How do we test an antenna for its receiver capability?

[denizduran]

Generally speaking, the antenna itself is not aware if it's supposed to be a transmitter or a receiver. How do we test an antenna for it's receiver capabilities? Do we look at its total isotropic sensitivity? I have found this term to describe the whole receiver system including the antenna. I want to find out if there is a test that can be done to understand only the antenna?

 

[BradtheRad]

Antenna size and shape favor it to resonate at one or more frequencies (and harmonics of a frequency).

Photons of that frequency strike (or pass nearby). This generates AC voltage in the antenna.

We can attach wires at a strategic location, thus converting energy to current.

As soon as we draw any amount of power (load the antenna), voltage drops.

By adding capacitors & inductors we can make it more sensitive to our desired frequency.

Our amplifier can detect energy in the antenna as voltage and/or current.

 

[PlanarMetamaterials]

Antenna size and shape favor it to resonate at one or more frequencies (and harmonics of a frequency).
By adding capacitors & inductors we can make it more sensitive to our desired frequency.

Antennas do not need to resonate.

Typically, when evaluating Rx antennas, we perform some sort of raster scan of a source around the antenna. This can be a simple rectangle, or can take the form of some sort of cylinder or sphere surrounding the antenna. By knowing the power emitted by the source antenna, the frequency at which it operates, and evaluating the power transfer at each point, we then know the amount of power the antenna receives at each three-dimensional angle at each frequency. These may be integrated to give common metric like gain, efficiency, etc.

Other common parameters are input impedance (S11 or VSWR for a one-port antenna) or radiation resistance, that can be determined using a VNA.

 

[Azulykit]

Antenna characterization can be difficult to understand at first. I would recommend a book by Kraus, Antennas as a place to start. Probably two of the most basic measurements are directivity (pattern shape) and gain (pattern shape and efficiency). These are usually measured in dB so study how that unit works.

Another really useful reference with lot's of pictures is Stimpson's "Airborne Radar" book. It is particularly useful to help solidify basic ideas.