHz OFF state and 3GHz switch ON state m5 m4 db(s(1,3)) db(s(1,2)) -4-8 m4 freq= 2.GHz = m6 freq= 3.GHz db(s(1,3))= m m5 freq= 2.GHz db(s(1,2))=-.162 Fig 28: S parameter response for Switch ON at 2 GHz and OFF at 3GHz Copyright 213 Published by IJESR. All rights reserved 833

10 m6 m5 db(s(1,3)) db(s(1,2)) -4-8 m4 m4 freq= 2.GHz db(s(1,2))= m6 freq= 3.GHz db(s(1,3))=-1.28 m5 freq= 3.GHz = CONCLUSION Fig 29: S parameter response for Switch ON at 2 GHz and OFF at 3GHz In recent years, the field of MEMS has grown very fast and merged with many defense and commercial applications. Much of this activity has been driven by the ability of MEMS to reduce the cost, and improve the performance of, transducers and actuators previously fabricated by hybrid techniques. These benefits have stemmed from the compatibility of MEMS with silicon-based microelectronics and surface and bulk micromachining. RF MEMS based switchable low pass filter has been proposed in this paper. From the simulation result it is clear that switchable low pass filter have low insertion loss and better isolation making it suitable for satellite application. Further we can implement MEMS tuning elements have been applied to demonstrate a high tunable dielectric resonator filter with a wide tuning range. The integration of MEMS with dielectric resonators can lead to the realization of miniature tunable filters with a reasonably high Q factor. REFERENCES [1] Okazaki H, Atusushi. MEMS based reconfigurable RF circuits for future mobile terminals. Asia pacific microwave conference, 27. [2] Huang F, Fouladi S. A Novel MEMS based Tunable Dielectric Resonator Filter, /11/$26. C211 IEEE. [3] Tripathi VK, Wolff I. Perturbation analysis and design equations for open and closed ring microstrip resonators. IEEE Transaction and Microwave theory Technology, April [4] Wu YS, Rosenbaum FJ. Mode Chart for Microstrip ring resonators. IEEE Transaction and Microwave theory Technology, July [5] Larson LE. Microwave MEMS technology for next generation wireless communication, IEEE MTT-S- Digest, [6] Qian JY, Li GP. A Parametric Model of MEMS capacitive operating at Microwave Frequencies. IEEE AP-S International Symposium Boston, 2. [7] Wang C, Guo XL, Lai Z-S. A Novel Tunable Low Pass Filter Based on MEMS and CPW, The Ninth International Conference on Electronic Measurement and instruments, IEEE 29 [8] Wang C, Guo XL, Lai Z-S. A Reconfigurable RF MEMS Low Pass Filter Based on CPW Periodic Structures, IEEE 28. [9] Johnson W, Lee CH. Novel Design for Coplanar Waveguide to Microstrip Transition, IEEE MTT-S Digest, 21. Copyright 213 Published by IJESR. All rights reserved 834

11 [1] Singh N, Dhiman S, Jain P, Bhardwaj T. Design of Stepped impedance Microstrip line Low Pass Filter for Wireless Communicatiion. International journal of Advances in Computer Networks and Its Security, March 211. [11] Singh N, Kumar A, Singh P. Low Pass Filter for L Band Application using stepped impedance Microstrip lines. Journal of Engineering research and studies 211; II(II). [12] Filter-Tunable,Low Pass SMT 2.2 GHz 4. GHz, Hittite Microwave Corporation vo1.11. [13] Yao H-W, Zaki A. Analysis and Design of Microstrip to Waveguide Transitions. IEEE Transcation on Microwave theory and techniques 1994; 42(12). Copyright 213 Published by IJESR. All rights reserved 835