Question:

(a) Describe the following antenna properties / characteristics:
(i) radiation pattern
(ii) the main beam and beamwidth
(iii) sidelobes
(iv) directivity
(v) antenna gain
(vi) efficiency
(vii) antenna resistance.

What would be the optimum values for (iii), (vi) and (vii) for a specific type of antenna of your own (e.g. monopole, dipole etc)?

(b) Evaluate the amplitude and direction of the principal maximum, the amplitude ratio of the largest secondary maximum (sidelobe) to the principal maximum and, the width of the principal lobe for the following linear arrays:

(i) 4 elements 0.4 λ apart and fed with equal amplitude and in-phase currents;

(ii) 12 elements λ/4 apart and fed with currents of equal magnitude but with a progressive phase shift of -90^o between elements.

(c) Consider the array pattern (as normalized electric field, ET / E0 versus Φ , where Φ is measured from the line of the array, that is, 90^o for broadside) for an array of 2 elements (considered non-directional radiators) spaced λ/2 apart fed with currents of equal amplitude and phase.

Determine, by the method of multiplication of patterns, the array pattern for an 8 element linear binomial array with λ/2 element spacing
and in-phase currents.

(d) For Question (c), determine the ratio ET / E0 for Φ = 0^o, 45^o, 80^o and 90^o.