Active frequency selective surfaces for antenna applications electronically to control phase distribution and reflective/transmissive amplification

A planar dipole grid antenna is described deposited on an active frequency selective (FSS) or polarization sensitive surface (PSS) electronically tuneable to control the spatial phase distribution and reflective/transmissive amplification. Such dipole grids can be used, for example, in reflector antenna systems composed of multiple reflective and/or transmissive subsystems to achieve and serve highly cost-effective multi-purpose applications. It is discussed how the resonant frequency or/and the type of polarization can be tuned just by varying the steering voltage or current of electronically tunable components such as varactor diodes or YIG films, respectively, implemented and integrated with each of the radiating dipole elements. The theoretical analysis for this paper is based upon a specific Floquet theory approach for single/double/triple periodic antenna structures. The resulting system of coupled vector integral equations for the unknown electric and magnetic current distribution is numerically solved by applying the method of moments supported by Galerkin´s process of weighting. The experimental investigations were performed by developing a waveguide simulation technique in the frequency range of 7 to 16 GHz. Results of selected measurements are presented for quantities such as: the spatially dependent reflection/transmission coefficients (magnitude, phase) as a function of signal frequency; the intrinsic input impedance/matching of the various dipole elements involved, etc.; and - in addition to that - the resulting electronically achievable phase advance/delay and amplification of the active antenna system as well. A one/two-dimensional enlarged planar dipole grid of about 40 mm × 25 mm in aperture size was deposited inside an adequately tapered waveguide to reduce tolerance problems and to suppress higher order modes. Typical results are presented and discussed to demonstrate, e.g., that the resonant frequency∼-10 GHz can electronically be tuned around 9.85 GHz by a bandwidth of 7 % and around 10.1 GHz by 14 % in case of capacitive or inductive tuning, respectively. Investigations show that electronic tunability is achieved preferably by using high-Ohmic voltage controlled components instead of low-Ohmic current - controlled components, for instance, supporting low-loss and low-noise performance. Using properly selected HEMT-type integrated transistors the achievable amplification measured turned out be about 5.4 dB at 10.3 GHz for an active one-element strip dipole grid (reflection-type amplifier) and about 3 dB at 9.3 GHz for an active one-element slot dipole grid (transmission-type amplifier), respectively. A concluding discussion indicates how such kind of planar/conformal dipole grids may set up an integrated system of multiple reflective/transmissive subreflectors of a powerful low-weight multi-purpose microwave antenna system of frequency multiplex and dual polarization capability to serve various technical applications at the same time and at a high degree of flexibility and cost-effectiveness as well.