A thin dipole antenna is λ/15 metre long. If Its loss resistance

A thin dipole antenna is λ/15 metre long. If Its loss resistance is 1.5 Ω. Find radiation resistance and efficiency—

1. Rr = 35 Ω, η = 80%
2. Rr = 3.5 Ω, η = 70%
3. Rr = 3.5 Ω, η = 80%
4. Rr = 7.0 Ω, η = 70%

R_r = 80 π²		dl		²	= 80 π²		λ/15		²
		λ					λ

=	80π²	= 3.5Ω
	225

η =	R_r	=	3.5
	R_r + R_l		3.5 + 1.5

η % =	3.5	× 100 = 70%
	5