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The opposition to current flow (impedance) in an antenna is made up from several constituents – resistance, capacitance and inductance of the antenna – and results from a number of factors including the size and shape of the RF antenna, the frequency of operation, and its environment. When transmitting RF in a waveguide, the feed probe and waveguide impedance must match. Conventional probes are often shaped to successfully match the transmission line’s impedance. But other resistively matched transitions require an external impedance matching network when the waveguide impedance differs from the coaxial transmission line impedance.
To address this, the Navy has developed a compact, simple, and highly effective feed which does not require substantial probe shaping or an external matching network to impedance match the waveguide to a coaxial transmission line. The impedance matching feed consists of a matching transformer located within the ridge of the waveguide. The feed matches a standard coaxial transmission line, which is generally fifty ohms and does not require an external matching network. A probe extends, from the transformer, vertically upward within the waveguide’s interior to the upper wall of the waveguide and is electrically connected to the waveguide. One end of the waveguide is terminated in a quarter wave choke. The quarter wave choke is a short circuit positioned at one-quarter of the waveguide’s wavelength.
- Matches the input transmission line impedance, which is generally fifty ohms, to the waveguide impedance
- The impedance matching feed may be used with single and double ridge waveguides, or other waveguide geometries, such as waveguides which are asymmetric
- US patent 7,315,222 available for express licensing