Compact First-Order Probe for Spherical Near-Field Antenna Measurements at Low Frequencies

Abstract

Abstract-Guidelines for designing compact and lightweight first-order probes for spherical near-field (SNF) antenna measurements at frequencies below 1 GHz that exploit first-order properties of electrically small self-resonant radiators combined into superdirective endfire arrays are established theoretically, exemplified numerically, and validated experimentally. A prototype of the probe designed to operate at 435 MHz central frequency exhibits the impedance bandwidth of 15 MHz with more than 9 dBi directivity and parasitic |µ| = 1 spherical modes suppressed to at least -42 dB. The probe height is just 343 mm above a 720 mm circular ground plane and it weighs about 5 kg.

Compact Superdirective Electric Dipole Array for Far-field Measurement in a Semi-Anechoic Environment

“…One of the main challenges in superdirective design is the narrowband behaviour of the system [6] [8] [9]. One way to extend the bandwidth consists in the use of Non-Foster elements [10], another way to do it is to rely on a better use of the Chu sphere improving its geometrical array Q-factor [9]. The latter bandwidth improvement method can be done as early as selecting the global shape of the array.…”