안테나설계 실습보고서

실습-05 Corner Reflector Antenna

II. Problems

1. Draw a cross-sectional diagram of a wire-grid corner reflector antenna with the following dimensions

(2a: grid wire's diameter)

(Solution)

2. Find the wire transmission coefficient in Problem 1.

(Solution)

From the Mumford nomograph with grid spacing of 0.25 wavelength and the ratio 10 of grid spacing to wire diameter, we obtain

|S21|(dB) = 10log(1-|Γ|²)= -11dB

3. Find the wire grid efficiency (for gain) in Problem 1.

(Solution)

4. Describe the design philosophy for each of the following parameters.

a) Corner angle

(Solution) A practical corner angle ranges from 60 to 90 degrees.

b) Apex to dipole distance

(Solution) The apex-to-dipole distance depends on the corner angle. We adjust the dipole length and the apex-to-dipole distance for good impedance matching. For 90-degree corner angle, the apex-to-dipole distance ranges from 0.25 to 0.50 wavelength.

c) Corner reflector length

(Solution) The corner reflector length has an effect on the antenna gain and the front-to-back ratio, both of which increase with the corner reflector length. Its minimum value is twice the apex-to-dipole distance. Its practical maximum value is two wavelengths.

d) Corner reflector height

(Solution) The antenna's gain and the front-to-back ratio depend less sensitively on the corner reflector height than on the corner reflector length. Suitable value ranges from 0.75 to 1.5 wavelengths.

e) Wire diameter in the wire grid reflector

(Solution) With the grid spacing fixed. the larger the wire diameter, the smaller the back radiation. The practical value of the wire diameter is determined considering the mechanical strength and the antenna weight. Suitable value is about 1/20 of the wire length.

f) Spacing between wires in the wire grid reflector

(Solution) The grid spacing determines the back radiation and thus the forward gain. The smaller the spacing, the less the back radiation. Suitable value ranges from 0.1 to 0.2 wavelength.

g) Broadening the bandwidth

(Solution) To increase the bandwidth of a corner reflector antenna, the dipole is modified into a thick dipole, a bowtie dipole, a fan dipole and a butterfly dipole.

III. Lab

1. Design

Dipole-to-apex distance = 0.44λ = 189mm

Wire grid: wire length = 0.6λ = 257mm

Wire spacing = λ/6 = 71.5mm

Number of wires in the grid reflector = 13

Wire length-to-diameter ratio = 20 → Wire diameter = 1.30mm

Dipole length = 0.32λ = 137mm

Dipole length-to-diameter ratio = 8 → Dipole diameter = 17mm

Dipole gap = same as the diameter = 17mm

2. Simulate

a) Antenna model generation

b) |S11|(dB)

c) Gabs pattern: 3D

d) Gabs pattern: polar pattern at phi = 0º (E-plane)

e) Gabs pattern: polar pattern at phi = 90º (H-plane)

3. Analyze the results.

a) Find the antenna bandwidth for |S11| < -10dB in MHz.

Δf = 834-647 = 187MHz

b) Find the maximum gain Gmax(dB).

Gmax = 9.64dB

c) Find the E-plane beamwidth BW-E(deg).

BW-E = 74.2º

d) Find the H-plane beamwidth BW-H(deg).

BW-H = 52.0º

e) Find the front-to-back ratio F/B(dB) over 180º±30º

F/B = 9.64-(-12) = 21.6dB