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823MANOHARAN et al : A NOVEL MINIATURIZED LOADED LINE PHASE SHIFTERJournal of Scientific & Industrial ResearchVol. 69, November 2010, pp. 823-829

*Author for correspondenceE-mail: vkmanoharan@ece.psgtech.ac.in

A novel miniaturized loaded line phase shifter

V K Manoharan 1, S Sindhuja 1, S Deepak Ram Prasath 2, S Raju 2 and V Abhaikumar 21PSG College of Technology, Coimbatore, India

2Thiagarajar College of Engineering, Madurai, India

Received 14 June 2010; revised 12 August 2010; accepted 16 august 2010

This study proposes a novel design of phase shifter for WLAN applications, by using Koch fractal curves to reduce size of conventional loaded line phase shifter (PS). Proposed PS provides an area reduction (41.88%) in comparison withconventional PS.

Keywords : Bluetooth, FR4, Koch fractal, Loaded line, Microstrip, Phased array, Phase shifter, WLAN

IntroductionPhase shifter (PS) in a phased array antenna shifts

phase of incoming RF signal depending on control input 1,enabling antenna main beam to be steered at a faster ratewithout rotating antenna mechanically. Demand for highperformance WLAN system at low cost has necessitateddevelopment of a miniaturized PS with reduced loss atlow cost 2. Design and development of various types of PSs (switched line, reflective line, loaded line and high-pass and low-pass types) are reported 3-10 . Out of differenttypes of PSs, loaded line PS offers simplicity and low

insertion loss 8. Practical design of C-band MIC PS usingpin diodes is reported 9. Miniaturized PSs have beenreported using MEMS technology 12 , MMICtechnology 13,14 and metamaterials 15. In addition, fractaltechnique has been used to reduce size of antenna 16. Also,usage of Koch fractal in miniaturizing a branch linecoupler and a hybrid coupler is reported 17,18 .

This paper presents a reduced size Koch fractal based3-bit loaded line PS, of which a single bit loaded linesection was fabricated and its performance was testedwith conventional PS.

Loaded Line Phase Shifters (PSs)Each section of a loaded line PS (Fig. 1) consists of

a /4 transmission line symmetrically loaded at its endsby small susceptances for mutually canceling reflectionsdue to /4 separation. Susceptance values are controlledby semiconductor switches such as pin diodes. Desired

PS is obtained by changing electrical length throughswitching pin diodes. Loaded line PS is designed usingwell known closed form expressions 10 as

(1)

(2)

where Z 0, characteristic impedance of transmission line; , electrical length of transmission line; , requiredphase shift; Z 0

1, characteristic impedance of equivalentcircuit; B i, shunt susceptances, where i=1 when diode isin on condition and i=2 when diode is in off condition.

Microwave Associates MA4P789-287 pin diodeswere used as a switch. Diode parameters for equivalentdiode model were Cr=0.35 pf @ 20V reverse bias voltageand Rf=1.5 @ 10 mA forward current. Switchingbetween two susceptace values of each bit is done byapplying proper bias voltages to PIN diodes.

Co-simulation of 3-bit conventional loaded line circuit(Fig. 2) is to produce a phase shift of 157.5 (a cascadeof 22.5, 45 and 90 bit sections). During cascade of 3-bit sections, matching between sections is taken careof for low insertion losses.

Miniaturization Using Koch CurvesFractals are fragmented space-filling containers used

to pack electrically large features efficiently into small

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824 J SCI IND RES VOL 69 NOVEMBER 2010

physical areas. Koch fractals are characterized byiteration factor and iteration order. Iteration factorrepresents construction law of fractal geometry, anditeration order depicts how many iteration processes are

to be carried out. Fractal geometries were utilized asreported 17. Generation law of Koch curve facilitates tobegin with a specified initiator. Then a generator isapplied repeatedly in a lower scale to form fractals. Fora straight microstrip line of /4 electrical length, Fig. 3shows generation process of a Koch-shaped microstripline with iteration factor of 1/5. The condition that mustbe satisfied to get a reduced size micro strip line byapplying Koch fractal curve is as 17

(3)

Koch fractals are applied to shunt quarter wavetransmission line and bias line of conventional loadedline PS with 0.2 iteration factor with iteration of one.Layout of 22.5 section Koch loaded line PS is shownin Fig. 4. Conventional 3-bit loaded line PS isminiaturized using Koch fractal technique (Fig. 5). Areduction in area (44%) is achieved by application of Koch technique for 3-bit loaded line PS circuit.

Fabrication, Testing and Simulation

Single bit (22.5 section) of conventional (Fig. 6) andKoch (Fig. 7) designs were fabricated using a copperetching process. Substrate was FR4 (thickness, 1.6 mm;

r , 4.6). PIN diode (MA4P789-287 with SOT-23package) and capacitors were soldered on PCB afterfabrication. PIN diodes were grounded through via holes.PSs were tested using E5062A ENA series vector network

Fig. 1Layout of a section of conventional loaded line phaseshifter

Fig. 2Co-sim of conventional loaded line phase shifter

Fig. 3Koch-Fractal-shaped microstirplines whose iteration factoris 1/5

Line lengthLine width