DESIGN AND IMPLEMENTATION OF 2-BIT LOADED LINE PHASE SHIFTER

Transcription

1 Proceedings of the 8 th National onference on DESIGN AND IMPLEMENTATION OF -BIT LOADED LINE PHASE SHIFTER MERY.J 1 MUTHUKUMARAN.P 1 M.E ommunication Systems, Sri Venkateswara ollege of Engineering, Sriprembudur, hennai, India. mercy.j89@gmailcom Assistant Professor, Department of EE, Sri Venkateswara ollege of Engineering, Sriprembudur, hennai, India muthu3nava@gmail.com Abstract - This paper proposes a newly designed -bit loaded line phase shifter for.4 GHz applications. The design use Koch fractal curves to reduce the size of the loaded line phase shifter. The concept is to be tested at.4 GHz using FR-4 dielectric material using microstrip technology. The reflection loss of the loaded line phase shifter is measured and it s found to be less than -db. The measured phase shift of 17.3 is obtained as against The insertion loss can be further improved by using lower loss dielectric material. Loaded line PS has the advantages of simplicity and low insertion loss for phase shifts of less than 45. The circuit consists of two equal two-state switchable admittances Y i = G i + jb i connected in shunt with a line section of characteristic impedance Z =1/Y and electrical length θ, where i =1, refers to the two bias states of the switching devices. Keywords - Bluetooth, FR4, Koch fractal, loaded line, Microstrip, d array, shifter, WLAN. I. INTRODUTION The shifters (PS) in a phased array antenna shifts phase of the incoming RF signal depending on control input [1], enabling antenna main beam to be steered at a faster rate without rotating antenna mechanically. Demand for high performance WLAN system at low cost has necessitated development of a miniaturized PS with reduced loss at low cost []. Design and development of various types of PSs (switched line, reflective line, loaded line and high-pass and low-pass types) are reported [3, 4]. Out of different types of PSs, loaded line PS offers simplicity and low insertion loss [5]. Miniaturized PSs have been reported using MEMS technology [6]. In addition, fractal technology has been used to reduce size of antenna [7]. Also, usage of Koch fractal in miniaturizing a branch line coupler is reported [8]. This paper presents a reduced size Koch fractal based -bit loaded line phase shifter, which was simulated using ADS and its performance is to be tested with conventional PS using Network Analyzer. II. LOADED LINE PHASE SHIFTERS(PSS) Each section of a loaded line PS (Fig.1) consists of a λ/4 transmission line symmetrically loaded at its ends by small susceptances for mutually cancelling reflections due to λ/4 separation. Susceptance values are controlled by semiconductor switches such as PIN diodes. Desired PS is obtained by changing electrical length through switching PIN diodes. Fig. 1: Layout of a section of conventional loaded line phase shifter The loading admittance of these elements is controlled with switching diodes to electrically shorten or lengthen the transmission line. The transition between the two admittance states produces a phase change of ((θ 1-θ ) these values are obtained from two different values of Y i ). The circuit design of the loaded-line phase shifter consists of the selection of values for the unknown parameters θ, Z, G i and B i (i= 1, ). The conductance G i results from ohmic losses in the loading elements Y i, and is typically small when low-loss switching devices are used. With low-loss loads, a good approximate solution is obtained by assuming that G i is equal to zero. The general expression for the electrical length θ and the characteristic impedance Y are given in (1) and (). Using these equations, the desired performance is therefore set by specifying B, Y, θ: 58

2 Proceedings of the 8 th National onference on θ = cos ( cos θ Z B sin θ ) 1 ' ' 1 B + B Y Y 1 (1) Y = Y cotθ () where Z is the characteristic impedance of the transmission line; θ is the electrical length of the transmission line and B is the shunt susceptances of the transmission lines. Open circuit Stub of λ/4 Short circuit stub of λ/4 Bias voltage supply Main transmission line Fig. Biasing circuit The design of loaded line phase shifter using micro strip lines requires the following parameters: 1. The characteristic impedance (Z T ) of the quarter wave transformer (λ/4 line).. The electrical length (βl) of the short stub. Microwave Associates MA4P789-87T pin diodes are used as a switch. Diode parameters for equivalent diode model were r =.35 V reverse bias voltage and Rf 1mA forward current. Switching between two susceptance values of each bit is done by applying proper bias voltages to PIN diodes. o-simulation of -bit conventional loaded line circuit (Fig.3) is to produce the phase shift of º (a cascade of 5.65º and 11.5º bit sections). During cascade of -bit sections, matching between sections is taken care of for low insertion losses. III. MINIATURIZATION USING KOH URVES Fractals are fragmented space-filling containers used to pack electrically large features efficiently into small physical areas. Koch fractals are characterized by iteration factor and iteration order. Iteration factor represents construction law of fractal geometry, and iteration order depicts how many iteration processes are to be carried out. Fractal geometries were utilized as reported [8]. For a straight microstrip line of λ/4 electrical length, the generation process of a Kochshaped microstrip line with iteration factor of 1/5 as shown in (Figure.4). Koch fractals are applied to shunt quarter wave transmission line and bias line of conventional loaded line PS with. iteration factor with iteration of one. Layout of 11.5º section of Koch loaded line PS is shown in (Figure.5). onventional -bit loaded line PS is miniaturized using Koch fractal technique (Fig.6). A reduction in area is achieved by application of Koch technique for -bit loaded line PS circuit 59 Fig 3: o-sim of conventional loaded line phase shifter Fig. 4 Koch-Fractal-shaped microstrip lines whose iteration factor is 1/5

3 T L 1 T L 1 9 T L r o s TL 1 5 T e e T L 1 4 T L 3 r o s 1 T L 5 T L 1 T L 1 3 T L T L 8 T L 1 T L 1 T e e 1 T L 6 T L 1 1 Proceedings of the 8 th National onference on line phase shifter. orresponding results are shown in Figure.7 and Figure.8. Fig. 5 Layout of 11.5º section of Koch Loaded line shifter (a) S-PARAMETERS S_Param SP1 Start=.3 GHz Stop=.5 GHz Step=1 MHz 1 V_D SR1 3 V_D SR 4 Term Term1 Num=1 Z=5 Ohm Term Term Num= Z=5 Ohm PinDiode1 PinDiode PinDiode3 PinDiode4 koch4 koch4_1 ModelType=RF Fig. 6 -Bit Loaded line PS using Koch-Fractal technique IV. SIMULATION RESULTS Both conventional and miniaturized loaded line phase shifters are designed for single bit and -bit sections on FR-4 substrate with 1.6 mm thick and ε r = 4.6. The design is simulated using Agilent-ADS 8(Advanced Design System). Table. I shows the simulated results for conventional 11.5 loaded line phase shifter. Table. II shows the simulated results for conventional 5.65 loaded line phase shifter. Table.III shows simulation results for conventional -bit loaded 6 (b) Fig. 7:onventional circuit magnitude plot and phase (11.5º): a) Diode ON; b) Diode OFF

4 Proceedings of the 8 th National onference on (a) (c) (b) (d) Fig. 8: onventional circuit magnitude plot and phase: a) Diodes (D1, D-ON); b) Diodes (D1-OFF, D-ON); c) Diodes (D1-ON, D-OFF); d) Diodes (D1, D- OFF) 61

5 Proceedings of the 8 th National onference on TABLE I. ONVENTIONAL 11.5º LOADED LINE PHASE SHIFTER Diode State Simulated Desired ON OFF TABLE II. ONVENTIONAL 5.65º LOADED LINE PHASE SHIFTER Diode State Simulated Desired ON OFF TABLE III. ONVENTIONAL -BIT LOADED LINE PHASE SHIFTER Bit Input Obtained Desired V ONLUSION A -bit loaded line phase shifter is designed using FR4 substrate at.4 GHz frequency. The ON and OFF state (forward and reverse bias) of the PIN diode is used to determine the phase shift of the circuit. The schematic, layout and co-simulation of -bit loaded line phase shifter are designed and simulated using ADS (Advanced Design System) software. The results are obtained for the schematic, layout and co-simulation -bit loaded line phase shifter. REFERENES [1]. Nakada K, Marumoto T & Iwata R, Stub switched phase shifter, in IEEE Antennas and propagation Society Int Symp, vol (salt Lake ity, Utah) July, []. Volakis J L, Antenna Engineering Handbook (McGraw 6 Hill, New ork, USA) 7. [3]. White JF, High power, p-i-n diode controlled, microwave transmission phase shifters, IEEE Trans Microwave Theory Tech, MIT-13 (1965) [4]. Opp F L & Hoffman W F, Design of digital loadedline phase shift networks for microwave thin-film applications, IEEE Trans Microwave Theory Tech, MIT-16(1968) 46. [5]. Bahl L J& Gupta K, Design of loaded-line p-i-n diode phase shifter circuits, IEEE Trans Microwave Theory Tech, MTT-8 (198) [6]. Tan G-L, Mihailovich R E, Hacker J B, DeNatale J F & Rebeiz G M, A -bit miniature X-band MEMS phase Shifter, IEEE Microwave Wireless omponents Lett, 13 (3) [7]. Ze-hai Wu, Sheng-li Lai, Xiao-zheng Lai & Rui-na Zhang, haracteristic investigation of Koch Island fractal patch, in Proc Int onf Asia-Pacific Microwave, vol 4 (Suzhou, hina) 5, pages 4-7. [8]. hen W-L & Wang G-M, Exact design of novel miniaturized fractal-shaped branch-line couplers using phase-equalizing method, IET Microwaves, Antennas & propagation, (8)