Active Delay Line
13 GHz - 18GHz active delay line.
Delay is typically achieved with pieces of a transmission line. This is a narrowband solution, since transmission lines exhibit dispersive behaviour. Long coaxial transmission lines are also quite lossy in Ku-band. To compensate for loss, microwave amplifiers are implemented in this design. The dispersion is equalized with a specially designed circuit.
Design
The delay line consists of five pieces of three meter H&S EZ 141 Al TP semi-rigid cable looped into compact delay line components, three gain blocks, and frequency compensating circuit (FCC).
The FCC consists of SMD resistors connected to open circuited transmission lines. Each transmission line represents a short circuit at certain frequency. The values of the resistors and length of the lines are chosen such that the FCC exhibits high loss in low frequency region and low loss in high frequency region.
Performance
Flatness in the frequency band 13GHz – 18GHz is about ± 1.7dB. Below is the response of the delay line. Red line – simulations. Blue line – measurements.
