Characterization of Spatial Power Waveguide Amplifiers

Transcription

1 Characterization of Spatial Power Waveguide Amplifiers Authored by: Matthew H. Commens Ansoft Corporation Ansoft 003 / Global Seminars: Delivering Performance Presentation #

2 Outline What is a Spatial Waveguide Amplifier Characteristics of High Power, High Frequency Amplifiers EM Simulation of Spatial Waveguide Amplifiers System Simulation and Comparison to Measurements Additional Considerations Conclusions and References

3 What is a Spatial Waveguide Amplifier Ø Technique for distributing amplification across a number of low power MMIC amps to produce higher total output power amplifier. Hybrid divider/combiner Ø Significant area of research for ~7 years

4 Characteristics of High Power, High Frequency Amplifiers Traditional approach utilizing vacuum tube/klystron devices: Expensive and bulky!

5 Why Spatial Waveguide Amplification? Solid state devices are attractive but high power types either unavailable or too expensive Distribute amplification across multiple, lower power and cost, solid state devices Traditional hybrid divider/combiners are lossy, especially at higher frequencies. Use Spatial Waveguide Power Combining as a high frequency, low loss, hybrid divider/combiner.[] Spatial Power Amplifier Using A Passive and Active TEM Waveguide Concept, Belaid, M; Wu, K.; IEEE MTT Vol 5, No. 3

6 Details of Spatial Waveguide Amplifier Example: Kµ band amplifier,.4 to 8 GHz. [] The hybrid combiner/divider Stage : WR6 waveguide (6 mil X 3 mil) Stage : Finline antenna with Klopfenstein Taper Stage 3: Slotline to microstrip transition Finline antenna w Klopfenstein taper Slotline to microstrip WR6

7 Details of Spatial Waveguide Amplifier, cont. Arranged in 6X tray topology along crosssection of waveguide., 50 ohm microstrips parallel feed 00mW (3 dbm) MMIC amplifiers. Finline, slotline and microstrip on 0mil Duroid substrate, e r =.

8 Details of Spatial Waveguide Amplifier Output stage is mirror of input stage GaAstek ITT350D

9 Simulation and Analysis of Spatial Waveguide Power Amplifier Overall structure is electrically large and relatively complex Be Smart. Break simulations down into manageable sections

10 Port Simulation and Analysis of Spatial Waveguide Power Amplifier, cont. Simulation in three stages Waveguide with finline array simulated in HFSS Slotline to microstrip transition simulated in Ansoft Designer Planar EM MMIC amp simulated with behavioral model in Ansoft Designer System tool Port Three stages combined in Ansoft Designer System tool Port Port

11 Waveguide and Finline Array Ansoft HFSS simulation of WR6 waveguide with 6 card finline array. TE0 field distribution at waveguide input

12 Waveguide and Finline Array, cont. Each card has two Klopfenstein tapers [, ]. Tapers are complex curves designed to transform from waveguide impedance to ~00 ohm slotline impedance.

13 Waveguide and Finline Array, cont.

14 Waveguide and Finline Array, cont. Coupling Parameters: Non-uniform due to field distribution of TE0 mode Problem: Non-uniform illumination not ideal for hybrid divider/coupler

15 Waveguide and Finline Array, cont. Solution: Excite uniform TEM mode in waveguide How? Define sidewalls as perfect H boundaries

16 Waveguide and Finline Array, cont. Perfect-H Boundary? Easy to do in a field simulator but how to realize in practice. Uniplanar Compact-Electromagnetic Bandgap (UC-EBG) structure UC-EBG: A class of Frequency Selective Surface (FSS) whose periodic loading creates an open circuit within a narrow passband. Behaves as a magnetic conductor.

17 Waveguide and Finline Array, cont. As a zeroth order approximation, simulate UC-EBG walls as perfect H boundary. Field distribution at waveguide input

18 Waveguide and Finline Array, cont. Coupling Parameters: Uniform due to TEM field distribution Uniform illumination of all twelve MMIC amps

19 Slotline to Microstrip Slotline to microstrip transition: Simulated in Ansoft Designer Planar EM Open quarter-wave stubs couple slotline to microstrip MMIC Port finline Port Quarter-wave section transforms 00? to 50? microstrip impedance

20 Slotline to Microstrip, cont.

21 Slotline to Microstrip, cont. Check continuity of waveguide to microstrip. Ansoft Designer Circuit tool Waveguide HFSS Planar EM Port Port Port3 Port4 Port5 Port6 Port7 Port8 Port9 Port0 Port Port Port3 TE0 Microstrips TEM

22 MMIC Amplifier Model Amplifier Model: Ansoft Designer System tool ~ 0 db SSG Psat=3dBm

23 Spatial Waveguide Amplifier Full Model: Ansoft Designer System tool Port Port Port Port Port Port HFSS N-port subcircuit

24 Spatial Waveguide Amplifier, cont. Full Model: Ansoft Designer System tool, HFSS subcircuit Use data normalized to Z pv from HFSS Use correct port impedances Port For TE0 configuration z0 = (B/A)pfµ 0 /ß 0 A=6mil, B=3mil ß 0 = k -(p /A)

25 Spatial Waveguide Amplifier, cont. Individual amplifier outputs Port Port Port3 Port4 Port5 Port6 Port7 Port8 Port9 Port0 Port Port Port3 TE0 TEM

26 Simulation and Analysis, cont. Simulation of Spatial Waveguide Amplifier Ansoft Designer System TEM (UC-EBG) TE0 Fig. : Spatial Power Amplifier Using A Passive and Active TEM Waveguide Concept, Belaid, M; Wu, K.; IEEE MTT Vol 5, No. 3

27 Appendix: HFSS Analysis of UC-EBG Surface UC-EBG: -D periodic lattice patterned on a metallized dielectric substrate. In narrow passband, behaves as a magnetic conductor. -Zeroth order, model as perfect H boundary

28 Appendix: HFSS Analysis of UC-EBG Surface, cont. st order: Represent surface as a high impedance boundary condition. Determine behavior by modeling unit-cell of structure excited with TEM mode. perfect-h TEM port S 5.5 GHz

29 Appendix: HFSS Analysis of UC-EBG Surface, cont. UC-EBG surfaces can be represented an effective complex surface impedance, ZL ZL=Z0(-G)/(+ G), where Gis the complex reflection coefficient

30 Appendix: HFSS Analysis of UC-EBG Surface, cont. Fit data to equivalent circuit lumped element model to represent frequency dependent impedance boundary condition. Port L C

31 Other Considerations UC-EBG surface is narrow band. Current research investigating tuning UC-EBG surface with varactor diodes. [] Other novel approach to uniform amplification distribution is arranging cards around coaxial waveguide. [7]

32 Conclusions Spatial Waveguide Power Combining is a viable approach for a high frequency hybrid combiner/divider amplifier network Implementing a TEM waveguide structures using EC-UBG sidewalls can improve overall efficiency and amplifier output by distributing power uniformly across amplifiers. Entire device can be simulated end-to-end with Ansoft s HFSS and Ansoft Designer

33 References [] Spatial Power Amplifier Using A Passive and Active TEM Waveguide Concept, Belaid, M; Wu, K.; IEEE MTT Vol 5, No. 3 [] A Transmission Line Taper of Improved Design, Klopfenstein, R. W.; Proceedings of the IRE, January, 956 [3] A Novel TEM Waveguide Using Uniplanar Compact Photonic Bandgap (UC- PBG) Structure, Yang et. al. IEEE MTT Vol 47, No. [4] 0 W Spatial Power Combining in Waveguide, Cheng et. al.; IEEE MTT-S, Int. Microwave Symposium Digest, June 988, pp [5] 40-W CW Broad-Band Spatial Power Combiner Using Dense Finline Arrays, Cheng et. al. IEEE MTT Vol 47, No. 7 [6] 0 W X-Band Spatially Combined in Power Amplifier, Cheng et. al. IEEE MTT Vol 47, No. [7] Broadband High Power Amplifier Using Spatial Power Combining Techniques, Jia et. al. RF and Microwave Group, Caltech