implementation of a wideband phase shifter for phased array antennas msc/m-tech electrical...

Implementation of a wideband phase shifter for phased array antennas

MSc/M-Tech Electrical Engineering FSATIE/CPUT

Vernon Davids

Supervised by

Dr. R. R van Zyl

© CSIR 2006 www.csir.co.za

Overview

• Introduction• Objective• Phase shifting• Wideband phase shifter overview

• Switched-filter• Reflection-type• Switched-line

• Methodology• Conclusion

Wideband phase shifters for phased array antennas29/11/2007 Vernon Davids


Introduction

• Modern microwave systems require large operating bandwidths• Phase shifters are utilised in phased array antennas to control

the phase in each element in the array in order to steer the direction of the beam

• Application areas include, phased array radars, satellite communication systems and measurement instrumentations

Wideband phase shifters for phased array antennas Vernon Davids29/11/2007


Objective

• Design and implement a wideband phase shifter for a phased array antenna


Phase shifting

• Time harmonic signal where • The time , , and • Solve phase • Possible to alter the phase by changing

tje phaset)(

v

lt

l

v

)2()( fltphase

frequencyf

lengthl

typermittivi

typermeabili


f 2 frequencyf


• Accomplished by series feeding the array and altering frequency

• From preceding equation

• , and results in phase in electrical length

• Signal travels physically and electrically to the

Phase shifting…Phase shifting by changing frequency (Frequency scanning)

1

c

klv

lc

v

lft .22

f

il ikl elementi th _

l l

c

f 2

k



Phase shifting…Phase shifting by changing length

• Utilised in series and corporate fed arrays• Different matched transmission line lengths

are switched in the signal path• Signal undergoes effective phase shift related

to the difference between selected line and reference line

• Switches used:PIN diodes, FETs

• Using substrate with high dielectric constant give rise to smaller designs

fsizephysical _



• Changing the dielectric properties of a medium that a signal propagates through

• Using gaseous discharge or plasma• Ferroelectric materials• Dielectric constant, function of the applied electric field over

material

Phase shifting…Phase shifting by changing permittivity

I

)(E



• Changing the permeability of the material that a signal propagates through

• Ferrimagnetic materials or ferrites magnetic field that the material is positioned in

• Ferrite phase shifter• Drive wire through ferrimagnetic rod • Cascading different lengths of ferrimagnetic rods give rise to

different discrete phase shifts

Phase shifting…Phase shifting by changing permeability

)(H



Wideband phase shiftersSwitched filter

• Switch between two filter networks (High/Low-pass)• Bandwidth ↔ Topology, bandwidth and isolation of switches used • Advantages

• Low cost• Small size• Low power• large Active Phased Array Radar (APAR)• Good broadband performance

• Disadvantages• Parasitics degrade performance

• PIN (P-type, Intrinsic, N-type) diodes, Field Effect Transistors (FETs) and Metal-Semiconductor Field Effect Transistors (MESFETs) are commonly used as switches



Wideband phase shiftersReflection type

• Utilises a directional coupler• Two equal reflection terminations• Bandwith≈1octave • Advantages

• If size reduced can be designed forapplications requiring compact size

• Can realize a phase shift of 0-360deg by cascading different loads • Good wideband performance

• Disadvantages • Coupler take up most of the PCB area • Careful design and optimization necessary for matching the coupler

and reflection terminations.



Wideband phase shiftersSwitched line

• Switch between appropriate lengths of matched transmission lines

• Signal undergoes an effective phase shift• PIN,FETs and MESFETs switches• Advantages

• Applicable phase shift characteristics • Simple structure, small number of

fabrication steps and negligible currentto drive RF switches when using FETs

• Good linearity for loaded type switched-line phase shifter

• Disadvantages • Susceptible to resonance and large phase deviation



Methodology

• Research• Simulation• Reflection and Switched-line phase shifters identified• RTPS:

• Good return loss and phase tuning range

• Switched-line:• Design simplicity

• Topology with best bandwidth performance is pursued• Phased array considered as end application and testing



Conclusion

• Phase shifters utilised in phased array antennas to control the phase in each element in the array

• Possible to alter phase of the signal by changing:• Frequency• Electrical length• Permitivity• Permeability

• Wideband phase shifters• Switched-filter• Reflection-type• Switched-line

• Bandwidth: Topology also isolation of switching device used



Thank you

Questions?


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