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94 GHz Switching Circulator Design Project


Requirements Specification


This project aims to develop a 94 GHz 3-port switching circulator for Millitech Corporation of Northampton, Massachusetts. A circulator is a microwave component which directs microwave energy from input ports to output ports in a circular fashion, with the ports being highly isolated in the reverse direction. This is accomplished with a specialized type of ferrite magnet. Switching circulators allow the direction of circulation to be reversed.

Circulators can be used to isolate RF components from each other in one direction so that a high power component does not damage other components if a mistake is made. Circulating devices are ideal for antenna interfaces because they can be used in transceivers to join a receiver and transmitter to a single antenna. They can be very advantageous in microwave design because of their low loss characteristics and high power handling capability. Switching circulators act as switches directing input energy on one port to either of the two others depending on the switching state.


Our team will provide the complete design for the circulator. This consists of the physical models and schematics of the circulator body with precise dimensions, circuit design for the driver. Tolerances on the ferrite and magnetic components are critical in the design and the device will have to be hand assembled, tuned and tested. Extensive empirical tuning information will also be provided. Millitech is interested in the 94 GHz circulator because of the ability to tap into a small niche market. The company will manufacture or provide the funds for the purchase of all necessary materials. All deliverables are the property of Millitech.

Special Restrictions

  • Bandwidth: 3%

  • Center Frequency: 94 Ghz

  • Isolation: 20 dB

  • Insertion loss: 0.8 dB

  • VSWR: 1.3:1

  • Switching time: 10 ns

  • Temperature range: -40C - 85C

  • Driver circuit CMOS/TTL compatible

Principle of Operation

The switch works by changing the polarization of internal ferrite, which is accomplished with the driver circuit. When the direction of polarization is reversed, the direction of power flow reverses. The driver circuit consists of control and power circuitry. The control circuitry senses the input and directs the power circuitry. The power circuitry applies a pulse of current to a coil which is wound around the ferrite such that they are tightly coupled. If the circuit is latching then the remnant magnetic field of the ferrite is enough to cause proper operation. If not then continuous power must be supplied in the "on" position to reverse the field of the ferrite.


The circulator will have 3 symmetrical ports. These ports serve as either input or output depending on the circuit topology. The driver circuit will respond to CMOS/TTL signals.

Acceptance Test

The acceptance tests will be performed with Millitech's equipment. They will consist of measuring the specification requirements as listed above.

Production Cost

There is no set cost limit for this project. Millitech will be funding all costs.

Statement of the Problem

Requirements Specification

System Block Diagram

Draft System Specification

Preliminary Design Review (PDR) Presentation Slides

Mid-course Design Review (MDR) Specification


Research Materials

UMass Amherst

College of Engineering



 Last Updated 11.20.05