Antennas Studies for UWB Radio

Transcription

1 Antennas Studies for UWB Radio Program Review May 22 Professor Daniel H. Schaubert Electrical and Computer Engineering University of Massachusetts at Amherst Amherst, MA 3 schaubert@ecs.umass.edu

2 UWB Radio Antenna and Electromagnetics Tasks. Full-Wave Calculation of Receive Antenna Voltage (arbitrary input voltage waveform, antenna types, angle of incidence, load impedance, polarization, and T/R matching/shaping networks) 2. Modeling of Antenna Link with Multipath (model LOS and multipath signals, variable amplitude, possible polarity reversals) 3. Optimization of Transmit/Receive Link (define optimum metric, pulse shaping constraints, power spectral density shaping, antenna efficiency, antenna patterns)

3 Highlights. Time-domain analysis method developed Time-Domain Integral-Equation-Based Solver for Transient and Broadband Problems in Electromagnetics, A.O. Boryssenko and D.H. Schaubert, AMEREM 22, June Equivalent circuits for typical UWB antennas Results of full-wave electromagnetic analysis converted to equivalent circuits compatible with circuit simulation/optimization. 3. Optimization of Pulse Radiation from Simple Antennas Three methods studied. Some results in Optimized Ultra-wideband Radiation of Dipole Antennas with Triangular Driving Pulses, A.O. Boryssenko and D.H. Schaubert, AMEREM 22, June 22.

4 Some Simple Antenna Shapes Ø Da Wa La La A ε tanδ ε tanδ W2 Wa F W F W W La R R2 B W A

5 Time-Domain Integral Equation Analysis.5-m Thin-Wire Dipole Reception Driving source, V Driving current, ma Normalized spectrum, /Hz Current Incident Electric Field Terminal Current Power Spectra Driving source, V Driving current, ma Normalized spectrum, /Hz Current Scattering Patterns

6 Time-Domain Integral Equation Analysis.5-m Thin-Wire Dipole Comparisons of computed results to reference cases Conductance, /mohm Susceptance, /mohm Input Admittance :: Computed and Reference Data 2 Computed 5 Reference Length/Lambda 5 Computed Reference Length/Lambda RCS, dbm Monostatic RCS via scattered field for Θ=9grad Computed Reference Computed Reference Input Admittance RCS Radiation Pattern

7 Equivalent Circuits for Simple Antennas Wa 5 L L 2 L 3 C L R R 2 R La C C 2 C 3 C L C L R C 2 L 2 R 2 C 3 L 3 R 3 pf nh pf nh Ω pf nh Ω pf nh Ω Higher order resonances are primarily for electronic circuit design/analysis

8 Optimization of Pulse Radiation from Simple Antennas Triangular Voltage Pulse 5 Wa La τ τ2 τ/τ2 τ2/(τ+τ2).683 Transients Bow-tie dipole of.cm length and 5.cm width Zg=5 Ohm Voltage Waveform Feed-Point Current Transients Bow-tie dipole of.cm length and 5.cm width Zg=5 Ohm Voltage Waveform Feed-Point Current Current Spectrum Density Required Shape Actual Optimized Triangular pulse with some ringing. Current Spectrum Density Required Shape Actual Optimized Nearly optimum triangular pulse.

9 Transfer Function Synthesis V(ω) = Z(ω) I(ω) i(t) = F - { V(ω) / Z(ω) } Wa R R2. La 3 Relatively simple voltage waveforms yield moderately well localized current. Loop antenna requires more complicated voltage source to achieve comparable bandwidth and time localization. (Linear phase assumed.)

10 Matching Antenna to Bandwidth and Frequency Requirements 9: bandwidth at 8% level 3La Wa Time localization α /BW Size scaling would maintain simplicity of voltage waveform while increasing operating frequency GHz GHz

11 H-Bridge Voltage Driver E +.3V S SET Q L L2 R CL R Q Antenna L R C2 Feed Voltage Zinp_S Voltage E +/-.3V C R2 Antenna Voltage Zinp_A Antenna L2

12 Single Pulse Excitation of Flat Dipole Input impedance:: Flat linear dipole of 3.75cm length and.5cm width La.5 Wa Resistance, Ohm Waveform Waveforms 2 - Reactance, Ohm H-bridge driver & antenna Feed Point Antenna Terminals L Feed Voltage Zinp_S Voltage R E +/-.3V C C2 R2 Antenna Voltage L2 Zinp_A Antenna Norm. spectra Feed Point Antenna Terminals Spectrum modified by circuit & antenna

13 Flat Dipole Driven by H-Bridge Waveform 3 La.4 Wa Waveforms 2 - H-bridge driver & antenna Feed Point Antenna Terminals Waveform Norm. spectra Feed Point Antenna Terminals Waveforms and system efficiency highly dependent on parasitic elements and antenna impedance.

14 Summary of Accomplishments. Time-domain analysis method developed Several improvements made during the year. Ready to use for UWB antenna analysis and design. 2. Equivalent circuits for typical UWB antennas Used to better understand interaction of antenna terminal characteristics and driver circuit. Future use for circuit optimization. 3. Optimization of Pulse Radiation from Simple Antennas Simple antennas and simple pulses (triangular) yield surprisingly good results, but limited degrees of freedom for further improvement. Good wideband antennas and low-parasitic circuits needed. Ready to incorporate full-wave radiation, propagation and reception into analysis/design studies.