1. ARO MURI K-band Spatial Power Combiner Using Active Array Modules LY. Vicki Chen, PengCheng Jia, Robert A. York PA Workshop, San Diego 2002

2. ARO MURI Presentation Outline Passive System Antenna array, Higher order mode problem, Performance Amplifier Design Two-stage Amplifier, Flip-Chip IC, CPW-line Power Combiner Design considerations, Performance Conclusions

3. Spatial Power Combining Tray Approach Tile Approach Normal incident/outgoing waves Limited bandwidth in general Easier for monolithic design Challenge in thermal management Parallel incident/outgoing waves Broadband characteristics Good heat-sinking property Consuming more substrate area ARO MURI

4. System Overview Gradual transition from WR42 to the oversized waveguide Oversized waveguide (TE10,TE20) Active Devices Tapered-Finline Antennas Extended work from the X-Band Spatial Combiner Design Oversized Waveguide Environment – TE10, TE20 from 18 to 22GHz Fin-line to CPW line Transition Monolithic Circuit Design – Flip-Chip IC ARO MURI

5. Antenna Design Reference paper: Design of Waveguide Finline Arrays for Spatial Combining. Submitted to IEEE transaction on MTTs Klopfenstein Taper CPW line Design is based on the optimal taper design of the X-band system.Design is based on the optimal taper design of the X-band system. Finline to CPW line transitions – Eliminate the bond-wires.Finline to CPW line transitions – Eliminate the bond-wires. Air-bridges are needed to provide good grounding in the middle ground plane.Air-bridges are needed to provide good grounding in the middle ground plane. Use HFSS for simulation.Use HFSS for simulation. Ground Signal AlN substrate Finline to CPW line transitions ARO MURI Ground Signal

6. HFSS Simulation Dielectric Fin-line EtEtEtEt EtEtEtEt PMC PECPEC air EtEtEtEt Metal Waveguide Wall metal metal PMC PEC Simulate for 2x4 system.Simulate for 2x4 system. Simplify the problem by applying the boundary conditions.Simplify the problem by applying the boundary conditions. Impedance & Gamma vs. Gap-sizeImpedance & Gamma vs. Gap-size Finline – CPW TransitionFinline – CPW Transition Reflection coefficient for the taper design.Reflection coefficient for the taper design. By forcing the PMC boundary condition, the even mode does not exist in the system. ARO MURI

7. Effects of Mounting Grooves short circuit grooves The depth of the short circuit grooves has huge effect on the return loss d=λ/5 d=2λ/15 d Reflection Coefficient (dB) d The mounting grooves affect the optimal values of many parameters: Operating frequencyOperating frequency Effective dielectric constantEffective dielectric constant Substrate thicknessSubstrate thickness Single mode unilateral finline d b Small slots are affected more severely than broader slots. ARO MURI

8. Combining Efficiency Symmetrical loading is necessary to avoid TE20 mode and achieve efficient combining.Symmetrical loading is necessary to avoid TE20 mode and achieve efficient combining. ~ 76% combining efficiency is achieved.~ 76% combining efficiency is achieved. 6 cards (4x6 system) 50ohm Termination & Through-line measurement Frequency (GHz) Measurement for one card (asymmetrical) and two cards (symmetrical) system ARO MURI

9. Two-Stage Amplifier Design Flip-Chip Technology using CPW-line Design Challenges – Substrate modes are excited easily. Biasing circuitry is complicated. Good grounding should be maintained. Power devicePre-amp ARO MURI Thermal Management – FCIC Gain Enhancement – pre-amplifier Optimal load matching ADS/Momentum Simulations Ground Signal 8.56mm 13.5mm

10. Two-Stage Amplifier Design CPW-line Substrate Mode ARO MURI Quasi-TEM  eff  AlN  AlN >  eff >  Air Substrate mode is excited easily! Increasing the substrate thickness or reducing the width of the CPW-line could reduce the effect of the substrate mode. S21(dB) of the Two-stage Amplifier

11. Pout Gain PAE Two-Stage Amplifier Performance ARO MURI Return loss <-10dB for the operating frequencies. 27.3dBm output power with 20% PAE and 9.5dB power gain was obtained. Thin film (on-chip) and chip capacitors were both needed for biasing circuitry.

12. Combiner Performance Two Cards Measurement Small Signal Performance & Power Measurement @ 18GHz Two cards system (8 amplifiers) with 34dBm output power. 12.5% PAE – 62% Combining Efficiency (optimal: 76%) Phase difference between cards degrades the output performance the most. ARO MURI Pout (dBm) Gain (dB) PAE

13. Measurement ARO MURI

14. Statistical Errors in Arrays Ref: R. York, “Some considerations for Optimal Efficiency and Low Noise in Large Power Combiners”, IEEE Trans. Microwave Theory Tech. Phase errors and device failures are most important in large combiners ARO MURI SplitterCombiner G1G1 G2G2 GNGN A B out Output voltage: Output Power: r i = 0 or 1 Probability of device survival Change in power due to errors: Ensemble average:

15. Combiner Performance 6 Cards Measurement ARO MURI Six Cards System (6x4) – 2 devices failed. 10dB small signal gain. Absorbing material were added to prevent the in-band oscillations. Each cards was biased individually. Improper grounding could result in oscillations. Some chip resistors were added to prevent bias-line oscillations. Absorbing Material Signal cross-talk between bond-wires could induce in-band oscillations

16. Phase Noise Reduction ARO MURI SplitterCombiner G G G Amplifiers degrade phase noise due to internal nonlineariities which up convert low-frequency amplitude and phase noise to the carrier Noise contributed by the ensemble is reduced by 1/N (-13.4dB) compared with a single amplifier

17. Power Measurement ARO MURI Non-uniform excitation profile 37.3dBm output power @18GHz was obtained. Non-uniform excitation. Chip resistors were added for bias-line stabilization. Combining Efficiency: 53.7%.

18. Conclusion ARO MURI Passive combiner achieved 76% combining efficiency. 34dBm output power has been obtained for 2-tray system. 62% combining efficiency was obtained. 37.3dBm output power has been obtained for 6-tray system. 53.7% combining efficiency was obtained. Phase noise reduction compared with single amplifier. Stabilization should be maintained for all frequencies.