Tuning elements such as trimmers and trimmer capacitors are used in filters and duplexers that should be tuned by the user on the field to a dedicated frequency range. The tuning elements have been coupled to stepper motors in order to remote control their position. Stepper motors are controlled by a microprocessor with a memory of the positions of the motors versus the requested frequencies through a computer command. This assures the reproducibility and the accuracy of the position of the tuning elements and thus of the associated frequencies.
Cobham Microwave designs and manufactures tunable reject filters operating in the microwave bands.
Following are specifications of a filter designed with a suspended board including printed resonators which are tuned with tuning elements coupled with remote controlled motors.
Frequency range: X-band
- Narrow filter < 1% with 70dB attenuation
- Less than 0.5dB insertion loss from "0" to 18GHz
- Loss dispersion between several filters <0.5dB
- Less than 2dB @ Fo ±2 x reject band
- Suspended microstrip lines with 7 tunable cells with stepper motors
- Frequency control of each cell
- Temperature stability <15 ppm within military temperature range under severe environmental conditions
- Accuracy of the tuning < ±1MHz
(*) Filter is represented without stepper motors for easier understanding. Seven stepper motors are mounted vertically to electrically adjust the frequency of each cell.
Each motor is remote controlled by a PC board with a micro processor using DRAM memory for the position versus frequency. Position detectors are included to check the good operation of each cell.