Abstract: Radio frequency antenna is buried in the earth with its top substantially flush with the surface with a significant portion of the antenna buried therebelow. The antenna is configured so that, if much of the top is removed, as by blast, the remaining portion of the antenna remains operative without significant functional deterioration.

Abstract: Method and apparatus for detecting tunnels, voids or other anomalies bene an area of the earth's surface wherein an oscillator couples a current into two conductors laid parallel to each other to generate two magnetic fields in the earth beneath the area. The magnetic field is measured along a line midway between the two horizontal conductors to detect for an increase in the measured field which is an indication of the presence of an anomaly.

Abstract: Improved method and apparatus for detecting anomalies beneath an area of earth's surface wherein an oscillator couples a current into two conductors laid parallel to each other to generate two magnetic fields in the earth beneath the area. The magnetic field is measured along a line midway between the two horizontal conductors to detect for an increase in the measured field which is an indication of the presence of an anomaly.

Abstract: A low profile transmitting antenna consisting of a circular slot in a coal cavity that is folded several times. The last inner fold of the coaxial cavity is loaded with the tuning coil. The tuning coil can in the alternative be connected in series with the transmitter leeds connected to the radiating slot. Concentric cylinders alternately attached to the top and bottom of the cavity are used to form the folded coaxial cavity that provides the equivalent of a tapered transmission line. Energy to be transmitted is fed across the circular slot of the antenna or in the alternative may be fed into the last inner fold in the center of the cavity. The antenna radiates energy out with the same radiation pattern as a vertical monopole antenna.

Abstract: A transmitting antenna that can be inflated with air or a liquid dielectric nd floated in seawater. It consists of a cuplike cavity backing a radiating annular slot antenna. It can be used to communicate to submarines or surface ships or as a navigation transmitting antenna. It is small compared to the wavelength of the operating frequency.

Abstract: A directional loop array antenna for very low frequency (VLF) reception. array comprises four closely spaced loop antennas forming a unidirectional reception pattern with a main beam of less than 43.degree. between half power points. The array combines two double loop coaxial antennas dispersed with their axis parallel along 45.degree. lines. The signal from one double loop array is delayed sufficiently such that a unidirectional reception pattern is formed.

Abstract: Method and apparatus for detecting tunnels beneath an area of the earth's rface wherein an oscillator couples a current into a linear conductor at the earth's surface to generate a magnetic field in the earth beneath the area. Phase angle measuring means measures phase difference between the vertical and horizontal components of the magnetic field at selected points along a line parallel to the linear conductor to detect abrupt changes in earth resistivity, changes in resistivity indicating the presence and horizontal position of a tunnel.