A.S. Podstrigaev1, A.V. Smolyakov2, A.S. Lukiyanov3

1–3 Electronic Instrumentation at V.I. Ulyanov (Lenin) SPbGETU «LETI» (St. Petersburg, Russia)

The means of RF spectrum management and cognitive radio systems use direction finding. These means are often installed on various carriers. Some carrier designs require signal processing equipment to be installed at a considerable distance from the antenna system. For example, on board an aircraft, the antennas can be located in the wings, and the processing equipment in the fuselage, at a distance of up to tens of meters. When transmitting a signal from antennas to equipment via a microwave cable, this leads to significant signal losses and, accordingly, a decrease in the sensitivity of the direction finder. Therefore, it is advisable to use a multichannel microwave photonic link (MPL) to maintain sensitivity when there is significant separation of antennas and processing equipment. However, with a sharp change in the temperature of the environment in which the radio direction finder operates (for example, when the aircraft flight altitude changes), the group delay time of the MPL channels can vary in different ways. This leads to an unpredictable change in the phase difference between the signals in the MPL channels. So, the accuracy of the phase or correlation direction finding reduces. Such a change is inertial and causes a gradual accumulation of a systematic direction finding error. One can eliminate this error by periodic calibration of the direction finder.

This work aims to study the possibility of using a microwave photonic link in a phase radio direction finder under dynamic temperature effects.

We assembled a test bench to assess the effect of temperature on the MPL. It consisted of a vector network analyzer and a two-channel MPL placed in a climatic chamber. Each channel of the MPL includes an optical modulator, a piece of optical fibre and a photodetector. Due to the limitations of the operation of the vector network analyzer, we performed all measurements in three narrow frequency subranges: 0,01–0,1, 9,9–10 and 17,9–18 GHz, corresponding to the studied frequency range from 0,01 to 18 GHz and the operating frequency range of the used MPL's components. Each subband's number of measurement points was set to 101, corresponding to a frequency resolution of 1 MHz.

Using specialized software, we obtained the time dependencies of the difference in the group delay time in the MPL channels as a result of the experiment. These dependencies correspond to room temperature and cases of sharp heating and cooling of the MPL.

An analysis of the obtained experimental data showed that the most significant and rapid changes in the difference in the group delay time of the MPL channels correspond to sharp cooling. The maximum modulo rate of change of this difference reached 0,43 ps/s.

Based on the data obtained, using the example of a two-antenna radio interferometer, we calculated the maximum allowable period of direction finder calibration, which ensures that the systematic error is kept within the specified limits. In the example of this interferometer, we confirmed the possibility of using a microwave photonic link in a phase direction finder of the microwave range under dynamic temperature effects. The percentage of useful information lost during the calibration is estimated. We revealed the expediency of increasing the identity of the MPL channels and taking some constructive measures.

Podstrigaev A.S., Smolyakov A.V., Lukiyanov A.S. Possibility of using a microwave photonic link in a phase direction finder of the microwave range under dynamic temperature effects. Achievements of modern radioelectronics. 2022. V. 76. № 9. P. 55–65. DOI: https://doi.org/ 10.18127/j20700784-202209-03 [in Russian]

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