An Electrically Small Antenna With Quasi-Isotropic Coverage for Linearly Polarized Receiver

An electrically small antenna (ESA) for a linearly polarized (LP) receiver with quasi-isotropic coverage is developed and investigated by theoretical and experimental analyses. This antenna comprises two perpendicular positioned split-ring resonators (SRRs) and a fixed pad. Each SRR could generate a quasi-isotropic radiation with a gain difference of around 3 dB, which is attributed to the fields’ combination of the equivalent magnetic and electric dipoles. By regulating the antenna configuration of the orthogonal substrates, the developed antenna could also produce a quasi-isotropic coverage. At the same time, a circularly polarized characteristic in the maximum radiation direction can be achieved, which is exactly the direction of the largest polarization mismatch level (PML) value of the developed ESA for the LP receiver. The measured results agree well with the simulated ones, which demonstrates that this proposed antenna could realize a quasi-isotropic coverage in the whole space for the LP receiver with the measured gain difference of about 1.42 dB. This developed ESA reveals an electrically small size (0.19
$\times0.15\,\,\times 0.15\lambda ^{3}$
, ka
$=0.89$
) and radiation efficiency of 91% with a fractional bandwidth of 1.6% at the center frequency of 748.5 MHz. Moreover, the measured and simulated realized gain differences of the quasi-isotropic ESA are, respectively, 3.33 and 2.77 dB, which demonstrates that the ESA has a very good uniform quasi-isotropic coverage of the whole space.