Characterisation of Ferrite Material in Remanent State for use in New High Peak Power Applications
ComDev International Systems Ltd
Project Funded in the CEOI-ST 7th Call for EO Technologies.
The next generation of radar missions cover a wide range of frequencies from C-band to Ka-band. A common feature of all these missions is the dramatic increase in the peak power requirement of the system. Whereas previous instruments operated at typical peak powers of 100W, the newer requirement is for peak powers in excess of 3kW, thus presenting new challenges to power amplifier, radar feeds, antenna, and switching element providers. Ferrite switches are the technology of choice for radar switching elements since they provide a very high number of switching actions over the instrument lifetime, low insertion loss, high reliability, fast switching time, and high peak and average power handling. A key issue for the design of ferrite switches capable of handling high peak power is the selection of the ferrite material, and being able to predict the power threshold at which the switch will start to behave in a non-linear manner.
In a ferrite switch (latching circulator) the ferrite material is used in its remanent state. This is significantly different from the majority of other ferrite-based RF applications. Consequently, the materials’ properties appropriate for operation in the remanent state are not generally available from ferrite vendors. This means that it is difficult to model and predict any ferrite switch performance, in particular identifying the peak power maximum threshold, above which the switch becomes non-linear (absorbs RF energy).
The goal of the proposed activity is to develop a low cost generic measurement system which will be used to characterise any ferrite material in its remanent state. Data will be gathered from a number of different ferrite materials at a selection of RF frequencies. This data will be used to generate and refine models for predicting peak power thresholds and magnetic (and hence insertion) losses.
If successful, this activity will result in a measurement and analysis process which will enable designers to confidently select the appropriate ferrite material for high peak power switch designs, thus removing the potential costly and lengthy re-iterative bread boarding and testing phase.
Project Outcome and Achievements
A test methodology was successfully developed to measure the spinwave linewidths as a result of the CEOI-ST activity, which is now complete. Using this methodology the linewidths of three different materials were measured in both the saturated and remanent state, at three different frequency bands (C, X, and Ku) and at various angles of orientation of magnetic field with respect to the incident RF field. The key results of the test
- At the standard measurement frequency and in the standard saturated condition a good correlation was found between the measured and published data
- Substantial differences were found between the published data and measurements at different frequencies and/or in a remanent state
The results give great confidence that the measurement technique is sound and that this approach should be used on future high power programmes to allow the optimum selection of the ferrite material. This will enable the design of ferrite switches that provides the best trade-off between linearity and insertion loss.
Further work is required to extend the developed technique to Ka-band frequency range.