Maximum Gain of an Electrically Small Cosines-Dipole-Based End-Fire Array

Electrically Small Antennas (ESAs) are of high interest in applications where a compact size wants to be preserved. With the objective of the realization of a highly efficient and superdirective array within a very compact space, a new radiating element and array design is proposed, optimized for maximum attainable gain. A cosines-dipole printed antenna is designed by adjusting the amplitude and periodicity of the cosine microstrip, to resonate at the desired frequency of 916 MHz. Then, to achieve high gain two elements are closely spaced, mirrored to their excitation point, one fed and the other parasitic. An analytical method for gain optimization based on the Spherical Wave Expansion (SWE) theory is used to maximize the array gain. Two different array geometries are compared by looking at the power distribution of the spherical modes, and the configuration that returns the highest gain is chosen. A realized gain of 6.5 dBi is achieved in simulation, for a total size included in a radiansphere of $\boldsymbol{ka}=\mathbf{1}$ , with the advantage of having a printed antenna, thus planar, easy to integrate, and low cost. The proposed antenna solution presents in theory an excellent trade-off between electrical size and realized gain.