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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 Overview • • • • • • Introduction Objective Phase shifting Wideband phase shifter overview • Switched-filter • Reflection-type • Switched-line Methodology Conclusion Slide 2 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Introduction • Modern microwave systems require large operating bandwidths • Phase shifters are utilised in phased array antennas to control • Slide 3 29/11/2007 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 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Objective • Design and implement a wideband phase shifter for a phased array antenna Slide 4 © CSIR 2006 www.csir.co.za Phase shifting • • • • Time harmonic signal e jt where (t) phase The time t vl , v l , 2f and f frequency Solve phase phase (t ) (2fl ) Possible to alter the phase by changing f frequency l length permittivity permeability Slide 5 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Phase shifting… Phase shifting by changing frequency (Frequency scanning) • Accomplished by series feeding the array and altering frequency c 1 2 • c , f and k results in phase in electrical length t 2f l l c l 2 . kl v v l • From preceding equation f • Signal travels physically il and electrically ikl to the i Slide 6 29/11/2007 © CSIR 2006 th _ element www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids 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 physical _ size f • Using substrate with high dielectric constant give rise to smaller designs Slide 7 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Phase shifting… Phase shifting by changing permittivity • Changing the dielectric properties of a medium that a signal • • • propagates through Using gaseous discharge or plasma I Ferroelectric materials (E ) Dielectric constant, function of the applied electric field over material Slide 8 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Phase shifting… Phase shifting by changing permeability • Changing the permeability of the material that a signal • • propagates through Ferrimagnetic materials or ferrites material is positioned in Ferrite phase shifter Slide 9 29/11/2007 • • (H ) magnetic field that the Drive wire through ferrimagnetic rod Cascading different lengths of ferrimagnetic rods give rise to different discrete phase shifts © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids 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 Slide 10 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids 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 • • Slide 11 29/11/2007 Coupler take up most of the PCB area Careful design and optimization necessary for matching the coupler and reflection terminations. © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids 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 • Susceptible to resonance and large phase deviation • Disadvantages Slide 12 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Methodology • • • • Research Simulation Reflection and Switched-line phase shifters identified RTPS: • Good return loss and phase tuning range • Design simplicity • Switched-line: • Topology with best bandwidth performance is pursued • Phased array considered as end application and testing Slide 13 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids 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 Slide 14 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids Thank you Questions? Slide 15 29/11/2007 © CSIR 2006 www.csir.co.za Wideband phase shifters for phased array antennas Vernon Davids