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[datin]

Antenna propagation for point to point connection


Hello,
I know that my question is very basic.But Im confused.

Please assume we have two points. a directional antenna located on A point and omni-directional antenna is located on B point.

radiation wave from A antenna able to reach to B antenna.So B antenna received wave and convert it to electrical signal.

For response from B, Does wave from B antenna have to able to reach to A antenna?

I want to show in diagram but couldnot upload it.

Thanks

[Espen Wium]

It doesn't matter if you're transmitting from A to B or from B to A, the path loss is the same given that you use the same antennas for transmit and receive. When you transmit from B to A, your directional antenna in A will be the receiver, and the directivity/gain it had in transmit mode is converted to a larger effective aperture (Ae) - meaning that it captures more of the RF energy coming from B. The fundamental relation between Gain and Effective Aperture is: G/Ae=4*pi/lamda^2

[datin]

Hi Espen,
Actually I want to ask that,
I assume RF signal transmitted from A able to reach B antenna.
and I assume transmitted RF signal from B doesnt able to reach A antenna.
Is RF signal coming from A antenna to B antenna working as a carrier for data transfer from B to A ?
Thanks for your interest

[Espen Wium]

Hi datin,

I have to make some assumptions about your RF link, and I'm assuming that you have a half duplex radio system that alternates between sending from A to B and from B to A. The same antenna is used for transmit and receive at both locations, a high gain antenna in A and an omni-directional antanna in B.

Also, I'm assuming that you have the same type of transceiver in A and B, meaning that they have the same output power and sensitivity when measured conducted at the transmission line between the antenna and the transceiver.

I think you have the wrong "model" of the problem; it's not a question of whether the RF signal "reaches" the other node. It always does - RF signals do not stop, but their intensity decreases as the same power is spread over a larger surface area when the signal propagates away from the source. An antenna's ability to capture this power is measured by a parameter called the Effective Aperture (Ae). The model here is that the receiving antenna captures all the RF power in a given surface area perpendicular to the direction of propagation, and this surface area is the effective aperture (m^2). The relationship between Gain and Ae means that when receiving, the antenna in A will capture RF power from a much larger area than the omni-directional antenna did in location B. That's why you will have the same link quality in both directions.