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# Quadrifilar antenna design and interference

## Quadrifilar antenna design and interference

(OP)

Hello everybody this is my first post, so nice to meet you all!
I am studying the use of 137mhz QHA antennas on the sides of a satellite. Unfortunately my experience with antennas is quite limited, so I would love if you could give me some insight!

First point is: I am using NEC2 and got the following results. Does this seem realistic to you?

Second point is: I would like to irradiate in different directions, so the plan is to place 3 QHA on different sides of the satellite. Do you think there are any constrains on this? Let's say I place them 2m apart (wavelength is roughly 2m), would that be ok?

thanks for help!
Romeo

### RE: Quadrifilar antenna design and interference

Is the satellite going to be attitude controlled, perhaps equipped with a camera aimed down; or will it be tumbling randomly?

If you drive multiple antennas at the same time, then it'll act as a phased array to some degree. Unless the patterns are truely non-overlapping.

QFHA are a good choice for CP and broad low gain pattern.

Scale implies this isn't a tiny cube sat.

### RE: Quadrifilar antenna design and interference

(OP)

Thank you for the feedback! It will be pointing down, but there is a need for redundancy, therefore the 3 antennas.
How can I quantify whether antennas are truely non-overlapping?
Thks
Romeo

### RE: Quadrifilar antenna design and interference

Analysis and test.

Another approach is to use voting for the receiver, and intelligent switching for the transmit.

In other words, select the best antenna.

This may assume that the transmissions are not continuous.

### RE: Quadrifilar antenna design and interference

Sounds like a job for an experienced satellite antenna engineer. Those launches are extremely costly. I see trouble brewing. If you don't analyze the antenna positioned X meters from the satellite, you really aren't analyzing the antenna cuz RF is going to bounce off the satellite. Isn't NEC 1970's software. Seems CST or HFSS is needed.

### RE: Quadrifilar antenna design and interference

Bear in mind that the antennna characteristics, standalone, can be radically different than the installed characteristics. I would strongly suggest that you an analysis with the antenna installed on the s/c. You'll find that there will be TONS of structure in the antenna pattern.

TTFN (ta ta for now)
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