Single-Balanced Mixer Project Final Presentation

1. Single-Balanced Mixer ProjectFinal Presentation RIT Senior Project Jared Burdick May 17, 2012

2. Introduction • What is a mixer? • A device used to convert frequencies. • Mixer is a term generally associated with converting higher frequencies to lower frequencies. • Where are they used? • Communication systems. • Radar applications. • How does a mixer work? • They take advantage of the non-linear properties of diodes. • The signal (RF) is “mixed” with another fixed (or tunable) frequency (LO) and a “difference” frequency (IF) is produced along with a number of predictable inter-modulation products. • There are several different configurations for mixers. • A single-balanced configuration was selected for this project. RF IF LO

3. Project Goals • Research Mixers • Understand theory, applications, configurations, and design trade-offs. • Design, Simulate, Prototype Mixer • Choose an appropriate configuration. • Develop design and simulation skills. • Mitigate risks and follow project plan. • Test mixer and compare simulated to actual performance. • Analyze results and offer possible future improvements / implementations.

4. Customer Needs Need to Update

5. Specifications Need to Update Several specifications were modified during the development (with customer approval)

6. System Block Diagram Need to Update

7. Components Used • Anaren 90º Hybrid Coupler (XC0900A-3S) • AvagoSchottky-Diode (HSMS-2822) • Coilcraft Chip Inductors (0805HT-12NTJB) • DLI Chip Capacitors (C06UL120G and C04UL2R7) • Gigalane SMA Connector (PAF-S05-007) • Murata Chip Inductor (LQW18AN39NG00D) • Rogers Substrate Material (RO4003C)

8. AWR Models 5th Order LPF Single-Balanced Mixer

9. Design Trade-offs & Decisions Made • Configuration • Use commercially available components wherever possible. • Removed BPF’s from the RF and LO paths due to not readily available. • Went to lumped-element LPF in the IF path for the same reason. • LO Leakage (LO to IF Isolation) • Increased to 5th order of LPF at IF port • Better rejection (approx. 20dB more) at 1GHz, which improved LO/IF isolation (SBM configuration offers no natural reduction of the LO). • Conversion Loss Flatness • Added micro-strip quarter-wave transformer to help match the impedance coming out of the diodes and going into LPF • Varied width of micro-strip line to see which gave the best conversion loss result • Changed the radial RF micro-strip choke into a shorted quarter-wave micros-trip stub • Tried Various angles for the radial choke and line width and found there was little improvement • Finally went to a true shorted quarter-wave stub • Gave the best result in simulation • Easy to provide ground to stub for physical layout • Added RF bypass capacitor shorted to ground after the diode provide additional filtering prior to the impedance transformation. • Improved conversion loss level and flatness

10. Simulation Results

11. Simulation Results Power Compression Approximate 1dB Compression Points

12. Circuit Layout &Assembled Unit Assembled Unit Circuit Layout SMA Conn Launch (RF In) λ/4 shorted stub λ/4 transformer Diode Pair Coupler RF Bypass Cap LPF SMA Conn Launch (LO In) λ/4 shorted stub SMA Conn Launch (IF Out)

13. Test Results – Summary Comparison All specifications were met by both units built. Both units had very similar performance.

14. Test Results Conversion Loss RF to IF Isolation 1-dB Compression Spurious Output

15. Test Results Unit #1 IF Output Spectrum LO = 1000 MHz RF = 850 MHz Horiz. Scale: 200 MHz/div Spurious Output

16. Conclusions • The prototype mixer met the target specifications. • There were differences between the simulated performance and the actual measured performance. • In general, the actual measured performance was consistent with the model. • LO to IF Isolation about 7-9 dB less. • Suspect that the LPF roll-off (rejection at higher frequencies) was less than modeled – this will need further evaluation to confirm. • RF to IF Isolation 3-5 dB less – LPF roll-off would contribute here as well. • Conversion Loss was slightly higher – connectors not modeled could be a contributor. • Future Iterations / Investigations. • Add BPF to the LO and RF input paths. • Investigate LPF performance. • Refine the AWR model (connectors, HFSS sub-models, etc.). • Work on final mechanical packaging concept.

17. Lessons Learned • Do your homework before starting to design • There are many trade-offs that need to be considered and decisions that need to be made in order to best match the expected performance to the application and requirements. • Ability to model the circuits accurately was key and greatly increased the probability of success. • Time is a scare resource • Valuable lessons can be learned even in non-ideal circumstances. • Figuring out project limitations early on in the process helped reduce risk and deliver the final product on time. • Look at contingency plans (alternate parts, fabrication alternatives etc.) • Identifying concrete action items helped to focus efforts and reduce wasted time. • Make use of all available resources • Eliciting feedback from other knowledgeable people proved invaluable. • There was a significant amount of information available on-line (technical papers, forums, etc.).