55 results about "Circular waveguide" patented technology

According to one embodiment, an introduction-side rectangular waveguide tube and a lead-out-side rectangular waveguide tube are each connected to a circular connection plate connected to an end surface of the circular waveguide tube, and at least one connection plate includes, in an outer circumference thereof, the other welding collar welded to the one welding collar, and both the one welding collar and the other welding collar include grooves or holes for a rotation regulation jig to regulate rotation in a circumferential direction, and an entire portion along the circumferential direction including the grooves or holes is welded and fixed thereto.

The application discloses a ternary computing method and system based on a double-chain difference coupling principle. A difference value (XnYn) is directly generated by a forward component Xn and a reverse component Yn in a difference coupling area, forming a three-value logic {‑1, 0, +1}, and a threshold comparison circuit is omitted, and operation follows BH=Σ(XnYn)×3^n. A hierarchical logic system composed of basic operators, minimum complete operators and global operators is constructed, and arbitrary three-value logic operation is realized; a circular waveguide structure is adopted to configure an optical path difference, so that coherent light directly forms three interference states at an output end, and optical three-value logic gates and optical full adders are realized; a double-chain six-bit structure is adopted for symbol coding, a two-dimensional geometric framework is driven to generate a symbol form, and logical and geometric expression unification is realized.

The invention discloses a spiral structure waveguide for vortex light topological charge conversion and an implementation method thereof, and belongs to the field of optical waveguides. The circular waveguide and the spiral structure are combined, the spiral structure is used for regulating and controlling the vortex light mode according to the mode conversion matching condition, and vortex light conversion between any topological charge orders is achieved; according to the invention, complete conversion between different vortex lights is realized, two vortex light mixed beams with different proportions can be generated, and the requirements of generation and utilization of vortex lights with different orders in an integrated photonics on-chip structure are met. According to the method, the problem that topological charges cannot be freely converted among different vortex light modes in a waveguide structure is solved, the application value of the waveguide structure in the aspect of vortex light regulation and control is expanded, and the possibility is provided for an integrated photon platform to utilize vortex light topological charge degree-of-freedom coding information and process calculation tasks. According to the invention, information coding, optical communication, calculation and other applications are carried out by changing the topological charge of the vortex light.

The invention discloses a quasi-single-mode circular waveguide conical horn antenna, a radar and a communication device. The quasi-single-mode circular waveguide conical horn antenna comprises a circular waveguide section and a conical horn section. Conductor loss is reduced by remarkably increasing the diameter of the circular waveguide, and axial periodic annular grooves are formed in the inner wall of the circular waveguide to form a spatial mode filter and a selective attenuation high-order mode, so that high radiation efficiency and high mode purity are realized at the same time in a millimeter wave frequency band. And the conical horn section adopts an index profile to realize high-directionality radiation. The antenna structure effectively solves the technical problems of large loss and impure mode in a millimeter wave high-frequency band in the traditional design.

The invention discloses an antenna optimization method, system and device based on a QVE frequency band feed source network, and a medium, and relates to the technical field of antennas. The method comprises the following steps: acquiring a QVE frequency band illumination angle parameter and an edge illumination level parameter; calculating the standard radius of the circular waveguide and establishing a longitudinal groove geometric parameter constraint relation to obtain longitudinal groove differential geometric parameters; determining a first orthogonal support arm length deviation value and a broadside structure parameter of the first-stage turnstile structure by taking a preset phase difference angle of orthogonal polarization radio frequency signals of the first-stage turnstile structure as a target; constructing a dual circular polarization network and a stepped transition structure; constructing a power combiner and a Chebyshev impedance matcher; and integrating the differential longitudinal slot feed source, the dual-circular polarization network and the orthogonal mode converter to obtain a QVE frequency band feed source network, and performing antenna feed through the QVE frequency band feed source network. By implementing the technical scheme provided by the invention, the feed efficiency of the antenna system can be improved, so that the performance of the antenna system is enhanced.

The invention discloses a high-power-capacity power divider based on a mixed mode, and belongs to a power distribution / synthesis technology in the technical field of high-power microwaves. The objective of the invention is to solve the problems of insufficient power capacity and coaxial inner conductor end surface electric field concentration caused by small cross section size when an existing power divider is applied to high frequency. The power divider integrates circular waveguide TM0n mixed mode excitation, conversion from a mixed mode to a coaxial waveguide TEM mode and an inner conductor end face strong field control technology, and comprises an input circular waveguide, inclined plane transition, a large over-mode ratio circular waveguide, a coaxial waveguide, a radial line and a rectangular waveguide, and a groove is formed in the inner conductor end face of the coaxial waveguide. While the waveguide section is increased to improve the power capacity of the main body structure, the end surface electric field peak value is effectively inhibited, and the system power capacity is improved. The invention is mainly applied to a microwave system requiring high power distribution or synthesis, and has the advantages of high power capacity, low surface electric field, high conversion efficiency and wide working bandwidth.

The invention discloses a photoacoustic sensing unit, an acoustic signal detection device and an acoustic signal detection method, and relates to the technical field of acoustic detection. The lower wrapping layer is arranged on the upper surface of the substrate, and a mounting groove is formed in the lower wrapping layer; the core layer is arranged in the mounting groove, the core layer comprises a straight waveguide and a circular waveguide, and a coupling distance is formed between the straight waveguide and the circular waveguide; the straight waveguide, the circular waveguide and the coupling space jointly form a light field regulation and control area; the exposed area covers the core layer and the lower wrapping layer, the exposed area comprises a groove, and the sensitive medium packaging layer is used for receiving sound pressure signals, generating corresponding deformation and transmitting the deformation to the core layer to cause the structure or state change of the light field regulation and control area, so that the effective refractive index of the circular waveguide is changed, and the sound pressure signal is generated. The change of the effective refractive index causes the drift of the harmonic peak wavelength, and the variation of the sound pressure signal is determined according to the displacement of the harmonic peak wavelength. The sensitivity of sound pressure detection is improved.

This invention discloses a method for operating in a circular waveguide TE 11 This invention relates to a millimeter-wave high-power rotating reflective waveguide phase shifter, belonging to the field of millimeter-wave transmission technology. It comprises a rectangular waveguide wide-side slot 3dB coupler, a rectangular-circular waveguide transition section, and a rotating circular waveguide phase shifting section, with its central plane divided into two symmetrical microwave channels. Electromagnetic waves are first injected through the first port of the rectangular waveguide wide-side slot 3dB coupler, then split into two paths entering the rectangular-circular waveguide transition section through the third and fourth ports of the coupler, and subsequently injected into the rotating circular waveguide phase shifting section. After propagating a certain distance within the two phase shifting waveguides, the waves are reflected by a rotating metal plate piston and finally output from the second port of the rectangular waveguide wide-side slot 3dB coupler. This invention modulates the phase at the output end by changing the electrical length of the electromagnetic wave propagating within the phase shifting section by rotating the position of the metal plate piston. Within the same operating frequency band, it possesses advantages such as high power capacity, compact structure, high phase shifting accuracy, and a large phase shifting range.

This invention relates to a high-efficiency and compact hollow circular waveguide mode purifier, comprising five parts: a main waveguide, an input waveguide, a spherical waveguide, a re-entry resonant cavity, and an output waveguide; this invention can maintain high TM over a wide bandwidth. 01 TM 02 - TM 01 The mode conversion efficiency is high, which can effectively adapt to application environments with various mode compositions. This invention adopts a spherical corrugated waveguide and a re-entry resonant cavity, which has a simple structure and compact axial length, providing a feasible technical route for achieving compact mode purification.

The application discloses a terahertz optical fiber-space mode adapter, which comprises an antenna, a rectangular waveguide, a power divider, a mode converter, a circular waveguide and a transition horn; the antenna is connected with the rectangular waveguide; the power divider is connected with the rectangular waveguide, and an output port is connected with an input port of the mode converter; the mode converter is provided with a plurality of output ports and is arranged on the circular waveguide in a circumferential symmetry mode; the transition horn is connected with the circular waveguide; the antenna is used for receiving a space electromagnetic wave and feeding the space electromagnetic wave into the rectangular waveguide; the rectangular waveguide is used for transmitting a TE10 mode; the mode converter is used for converting the TE10 mode into a TE01 mode in the circular waveguide; and the circular waveguide is used for propagating the TE01 mode to the transition horn and filtering a terahertz wave of an unwanted mode. The adapter provided by the application can receive a space electromagnetic wave through the antenna, then generate a required high-purity electromagnetic mode through the mode converter, efficiently excite a required mode of an optical fiber, and avoid an impure excitation mode.

FIELD: antenna technology.SUBSTANCE: invention is intended for receiving and transmitting electromagnetic waves as part of reflector antennas. A dual-band reflector antenna feed is proposed, consisting of a circular waveguide, a radiator with external corrugation, a counter-reflector located opposite the end of the circular waveguide, two dielectric inserts and a metal rod. The first dielectric insert is made in the form of a hollow cylinder, secured on one side in the groove of the counter-reflector, and on the other side in the groove of the emitter. The second dielectric insert is installed inside the emitter and secured on a metal rod, which is connected on the opposite side by a threaded connection to the counter-reflector.EFFECT: increase in the level of matching of the antenna system with the load.1 cl, 3 dwg

The application discloses a relativistic magnetron with an energy feedback structure and belongs to the microwave technical field.The relativistic magnetron is a full-cavity extraction structure and comprises an anode, a cathode, an energy extraction structure and a guide magnetic field coil; wherein the energy extraction structure is provided with a ring-shaped microwave reflection plate in an output circular waveguide part, part of energy is reflected back to a cathode-anode gap, the interaction between an electron cloud and a space electromagnetic wave is enhanced, and the output power of the relativistic magnetron is improved. The application effectively improves the output power of the relativistic magnetron while guaranteeing the compactness of the device; meanwhile, the energy feedback structure is simple and easy to process.

A rotatable circular waveguide structure is described that may include a circular waveguide segment configured to propagate electromagnetic radiation. The circular waveguide segment may enable transmission of data signals between portions of an electronic device, such as a chassis portion and a display portion, which may be rotatable relative to each other. The rotatable circular waveguide structure may include one or more circular waveguide segments routed through a hinge of the electronic device, and one or more rotatable junction points. The rotatable junction enables rotation of the circular waveguide segments relative to each other when the coupling portion of the electronic device is also rotated. The rotatable circular waveguide structure may replace the use of a data cable conventionally used to carry data signals between portions of an electronic device.

The objective is to provide a wideband mode converter that can convert an input in TE10 mode, used in rectangular waveguides, etc., to an output in TM01 mode, used in circular waveguides, etc. [Solution] The mode converter includes an input unit, a first rectangular output unit, and a second rectangular output unit, and comprises an inverse phase conversion unit that converts the TE10 mode electromagnetic wave input to the input unit into two electromagnetic waves with a phase difference of 180° from each other and outputs them to the first rectangular output unit and the second rectangular output unit, a first semicircular output unit connected to the first rectangular output unit and equipped with a first semicircular output unit, a second semicircular output unit connected to the second rectangular output unit and equipped with a second semicircular output unit, and a TM01 mode generation unit connected to the first semicircular output unit and the second semicircular output unit that generates the TM01 mode and outputs it to the circular output unit.

The invention discloses a compact broadband circular waveguide TM01 mode bending structure, and aims to solve the technical bottleneck that an existing circular waveguide TM01 mode bending structure is difficult to consider the aspects of bandwidth, structural compactness and power capacity at the same time. The antenna is composed of two circular waveguide TM01 mode power dividers, two E-plane U-shaped folded waveguide arrays and two E-plane rectangular bent waveguide arrays. The coaxial waveguide TEM mode and the multi-path rectangular waveguide TE10 mode are adopted as the middle transition mode of the antenna, and the problem of mode competition in a traditional bending structure is effectively solved. Meanwhile, by utilizing an E-plane U-shaped folded waveguide phase compensation technology, the length of each rectangular waveguide transmission path between the two circular waveguide TM01 mode power dividers is ensured to be consistent, the relative working bandwidth of which the transmission efficiency of a bent structure is greater than 95% is widened to be more than 40%, the power capacity is improved to the GW magnitude, and the distance between input / output ports is shortened to be within 5 times of the central wavelength.

Embodiments described herein relate to an apparatus that includes a microwave power generator, and a rectangular waveguide coupled to the microwave power generator. In an embodiment, the apparatus may also include an impedance tuner that is coupled to the rectangular waveguide, and a coaxial waveguide that is coupled to the rectangular waveguide. In an embodiment, the coaxial waveguide includes a conductive pin with a first end and a second end. In an embodiment, the apparatus further includes a circular waveguide cavity around the second end of the conductive pin, and a slotted antenna in the circular waveguide cavity.

The application discloses a composite shielding wall device which takes into account electromagnetic shielding and ventilation and heat dissipation, comprising a metal shielding wall, a circular waveguide array 1, a circular waveguide array 2 and a plastic conduit, two groups of independent circular waveguide arrays with the same size are arranged in parallel and staggered on two opposite wall surfaces of the metal shielding wall. The circular waveguide array 1 and the circular waveguide array 2 are arranged in parallel and staggered, which is equivalent to obtaining twice the length of the transmission waveguide of a single circular waveguide and twice the cutoff waveguide loss. While enhancing the attenuation of electromagnetic wave signals, the problem of the metal shielding wall being too thick caused by the direct opposition of the two groups of circular waveguide arrays is avoided, and the space of the metal shielding wall is saved. Air flow passes through the complete straight-through air flow channel formed by the two groups of circular waveguide arrays and the plastic conduit connecting the two groups of circular waveguide arrays, realizing the air flow exchange between the inside and the outside of the electrical equipment, so that the effect of ventilation and heat dissipation is achieved.

This utility model discloses a miniaturized wideband beam millimeter-wave antenna, including an radome, an antenna cavity, and a mounting component. The radome is fixedly mounted on the antenna cavity via the mounting component. The antenna cavity includes a circular waveguide with cylindrical grooves around its periphery, giving the antenna a wide beam characteristic within the operating frequency band and improving the antenna pattern in the low-frequency band. The radome includes a matching medium located inside the circular waveguide to extend the low-frequency operating bandwidth, thereby ensuring a gain greater than -0.5 dBi within a ±60° range in the 26 GHz to 40 GHz operating frequency band. Filling the circular waveguide opening with the matching medium reduces the diameter of the circular waveguide, achieving antenna miniaturization. Furthermore, the built-in radome reduces manufacturing costs, and mounting it externally to the equipment chassis avoids the influence of the internal structure of the chassis on performance, thus improving the antenna pattern.

A design method of a TE01 and TM11 circular waveguide dual-mode filter, the filter comprising two hollow circular cavities, an input coupling cutoff waveguide, an output coupling cutoff waveguide, a coupling cutoff waveguide, a cavity, and a cover plate, the two hollow circular cavities being connected to the input coupling cutoff waveguide and the output coupling cutoff waveguide respectively, the coupling cutoff waveguide being connected to the two hollow circular cavities, the cavity being provided with a recess corresponding in shape and size to the two hollow circular cavities, the input coupling cutoff waveguide, the output coupling cutoff waveguide, and the coupling cutoff waveguide after being connected for embedding, and the cover plate being fixed on the cavity by screws to form a seal.

A low-frequency-band input rectangular waveguide is located on the outer wall of the outer side of a four-groove coaxial resonant cavity, the low-frequency-band input rectangular waveguide and the four-groove coaxial resonant cavity are connected through a rectangular coupling hole in the four-groove coaxial resonant cavity, and a Bragg reflector is arranged on the low-frequency-band input rectangular waveguide; the microwave screening device is used for screening microwaves with different frequencies; the high-frequency-band input rectangular waveguide is also located on the outer wall of the outer side of the four-groove coaxial resonant cavity, is connected with the four-groove coaxial resonant cavity through a rectangular coupling hole, and is spaced from the low-frequency-band input rectangular waveguide by 180 degrees; the four-groove coaxial resonant cavity is connected with the output circular waveguide through four coupling slots uniformly arranged on the outer wall of the inner side, and the cut-off circular waveguide is centered with the axis of the output circular waveguide. Compared with an existing dual-working-condition input coupler, the dual-working-condition input coupler is simpler in structure, screening of microwaves with different frequencies is guaranteed only through the cut-off function of the Bragg reflector on the low-frequency-band rectangular waveguide, and efficient output from a high-frequency-band TE10 mode to a high-frequency-band TE02 mode is achieved.

The invention provides a circularly polarized substrate integrated waveguide conversion device, which comprises an input end, a straight-through end, a coupling end, a receiving end, a first substrate integrated waveguide, a second substrate integrated waveguide and a circular waveguide, and is characterized in that the input end is connected with a pin of a chip transmitting end, the left side of the output of the input end is connected with the straight-through end, and the right side of the output of the input end is connected with the receiving end; the receiving end is connected with a chip receiving pin, the right side of the output end of the receiving end is connected with the coupling end, the end portion of the straight-through end is connected with the first end of the first substrate integrated waveguide, and the end portion of the coupling end is connected with the first end of the second substrate integrated waveguide. The second end of the first substrate integrated waveguide and the second end of the second substrate integrated waveguide are perpendicular to the axis of the circular waveguide and extend into the circular waveguide. According to the invention, the structure is simple, the integration is high, the miniaturization is realized, a waveguide converter and a circular polarizer are combined into one, an independent circular polarizer assembly is omitted, the size and the weight of the system are obviously reduced, and the antenna is especially suitable for scenes with harsh space requirements.

This invention relates to a vacuum-sealed telescopic circular waveguide, comprising: multiple circular waveguides and a sliding limiting assembly; adjacent circular waveguides are coaxially connected by a sleeve arrangement; the sliding limiting assembly is connected to one end face of the larger-diameter circular waveguide, and one end of the smaller-diameter circular waveguide is a sliding end that extends through the sliding limiting assembly into the larger-diameter circular waveguide, with a sliding seal between the smaller-diameter circular waveguide and the sliding limiting assembly; a sliding fixed-axis 4F ring is provided on the outer surface of the sliding end of the circular waveguide, and a circular waveguide retaining ring is installed on the inner side of the sliding limiting assembly; the inner diameter of the circular waveguide retaining ring is smaller than the outer diameter of the sliding fixed-axis 4F ring; the sliding fixed-axis 4F ring and the larger-diameter circular waveguide, and the circular waveguide retaining ring and the smaller-diameter circular waveguide, are connected by transition fits. This solution employs a multi-stage telescopic design to achieve a greater telescopic stroke.

The invention discloses a compact broadband circular waveguide TE01 mode bending structure, and aims to solve the technical bottleneck of the existing circular waveguide TE01 mode bending structure in the aspects of bandwidth and structure compactness. The antenna is composed of two circular waveguide TE01 mode power dividers, two H-plane U-shaped folded waveguide arrays and two H-plane rectangular bent waveguide arrays. A multi-path rectangular waveguide TE10 mode is adopted as a middle transition mode, and the problem of mode competition caused by direct bending of an over-mode circular waveguide in a traditional bending structure is effectively solved. Meanwhile, the H-plane U-shaped folded waveguide phase compensation technology is utilized to ensure that the lengths of transmission paths of the rectangular waveguides between the two circular waveguide TE01 mode power dividers are kept consistent, so that the relative working bandwidth of which the transmission efficiency of a bent structure is greater than 98% is widened to be more than 40%; and the power capacity is improved to GW magnitude under a vacuum condition, and the distance between input / output ports is shortened to be within 6 times of the central wavelength.

The invention belongs to the technical field of antennas, and particularly relates to a broadband and wide-angle scanning dual-circularly-polarized circular waveguide antenna array. The unit of the antenna array comprises a feed port, an impedance matching structure, a circular polarizer, a metal waveguide wall and a dielectric material filled in the waveguide. The two feed ports correspond to left-hand circular polarization and right-hand circular polarization; the circular polarizer converts linearly polarized electromagnetic waves from a port into two electromagnetic waves which are vertical in direction, equal in amplitude and 90-degree in phase difference, and the two electromagnetic waves are synthesized into circularly polarized electromagnetic waves; a conical dielectric material is loaded at the junction of the dielectric material and an air interface, and smooth impedance conversion from waveguide aperture impedance to free space impedance is provided; and the metal waveguide wall is provided with a conical electromagnetic band gap structure at the waveguide opening. When the antenna works, a signal of a port is changed into a circularly polarized signal after passing through the impedance matching section and the circular polarizer, the circularly polarized signal is radiated out at the waveguide opening, and the array can realize broadband and wide-angle scanning due to the integration of the impedance gradual change structure and the electromagnetic band gap structure.

A rotatable circular waveguide structure is described that may comprise circular waveguide sections configured to propagate electromagnetic radiation. The circular waveguide sections may enable data signals to be transmitted between portions of an electronic device, such as a chassis and display portion, which may be rotatable with respect to one another. The rotatable circular waveguide structure may comprise one or more circular waveguide sections that are routed through a hinge of the electronic device, as well as one or more rotatable junctions. The rotatable junctions enable a rotation of circular waveguide sections with respect to one another as the coupled portions of the electronic device are also rotated. The rotatable circular waveguide structure may replace the use of data cables that are conventionally used to carry data signals between portions of an electronic device.

The application provides a shielding structure of a plasma source and a design method thereof and a plasma processing device, and relates to the technical field of electromagnetic shielding. The plasma source comprises a solenoid, and the shielding structure comprises a shielding body surrounding the solenoid. At least one shielding channel based on the cutoff waveguide theory is arranged on the shielding body, and is used for inhibiting electromagnetic leakage under the premise of ensuring physical communication. The shielding channel comprises a ventilation window arranged on the side surface of the shielding body and used for heat dissipation, a threaded circular waveguide tube used for allowing a pipeline to pass through and connected with an external hose fixing member, and a segmented waveguide tube used for allowing a growth sample cavity to pass through. The solenoid in the plasma source is shielded in all directions by constructing the shielding body. By reasonably designing the size and layout of the waveguide structure, efficient inhibition of radio frequency energy is realized, the failure of a sensor caused by electromagnetic interference is solved, and the stable operation of the plasma processing device is ensured.

A radiator assembly has at least one dual frequency band antenna assembly (DFBAA). The DFBAA collocates two isolated frequency band antennas into a single volumetric space. A high-band antenna assembly (aperture and feed structure) is within the same or similar low-band antenna structure while improving gain and field-of-view angular coverage for both bands. There may be quad-ridges that define the low band antenna and a circular waveguide antenna that defines the high band antenna.

The application relates to a high-power directional coupler for real-time measurement of high-power circular waveguide transmission energy. The design comprises a circular waveguide, two coupling holes and two rectangular waveguides vertically connected with the circular waveguide. High-power microwaves are transmitted in the circular waveguide, the two coupling holes are arranged on the wall surface of the circular waveguide, and the center distance is lambda / 4+n*lambda / 2 (lambda is the transmission wavelength, and n is a non-negative integer). The rectangular waveguide is vertically connected with the circular waveguide through the coupling hole, and the short side of the rectangular waveguide is parallel to the axial direction of the circular waveguide, which is used for receiving coupled energy and measuring transmission power through a power sensor. By averaging the transmission energy at the two coupling holes, the interference error caused by the echo is eliminated, and the forward transmission energy is accurately measured. The design effectively avoids the fluctuation problem in single-hole measurement, has the advantages of wide frequency band, low coupling coefficient, high reliability and high power resistance, and is suitable for real-time measurement and monitoring of high-power microwave system energy.

The utility model relates to radio engineering, including ultra-high frequency equipment and technology. It consists of rectangular waveguides, a ferrite element and a magnetizing device. In the ultra-high frequency circulator, the rectangular waveguides are connected to a circular waveguide through a soft connection, a ferrite core is placed inside the circular waveguide, and a solenoid is installed around the ferrite core to create a magnetic field. As a result, the device can be used in radar and radio navigation systems at the same time, including having more compact dimensions, less weight, higher performance, lower losses, and a 5% increase in the useful work factor.

The invention discloses a high-efficiency transmission method for high-power microwaves and a biconical horn transmission antenna thereof, and the method comprises the steps: accessing the high-power microwaves through employing a transition circular waveguide, enabling the high-power microwaves to be preliminarily matched with the impedance characteristics of a transmission airspace through a small-angle beam-expanding transmission space, and reducing the near-field reflection; and the mode field impedance is further gradually changed to the free space impedance through the large-angle beam expanding transmission space, so that the guided wave is converted into the radiation wave, and finally the radiation wave is radiated in the free space through the low-loss sealing layer. The large conical horn mouth surface is sealed by the high molecular weight polyethylene antenna housing, so that an airtight environment in which inert gas is filled or vacuumized can be realized, the risk of air breakdown is effectively avoided, and the high power endurance capability of the antenna is greatly improved. The horn taper angle and transition structure design is matched with the low-loss high-molecular antenna housing, so that efficient transmission and radiation of broadband electromagnetic waves are realized. And the large conical horns and the large conical horns adopt a segmented processing mode, so that the processing difficulty is reduced.