S INGLE -B ALANCED M IXER P ROJECT F INAL P RESENTATION RIT Senior Project Jared Burdick May 17, 2012 Multidisciplinary Senior Design Conference Kate Gleason College of Engineering Rochester Institute of Technology Rochester, New York 14623

I NTRODUCTION 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 LO IF

P ROJECT G OALS 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.

C USTOMER N EEDS Need to Update

S PECIFICATIONS Need to Update Several specifications were modified during the development (with customer approval)

S YSTEM B LOCK D IAGRAM Need to Update

C OMPONENTS U SED Anaren 90º Hybrid Coupler (XC0900A-3S) Avago Schottky-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)

AWR M ODELS Single-Balanced Mixer 5 th Order LPF

D ESIGN T RADE - OFFS & D ECISIONS M ADE 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 5 th 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

S IMULATION R ESULTS

Power Compression Approximate 1dB Compression Points

C IRCUIT L AYOUT & A SSEMBLED U NIT SMA Conn Launch (RF In) SMA Conn Launch (LO In) SMA Conn Launch (IF Out) LPF λ/4 transformer Diode Pair Coupler λ/4 shorted stub RF Bypass Cap Circuit Layout Assembled Unit

T EST R ESULTS – S UMMARY C OMPARISON All specifications were met by both units built. Both units had very similar performance.

T EST R ESULTS Conversion LossRF to IF Isolation 1-dB CompressionSpurious Output

T EST R ESULTS Unit #1 IF Output Spectrum LO = 1000 MHz RF = 850 MHz Horiz. Scale: 200 MHz/div Spurious Output

C ONCLUSIONS 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.

L ESSONS L EARNED 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.).