Design and Analysis of a Tunable Miniaturized-Element Frequency-Selective Surface Without Bias Network

A novel, tunable miniaturized-element frequency-selective surface that does not require additional bias networks is presented. This spatial filter is composed of two wire-grids printed on opposite sides of a substrate and connected to each other with an array of varactors using plated via holes. Varactor diodes are positioned between the grids. Via sections and metallic pads are fabricated and create a dc path for biasing the varactors with the grids themselves. This configuration eliminates the need for any additional network, and therefore resolves the design difficulties associated with the spurious response of the bias network. An equivalent circuit model is developed to facilitate the design procedure. Full-wave numerical simulations are used to validate the results based on the circuit model. Simulations show that by altering the capacitance of the varactors from 0.1 to 1 pF, a frequency tunability from 8 to 10 GHz with an almost constant bandwidth can be achieved.