In this paper, a symmetric four-port microwave varactor based 90 directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. By applying suitable biasing voltages to the varactors, the power-dividing ratios between the two output ports (i.e., port 2 and port 3) of the coupler can be easily controlled. Moreover, it is found that the realizable power ratio using the proposed structure is very flexible (it could be extremely large or small). Therefore, under the special case when the coupling ratio is tuned to be 1, the proposed coupler is reconfigured to be a crossover. Good isolation and return-loss performance have been maintained for different power-dividing ratios. To theoretically analyze the proposed device, closed-form design equations are derived using the even-odd mode method. Based on these analytical equations, an experimental prototype working at 1 GHz is designed, fabricated, and characterized. The measurement results match well with the simulation and theoretical results, validating the proposed design theory.Index Terms-Crossover, even-odd mode, symmetrical, tunable coupling ratio, 90 directional coupler.

No abstract

No abstract

In this study, a water‐based rectangular dielectric resonator antenna is designed and analysed. The compactness of the antenna because of the high relative permittivity of water is demonstrated in both simulation and experiment. In addition, a dielectric resonator antenna‐based technique is proposed for measuring liquid permittivities. The resonance frequencies of the antennas with fixed configurations are obtained from finite‐element electromagnetic (EM) simulation for liquids with different permittivity values. An analytical model of liquid permittivity as a function of the antenna resonance frequency is then developed. Based on this predictive model, the measurement of the liquid real relative permittivity can be easily achieved by measuring the antenna resonance frequency. The measured permittivity values of distilled water and 10% glucose solution are in agreement with previous data in the literature, demonstrating the effectiveness of the proposed liquid permittivity measurement technique.

No abstract