Calibration of broadband antenna and confirmation through measurement at a 10 m site. A case study

Broadband antennas like logperiodic and biconical antennas are used to receive radiated emissions from equipment under test for frequency range 30 MHz to 1000 MHz. This paper presents a case of calibration of antenna factors of 2 sets of broadband antennas (biconical and logperiodic antennas) and 1 set of tunable dipole antennas and their confirmation through measurement of site attenuation of 10 m open area test site using the same. The standard site method as described in ANSI C 63.5-1988 with modification has been used to compute the antenna factors for the frequency range 30 MHz to 1000 MHz. Instead of the attenuators mentioned in ANSI 63.5, an alternative method has been devised to determine site attenuation A1, A2 and A3, thereby eliminating the inaccuracies of the attenuators. The values obtained are found to be within +/- 2 dB of that given by the manufacturer of the antennas. The validity of calibration data has been further confirmed by measuring the normalized site attenuation of a 10 m open area test site of ERTL(E) for a frequency range 30 MHz to 1000 MHz employing these broadband antennas, following the procedure laid down in ANSI C63.4-1992. The results obtained are very encouraging and accurate. They are found within +/- 1.2 dB and +/- 2.4 dB of theoretical values in both horizontal and vertical polarizations respectively.