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

Slide 2 © CSIR Overview Introduction Objective Phase shifting Wideband phase shifter overview Switched-filter Reflection-type Switched-line Methodology Conclusion Wideband phase shifters for phased array antennas 29/11/2007 Vernon Davids

Slide 3 © CSIR 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 Davids 29/11/2007

Slide 4 © CSIR Objective Design and implement a wideband phase shifter for a phased array antenna

Slide 5 © CSIR Phase shifting Time harmonic signal where The time,, and Solve phase Possible to alter the phase by changing Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 6 © CSIR 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) Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 7 © CSIR 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 Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 8 © CSIR 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 Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 9 © CSIR 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 Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 10 © CSIR Wideband phase shifters Switched 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 shifters for phased array antennas Vernon Davids 29/11/2007

Slide 11 © CSIR Wideband phase shifters Reflection type Utilises a directional coupler Two equal reflection terminations Bandwith≈1octave Advantages If size reduced can be designed for applications 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 shifters for phased array antennas Vernon Davids 29/11/2007

Slide 12 © CSIR Wideband phase shifters Switched 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 current to drive RF switches when using FETs Good linearity for loaded type switched-line phase shifter Disadvantages Susceptible to resonance and large phase deviation Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 13 © CSIR 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 Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 14 © CSIR 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 Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007

Slide 15 © CSIR Thank you Questions? Wideband phase shifters for phased array antennas Vernon Davids 29/11/2007