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What Is an Antenna Feed?

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  • Written By: C. Daw
  • Edited By: O. Wallace
  • Last Modified Date: 02 December 2016
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The antenna feed is the combination of all of the components of the antenna that are used for the receiving and transmitting purposes of radio frequency waves. The antenna feed can be regarded as that portion of the antenna ranging from the first amplifier to the front end transmitter in the case of the receiving antenna. In a transmitting antenna, the antenna feed can be regarded as the portion after the last power amplifier. The antenna feed includes the functions of transforming the radio waves into electrical signals and transmitting them to the receiver components. In general, it is considered to be part of the antenna that is being used for the conversion purposes of the radio waves into the electric signals and vice versa.

Antenna design should be made considering the maximum power transfer possibilities and the efficiency. For that purpose, the antenna feed impedance must be matched with the load resistance. The antenna feed impedance is the combination of the resistance, capacitance, and the inductance. To ensure the maximum power transfer conditions both impedances — load resistance and feed impedance — should be matched. The matching could be done by considering the frequency requirements and the design parameters of an antenna such as gain, directivity and radiation efficiency.

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The feed impedance includes two resistive elements, which are the loss resistance and the radiation resistance. The loss resistance is the resistance that is offered by the actual components of the antenna and the feed impedance is the resistance offered at the input of the antenna to the signal. Thus, the loss and the feed impedance must work together in order to achieve a proper working antennae feed. The radiation resistance is the resistance offered by the antenna to the radiation power, or in other words, it presents the dissipated radiation power.

The efficiency, gain, and absolute gain are very important considerations in the design of the antenna feed. The total efficiency of the antenna describes the losses at the input terminal and through the antenna components. It accounts for the reflection, conduction, and the dielectric losses inside the antenna. The gain of an antenna can be regarded as the ratio of the radiation efficiency to the total input power. It is the product of the radiation efficiency and directivity. The absolute gain is the product of maximum efficiency and the directivity. The polarization of the antenna is also a very important consideration for the design and function of the antenna.

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parklinkz
Post 3

@SushiChamp – That’s a nice, simple explanation. And speaking of feeds and feed horns, I recently learned about offset feed antennas, and thought someone here might want to know about them too. I’m a radio enthusiast and find this stuff to be fascinating.

Anyway, offset feed antennas are usually less than three feet wide, so about the size you could have in your backyard, if you wanted. Being small, they have less area with which to capture signal feeds. Traditionally, feed horns sit in the center of the reflector, blocking some of the incoming signals.

With an offset feed, the horn is set at the bottom of the dish. That way, it can perform its duties without interfering with incoming signals, so the antenna can work to its full potential.

SushiChamp
Post 2

@ginSoul – I can’t stand it when TV shows do that! I always think “why did you even bring up the subject if you’re not going to explain what it is?” Luckily for you, I know something about antenna feed horns.

Feed horns are used a lot in satellite dish and antenna design, as a bridge between the transceiver and the reflector. The feed horn “feeds” the signal from the transceiver to the reflector so the reflector can broadcast it.

Some feed horns also block unwanted signals so the transceiver only picks up the desired feed. That’s really important now, because there are millions of devices sending and receiving data streams on and around the planet at any given time. The feed horn antenna helps keep signals free of all that unwanted noise.

ginSoul
Post 1

This may be a little off topic, but what in the world is a feed horn antenna? I was watching a show about electronic communications and they mentioned them, but didn’t explain what they do. Are they related to antenna feeds in any way?

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