Earlier the response of an antenna system was measured by a bridge voltmeter or a reflected power meter on a transmitter but they had their disadvantages like they would take too much time in measuring data, and the measured data would have frequency induced considerable errors. With the reflected power meter, the antenna might get mistuned resulting in a explosive crash.
The updated comprehensive tool to measure antenna and radio frequency broadcasting is network analyzer. A network analyzer is an instruments that measures the network parameters such as y, z, h parameters of the interconnection of electrical elements. A network analyzer has four parts: signal source, signal separation device, receiver and signal processor/display.
The signal source provides the signal, the signal separation device separates incident, reflected and the transmitted signals. The receiver converts microwave frequency to a lower IF Frequency, which gets processed by the signal processor and is displayed at the CRT Screen. Although they can be used on network with any number of ports, their common application is seen in two port system. It is one of the most comprehensive technique of radio frequency broadcasting.
There are two types of network analyzer to measure, verify and optimize the performance of an antenna.
SCALAR NETWORK ANALYZER:
It measures the magnitude related parameters of an instrument i.e the outside of the antenna. The RF power detection process of a scalar network analyzer is simple and economical. It performs faster frequency sweeps when compared to it’s vector counterpart.
VECTOR NETWORK ANALYZER
It measures the inside of the antenna i.e the feed impedance. Through this form of RF network analyzer, gain i.e the amplitude as well as the phase is measured by installing a full heterodyne structure in the receiver. The performance of RF devices and microwave devices are enabled by this test system to be identified by their S parameters. Also called as the Automatic Network Analyzer, this is a necessary instrument for RF Designer. They are highly efficient in comparison with the scalar network analyzer.
With the help of a network analyzer the transmission transmission coefficient, gain measurements, VSWR, return loss, reflection coefficient and scattering parameters can be measured .
Antenna Measurement with a network analyzer
Defined as the ratio of the intensity of the antenna in the direction of peak radiation with relative of isotropic antenna An isotropic antenna is a hypothetical antenna that radiates without any losses, with equal intensity in every direction.
It is an essential parameters in devising a wireless transmission equipment. With a low antenna gain, a microwave/RF signal will not reach the destination whereas a high signal can cause distortion in the products and receiver.
Network analyzer utilizes the gain transfer method to measure antenna gain.
In a gain transfer method, three antenna are required ; first is the antenna under test, of which we have to determine the gain. The second antenna is the benchmark antenna that is polarized and has a high degree of dimensional stability with it’s accurate gain known. The third antenna, call it Y is used for the sole purpose of transmitting signals over to the antenna at a wider range.
By setting the system properly, gain can be calculated with the help of this equation:
G (Aut)= G (ref) + G (relative)
Using identical antennas for Y and ref will make it easier to align and match the antennas together.
The Antenna under test (Aut) and reference antenna should be positioned in such a way that they swivel 180 degrees.
Tuning the antenna right and measuring the accurate antenna gain is essential in designing RF transmission devices. You can find an adept cable and antenna network analyzer , spectrum analyzer , power loss kit , vector signal generator and other comprehensive instruments and network related solutions at any credible online source.