The Active Circulator Insertion V tr Isolation V ant V rx Specs Insertion Loss < -.5dB Isolation > -15db Frequency > 30 MHz 10W < Power < 50W

3 NPN Circulator Small Signal Diagram Purpose: Design a CCW circulator out of a 3-port, 3-transitor network. Design: Construct h-parameter admittance matrix. Then find transistor parameters that make it behave like a circulator.

Tanaka-Lee Schematic

Experiment Results Operating Points: V trs = 100mV, f = 1kHz Results: Isolation = dB, Insertion Loss = dB Power = 1.13mW Power = 1.13mW

Simulation

Considerations Cons: Bias Current V be Overdrive R pi Sensitivity Pros: High Frequency Parameters Easily Calculated Symmetric

Basic Model Purpose: A more “flexible” op-amp Design Specs: V1=V2=7.5VV3=-0.8VIR1=IR2=1mA

3-Port Scheme Idea from the topology in the proposal

Continued: Simulation Result Insertion Loss: -1.41DB Need simplification for analysis purpose.

Simplified Topology

Continued-Simulation Result

Continued-Small Signal Test Signal From the Transmitter (f_input=1kHz) Vtransmitter=49.60mVVantenna=25.2mVVreceiver=1.84mvF(-3db)=298.7kHz Insertion Loss=-6DB Isolation Loss=-31.50DB Signal From the Receiver (f_input=1kHz) Vantenna=49.8mVVreceiver=43mvVtransmitter=0mVF(-3db)=805.3kHz Insertion Loss=-1.27DB Isolation Loss=-Inf

Continued Large Signal Test Signal From the Transmitter (f_input=1kHz) The largest input signal before distortion is 11.5V Signal From the Receiver (f_input=1kHz) The largest input signal before distortion is 4.0V Clipping Distortions

Continued-Bandwidth Vantenna50mV500mV1V4V -3DB Voltage35.4mV353.56mV0.707V2.828V Bandwidth(KHz)

Basic Model 3-Port, Symmetric, Op-Amp Topology Purpose: To understand the limiting factors involved with Op-Amps used in this topology Method: Push the limits of readily available LM741 Op-Amps, to better understand the capability of this topology.

Testing Results Small Signal Test: R o : 11k V BIAS : +/- 20 DC V tr : 250mV pp V ant (-3dB) occurred at 180 kHz Large Signal Test: R o : 11k V BIAS : +/- 20 DC V tr : 17V pp V ant (-3dB) never occurred, clipping Clipping occurred at 8kHz, yielding calculated slew rate of.427 V/us Isolation: Ideal operating condition, 1 V 1 kHz : dB Small Signal max frequency: dB Large Signal max frequency: dB

Alternative Model This model was determined to be too finicky with resistance mismatching. Far too much distortion was found in the experiments, and the topology was abandoned The input was a sinusoid…

Topology Modeled for our purpose, not a true circulator

Simulation Results

Testing Results Small Signal Test: R o : 11k V BIAS : +/- 20 DC V tr : 200mV pp V ant (-3dB) occurred at 224 kHz Large Signal Test: R o : 11k V BIAS : +/- 20 DC V tr : 1V pp V ant (-3dB) occurred at 200kHz Dr. Young mentioned frequency should be our focus, not power, Dr. Young mentioned frequency should be our focus, not power, hence, the significantly smaller large signal voltage. Isolation: Ideal operating condition, 1 V 1 kHz : dB Small Signal max frequency: dB Large Signal max frequency: dB

Summary Pros: Simplest design Specifications easiest realized Cons: Voltage divider Frequency limited to available Op Amps Heating Issue Phase shift at frequency limits

Conclusion There are many paths we can take. Pursue high power: Op/Diff amp design Pursue high frequency: 3 transistor Pursue a compromise… We recommend the Op/Diff amp design because it is the most realizable.

Questions?