A circularly polarized HTS microstrip antenna array

The primary advantage of using superconducting materials in antenna systems is the reduction of the loss associated with transmission line matching circuits and feed networks, particularly at microwave and millimeter-wave frequencies where the ohmic losses begin to significantly affect system performance. For large antenna arrays with long, elaborate corporate feed networks, the use of HTS transmission lines can substantially increase the efficiency of the antenna. The benefits of HTS materials have been demonstrated by the development of high quality superconducting transmission line, filters and resonators. Superconducting microstrip antennas with enhanced efficiencies have also been demonstrated. In many microstrip designs the substrate upon which the microstrip antenna is patterned is made electrically thin (less than 0.01 /spl lambda//sub 0/). On these thin substrates, the coupling into the surface waves is reduced; unfortunately, this benefit is often countered by a substantial decrease in the impedance bandwidth and antenna efficiency due to conductor and dielectric loss. These losses can be significantly reduced by constructing the antenna from thin films of high temperature superconductor on low loss substrates. We summarize our efforts to design and characterize a 20 GHz, circularly polarized HTS microstrip antenna array.