Abstract: An apparatus and method for diagnosing antennas using switches, wherein a system is configured in such a manner that a plurality of switches determine a data flow of a signal for test. Therefore, the antenna diagnosing apparatus can be so simplified in circuitry construction that it can be easy to manufacture at low cost. Further, the antenna diagnosing apparatus can accurately measure standing wave ratios of the antennas without being subject to any error, so as to accurately diagnose the performance of the antennas.

Abstract: An antenna unit includes an antenna, a high-frequency amplifier, an attenuator circuit, an output cable, and a voltage detector circuit. An operating voltage is supplied from a receiver to the high-frequency amplifier through the output cable. The operating voltage changes in accordance with an AGC voltage. The voltage detector circuit detects a change in the operating voltage. In response to the detector output, one of the high-frequency amplifier and the attenuator circuit is selectively connected to a signal line between the antenna and the output cable.

Abstract: A directive antenna includes plural antenna elements in an antenna assemblage. A feed network connected to the antenna elements includes at least one switch to select a state of one of the antenna elements to be in an active state in response to a control signal. The other antenna elements are in a passive state, electrically coupled to an impedance to be in a reflective mode. The antenna elements in the passive state are electromagnetically coupled to the active antenna element, allowing the antenna assemblage to directionally transmit and receive signals. The directive antenna may further include an assisting switch associated with each antenna element to assist coupling the antenna elements, while in the passive state, to the respective impedances. The antenna assemblage may be circular for a 360° discrete scan in N directions, where N is the number of antenna elements.

Abstract: When the antenna is extended, the length of the ½&lgr; whip antenna 102 operates as an antenna thus causing only a negligible quantity of high-frequency currents to flow into the ground for the circuit board 108. When the antenna is housed, the entire length of a ¼&lgr; helical antenna 101 and a ¼&lgr; radial 109 operates as an antenna thus causing only a negligible quantity of high-frequency currents to flow into the ground for the circuit board 108. When the antenna is extended, the second contact 104 makes adjustments so that high-frequency electric signals from the ½&lgr; whip antenna 102 may be transmitted to the circuit board 108 and matching may be provided at the second matching section 106 when the antenna is extended.

Abstract: At least one electromagnetic lens having a first contour is disposed proximate to a dielectric substrate having a first edge having a second contour. A plurality of antenna feed elements, for example, end-fire antennas, are disposed on the dielectric substrate along the second contour. A signal applied to a corporate feed port is switched to the antenna feed elements by a switching network, wherein each antenna feed element launches an electromagnetic wave that is diffracted by the at least one electromagnetic lens so as to form an associated beam of electromagnetic energy. Different antenna feed elements generate different beams of electromagnetic energy in different directions. A pair of electromagnetic lenses with associated antenna feed elements at different edge locations on the dielectric substrate provide for bi-static operation. A reflector may be used to redirect the beams of electromagnetic energy.

Abstract: An antenna for a transceiver. The antenna is switchable between a receive and a transmit mode. In receive mode, the antenna is configured to provide increased sensitivity for improved inductive pickup of signals. In transmit mode, the antenna is configured to provide efficient power output without undue losses. The antenna coil comprises a plurality of conductor bundles. In receive mode, the conductor bundles in series to increase the number of effective turns in the antenna coil and thereby increase the inductive pickup of the coil for receiving signals. In transmit mode, the conductor bundles are configured in parallel. The parallel configuration of the conductor bundles reduces the AC and DC resistance of the antenna coil, and therefore the power loss, to allow the antenna to be driven efficiently to transmit signals.

Abstract: An isotropic antenna system includes a first antenna for transmitting/receiving electric waves when a cover member installed to be capable of being open or closed with respect to a main body is open, a second antenna for transmitting/receiving electric waves when the cover member is closed, and a switch for selectively switching at least one of the first and second antennas to a predetermined RF circuit module according to the opening or closing of the cover member.

Abstract: A polarizing antenna for a magnetic resonance apparatus for irradiating an imaging volume surrounded by the antenna, has two or a multiple of two longitudinal conductors that are arranged with the same lateral spacing parallel to an axis and which are terminated with electrically coupled end rings. The size of the imaging volume is dependent on the distance of two end rings terminating the longitudinal conductors from one another. The longitudinal conductors have a number of end rings allocated to them, by which the longitudinal conductors can be terminated and that can be optionally switched into coupling connection with the longitudinal conductors for varying the illuminatable imaging volume.

Abstract: An antenna diversity receiver is disclosed. The diversity receiver has a multipath detector for controlling an antenna selective switching circuit. The switching circuit couples one of a plurality of antennas to a RF receiver input. The receiver allows suppression of adjacent channel interferences without unwanted side effects by employing a switching disabling circuit to automatically disabling the switching circuit when the signal delay between the occurrence of multipath distortions in the RF reception signal and the switching between antennas exceeds a predetermined critical signal delay value.

Abstract: A multiband antenna has first and second antenna devices for transmitting or receiving. Each device has a dipole structure and associated dipole halves disposed opposite a base plate or reflector by baluns. The antenna devices are provided with a feed from a common antenna input line and a branch circuit. Frequency selective components are respectively associated with the first and second antenna devices. An electrical length of branch lines between a branch point and a feed point on the associated antenna devices having the dipole structure enables the frequency selective components respectively to reject a frequency band range transmitted via another of the first and second antenna devices.

Abstract: A switching interface for routing RF signals. The interface comprises a buffer decoder which receives first, second and third control signals and then decodes the signals to selectively turn on five RF switches. The decoded output signals from the buffer decoder are supplied to five pair of switch drivers for the RF switches. When a logic one is provided to a switch driver, the switch driver sets the RF switch to an ON position. When a logic zero to a switch driver, the switch driver set the RF switch to an OFF position. A window comparator monitors the outputs of the switch drivers for each of the five RF switches. Whenever one of the two output signals from the switch drivers is within a preset voltage range the window comparator provides a logic one and a logic zero which are supplied to a bit decode circuit.

Abstract: A method and system for transmitting, and a signal comprising multiple frequency bands from a single slot antenna are disclosed. The system comprises a slot antenna and a micro-electro-mechanical (MEM) switch, coupled to the slot antenna. The MEM switch is opened and closed, thereby changing the resonant frequency of the slot antenna. The slot antenna transmits a first frequency when the MEM switch is open and a second frequency when the MEM switch is closed. The method for transmitting a first frequency and a second frequency from a slot antenna comprises the steps of transmitting the first frequency from the slot antenna, closing a micro-electro-mechanical (MEM) switch coupled across the slot antenna, therein changing the resonant frequency of the slot antenna, and transmitting the second frequency from the slot antenna after the MEM switch is closed.

Abstract: An antenna having a dielectric layer configured about a longitudinal axis, and having at least two surface portions which face outwardly from the longitudinal axis in at least two different directions. A conductive ground plane is bonded to each of the at least two surface portions, and at least two conductive antenna elements are bonded to each dielectric layer on each of the at least two surface portions for radiating a signal therefrom. A transmission strip configured for transmitting a signal is connected through a switch to each of the at least two conductive elements.

Abstract: An antenna system for a radio telephone in a vehicle that has a primary antenna to realize telephone communication with optimal connection quality connected to the radio telephone by an antenna wire, a secondary antenna that at least allows for telephone communication with limited connection quality when the primary antenna fails and an electric switch that connects the secondary antenna to the radio telephone after the primary antenna fails. This is realized in that the primary antenna is mounted on the vehicle with a breakable fastening element and that the switch automatically connects the secondary antenna to the antenna wire by mechanical means in place of the primary antenna when the fastening element is broken off.

Abstract: An antenna system (10) capable of transmitting electromagnetic radiation using the technique of combining two quadrature signals for either right hand circular polarization or left hand circular polarization using a circularly polarized antenna (30), or alternately, either horizontal or vertical polarization using a linearly polarized antenna (36) while incorporating feedback for automatically correcting for amplitude and phase variations in the quadrature paths using a switch (12) which selects the sense of the polarization and electronic optimization of the transmit antenna (30, 36). The antenna system includes a control circuit having a polarization switch (12) for receiving a transmission signal. The switch (12) generates first and second output signals which are substantially similar to the transmission signal, and determines whether to apply the transmission signal to one of a first or a second switch output.

Abstract: A switchable antenna (10) with a base antenna assembly (11), a secondary antenna assembly (12) and a switch. Base and secondary antenna assemblies (11,12) have respective housings (21,23) to respectively house helical antennas (31,40). Secondary antenna assembly (12) is mounted to and operably coupled to base antenna assembly (11) with a connector (13). A contact member (18) of base antenna assembly (11) has a contact ball bearing (20) and a conductive plate (22). Secondary antenna assembly (12) has a contact member (19) with a conductive plate (25) and a dimple (26). The switch is formed by connector (13), ball bearing (20) and conductive plates (22,25) and selectively electrically couples adjacent ends (32,41) of helical antennas (31,40) by relative rotation about a common longitudinal axis (43).

Abstract: A dual LNB/TV antenna multi-switch allowing DC voltage provided by a satellite receiver to travel through the terrestrial antenna input without causing interference, distortion or lowering the signal strength of the satellite and terrestrial antenna pictures. By including an external DC block adapter with the invention, the multi-switch can be used with both amplified and non-amplified antennas and not require an external power injector.

Abstract: A double pole limit switch (340) includes an insulator (410), a conductive spring element (420), and a conductive element (430). The conductive spring element is attached to the insulator for providing spring coupling between a substrate (210) and the insulator, and has a first electrical contact (355) and a conductive substrate attachment portion (425). The conductive element is attached to the insulator and has a second electrical contact (350) and a conductive actuator feature (435). The first and second electrical contacts are moved into a plane of the conductive substrate attachment portion by application of opposing forces to the conductive actuator feature and the conductive substrate attachment portion.

Abstract: A variable geometry antenna including first and second conducting sections and electrically separated by a gap, and a sliding switching module assigned to the gap. The sliding switching module includes a mechanical relay, a moveable rod having a first end secured to a conducting piece included in the mechanical relay and configured to slide parallel to the first and second conducting sections so as to couple the first and second conducting sections, and a control mechanism.

Abstract: An electronically steerable antenna array which includes time delay units connected to individual antenna elements for time delaying a microwave signal to and/or from the antenna elements. Each time delay unit includes small mercury wetted switches for controlling signal flow via a time delay path or a bypass path, through the time delay unit from a signal input to a signal output.

Abstract: In antenna device which is to be used in a portable radio receiver, plural loop antennas 1 and 3 which are formed along different faces of a case 9 of the radio receiver, respectively, and switching means 5 for selecting one of received signals from the plural loop antennas are disposed. Reception is performed while selecting a loop antenna having a higher received signal level. When an antenna having the directivity or the plane of polarization which are more advantageous is selected, it is possible to ensure high reception performance.

Abstract: The invention relates to small-sized antenna systems, especially planar antenna structures operating on several frequency bands. The antenna structure of the invention comprises a radiating antenna element with at least two lips. Thus, the antenna structure has two basic resonance frequencies, which are defined by the dimensions of the lips of the antenna element, gaps between them, and the other dimensions of the antenna structure. The radiating antenna structure is connected to the ground plane at least at one place. The radiating antenna element comprises at least two connection points, which are used for connecting the feed lines of the transmitter and receiver, and for connecting special tuning elements. The resonance frequencies of the antenna structure may be adjusted by connecting the said tuning elements to the connection points and antenna feed lines so that the antenna structure is operable on more than two frequency bands.

Abstract: An antenna for use with low-band, mid-band and high-band signals, including a coaxial member, a low-band and mid-band signal input connected between one end of the coaxial member outside conductor and the device chassis ground, and a high-band signal input connected between one end of the coaxial member outside conductor and the corresponding end of the coaxial member inside conductor. A first isolation filter adapted to block low-band and mid-band signals from the coaxial member is between the coaxial member and the high-band signal input. A parallel resonant circuit is at the other end of the coaxial member outside conductor and a solid conductor is connected to the parallel resonant circuit and to the other end of the coaxial member inner conductor. The low-band signal input is disconnected from high-band signals by, for example, an RF switch or a second isolation filter between the coaxial member and the low-band signal input.

Abstract: To control a converter of a satellite receiving system, the converter receives not only a dc voltage but one of two different voltages (normally 13 or 17 volt) also an alternating voltage (normally 22 kHz). It has to be possible to control more equipment along the same (coax) cable like amplifiers and switchers and to switch between more sub-bands than two. To achieve this the satellite receiver includes a power supply unit having switching apparatus which can combine the supplying of one of the two dc voltages with an alternating voltage continuous tone or burst as (switching) information.

Abstract: A means is disclosed for increasing the power and field strength radiated by a solid state switched array radiator such as those used for example in ultrawideband radar systems. The incorporation of a specially designed pulsed transmission line is designed to preserve very fast rising pulses produced in each of a number of Blumleins that are triggered simultaneously or with appropriate delay to provide at the output of the stack of Blumleins a voltage that is applied to an antenna radiating element.

Abstract: A windowpane antenna apparatus for use in a vehicle according to the present invention, includes a plurality of conductive strips arranged in a windowpane of the vehicle so as to have a predetermined pattern, function designation switches turned on to transmit/receive predetermined waves, an arithmetic unit for performing an arithmetic operation of obtaining a combination of the plurality of conductive strips in order to form a desired antenna having antenna characteristics matching a function designated by the function designation switches, and a selective connecting switch for selecting one or some of the conductive strips based on the combination of the conductive strips obtained by the arithmetic unit and connecting the selected some of the conductive strips to form the desired antenna.

Abstract: A switched gain antenna array comprising a plurality of dipole elements disposed in series with a phasing stub coupled between adjacent ones of the dipole elements. An antenna feed line is coupled to a first one of the dipole elements to couple the RF signals into and out of the plurality of dipole elements. The phasing stubs are adapted to adjust phase of the RF signals provided to each of the dipole elements so that the dipole elements operate in phase. A switch is disposed between the first one of the dipole elements and a second one of the dipole elements. The switch is adapted to disconnect the first one of the dipole elements from remaining ones of the dipole elements during transmit operations of the antenna array and to connect each of the dipole elements together during receive operations of the antenna array. As a result, the antenna array has greater gain during receive operations than during transmit operations.

Abstract: A radio frequency antenna arrangement for selective operation at orthogonal polarizations of electromagnetic radiation. The antenna arrangement comprises at least one radiating element, such as one or more antenna patches, each having a vertical polarization feed point and a horizontal polarization feed point. The arrangement also includes a vertical feeder circuit for coupling a radio frequency modulated electromagnetic signal to the vertical polarization feed point of the or each radiating element, a horizontal feeder circuit for coupling a radio frequency modulated electromagnetic signal to the horizontal polarization feed point of the or each radiating element and a terminating resistive load. A switch mechanism is provided for selectively coupling the electromagnetic signal to one of the horizontal feeder circuit or the vertical feeder circuit and for selectively coupling the load to the other of the horizontal feeder circuit or the vertical feeder circuit.

Abstract: A low power switched diversity antenna system (200) includes two varactor tuned antennas (205, 207), each including an antenna element (505) and a varactor (515). The varactor tuned antennas intercept components of electromagnetic radiation that are substantially orthogonally polarized. One of the varactor tuned antennas is tuned to a desired frequency and the other is detuned, achieving a relative gain of the tuned varactor tuned antenna to the detuned varactor tuned antenna of at least 3 dB at the desired frequency.

Abstract: A crossed-dipole antenna having four antenna elements, the polarization of hich is easily changed from vertical linear polarization to horizontal linear polarization. A switching network coupled to the crossed-dipole antenna includes pin diodes operating as radio frequency switching elements which provide a means for electronically switching the polarization of the crossed-dipole antenna. A positive biased voltage applied to the switching network results in the crossed-dipole antenna being polarized linearly in a horizontal direction. A negative biased voltage applied to the switching network results in the crossed-dipole antenna being polarized linearly in a vertical direction.

Abstract: In order to minimize switching losses occurring in antenna switches for wireless antenna diversity telecommunications devices with two antennas, for example base station of a DECT cordless telephone, in each case an electronic switching element (SE1 . . . SE4), constructed for example as a PIN diode or switching diode, is arranged in a first signal path (SW1) from a transmitter (TR) to a first transmission/reception antenna (A1), a second signal path (SW2) from the transmitter (TR) to a second transmission/reception antenna (A2), a third signal path (SW3) from a receiver (RE) to the first transmission/reception antenna (A1) and a fourth signal path (SW4) from the receiver (RE) to the second transmission/reception antenna (A2). The switching elements (SE1 . . . SE4) form here, together with the signal paths (SW1 . . . SW4), a ring circuit.

Abstract: An antenna assembly (10) has a rotatable antenna arm (15) with an active portion (20) and a switching portion (25), a ground plane (30) and an inductive loop element (35) connected to the ground plane. In a first position of the arm (15), the arm is generally parallel to the ground plane (30) and the switching portion (25) is connected to the inductive loop element (35), forming a transmission line antenna. In a second position of the arm (15), the arm is extended away from the ground plane (30) and the switching portion (25) is disconnected from the inductive loop element (35), thus forming a whip antenna.

Abstract: Antenna systems for radiotelephones and other electronic devices include a first impedance matching circuit that electrically connects to a retractable antenna via a feed terminal when the retractable antenna is in an extended position and a second impedance matching circuit that electrically connects to the retractable antenna via the same feed terminal when the retractable antenna is in a retracted position. A switch opens and closes in response to detected positions of a retractable antenna to allow the first and second impedance matching circuits to electrically connect with an antenna via the same feed terminal.

Abstract: A fading phenomenon is eliminated by integrally providing two monopole antennas on a printed circuit board, alternately feeding a high frequency signal to the two monopole antennas by a switching device, and differently forming distances and patterns of the two monopole antennas whereby making a diversity.

Abstract: A high frequency, high speed data communication system for providing electronic mail, file transferring, Internet access, weather forecasts and other database and communication options to remote HF/MF users, such as vessels at sea. A conventional, multi-featured, land-line bulletin board system is employed at a central communication facility for the provision of data communication services. A remote computer accesses an HF/MF link at the central communication facility via an HF/MF modem coupled to an HF/MF radio and antenna. The HF/MF link includes an antenna, HF/MF radio, HF/MF modem, and an interface computer for performing protocol and interface conversion between the land-line BBS and the HF/MF modem. Multi-user capability is provided through the simultaneous employment of multiple HF/MF links at the central communication facility. Multi-frequency operation of each HF/MF link is provided through the scanning of each HF/MF radio in conjunction with an antenna tuning system.

Abstract: The invention provides a microstrip patch antenna for emitting backscatter-modulated signals in response to a received signal. The antenna has two segments that are connected together by a switch. When the switch is ON, the antenna is a full wave length antenna with its two segments out-of-phase with each other, thus producing minimal backscatter. When the switch is OFF, the two segments of the antenna act in concert with each other to produce a backscatter-modulated signal. Multiple pairs of such antennas can be connected together to make a single antenna with increased signal power.

Abstract: A fixed body wide field-of-view conformal antenna array suitable for broadband precision direction finding on missile platforms. The array is configured as multiple sub-arrays of spiral antennas that cover particular regions within the desired field-of-view of the entire array. A lower cost, more reliable and more accurate direction finding solution for missile needs is provided, primarily by the elimination of conventional radomes and antenna gimbal structures. The array can be configured to include multi-mode sensors.

Abstract: A fixed body wide field-of-view conformal antenna array suitable for broadband precision direction finding on missile platforms. The array is configured as multiple sub-arrays of spiral antennas that cover particular regions within the desired field-of-view of the entire array. A lower cost, more reliable and more accurate direction finding solution for missile needs is provided, primarily by the elimination of conventional radomes and antenna gimbal structures. The array can be configured to include multi-mode sensors.

Abstract: A multiplexing arrangement for an electronic article surveillance and identification system interconnects a transmitter and a plurality of antennas. The transmitter has first and second terminals and each of the antennas includes an antenna coil. The multiplexing arrangement includes a step down transformer that has a primary winding connected across the first and second terminals of the transmitter, and also has a second winding. A first winding is positioned for inductively coupling with the antenna coil of a first antenna and a second winding is positioned for inductively coupling with the antenna coil of a second antenna. The multiplexing arrangement also includes a first switch and wiring that forms a series loop connection including the first winding, the second winding, the first switch and the secondary winding of the transformer. The first switch is arranged to selectively open-circuit the series loop connection.

Abstract: Apparatus for use in a geophysical prospecting method from a vehicle for site plan pictorial representation of inclusions present in substratum soil which reflect modulated electromagnetic oscillations. This apparatus is particularly useful for detecting inclusions such as veins of water, ore beds, pipelines, unexploded bombs, cavities, ammunition and residual fissures. A transmitter and receiver are mounted in the vehicle with a common quartz oscillator in a sawtooth generator. A transmitting antenna and receiving antenna are provided with an amplifier connected to the latter. A pulse shaper employs the width of received triangular pulses from the amplifier to give needle pulses and a color transmitter has four power amplifiers and is a goniometrically scanned four-cycle transmitter, and accordingly the cathode ray tube has four crosswise arranged horizontal sweep coils in addition to the frame coil.

Abstract: A fixed body wide field-of-view conformal antenna array suitable for broadband precision direction finding on missile platforms. The array is configured as multiple sub-arrays of spiral antennas that cover particular regions within the desired field-of-view of the entire array. A lower cost, more reliable and more accurate direction finding solution for missile needs is provided, primarily by the elimination of conventional radomes and antenna gimbal structures. The array can be configured to include multi-mode sensors.

Abstract: An antenna for transmitting electromagnetic signals having a frequency less than 500 Hz includes a beam of dielectric material and a conductive sheet wound in a helical pattern around the beam of dielectric material. The antenna further includes a core fabricated from a silicon and iron alloy, the cote disposed between the beam of dielectric material and the conductive sheet. With such an arrangement, a magnetic dipole antenna is provided capable of providing a magnetic moment of approximately 10.sup.6 to 10.sup.7 Am.sup.2.

Abstract: The invention provides for antenna apparatus having antenna members extending parallel to a ground plane, which members are L-shaped and can be provided in advantageously miniaturized form. Two such antenna members can be provided on the same ground plane so as to achieve antenna diversity and a switch mechanism is provided for switching between the antenna member in a receive mode, and for switching to only one of the antenna members for operation of the apparatus in a transmit mode. The switch mechanism is arranged to ground a feed connector of the antenna member that is not selected for transmission or reception so as to render that antenna member passive.

Abstract: A printed circuit board antenna is provided which includes an electronic switch (38) whereby a single compact radiating structure consisting of a split dipole antenna (10) with associated balun structure (11) may be selectively driven in either of two modes to provide orthogonal polarization and pattern diversity: as a split dipole antenna with a quarter wave balun relying on the split dipole antenna (10) as the radiating element; or as a top-loaded monopole relying on the quarter wave balun structure (11) as the radiating element against a ground plane (12). Orthogonal polarization and pattern diversity are achieved as a result of the mutually perpendicular orientations of the split dipole antenna (10) and its integral balun structure (11).

Abstract: The disclosure relates to broadcasting by means of rotary antennas using rigid dipoles. Each of two distinct channels passes through the joint between the fixed support of the mobile part of the antenna and rise vertically into the interior of the mast to respectively reach two distinct vertical groups of dipoles. It is thus possible to carry out two simultaneous transmissions from one and the same rotary antenna. Application to broadcasting in decameter waves.

Abstract: A convertible antenna system for enabling immediate installation of an antenna for continuing the broadcasting of conventional signals in the currently available channel ranges, but which allows for eventual convertibility to HDTV (high definition television) operation. Thus, field convertibility adjustments or modifications are made to the initially installed system after the point in time at which a channel has been assigned for HDTV broadcasting. Such channel assignment is in one of a number of possible frequency spectrum locations such as a channel adjacent to the conventional broadcast channel, or a significantly removed VHF channel, or even a UHF channel. The field adjustments can simply involve coupling or decoupling lines and associated components, or can include replacing an antenna portion.

Abstract: A wireless communication system includes a plurality of stations each having a plurality of antennas. A first packet, containing a training signal portion is transmitted from a transmitting station using a first selected antenna and received at a receiving station using a second selected antenna which is selected as the antenna giving the best received signal quality, determined during the training signal period. Following transmission of the first packet, a control signal (ACKCNTL) is generated in both the transmitting station and the receiving station to condition these stations for the transmission from the receiving station of a response packet via the same antenna pair used for the information packet transmission. Thus, the response packet need have only a relatively short training signal portion.

Abstract: An antenna system capable of receiving electromagnetic radiation having either right or left helical polarization, and either vertical or horizontal linear polarization includes an energy concentrator which concentrates energy at a focal point. A helical antenna is arranged in the proximity of the focal point. A first switch switches the helical antenna to a backfire mode of operation and a second switch switches the helical antenna to an end fire mode of operation. A control mechanism controls the switches to select the nature of the polarization.

Abstract: An antenna system for use in an Automatic Vehicle Identification (AVI) system 10 having a plurality of non-resonant antenna loops 14 which operate as a single loop antenna during a transmit cycle and individual antenna during a receive cycle. The antenna system includes individual antenna 14 each having amplifier 29 connected to a single source. A switch circuit selectively switches the system from a transmit to receive mode and from a receive to a transmit mode.

Abstract: The invention provides for antenna apparatus having antenna members extending parallel to a ground plane, which members are L-shaped and can be provided in advantageously miniaturized form. Two such antenna members can be provided on the same ground plane so as to achieve antenna diversity and a switch mechanism is provided for switching between the antenna member in a receive mode, and for switching to only one of the antenna members for operation of the apparatus in a transmit mode. The switch mechanism is arranged to ground a feed connector of the antenna member that is not selected for transmission or reception so as to render that antenna member passive.