Directivity of a Receiving Antenna: Effects on Intercept Area, Noise, and Signal Discrimination Consider the statements: 1) Increasing directivity increases the effective intercept area in the forward direction. 2) Increasing directivity reduces noise picked up from other directions. 3) Increasing directivity provides angular discrimination against undesired signals not aligned with the desired transmitter. Which statements are correct?

Introduction / Context:
Directivity describes how concentrated an antenna's radiation or reception pattern is in a preferred direction. For receiving antennas, higher directivity effectively increases sensitivity from the look direction while suppressing energy from elsewhere.

Given Data / Assumptions:

• Three qualitative statements relate directivity to effective area, noise pickup, and discrimination.
• Broadband/system noise is often dominated by off-axis interference and environmental sources.

Concept / Approach:

Effective aperture A_e is related to gain G by A_e = (lambda^2 * G) / (4 * pi). For a given wavelength, increasing gain (and thus directivity for lossless antennas) increases A_e in the main lobe. A narrower beam also rejects off-axis noise and interference.

Step-by-Step Solution:

Verification / Alternative check:

Standard antenna theory links directivity, gain, and effective aperture; pattern plots show how beam narrowing reduces reception from unwanted angles.

Why Other Options Are Wrong:

Options A, B, D, and E omit at least one correct statement, so they are incorrect.

Common Pitfalls:

Confusing directivity with efficiency; assuming higher directivity always raises received SNR without considering pointing accuracy and bandwidth.

Final Answer:

1, 2 and 3.