Time-modulated arrays for smart WPT

Transcription

1 Time-modulated arrays for smart WPT Diego Masotti RFCAL: RF circuit and antenna design Lab DEI University of Bologna, Italy Graz, March 3, 25

2 Outline Time-modulated arrays (TMAs) architecture TMAs possible applications Description of the nonlinear/electromagnetic CAD tool for time-modulated array (TMA) analysis/design Smart WPT with TMA 2

3 TMA architecture Switches controlled by pulse sequences T M Array factor of a standard linear array AF( θ, φ) = N k= Λ k e jδ k e jkβlcosψ Array factor of a linear TMA AF( θ, φ, t) = N k= Λ k e jδ k U k ( t) e jkβlcosψ 3

4 TMA regime T M, f M : period and frequency of switch modulation T, f : period and frequency of sinusoidal RF carrier Pulse of a generic control sequence T M Time T M >> T T Carrier n j2π ( f + ) = = hfm t jkβlcosψ AF( θ, φ, t) AFh ( θ, φ, t) e Λkuhk e h= h= k= The superimposed switch modulation makes the array able to radiate not only at the fundamental carrier (h=), but also at the sideband harmonics (h ) 4

5 TMA radiation Fundamental radiation pattern f ) Sideband radiation pattern (@ f ± hf M ) Normalized far-field (db) 5

6 TMA high reconfigurability The use of time as a further design parameter allows an almost unlimited control sequence combinations in TMAs The ease of implementation (no phase-shifters) The fast software control Antenna reconfiguration in real time! Make TMA a versatile and adequate radiation system for modern wireless applications (e.g. Software Defined Radio) 6

7 TMA applications Reduce self-interference in the broadside direction (θ= ) due to the desired signal f ± hf M (h ) (Sideband radiation suppression) Normalized E (db) h= h= h= θ ( ) L. Poli, P. Rocca, L. Manica, A. Massa, Pattern synthesis in time-modulated linear arrays through pulse shifting," IET Microwaves, Ant. & Prop., vol. 4, no. 9, pp , Sept. 2 7

8 TMA applications Suppress undesired interference coming from f ± hf M (h =,, 2, ) (Harmonic nulling) L. Poli, P. Rocca, G. Oliveri, and A. Massa, Adaptive nulling in time modulated linear arrays with minimum power losses, IET Microwaves, Antennas & Propagation, vol. 5, no. 2, pp , 2 8

9 TMA applications Exploitation as a multi-channel system (Harmonic beamforming) Normalized switch-on time Switch number Normalized E (db) h= h= h= θ ( ) L. Poli, P. Rocca, G. Oliveri, A. Massa, Harmonic beamforming in time-modulated linear arrays through particle swarm optimization", IEEE Trans. Ant. & Prop., vol. 59, no. 7, pp , July 2 9

10 TMA optimization TMA design methods focus on control sequence optimization Variable Aperture Size (W. H. Kummer et al. 963) Ideal radiating elements Normalized switch-on time Switch number Binary Optimized Time Sequences (S. Yang et al. 25) Ideal control switches design parameter: impulse length Pulse Shifting (L. Poli et al. 2) design parameter: impulse sub-intervals design parameters: impulse length switch-on instant

11 NL/EM TMA co-simulation Piecewise Harmonic-Balance method EM-based linear subnetwork 5 Ω nh D D3 D5 D7 D9 D D3 D5 5 Ω. pf D2 D4 D6 D8 D D2 D4 D6 5 Ω Nonlinear subnetwork Linear subnetwork nh A nonlinear subnetwork, containing the diodes A linear subnetwork, including the EM-based part (the array and the feeding network, in the present case) the lumped components used for biasing and DC-blocking Symmetrical bias

12 NL/EM TMA co-simulation Modulated far-field evaluation T M =2π/ω M >> T =2π/ω D2 D4 D6 D8 D D2 D4 D6 circuit-envelope HB D D3 D5 D7 D9 D D3 D5 fast carrier time i ( i) A harmonics of the unmodulated regime time-dependent complex k-th envelope (or modulation law) n H N B ( i) ( i) ( i) ( t, tm ) = Re I A, k ( tm ) exp( jkωt) I A k ( tm ) = I A, kh exp( jhωmt k= h= N B no. of harmonics for modulation slow modulation time spectrum description, M ) 2

13 3 ( ) ( ) ( ) [ ] ( ) ( ) ( ) [ ] { } + + = = = = M M i A i i n i n i M i A i i M dt t di A A r j r j t I A A r r j t r A A ) ( ;, ˆ ;, ˆ exp ) ( ;, ˆ ;, ˆ exp ) ;,, ( ) (, ) ( ) ( ) (, ) ( ) ( ω ω φ θ φ θ ω ω φ θ ω φ θ β ω φ θ ω φ θ β φ θ φ θ φ θ E NL/EM TMA co-simulation Field envelope at the fundamental harmonic are the scalar components of the normalized field are generated by EM simulation with only the i-th monopole excited by a unit-current sinusoidal source of angular frequency ω The EM analyses are carried out once for all ) ( ) ( θ, i i A A φ EM data-base

14 Co-simulation results 6-monopole planar linear array operating at f =2.45 GHz The substrate is a.635 mm-thick Taconic RF6A (ε r = 6.5, GHz) 7.8mm λ/2 partial ground plane for the feeding network y Nonlinear subnetwork containing the diodes D. Masotti, P. Francia, A. Costanzo, V. Rizzoli, "Rigorous Electromagnetic/Circuit-Level Analysis of Time-Modulated Linear Arrays," IEEE Trans. Ant. & Prop., vol.6, no., pp , Nov. 23. x 4

15 TMA with Dolph-Chebyshev pattern Sinusoidal carrier f = 2.45 GHz, P RF = dbm Switch modulation frequency f M = khz (f M << f ) Rectangular pulses with repetition period T M =. ms and amplitude V bias = 3 V are applied at the 8 bias ports (symmetrical excitation) A uniform sequence of N S = envelope sampling instants t n is chosen within the.9.8 pulse repetition period.7.6 A VAS pulse sequence.5 reproducing the Dolph-.4.3 Chebyshev pattern with.2. side lobe level (SLL) = -3 db is chosen Normalized switch-on time Switch number 5

16 Radiation patterns E N B k ( tm ) = Ekh exp( jhωmtm h= N B k=, h=: 2.45 GHz fundamental k=, h=: 2.45 GHz first harmonic ) Normalized E (db) h= h= h=2 k=, h=2: GHz second harmonic θ ( ) Known problem of VAS sequences: unwanted sideband radiation 6

17 Normalized E (db) Modulation frequency range Control sequence modulation frequency (f M ) variation f M=kHz f M=kHz f M=MHz f M=MHz Radiation patterns at 2.45 GHz -3-3 θ ( ) E [V/m] High values of f M result in the gradual disappearance of some commutations and unwanted SLL increase f =khz M f =khz M f =MHz M f =MHz M Broadside field envelopes at 2.45 GHz Sampling instant f M max khz 7

18 Normalized E (db) Nonlinear diodes effect Input power level (P RF ) variation P =dbm P =dbm P =2dBm P =3dBm RF RF RF RF h = Radiation patterns at 2.45 GHz θ ( ) At high power levels the bias voltage is completely overrun, because a bigger portion of RF signal is rectified by the nonlinear diodes and superimposed to bias Normalized E P RF=dBm P RF=dBm P =2dBm RF P =3dBm RF Broadside field envelopes at 2.45 GHz Time (µs) P RF max dbm 8

19 TMA with Pulse Shifting pattern A symmetric PS pulse sequence with SLL = -3 db is chosen h= h= h=2 Note that the time-consuming EM-based database ( i) ( i) consisting in the A A coefficients is always the same θ, φ Normalized E (db) Radiation patterns at 2.45 GHz and first two harmonics θ ( ) 9

20 Smart WPT with TMA The versatility of TMAs allows a smart transfer of power by means of a two-step procedure Scenario: room with randomly placed tagged objects st step: Localization of tags the sole two-inner-element sub-array is operating in this phase (the other 4 peripheral switches are left open) partial ground plane nonlinear switches 2

21 Localization of tags By properly driving the switches of an array of two isotropic elements the pattern can be steered: U (t) U τ 2 (t) d d τ Sum (Σ) f.5t M T M t.5t M T M t A. Tennant, B. Chambers, A Two-Element Time-Modulated Array With Direction-Finding Properties," IEEE Antennas and Wireless Prop. Lett., vol. 6, pp , θ ( ) Difference ( ) f +f M Difference ( ) f -f M 2

22 Localization of tags By properly driving the two inner switches of two real dipoles: Received Maximum Power Ratio db db MPR( θ ) = Σ ( θ ) ( θ ) RSSI RSSI θ i peak ; i=,, N tag List of tags position Normalized field (db) Σ ( d=) ( d=8%) ( d=6%) ( d=24%) ( d=32%) θ ( ) f + f M f - f M D. Masotti, R. Marchukov, V. Rizzoli, A. Costanzo, Far-field Power Transmission by Exploiting Time-modulation in Linear Arrays," IEEE WPTC 25, accepted for publication 22

23 Transfer of power to tags Once the tags position has been recordered: 2 nd step: Transfer of power to tags The whole 6-element array is driven by proper pre-loaded control sequences involving all the switches Possible decision rule: i. split the scanning region (θ [-6 6 ]) into sectors of amplitude equal to the half power beam width (HPBW) ii. for each θ peak falling in the sector centered around θ HPBW, the preloaded control sequence pointing the first harmonic to the θ HPBW direction is used Normalized E (db) θ j HPBW HPBW= θ ( ) 23

24 Transfer of power to tags Case : θ peak falling into the sectors centered around θ HPBW = -3,, 3 f Normalized switch-on time Switch number Normalized E (db) θ ( ) Simultaneous powering of the 3 tags f + f M f - f M 24

25 Transfer of power to tags Case 2: θ peak falling into the sectors centered around θ HPBW = -2, 2 Fundamental radiation is switched-off U k (t) - t r τ/2 New driving sequence t f τ * T M τ/2 t f f + f M Normalized switch-on time Switch number Normalized E (db) - f - f M θ ( ) 25

26 Diego Masotti University of Bologna 26