Spectrum Analyzer - Characterization of Antenna (Yagi)

can some one explain me in detail how to check the antenna manufactured/made at home physically is having the same specifications we have opted for using spectrum analyzer

I think VNAs are more costlier than Spectrum Analyzers. i have got spectrum anlyzer 1KHz - 3GHz. antenna centre freq is supposed to be 437.33 MHz..a general freq for ham radio hobbiers..

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and by the way can you suggest some good Electronic outlets in india from where i can get VNAs and their price range

Connect yagi to spec analyser with long lead. Look on spectrum analyser for a strong signal. .Rotate yagi and note angle against signal strength. - Job done?
Frank

A spectrum analyzer is used to determine features of SIGNALS. The only effect of any antenna upon a selected signal (evaluated on a spectrum analyzer) is the signal power. And signal power will vary with rotating the antenna towards a remote signal source. You can use a directional antenna to find a direction to a remote source, you can also see the effect of polarization by turning the antenna on its axis.
But all the above can be done easier way, by using a power meter or a detector connected to an antenna. Spectrum analyzer will tell you nothing more about an antenna than much simpler devices indicating signal power.