Innovative microwave design of frequency-independent passive phase shifter with LCL-network and bandpass NGD circuit

The present paper develops an application of the bandpass (BP) negative group delay (NGD) circuit for the design of an independent frequency phase shifter (PS). The design principle of the innovative PS is constituted by an inductor-capacitor-inductor (LCL) T-shape passive cell in cascade with RLC-network series-based BP NGD circuits. The S-matrix analytical model of the LCL-NGD PS is established in function of the circuit elements. Then, the design equations of the PS elements in the function of the expected PS value and center frequency are formulated. The NGD PS topology is validated with a comparison between the calculated and simulated results of phase, transmission coefficient, and reflection coefficients. As expected, a very good correlation between the analytical model and the simulation is confirmed by the obtained results. It is found that the LCL-NGD PS presents an outstandingly flat phase shift of −120^◦ ± 5^◦ with 1.2 GHz center frequency. The LCL-NGD PS operates with about 18% relative bandwidth. The PS reflection coefficient presents a magnitude flatness around −3 ± 1.5 dB. Moreover, the reflection coefficient is kept better than −15 dB. The sensitivity of the LCL-NGD PS performances over the NGD circuit element ±5% relative variation is studied. It is found how the PS value and center frequency change with the R, L, and C components of the NGD circuit.