User:KevinCoffey0/sandbox/Coaxial Antenna

Coaxial Antenna The coaxial antenna, or coaxial dipole antenna, is a type of antenna that has its both its transmitter and receiver facing the same way. Usual dipole antennas (see: rabbit ears antennas) have their transmitter and receiver at an angle to each other. The coaxial antenna is a type of dipole antenna, which are a type of antenna that have 2 poles, one used for receiving signals and one used for transmitting signals. In the past, the Coaxial Antenna was mainly used in radios for short distance communication and Citizens band radios, but also has seen other uses in the medical and geological field. Nowadays, the coaxial antenna is a more niche, but can still be used for radio communications.

Components and Function

The coaxial antenna is made from 2 main parts: an outer conductor and an inner conductor (also can be called a center conductor). The outer conductor needs to be able to hold the inner conductor and take inputs from cables. To meet these 2 requirements, the outer conductor usually ends up being a hollow metal tube. The purpose of the outer conductor is to connect to that cable's shield by letting the cable attach into one of its openings. The inner conductor, which tends to be solid metal tubing, is mounted on the outer conductor, usually opposite where the cable attached. Although the inner conductor is an omnidirectional antenna and can therefor be mounted in any direction, it is usually mounted upright, to get the most coverage. The size of the inner conductor depends on the frequency that it is trying to receive, through the equation height = 460/frequency(MHz). The coaxial antenna tends to operate at and around VHF, which is a band of frequencies that range from around 30 MHz to up to 300 MHz.

History & Current Uses

The coaxial antenna was used in Citizens band radios in the 1940's. Coaxial antennas could access the 27 MHz frequency, which corresponded to an unusually long wavelength for antennas at the time. The CB radio eventually fell out of fashion, and is only really used by radio enthusiasts.

It has seen potential use in the medical field, where it was used for microwave interstitial coagulative therapy(therapy for dead cells using microwaves) . Researchers wanted to create a minimally invasive interstitial heating techniques using electromagnetic sources for use in treating cancer and decided that a modified coaxial antenna could be used for this.

In 1989, researchers found a way of measuring rock deformation using coaxial antenna cables. It did this by grouting a coaxial antenna cable into a block of cement and having it reflect voltage pulses, which were then read out by a TDR Cable tester .

The coaxial dipole antenna is even still used today to tune into radio frequencies as well as an antenna option for TV Broadcasting, TV reception and military aviation by companies like Boeing, Lockheed martin, Airbus, etc.

Patent History

Overview:

This section has patents that contain a type of modified coaxial antenna as their core component.

These are not traditional coaxial antenna's, but share enough aspects with them to still be considered coaxial antennas.

Coaxial waveguide antenna:

This is a coaxial antenna that is constructed with a open-ended coaxial radiator and has the inner (or center) and outer conductors of normal coaxial antennas. This particular coaxial antenna has multiple electromagnetic coupling modules positioned in and around the waveguide component of the antenna. To transmit waves, each of these electromagnetic coupling modules samples, amplifies, and adjusts the phase of an electric field. The electric fields affected by the electromagnetic coupling modules are then radiated out of the antenna, and serve as transmitted waves. To receive waves, it just has to detect similarly affected waves and radiate them into the antenna.

Leaky coaxial antenna:

This is a coaxial antenna with an inner (or center) conductor, a dielectric that envelops the inner conductor, and a 2 layers of shield conductors. The first layer of shield conductor is put around the dielectric with openings along the direction of the inner conductor. The second layer shield conductor is the arranged in the same direction of these opening and cover at least some of them. This sort of coaxial antenna is optimized for aerospace applications.

Coaxial antennas with ungrounded outer conductor section:

This coaxial antenna is composed similarly to a normal coaxial antenna, with a an outer conductor and an inner conductor. This difference with this coaxial antenna is that the outer conductor has 2 sections, being separated by a gap. The gap's location isn't set and can be shifted around, which allows the feed and transmission component lines to also be shifted around. This allows this antenna to be more adaptable in uncontrollable environments.

Controversy

On September 21st 2016, a podcast show called Ham nation, had an episode about a type of coaxial antenna called the "Bazooka dipole coaxial antenna". In this podcast, the host Bob Heil claimed that the Bazooka antenna was extremely broadband, that whole bands can be covered with no tuner, and that no static charges could build up because there was no exposed metal. On October 4th 2016, a thread was started on an amateur call sign website that pointed out that there was no evidence backing Bob's claims. The author of the thread even created their own Bazooka antenna to show that there was no difference in performance between it and a normal dipole. The author accused Bob of re-using claims by the company (IAC) who had invented the Bazooka and sponsored the Ham nation episode.