An antenna apparatus includes a ground plane having an edge; a monopole type first antenna element having a first feed point and configured to communicate at a first frequency; and a monopole type second antenna element having a second feed point and configured to communicate at a second frequency, the second antenna element extending from the second feed point in a direction away from the edge. An end portion of the first antenna element is arranged closer to the ground plane than an end portion of the second antenna element is. A length of an interval between the first feed point and the second feed point is in a range of from 0.25-fold to 0.7-fold of an electrical length of a first wavelength at the first frequency. A length of the second antenna element is a length in a range of from 0.15-fold to 0.55-fold of the electrical length.

A cognitive HF radio is disclosed having a cognitive engine that optimizes HF transmission parameters on the basis of learned experience with previous transmission under varying transmission and environmental conditions. Additionally, electrically small HF antennas optionally using non-Foster matching elements are disclosed. Furthermore, another electrically small HF antenna and associated impedance matching networks are disclosed, including an impedance matching network using non-Foster matching elements.

A cognitive HF radio is disclosed having a cognitive engine that optimizes HF transmission parameters on the basis of learned experience with previous transmission under varying transmission and environmental conditions. Additionally, electrically small HF antennas optionally using non-Foster matching elements are disclosed. Furthermore, another electrically small HF antenna and associated impedance matching networks are disclosed, including an impedance matching network using non-Foster matching elements.

A dielectric loaded sleeve monopole antenna has a dielectric loading within the sleeve enables stable impedance in a dynamic operating environment. The use of a dielectric filling in the sleeve portion of the antenna enables tight control of the input impedance over frequency establishing stable broadband operation in challenging operating environments. The effective dielectric constant inside the sleeve of the antenna is designed to exhibit spatial variability. As a result, the sleeve essentially acts as an impedance transformer enhancing control over the input impedance to the antenna. The spatial variability in the dielectric filling may be realized as arrangements of single or multiple dielectric materials machined to synthesize the desired effective dielectric properties. The antenna may also include the addition of filtering elements inserted into the sleeve to reduce interference for multi-band wireless communication systems.

A dielectric loaded sleeve monopole antenna has a dielectric loading within the sleeve enables stable impedance in a dynamic operating environment. The use of a dielectric filling in the sleeve portion of the antenna enables tight control of the input impedance over frequency establishing stable broadband operation in challenging operating environments. The effective dielectric constant inside the sleeve of the antenna is designed to exhibit spatial variability. As a result, the sleeve essentially acts as an impedance transformer enhancing control over the input impedance to the antenna. The spatial variability in the dielectric filling may be realized as arrangements of single or multiple dielectric materials machined to synthesize the desired effective dielectric properties. The antenna may also include the addition of filtering elements inserted into the sleeve to reduce interference for multi-band wireless communication systems.

The invention relates to a surface wave antenna system, comprising at least one antenna that is electrically short in the vertical plane, with vertical or elliptic polarization and emitting a radiation, said antenna being linked to a conducting medium exhibiting a substantially horizontal surface. The antenna system being characterized in that it comprises furthermore at least one parasitic wire extending in a direction substantially parallel to the surface of the conducting medium, electrically insulated from each antenna, and arranged in the vicinity of at least one antenna in such a way as to be able to radiate by virtue of the current induced by said radiation of this antenna. The invention makes it possible to combine the resultants of each radiating element in such a way as to control the radiation pattern in the vertical plane.

Cage antennas and related components are described. Such cage antennas include a shortened antennal element, such as a monopole (e.g., of approximately -wave height of a desired operational wavelength), which can be placed on a shortened ground plane (e.g., roughly quarter-wave size). A cage-like ensemble (e.g., a cage) can then be placed on top of but not touching the antenna element. The cage structure can have a fractal-based, folded, and/or pleated structure, among others. This cage structure can be produced either through a variety of means including but not limited to 3-D printing with either conductive materials or inductively coded materials.

Cage antennas and related components are described. Such cage antennas include a shortened antennal element, such as a monopole (e.g., of approximately -wave height of a desired operational wavelength), which can be placed on a shortened ground plane (e.g., roughly quarter-wave size). A cage-like ensemble (e.g., a cage) can then be placed on top of but not touching the antenna element. The cage structure can have a fractal-based, folded, and/or pleated structure, among others. This cage structure can be produced either through a variety of means including but not limited to 3-D printing with either conductive materials or inductively coded materials.

A wireless communication device for use in a load control system for controlling one or more electrical loads may comprise a counterpoise, a first and second antennas, a RF communication circuit and a control circuit. The two antennas may be oriented differently and spaced apart from each other. For example, the first antenna may extend perpendicularly from the counterpoise while the second antenna extends in a plane substantially parallel to the counterpoise. The first antenna may extend from the counterpoise at a point substantially central to the counterpoise while the second antenna may extend along a perimeter of the counterpoise. The RF communication circuit may transmit wireless signals via the first and second antennas. The control circuit may cause the RF communication circuit to transmit a first wireless signal in a first time slot and a second wireless signal in a second time slot.

A wireless communication device for use in a load control system for controlling one or more electrical loads may comprise a counterpoise, a first and second antennas, a RF communication circuit and a control circuit. The two antennas may be oriented differently and spaced apart from each other. For example, the first antenna may extend perpendicularly from the counterpoise while the second antenna extends in a plane substantially parallel to the counterpoise. The first antenna may extend from the counterpoise at a point substantially central to the counterpoise while the second antenna may extend along a perimeter of the counterpoise. The RF communication circuit may transmit wireless signals via the first and second antennas. The control circuit may cause the RF communication circuit to transmit a first wireless signal in a first time slot and a second wireless signal in a second time slot.