Abstract: A direction finding system utilizing a single monopole/crossed slot antenna in combination with associated electronic circuitry. Each of the four ports of the antenna are connected to amplitude varying elements whose outputs are combined by a power combiner. A microcontroller stores the signal. The microcontroller also generates the signals which control the amplitude variation supplied by each of the amplitude varying elements. Two configurations of the amplitude varying elements are provided by predetermined settings within the microcontroller. The two settings are selected to configure the antenna on two distinct reception patterns, each with a predetermined angular offset from a reference direction. In operation the antenna will be configured for a first reception pattern. The signals received will be detected, quantified, and stored by the microcontroller which subsequently reconfigures the antenna for a second reception pattern.

Abstract: A diversity antenna assembly for use with portable radiotelephones includes plural antennas physically connected by a non-conducting member to effect simplicity of deployment of the antenna assembly. The antennas are spatially separated to provide space diversity to minimize the deleterious effects of Rayleigh fading.

Abstract: An embodiment of the present invention is a system for automatically pointing a directional antenna. The system comprises two GPS antennas mounted at horizontally opposed extremities of the directional antenna, the placement is such that the GPS antennas lie on a line having a normal vector approximately parallel to a boresight of the directional antenna. The outputs from the GPS antennas are downconverted to a measurement frequency and differentially phase compared for each of a plurality of radio visible GPS satellites. A measurement controller that receives the phase comparisons. A navigation computer receives measurements from the measurement controller and uses a microprocessor to calculate the GPS latitude and longitude and the attitude angles of the pair of GPS antennas. A servo points the directional antenna at a particular target communications satellite, based on the computed azimuth, elevation, latitude, and longitude, as provided by the navigation computer.

Abstract: A dual-mode, radio frequency, optical-wavelength detector apparatus includes RF-transparent optical elements adapted to focusing optical energy in a wavelength range including ultraviolet through infrared wavelengths, on an optical detector, and an RF antenna located behind the optical elements. One embodiment of the apparatus employs a Cassegrain infrared optical telescope system having a concave primary mirror, the front surface of which has applied thereto multiple layers of dielectric material comprising an interference filter reflective in a band of infrared wavelengths, and transmissive to radio frequency energy. A convex secondary mirror having a similar reflective coating is so located as to reflect infrared energy backwards through a central coaxial perforation through the primary mirror onto an infrared detector.

Abstract: An antenna comprises a quarter-wavelength skirt antenna adapted to be disposed over an artificial ground and comprising a vertical cylindrical tube closed at the upper end and a coaxial feed inside the tube. The radiation pattern of the skirt antenna is essentially omnidirectional with a low elevation angle. The skirt antenna is combined with a helical antenna disposed vertically above the skirt antenna and coaxially therewith. The surface closing the upper part of the tube of the skirt antenna constitutes a reflective plane for the helical antenna favoring a hybrid radiation mode specific to the latter, partially axial and partially radial, by lowering the receive lobe of the radiation pattern towards an elevation angle suitable for receiving signals transmitted via satellite. A coupling device combines the signals received by each of the two antennas and feeds them to a common coaxial line.

Abstract: A multi-spectral seeker system for detecting radiation in the infrared (IR) band and a plurality of radio frequency (RF) bands suitable for use in a guided missile is disclosed. The IR and RF seekers are coaxially integrated on a single gimbaled platform and share a common aperture without significant performance degradation. In the preferred embodiment, the IR seeker uses a Cassegrainian reflector assembly with surfaces reflective to IR but transparent to RF signals. The first RF seeker uses a resonant dichroic reflector antenna which is transparent to RF signals at frequencies no closer than 0.5 octaves from the dichroic reflector system operating frequency. The second RF seeker may use any suitable RF antenna system although a planar-array of multi-mode spiral antennas or a standard flat plate slotted array are preferred. The second RF seeker may operate in an active, semi-active, or passive mode.

Abstract: A coaxial multiple-mode antenna system (10) is disclosed, including a coaxial input section (14) for coaxially collecting, for example, MMW and IR electromagnetic radiation. The IR radiation is focused to a point at the input section's focal plane, while the MMW beam has a relatively large width in this plane. An interface section (16) includes an IR section (18) and MMW section (20) that allow the two beams to be separately processed with a minimum of losses. In that regard, the MMW section includes a lens (42), having an incident surface, the center of which is positioned at the focal plane. An optical fiber (46) extends axially through the lens and has an incident end that is aligned with the incident surface of the lens. The lens quasi-optically transmits the MMW beam to a detection circuit (26), while the optical fiber transmits the IR beam to detection circuit (22). Because the optical fiber receives the IR beam before it is processed by the lens, IR losses are limited.

Abstract: A small-sized antenna device is used for portable telephone equipment and is capable of preventing the receiving strength from being degraded due to a change in the application environment as well as the mounting thereof onto a small radio equipment case. The antenna device has a linear antenna for producing an electric current flux and a coil-shaped antenna for producing a magnetic current flux including a plurality of half-wavelength helical coils connected in series so as to have two adjacent coils coiled in opposite directions with respect to each other, and carries out polarization diversity. Degradation in the characteristics of both antennas due to differences in operational principle can be prevented from taking place simultaneously, resulting in realizing a good reception of a radiowave. In addition, the antenna axes of both antennas can be disposed in parallel and close to each other, thus miniaturizing the device itself.

Abstract: A shared antenna aperture has two or more sets of interleaved antenna elements. Open-ended waveguides are used for the elements of the higher frequency antenna array and are selectively interconnected to form the elements of the other sharing antenna arrays. Plates are used to short walls of adjacent waveguides to form notch antennas. Coaxial feeds are used to excite the notches at a lower frequency than the waveguides. In one embodiment, the notch antennas formed of two interconnected waveguides operate at half the frequency of the waveguides. To form a third sharing antenna, four adjacent waveguides are interconnected to form notch antenna elements and these notches are excited at an even lower frequency.

Abstract: A combined infrared-radar detection system wherein a radar antenna also serves as the primary mirror in an infrared focusing arrangement.

Abstract: A multi-layer array antenna having high frequency band microstrip antennas formed on a surface of a first dielectric substrate, comb-shaped low frequency band microstrip antennas formed on a surface of a second dielectric substrate which is disposed on the first dielectric substrate, and through-holes for supplying microwave power to the comb-shaped low frequency band microstrip antennas through the first and the second dielectric substrates.

Abstract: An antenna assembly comprises an elongate radiating element (11) movable between a retracted position and an extended position, and a substantially planar radiating element (12) extending transversely to the elongate element. The elongate element extends through an aperture (25) in the planar element. A pair of concentric conductors (9,10) provide coaxial feed to the radiating elements and the elongate element is slidably mounted within the inner conductor (9). In the retracted position the elongate element forms part of the coaxial feed to the planar element and is itself rendered inoperative as a radiator. The invention provides a compact and convenient dual antenna arrangement ideally suited for use in a portable cellular radio telephone.

Abstract: The present invention is an integrated millimeter wave (MMW) and an infrared (IR) common aperture sensor employing a common primary reflector for infrared and millimeter wave energy. An active transmitter/receiver millimeter wave horn assembly located at the focus of the primary mirror transmits and receives millimeter wave signals off the primary reflector. A selectively coated dichroic element is located in the path of the millimeter wave energy on the axis between the feed and the primary reflector. The dichroic element reflects infrared energy from the primary reflector to a focal point and at the same time transmits and focuses millimeter wave energy. An optical system relays the infrared energy to a focal plane behind the primary mirror. The dichroic element transmits and focuses millimeter wave energy without significant attenuation such that optical and millimeter wave energy may be employed on a common boresight.

Abstract: A lightweight phased array antenna systems that is conformable to an aircraft fuselage combines air-filled cavity-backed slots with printed circuit elements for operation in two or more frequency bands. The printed circuit elements are separated from a conductive ground plane in which the slots are cut by a dielectric honeycomb material. The slots and printed circuit elements are individually excitable by a multiband feed network and transmit/receive modules for operation in the UHF band and S band or L band, respectively.

Abstract: An antenna for a wide bandwidth electromagnetic field polarized in a predetermined direction at right angles to the field propagation direction includes plural metal elements that are not resonant in the bandwidth. The metal elements are excited to transduce an electric field in the polarization direction over the bandwidth range. The plural elements have an extent in the polarization direction no greater than an order of magnitude of the shortest wave length in the bandwidth. A structure between the element, which may be either a coil or parallel electrodes which derive a displacement current, transduces a magnetic field having lines of flux at right angles to the polarization and propagation directions. The electric and magnetic fields are excited by power from the same source with phases so that in an interaction region of the field between a pair of the metal elements there is E.times.H synchronism and a radiation Poynting vector having rotational E and H fields to transduce the electromagnetic field.

Abstract: A common aperture, dual mode receiver for receiving and sensing radiation in the infra-red and microwave waveband comprises an input lens 1, a beamsplitter 2 which deflects microwave radiation and passes infra-red radiation to a microwave focussing sub-system (7, 8) and an infra-red focussing sub-system (3, 4, 5) respectively. The microwave sub-system includes an array of integrated antenna/mixer circuits positioned on the rear surface of the final lens 8.

Abstract: A broadband frequency meter probe utilizes a high frequency antenna and a low frequency antenna to sense wideband electromagnetic energy wherein the different frequency band antennas are closely based monopole and disk antennas. A three-dimensional probe is disclosed having three mutually orthogonal antenna pairs. Damping is provided to decouple resonance which would otherwise occur between the monopole and disk antenna. Self-checking for sensing operation of associated electronics and for providing an indication of normal and abnormal operating conditions is included.

Abstract: A diplexing radiating element comprising at least a first radiating element in which two radiating electrical currents flow which are spaced apart from each other, and at least one second element in which two radiating magnetic currents flow which are spaced apart from each other. The invention is particularly applicable to space telecommunications.

Abstract: A multiple band antenna feed used with parabolic reflector antennas and the like. The feed is arranged as two coaxially disposed waveguides. A planar array of patch elements is disposed at the end of the coaxial waveguides so the energy in each band radiates from a common phase center. This simplifies the arrangement of associated subreflectors.

Abstract: A single aperture antenna system disposed to operate simultaneously in active radar and passive broadband modes is disclosed herein. The dual mode antenna apparatus 40 of the present invention includes a waveguide antenna array 50 which generates a first radiation pattern of a first polarization within an antenna aperture A described thereby. The antenna apparatus 40 of the present invention further includes a broadband antenna array 60 coupled to the waveguide antenna array 50 for generating a second radiation pattern of a second polarization within the aperture A.

Abstract: A broadband, polarization diversity, monopulse antenna comprising a body celed current array and radial arm-coupled log periodic loop antenna in combination with associated mode forming, beam forming and feed networks.

Abstract: An omnidirectional antenna assembly for use with a satellite and others includes a four-element whip antenna, a first and a second reflector which are positioned to face each other, and a third reflector connecting the first and second reflectors to each other. The third reflector is provided with a frustoconical configuration and is highly conductive, whereby the range of antenna gain is broadened.

Abstract: An antenna includes a half-wave dipole antenna and a semicircular patch antenna to form a complementary antenna assembly. The respective antennas are supplied with power to 90.degree. phase difference to generate a circular polarized wave.

Abstract: A unitary, multiband and dual polarity mobile antenna (A) is disclosed for vehicles and the like which includes a television antenna (B) having a horizontally polarized radiation pattern and a 2-way communications antenna (C) having a vertically polarized radiation pattern. A null current point (50) is created on communications antenna (C) by a phasing coil (34) which is intersected by a horizontal plane (52) in which television antenna (B) lies. This reduces cross-coupling, cross-polarization, and interference between the two antenna during operation. Horizontal television antenna (B) includes a J-folded, generally boomerang shaped, curved antenna configured to have a radiating element (20) and a half radiating element (22). These elements together form a third radiating element providing operation at three resonant frequencies.

Abstract: A multi-spectral imaging apparatus with a common collecting aperture, which combines a high performance infrared imaging system with a high performance millimeter wave transceiving system. Two mirror surfaces are combined with a refractive corrector in the infrared mode and with a single reflective parabolic antenna in the millimeter wave mode. The dual mode system functions well in a scanning as well as a staring configuration.

Abstract: A primary slotted array antenna operates at 10 GHz. In front of the primary antenna there is disposed a secondary antenna which operates at 1 GHz and is substantially transparent at 10 GHz. The secondary antenna is formed by an array of patch radiators and a transmission line feed network. The radiators and feed network are all formed by a conductive grid sandwiched between dielectric layers and designed to achieve the transparency at 10 GHz. At 1 GHz the grid appears as a continuous conductor forming one conductor of a microstrip transmission line. The other conductor (ground plane) is formed by the conductive front surface of the primary antenna. The grid/dielectric sandwich is suitably spaced from the ground plane by low dielectric pads. Other embodiments use slotline or coplanar stripline techniques. The ground plane may be an integral part of the secondary antenna, also constructed to be transparent at primary frequency.

Abstract: An avalanche rescue system in which reliable triggering conserves power and permits a high power alarm to be transmitted from a victim to a survivor. Triggering is provided by light sensitive elements on the user, or by a signal transmitted from a survivor. Microprocessor control synchronizes VHF information signal transmission and burst microwave transmission from a victim as well as received signal processing by a survivor. A directional multiple antenna array is switched to provide directional signals displayed to the survivor. A garment is used to affix the system to the person of the user. A unit includes a case and a cover, and the directional antenna array is extended when the cover is opened.

Abstract: An array antenna is provided wherein each adjacent pair of a plurality of antenna elements in such array antenna have a common, conductive wall having a castellated radiating edge. Radio frequency energy resistive material is disposed within slots formed in the radiating edge. With such arrangement, electrical coupling between the adjacent pair of antenna elements is reduced thereby improving the gain of the antenna at the lower frequency operating band of the antenna. Further, the electric field distribution is redistributed by the slotted radiating edge from a cosine distribution associated with a linear edge to a more flattened, uniform distribution to increase the effective aperture of the element in the H-plane.

Abstract: A central aperture provides at least two radiation pattern modes. A second aperture concentric with the central aperture provides at least two radiation pattern modes. A first feed system excites the central aperture and a second feed system excites the concentric aperture. Circuit means associated with the second feed system provides an auxiliary excitation to the concentric aperture which results in optimizing the radiation pattern obtained during excitation of the central aperture.

Abstract: A multimode, multispectral antenna system (14) for detecting radiation from selected target regions in each of at least a pair of selected spectrum bandwidths through collimating lens (35), and rotatable, cooperative prisms (21) effective for collimating and scanning beams of radiation controllably with respect to said target regions.

Abstract: A dielectric member may be thin and planar and may have first and second opposite surfaces. An electrically conductive material is disposed on the first surface at one end of the first surface and an electrically conductive material is disposed on the second surface at the opposite end of the second surface. The conductive materials in the first and second surfaces define a first antenna operative at a first frequency. Slots are provided in the conductive material in the first surface. The slots define a second antenna operative at a second frequency greater than the first frequency. The slots include first and second slots extending in a direction transverse to the relative direction of the conductive materials on the first and second surfaces. The first and second slots may have substantially equal lengths and may be aligned with each other. The slots also include third and fourth slots extending in such relative direction and respectively communicating with the first and second slots.

Abstract: A two-frequency planar antenna incorporates a resonant antenna and a slot antenna which are arranged in a superposed manner on the same dielectric substrate so as to be operable independently without interfering with each other. The two-frequency planar antenna includes a front conductor plate arranged on one surface of a dielectric substrate to serve as a radiation conductor plate of a resonant antenna and a slotted conductor of a slot antenna, a back conductor plate arranged on the other surface of the dielectric substrate to serve as a grounding conductor of the resonant antenna and a reflector of the slot antenna, and a slot antenna feed line embedded in the dielectric substrate. The slot antenna feed line is arranged along an axis where an electric field in an excitation mode of the resonant antenna is reduced to zero and at least one slot is formed in the front conductor plate along the feed line.

Abstract: In one embodiment, a horizontal antenna is mounted electrically separated from but near the top of a vertical antenna. For a given wattage and frequency and for two stations separated a known distance apart, the proscribed angle of elevation for ionospheric reflection for each station can be computed. The current and phase of the signal applied to the horizontal antenna can be adjusted to cancel the electromagnetic field waves emitted from the vertical antenna in the selected azimuth and angle of elevation. The cancellation effects waves of a certain angular orientation at the proscribed angle of elevation for ionospheric reflection.

Abstract: A dual mode target seeking system for airborne vehicles which operates under two different frequencies simultaneously includes a radio frequency antenna comprising a slotted plate defining a ground plane with an image plate positioned in front of the ground plane at a distance chosen such that multiple reflected rays are in phase with each other and with waves incident on the image plate. The slotted plate and image plate have aligned central openings through which an electro-optical system for operating under a chosen electro-optical frequency range, for example under infrared frequencies, projects. The electro-optical system includes a detector unit positioned behind the antenna and a focussing system for directing incoming electro-optical radiation into the detector unit. The focussing system includes first and second lenses mounted in the openings in the image plate and slotted plate, respectively.

Abstract: A microwave antenna comprising a dielectric substrate, carrying on one side thereof a microstrip antenna suitable for operation within a first frequency band and on the other side thereof a conductive ground plane, a first microwave feed coupled between the microstrip antenna and the ground plane for conducting microwave signals in the first band, at least one radiation aperture formed in the ground plane for operation within a second frequency band and arranged to communicate with a resonant microwave cavity defined between the ground plane and a conductive enclosure arranged to extend therefrom, and a second microwave signal feed coupled between the ground plane and the said enclosure for conducting microwave signals in the second band.

Abstract: A reduced height monopole/crossed slot antenna having generally parallel spaced ground planes, the upper one of which has a capacitively loaded slot therein formed by crossed slot portions. A stripline is located between the ground planes offset toward the upper ground plane, and is formed by crossed stripline portions. A monopole extends from the intersection of the crossed stripline portions through the intersection of the crossed slot portions orthogonally to the upper ground plane, and is top hat loaded at the outer end thereof. The stripline is fed at selective ends thereof.

Abstract: A radio frequency antenna is provided comprising: a waveguide section; first means for establishing radio frequency energy in such waveguide section having a first linear polarization with an electric field disposed normal to opposing wide walls of the waveguide section; a planar microwave circuit means, for establishing a second linear polarization having an electric field disposed perpendicular to the electric field of the first linear polarization, such microwave circuit means being disposed within the waveguide between the wide walls and relative to the feed means to provide the first linear polarization and the second linear polarization with substantially coincident phase centers. In a preferred embodiment of the invention, the microwave circuit means includes a strip conductor feed separated from a ground plane conductor by a dielectric, such ground plane conductor having a notch formed therein and fed by the strip conductor.

Abstract: A combination of two juxtaposed rhombic antennas and a V-antenna on a single, longitudinal, non-conductive support boom. The two rhombic antennas lie flat upon one another in substantially the same plane and are supported on the boom with insulating transverse spreader rods.

Abstract: A dual mode antenna that allows both millimeter wave and infrared radiation o enter a single aperture and propagate through a common transmission device to a point where the respective energies are divided to follow separate paths for subsequent processing. An electromagnetic transmission guide or waveguide for the system comprises a tubular waveguide member, having a beam directing lens or lenses therein, for maintianing low-loss, gaussian beam propagation of millimeter wave energy therethrough. A waveguide fiber array is coupled into or adjacent to the tubular member at one end and retrieves the infrared radiation but allows the millimeter wave radiatin to pass. Cassegrainian optics are positioned adjacent the other end of the tubular member for directing incoming millimeter and infrared energy into the guide. Subsequently, the energy impinges on the beam directing lens means that separates the respective energies, dividing them into two separate and distinct paths.

Abstract: Unidirectivity is achieved in an antenna including a microstrip portion and a unipole portion. The microstrip portion includes a ground plane conductor, a radiation plane conductor dielectrically spaced from the ground plane conductor, and a conductive member connecting the radiation plane conductor to the ground plane conductor., The unipole portion of the antenna comprises a unipole coupled to the radiation plane conductor. The radiation fields of the microstrip and unipole portions intensify each other in a single direction to achieve unidirectivity.

Abstract: A dual mode antenna that allows both millimeter wave radiated energy and rared radiated energy to enter a single aperture and propagate through a common transmission device to a point where the respective energies are divided to follow separate paths for subsequent processing. An electromagnetic transmission guide for waveguide comprises first and second parallel tubular members having beam directing reflectors and lenses therein for maintaining low-loss, gaussian beam propagation of radiated energy therethrough. Cassegrainian optics of a cassegrainian antenna system are positioned for directing the millimeter and infrared energy into a common, circular end of said tubes where the energy impinges on beam directing means that separates the respective energies, directing them into the respective parallel tubes along two separate and distinct paths.

Abstract: The antenna of the invention is suitable for use with an aircraft and is capable of receiving a plurality of frequency ranges in the communication band and provides a directional antenna. To this end there is provided an upper wing element from which extend vertically two outer leg elements and a central leg element. The central leg element extends into a fairing disposed below and substantially coextensive with the wing element. Two symmetrical slots are disposed in the wing element symmetrically disposed about the central axis. Another slot extends through the central leg element and the fairing. The slots are provided with capacitors to provide antiresonant circuits at predetermined frequency ranges.

Abstract: A television broadcast antenna includes a high-gain pylon consisting of a vertical array of slots in a conductive cylinder for radiating with high gain towards distant locations. An auxiliary low-gain vertically-polarized portion of the antenna has its phase center coincident with or near the phase center of the pylon for radiating a vertically polarized signal component. This position of the auxiliary portion reduces wind load and feed-line length by comparison with a location above the pylon. In a particularly advantageous embodiment of the invention, the horizontally-polarized radiation pattern of the pylon in the region within a few degrees below the main beam, which is the region directed towards local television viewers, has a low but relatively constant amplitude and phase.

Abstract: A spiral antenna has a plurality of interleaved radiating elements winding outwardly in a spiral pattern about a common axis. The spiral pattern is deformed at outer regions of the antenna to define one or more circumferentially disposed concavities in the body of the antenna. Each concavity is adapted to receive another antenna such as a spiral antenna or horn antenna.

Abstract: A combined RF/IR system in which a common surface is used in the dual modes of radiating and absorbing RF energy and of reflecting and focusing IR energy. The common surface is structured, configured, and used as the slotted array antenna for the RF energy and as the primary mirror of a Cassegrain optical subsystem for the IR energy.

Abstract: A bifunctional antenna of a primary/secondary radar system comprises a reflector having a concave front surface illuminated by a source of primary radiation and formed with a row of circular ports along a horizontal generatrix, the ports lying forwardly of respective cavities or waveguides of cylindrical configuration excitable to emit circularly polarized secondary radiation. In some embodiments the polarization may be changed to a linear or an elliptical mode under the control of inserts rotatable about the cavity axis.

Abstract: An antenna array system which comprises at least one balanced antenna having an electric neutral point and two output end terminals positioned closely to each other, at least one unbalanced antenna having one end thereof dc-coupled with the electric neutral point of the balance antenna and the other end thereof positioned closely to the end terminals of the balanced antenna, first means for picking up a first frequency wave signal such as FM wave signal from the balanced antenna, and second means for picking up a second frequency wave signal such as an AM wave signal from the unbalanced antenna.

Abstract: Reflected signal distortion in vehicular FM receivers is eliminated or largely suppressed by providing a plurality of antenna elements of the vehicle antenna (13, 100) with different directional characteristics, which are selectively connected to the vehicle receiver (10, 30; 104, 106) if a reflection is sensed in the reflection recognition stage (30, 106). In one embodiment (FIG. 1), the antenna (13) is subdivided into an upper and a lower portion (14, 15), about one-third down its length, the lower portion being surrounded by shielding elements (17-20) positioned about 90.degree. offset from each other, and selectively connectable to, or disconnectable from, ground or vehicle chassis in dependence on sensed distortion or reflection recognition pulses, to reduce the effective antenna length and change the directivity.

Abstract: The present invention relates to the orientation of antennae on a satellite possessing at least one antenna comprising a horn rigidly connected to the body of the satellite, a movable reflector mounted on an orientable platform and at least one radio-frequency sensor in the horn using said antenna to control the orientation of said reflector. The invention consists of: using a signal characterizing the pivoting of the orientable platform with respect to the body of the satellite to orient said satellite correctly with respect to the reflector in order to limit the pivoting of said platform; using the signals from at least one earth sensor in the same way as the signals from the radio-frequency sensor to control said reflector, so as to orient the beam towards the point sighted on the earth. The invention is particularly useful for the control of the orientation of antennae, particularly on a satellite.

Abstract: In one embodiment, a horizontal antenna mounted electrically separated from but near the top of a vertical antenna. For a given wattage and frequency and for two stations separated a known distance apart, the proscribed angle of elevation for ionospheric reflection for each station can be computed. The current and phase of the signal applied to the horizontal antenna can be adjusted to cancel the electromagnetic field waves emitted from the vertical antenna in the selected azimuth and angle of elevation. The cancellation effects waves of a certain angular orientation at the proscribed angle of elevation for ionospheric reflection.