# Homework Help: Some questions on antennas

1. Apr 20, 2010

### Tezuka

hi,

need some help answering some antenna questions...

2 isotropic radiators at x = -d and x = +d on the horizontal x-y plane. for primary radiation lobes to be in +/- y directions, the radiators are fed by 100Mhz sources having equal amplitudes with no phase difference.

1) a strong signal is arriving from distant radar station at φ = 60 deg.( φ is angle with x-axis). find value of d for minimize interference posed by distant radar station.

2)determine the power levels in the side lobes(if any) relative to the power in each primary lobe.

3)the 2 isotropic radiators are replace with 2 half-dipoles(with their axes vertical to x-y plane) does the result of part 1 & @ need to be re-computed?

i have no idea where to start..

2. Apr 20, 2010

### skeptic2

What is the relative phase between the two antennas so that the signal from the distant radar station is minimized?

In other words, how much farther does the signal have to travel to the farther antenna for the sum of the the signals from both antennas to be at minimum?

3. Apr 20, 2010

### Tezuka

how do i find the distance between the two elements? some function of wavelength?

4. Apr 21, 2010

### Antiphon

You absolutely have to draw a picture of everthing. There's no point trying to solve this problem unless you work out the precise geometrical relationships between the antennas and the station.

Once you make a picture, pick D so the antenna phases cancel toward the radar.

5. Apr 21, 2010

### Tezuka

i m quite new to this,
i' ve drawn the picture, but wads the relationship between phases, D, wavelength?
is there some link where i can find out more?

thks