2010 Wideband, High Frequency, and High Power Circulator

ResultsMethod

Team Laplace Sauce

Andrew Wadja Jake Smith

Further Work & FeasibilitySpecifications

ProblemThe United States Navy uses HF, UHF, and VHF frequency bands for person-to-person, ship-to-person, and ship-to-ship communication systems. To reduce size, weight, and cost it is common to use a single antenna for both transmit and receive mode. This is accomplished by means of a circulator that can direct a signal to a particular port depending on the direction of signal flow.

Modern circulator technology has yet been able to achieve high power in the HF, UHF, and VHF bands. However, with improvements in the bandwidth and power capabilities of discrete and integrated transistors there is now reason to believe that active circulators may in fact be suitable for this Navy application.

This project was funded by the US Navy under BAA 07-037. The faculty advisers are Dr. Jeffrey Young , Dr. Ken Noren, Dr. Herb Hess, and Dr. Greg Donohoe. Special thanks to Greg Klemesrud and Chris Wagner.

Transistor Design Op-Amp Design

Our senior design team, Laplace Sauce, was challenged to develop an HF circulator that pushes the envelope in terms of power, bandwidth, or both in the HF band.

Solution

Insertion Loss < -.5dB

Isolation > -15db

Frequency > 30 MHz

10W < Power < 50W

Circulator Model

Design

The team worked independent of each other , using a “divide and conquer” approach. Andrew choose to pursue a topology that consisted of transistors with theories derived from “The Design of Active Circulators” by Larry Lee Lamb, while Jake worked on a schematic consisting of three cascading Op-Amps from “Low Frequency Circulator/Isolator Uses No Ferrite or Magnet” by Charles Wenzel.

Op-Amp Design

The graph above shows the S-parameters measured from port A to C. Since the design is symmetric, all ports have all the same parameters. The limiting factor in this design proved to be the reflection coefficients, while the forward and reverse gain passed expectations.

Maximum Frequency = 44.38 MHz(Small Signal)

Transistor Design

THSTHS3061

Both candidates, especially the op amp design, are exceptionally suited for small signal operations. However, to incorporate high power into the design; available current technology dictates use of RF amplifiers on the output stages of the circulator.

This graph is only a simulation of the HF design using the MPSH10 transistor because a working physical circuit could not be realized. A 2N3904 transistor circuit was constructed in the first semester and still has the highest bandwidth for this design at 7.3 MHz.

RF Amplifier