A direction-finding antenna includes at least a first set of radiating elements configured to radiate at least a first wavelength (λ.sub.1) and a second set of radiating elements configured to radiate at a second wavelength (λ.sub.2) that is shorter than the first wavelength (λ.sub.1). The first set of radiating elements defines a first circle having a first radius. The second set of radiating elements defines a second circle having a second radius that is smaller than the first radius of the first circle. The direction-finding antenna further includes a transmission line-based multiplexer configured to selectively couple the first set of radiating elements or the second set of radiating elements to a radio frequency (RF) feed line, or a plurality of switches configured to selectively couple selected radiating elements of the first set of radiating elements or the second set of radiating elements to the RF feed line.

A portable Electromagnetic Countermeasure (ECM) device is disclosed for military and civilian population protection from electromagnetic communications and attack, including cell phones, radios, radio-triggered explosive devices, and other personal and portable devices comprising transmitters and receivers. The portable ECM device is usable by a person such as a soldier or policeman to protect themselves and other people around them from spy, guerrilla, military and terrorist threats. The portable (ECM) device comprises a first antenna and a second antenna, both to communicate radio signals with a software defined radio (SDR), and a control pack having a microprocessor operable by remote network connection, or by a mode selector on board the device, to control the SDR according to a mode selected, to receive, produce, and classify radio signals.

A direction-finding antenna includes at least a first set of radiating elements configured to radiate at least a first wavelength (λ.sub.1) and a second set of radiating elements configured to radiate at a second wavelength (λ.sub.2) that is shorter than the first wavelength (λ.sub.1). The first set of radiating elements defines a first circle having a first radius. The second set of radiating elements defines a second circle having a second radius that is smaller than the first radius of the first circle. The direction-finding antenna further includes a transmission line-based multiplexer configured to selectively couple the first set of radiating elements or the second set of radiating elements to a radio frequency (RF) feed line, or a plurality of switches configured to selectively couple selected radiating elements of the first set of radiating elements or the second set of radiating elements to the RF feed line.

An antenna array containing two or more radiating elements, with nearest neighbor radiating elements connected together with a non-Foster circuit at terminals of the radiating elements such that mutual reactance of the elements is reduced over a wider bandwidth than which would be obtained if the non-Foster circuits were omitted.

An antenna array containing two or more radiating elements, with nearest neighbor radiating elements connected together with a non-Foster circuit at terminals of the radiating elements such that mutual reactance of the elements is reduced over a wider bandwidth than which would be obtained if the non-Foster circuits were omitted.

Provided are an antenna, an antenna array, and a wireless communication device with which it is possible to achieve size reduction while suppressing degradation in radiation efficiency. This antenna comprises two antenna elements and a conductor reflection plate. The antenna element includes: a C-shaped conductor which is a substantially C-shaped conductor in which a split part is formed such that a portion of an annular conductor is made discontinuous; and a conductor power feed line that is electrically connected to one of the two parts of the C-shaped conductor that oppose one another across the split part, the conductor power feed line constituting an electric circuit for feeding power to the C-shaped conductor. The two antenna elements are arranged substantially orthogonal to one another such that, when the elements are projected onto the conductor reflection plate, one antenna element and a portion of the other antenna element overlap one another.

Provided are an antenna, an antenna array, and a wireless communication device with which it is possible to achieve size reduction while suppressing degradation in radiation efficiency. This antenna comprises two antenna elements and a conductor reflection plate. The antenna element includes: a C-shaped conductor which is a substantially C-shaped conductor in which a split part is formed such that a portion of an annular conductor is made discontinuous; and a conductor power feed line that is electrically connected to one of the two parts of the C-shaped conductor that oppose one another across the split part, the conductor power feed line constituting an electric circuit for feeding power to the C-shaped conductor. The two antenna elements are arranged substantially orthogonal to one another such that, when the elements are projected onto the conductor reflection plate, one antenna element and a portion of the other antenna element overlap one another.

Provided are an antenna, an antenna array, and a wireless communication device with which it is possible to achieve size reduction while suppressing degradation in radiation efficiency. This antenna comprises two antenna elements and a conductor reflection plate. The antenna element includes: a C-shaped conductor which is a substantially C-shaped conductor in which a split part is formed such that a portion of an annular conductor is made discontinuous; and a conductor power feed line that is electrically connected to one of the two parts of the C-shaped conductor that oppose one another across the split part, the conductor power feed line constituting an electric circuit for feeding power to the C-shaped conductor. The two antenna elements are arranged substantially orthogonal to one another such that, when the elements are projected onto the conductor reflection plate, one antenna element and a portion of the other antenna element overlap one another.

Provided are an antenna, an antenna array, and a wireless communication device with which it is possible to achieve size reduction while suppressing degradation in radiation efficiency. This antenna comprises two antenna elements and a conductor reflection plate. The antenna element includes: a C-shaped conductor which is a substantially C-shaped conductor in which a split part is formed such that a portion of an annular conductor is made discontinuous; and a conductor power feed line that is electrically connected to one of the two parts of the C-shaped conductor that oppose one another across the split part, the conductor power feed line constituting an electric circuit for feeding power to the C-shaped conductor. The two antenna elements are arranged substantially orthogonal to one another such that, when the elements are projected onto the conductor reflection plate, one antenna element and a portion of the other antenna element overlap one another.

An antenna arrangement 10 comprises a first elongate limb 12 and a second elongate limb 14. The first and second elongate limbs converge towards one another at a first electrical connection point 16 and a spaced anti-phase electrical connection point 18. The first and second limbs collectively forming a closed figure with a first appendage 22, a second appendage 24, a third appendage 26 and a fourth appendage 28 to the closed figure.