Doubly-mirrored Balanced Antipodal Vivaldi Antenna (DmBAVA) for high performance arrays of electrically short, modular elements
Extensive numerical simulations and measurements have shown that Balanced Antipodal Vivaldi Antennas (BAVA) are broadband elements when operating as isolated antennas. However, BAVAs behave very differently in large array environments with impedance anomalies limiting the array's most useful bandwidth. Two techniques are developed in this thesis to overcome these performance limiting anomalies. First, a double-mirroring technique is introduced to eliminate one of the anomalies at broadside beam. Second, the antenna depth has been limited < λ highest-frequency</sub>/2 in order to move the second anomaly beyond the grating lobe onset frequency, and hence beyond the array's upper frequency bound. The two techniques are used along with metallic crosswalls, metallic poles and magnetic slots to design modular low profile BAVA elements in an array that operates over one-half of a decade of bandwidth and scan up to 60 degrees half angle conical volume.
A linearly polarized doubly-mirrored BAVA (DmBAVA) array is fabricated and measured in a parallel plate waveguide simulator. Results from simulations and measurements are in close agreement. Finite arrays of SP- and DP-DmBAVA elements were simulated to explore the active element and array's radiation patterns. The cross-polarized farfield was less than -20dB relative to co-polarized farfield pattern peak at all scan angles. Floquet modes were calculated to prove that no grating lobe problem exists if all the elements are properly excited. The metallic crosswalls in the single-polarized DmBAVA array can be replaced by orthogonal DmBAVA elements to realize a dual-polarized antenna with only a minor degradation in the impedance match.
The design methodology presented in this thesis represents a philosophical shift away from traditional design practices. Rather than providing design curves and/or analytical expressions for equivalent circuit models, simple first-order design rules (generated via parametric studies and extensive examinations to the surface currents and electromagnetic fields distribution) provide a framework for reduction of design complexity, and have eliminated the impedance anomalies in BAVA. This will increase the use of BAVA radiating elements in high performance arrays.