Increase beamwidth of reflector antenna

[mostafa ewaiha]

hi,

Plz, I wanna some ideas to improve the beamwidth of reflector antenna and keep the gain fixed

bye

Mostafa

 

[HMS1021]

hi,

Plz, I wanna some ideas to improve the beamwidth of reflector antenna and keep the gain fixed

bye

Mostafa

As the beam narrows the flux density in volts per meter in the beam increases. The ratio of the increase when compared the flux density of a dipole at the same range is gain.

Stated another way if you change beamwidth you change the gain.

 

[mostafa ewaiha]

Thanks HMS1021

as I see from your words that the gain increase as the beam narrows.

is there another factor affect on beamwidth?

 

[vfone]

The beamwidth of a reflector antenna may be varied by de-focusing the feed.
For small de-focusing values the antenna gain it will not change as much as the beamwidth.

 

[mostafa ewaiha]

thanks vfone

I try it now

 

[mostafa ewaiha]

The beamwidth of a reflector antenna may be varied by de-focusing the feed.
For small de-focusing values the antenna gain it will not change as much as the beamwidth.

I try to make the de-focusing small, and my observation is beamwidth decrease and the gain increase

so what ?????

 

[HMS1021]

I try to make the de-focusing small, and my observation is beamwidth decrease and the gain increase

so what ?????

True physics at work. You illuminate a smaller area with a constant amount of energy, and the energy in the illuminated area increases, which defines an increase in gain. Also as opposed to defocusing the feed you have actually improved the focus since the beam-width was narrower.

The conundrum of needing more antenna area due to weak signals thus causing the antenna to have a narrower beam-width (by definition: higher gain) lead to gimbaled antennas that are steered (pointed) and electronically scanned phased arrays. In many cases these are not practical, a wider beam antenna may be the only solution. In this case the transmit power is increased, the received bandwidth and data rate are reduced to lower the noise floor, or the system noise figure is improved.

There is a bit of an exception. While the gain of an antenna is defined by its beam-width and two antennas with the same beam-width have the same gain by definition it does not mean they will perform the same. If one has lower losses it performs better. The losses can be real, mismatch losses, or energy lost in side lobes. This performance is captured in the antenna specification for efficiency.



You will want to measure the return-loss of the antenna.

 

[mostafa ewaiha]

While the gain of an antenna is defined by its beam-width and two antennas with the same beam-width have the same gain

That's mean "the gain and the beamwidth depends on themselves" and this was my thought. but in the picture below explain that de-focusing increase the beamwidth can you comment on it



and this is the link of the picture

https://www.alternatewars.com/WW3/WW3_Documents/ABM_Bell/ABM_Ch1.htm

 

[SpaceDust]

Is it really possible to Keep the Gain constant and increase the Beamwidth. !! As of My knowledge goes it can't be, If the beam width increases the gain has to decrease..!!

 

[HMS1021]

The amount that you under fill, or over fill, the reflector as shown in the graphic will impact efficiency.