Abstract: An EHF array antenna backplate that integrates thermal cooling structure and signal processing structure together into one unified structure. In one embodiment, forced air is employed to conduct heat from active modules; while in another embodiment, embedded heat pipes are employed. The array backplate is made by using four layers. The layers are: a high density multichip interconnect board, a metal matrix composite motherboard, an integrated waveguide/cavity/cooling structure, and a metal matrix composite baseplate. Each module uses solder bumps to connect to the high density multichip interconnect board where DC power and control logic signal distribution takes place. The modules are soldered in four locations to the metal matrix composite motherboard through openings in the high density multichip interconnect board. EHF signals are coupled to the modules from a resonant cavity via probes that protrude through the high density multichip interconnect board.

Abstract: A polyphase divider/combiner is provided and which includes a common input/output port and a plurality of N output/input ports, wherein N is an even integer greater than two. N electrical signal transmission paths are provided with each extending from the common input/output port to a respective one of the N output/input ports. The N electrical signal transmission paths are of N different electrical lengths such that the output/input ports are out of phase relative to each other by 180/N degrees.

Abstract: A coaxial coupler unit has an outer conductor fastened to the outside of a first rigid metallic wall on one side of a microwave cavity, and the unit also has an inner conductor having at its front end an axially-fixed, angularly-turnable pin axially extending through a port in such first wall through said cavity to be inserted on the cavity's opposite side in a hole in a second deformable metallic wall bounding such side of the cavity. The pin has helical threads thereon engaging helical threads on the inside of the hole. The pin may, while remaining axially fixed, be angularly turned in opposite directions to displace the deformable cavity wall in opposite axial directions relative to the rigid cavity wall to thereby tune the cavity.

Abstract: Coaxial units are disclosed for conducting microwaves to and from amplifying apparatus with splitter and combiner cavities. Each coaxial unit comprises an outer conductor, a dielectric sleeve having an unsheathed portion extending forward of the front end of the outer conductor, and an inner conductor pin projecting forward of the sleeve, the pin having a forward portion which is resiliently compressible radially inward. The coaxial unit is coupled to an associated cavity by having its sleeve and pin forward portions, respectively, received in large and small bores respectively formed in metallic plates on opposite sides of the associated cavity. The forward portion of the pin makes direct yieldable-pressure electrical contact with metallic regions around the wall of the small bore at a location adjacent the opening of such bore into the cavity.

Abstract: A technique and arrangement for lowering the mismatch normally obtained, thereby increasing the bandwidth, in a standard rectangular-to-coaxial waveguide "T" junction coupling in an antenna system, such arrangement including, in a T-junction of a coaxial transmission line to a waveguide transmission line in which measured impedance values in the range of approximate 30 MHz in the UHF band must be within a 1.1:1 circle of voltage standing wave ratio, the improvement which achieves minimal reflection over said range of frequencies, according to which a diconical slug is connected between an upper and lower portion of the coaxial transmission line and mounted for support within the structure of the waveguide transmission line, and in which said diconical slug includes back-to-back conical sections such that the large diameter rims of the sections confront each other.

Abstract: Coaxial units are disclosed for coupling an r.f. amplifying microstrip to splitter and combiner wave guides, respectively, of a splitter-combiner apparatus. Each coaxial unit comprises an outer conductor sleeve and an inner conductor pin projecting forward of the sleeve, both the sleeve and pin having forward portions which are resiliently compressible radially inward, and the sleeve being radially enlarged at its front end. The coaxial unit is coupled at its front to its associated wave guide by having its sleeve and pin forward portions, respectively, received in, and radially inwardly compressed in, large and small bores respectively formed in the metallic plates on opposite sides of the dielectric chamber of the associated wave guide. Those forward portions make direct yieldable-pressure electrical contacts with metallic walls of these bores at locations adjacent to the openings of such bores into that chamber.

Abstract: An H-plane waveguide `T` junction is described in which matching is achieved over a full waveguide band at the waveguide which forms the stem of the `T`. Reflection from the wall facing the stem is reduced by using a probe as a monopole located about a quarter of a wavelength from the said wall. Variations with frequency in the reflection coefficient at the stem are reduced by a disc, at the foot of the probe, which acts as a radial reduced quarter wave transformer.

Abstract: The invention provides a device including a radial combiner for electromagnetic waves and a method using a radial combiner. The invention provides a radial combiner with resistors disposed between the impedance matches capable of combining these signals from a plurality of radially disposed amplifiers or transmitters. By applying desired phase shifts to the signals transmitted by certain amplifiers or transmitters, amplitude-phase modulation of the total signal transmitted can be provided. It is more particularly possible to provide radar pulse modulation for reducing the frequency spectra of the transmitted signal.

Abstract: An electrical energy transport arrangement has an arcuate boundary region of substantially constant radius. A first port is disposed substantially at the center of the curvature of the arcurate boundary region and lies at the boundary of the transport arrangement and in electrical communication with it. A plurality of second ports are disposed around the arcuate boundary region and in electrical communication with it. A preferred embodiment provides a purely planar configuration, which may optionally provide balanced phase and amplitude outputs. In other preferred embodiments, there are provided unequal amplitude outputs.

Abstract: Disclosed is a device to combine or divide the power values of electromagnetic signals and, more particularly, a device of the radial mode. In a combiner/divider which comprises two metallic disks defining an annular space of propagation, each channel is separated from the adjacent channel by a radial slot which is placed in the lower disk and extends from the central aperture to the peripheral ring. Furthermore, each channel thus defined has a radial ridge. The invention can be applied to transmitters, notably those used in radars.

Abstract: In a radial power combiner/divider in which radial slots are provided for suppression of undesired modes, certain undesired modes which are not adequately suppressed by the radial slots are allowed to be propagated in a central coaxial transmission line and suppressed therein by means of longitudinal slots in the outer conductor. In an alternative embodiment, the central transmission line of the combiner/divider is in the form of a circular waveguide, and the suppression means comprises thin, spaced coaxial cylinders of dissipative material.

Abstract: The invention relates to matching asymmetrical discontinuites in transmission lines to give low reflection coefficients (less than five percent) over a wide frequency band (corresponding to at least an octave in wavelength). A group of asymmetrical discontinuites, such as impedance steps in a waveguide, are matched by considering a reference plane whose position varies with frequency at which the reflection coefficient for waves transmitted in one direction is equal to that for waves transmitted in the opposite direction. Matching elements are then provided which have a reflection coefficient at the reference plane which is equal and opposite to the reflection coefficient of the discontinuities. Matching is less difficult if the distance between the steps is less than a quarter of a guide wavelength at all frequencies in the wide band mentioned above and such an arrangement is a "reduced quarterwave transformer".

Abstract: A broadband, constant voltage multicoupler including an input port and a plurality of output ports wherein the impedance rises in the same proportion as the power falls in the internal branches so that the voltage is substantially constant therein. The multicoupler comprises a signal splitter transmission line network having an electrical characteristic which maintains the same voltage throughout and a plurality of active devices associated therewith. In particular, the signal splitting network comprises a first transmission line connected at one end to the input and terminating at the opposite end, and a plurality of additional transmission lines having an impedance equal to n times the impedance of the first transmission line where n equals the number of the outputs.

Abstract: An orthogonal mode tee to use at microwave frequencies and having a junction for three ports, two of the ports propagating the TE.sub.10 mode and the common port propagating the TE.sub.11 mode.

Abstract: Disclosed herein is an N-way, broad band planar power divider/combiner circuit for dividing or combining RF signals which includes a tapered strip of electrically conductive material having a plurality of conductor fingers which define a plurality of ports at the wide end of the taper, and having a narrow end which defines single port. The tapered metal strip is mounted onto a dielectric slab, and isolation resistors connect adjacent fingers. A single RF signal can be fed into the single port which will be divided into a plurality of signals of equi-amplitude and equi-phase. Conversely, a plurality of RF signals can be fed into the ports at the wide end which will be combined into a single signal.

Abstract: In a stripline power divider having a pair of conductive stripes, which are n opposite sides of a dielectric board, overlap at an input port, and then diverge oppositely to a pair of output ports individual to the stripes, the improvement characterized by the divider having an opening extending through the board and between the strips in the region where they diverge, by conductive plating extending from each stripe along the adjacent edge of the opening, and by a plug of elastomeric, lossy material fitted in the opening to electrically connect the plated edges and suppress odd mode fields between the stripes.

Abstract: Disclosed is a power divider/combiner using two parallel plate radial transmission lines having parallel plate spacing of less than .lambda./2 and which operates in a higher order mode, preferably the first higher order circumferential mode TE.sub.11. High isolation between amplifiers coupled to the radial transmission lines at their circumferences is achieved by coupling an arrangement of circulators between the amplifiers and the radial transmission lines. This isolation arrangement reduces the effects of any spurious signals that are generated by means such as imperfections and imbalances in any active devices coupled to the radial line and permits de-energizing amplifiers as desired for lowering power output without degrading performance.

Abstract: A polarizer for connection to a first and a second wave guide includes a feed tube and the first wave guide connected laterally to the feed tube whereby a long dimension of the wave guide extends in the direction of the axis of the feed tube. A short circuiting element is disposed in the feed tube between the connection of the first wave guide and one end of the feed tube. The second wave guide extends parallel to the first one and is laterally connected with a wide side to that one end of the feed tube, closing the same. The wide dimensions of the two wave guides are turned by 90.degree.. The second wave guide is short circuited at its end, and a trimming pin is disposed on the second wave guide in axial alignment with the axis of the tube. The other end of the feed tube is connected to a single wave guide. The wave guides may have rectangular or elliptical cross section.

Abstract: Disclosed is a parallel plate radial transmission line having parallel plate spacing of less than .lambda./2 and which utilizes a specific higher order mode, preferably the first higher order circumferential mode. Undesired modes are suppressed by mode supression slots formed in one or both of the parallel plates and which are oriented parallel to the current flow lines of the particular mode that is used. These slots have a negligible effect on the mode being used but they couple out other modes that are generated by means such as by imperfections and imbalances in any active devices coupled to the radial line. A centrally located feed is used to launch circularly polarized energy of the TE.sub.11 mode in the particular circumferential mode in the radial line. The feed may also receive circularly polarized energy of the particular circumferential mode in the radial line, linearly polarize that received energy and conduct it in the TE.sub.11 mode.

Abstract: The present invention relates to a combining network for use in combining a plurality of coherent radio frequency sources. The combining network is comprised of a plurality of arms, one for each radio frequency source. Each arm has a first end which forms an input port and a second end which is connected to an output port which is common to all of the arms. The electrical length of each arm ranges from 55.degree.+m(180.degree.) to 70.degree.+m(180.degree.) where m=0, 1, 2, . . . of the wavelength of the radio frequency sources.

Abstract: A linearally polarized multiport multimode feed for a reflector type antenna generates a plurality of beams, each in a different pointing direction, from a single radiating aperture. Each beam possesses a distinct phase center determined by the waveguide modes establishing the aperture distribution for that beam. The feed is linear and bilateral, therefore may be utilized in a receiving or transmitting antenna.

Abstract: Inside a parallelepipedic guide section there is provided at least one partition located so as to divide the inner volume of the guide section into a main waveguide portion capable of supporting an orthogonally polarized signal and two secondary waveguide portions extending in the same direction as the main waveguide portion. The secondary waveguide portions are so dimensioned such that one of these waveguide portions is capable of supporting a horizontally polarized signal and that the second waveguide portion is capable of supporting a vertically polarized signal.

Abstract: A rectilinear waveguide junction apparatus in which the input and output guides are parallel to the longitudinal axis of the apparatus. This apparatus is characterized in that it takes the form of a parallelipiped guide the internal volume of which is divided up by metal partitions which form two parallel input guides, two parallel output guides and a main intermediate guide of same section as the parallelipiped guide. This apparatus is used in very high frequency circuits, for example the supply circuits for satellite or radar antennae.

Abstract: A very wide pass band polarization diplexer having a power divider, a transition element and a wave guide containing an impedance adapter, and applicable to all devices requiring the use of a wave guide in which two waves in orthogonal modes propagate.

Abstract: A waveguide power divider (10) for splitting electromagnetic microwave power and directionally coupling the divided power includes an input waveguide (21) and reduced height output waveguides (23) interconnected by axial slots (22) and matched loads (25) and (26) positioned at the unused ends of input and output guides (21) and (23) respectively. The axial slots are of a length such that the wave in the input waveguide (21) is directionally coupled to the output waveguides (23). The widths of input guide (21) and output guides (23) are equal and the width of axial slots (22) is one half of the width of the input guide (21).

Abstract: A polarization diplexer which branches from a circular or quadratic waveguide in the axial direction into pairs of rectangular waveguides respectively lying opposite each other with the first pair of two rectangular waveguides lying opposite one another and fed by a symmetrical hybrid junction comprising straight subarms and wherein the first pair are symmetrical. The second pair of rectangular waveguides comprises two rectangular waveguides lying opposite each other which is fed by a second electrically symmetrical hybrid junction having subarms straddled over their broad dimension. The invention can also be utilized as a polarization frequency diplexer.

Abstract: Radially fed microwave signal combiner/distributor apparatus comprising a central coaxial connector which is coupled via radially extending paths to several circumferential coaxial connectors which are equiangularly disposed on the circumference of a circle surrounding the central connector, the apparatus including a generally discoidal microwave transmission cavity through which the paths extend, which cavity communicates at the center thereof with the central coaxial connector and which cavity communicates at the circumferential periphery thereof with the circumferential coaxial connectors via a conductive annulus, which annulus is spaced away from the internal circumferential periphery of the cavity, and to which annulus the inner conductors of the circumferential coaxial connectors are electrically connected at locations equiangularly spaced around the annulus.

Abstract: A microwave radial power divider/combiner device having desirably broad bandwidth response over a selected frequency range. The device includes a radial waveguide that has a number of adjoining annular sections, each of selected radial length and axial height, to provide lumped circuit parameters closely euqivalent to those of an ideal filter with the desired passband characteristics. The ideal filter is first designed using conventional synthesis techniques, then modified, if necessary, to allow its realization in radial waveguide form. The waveguide sections are selected to have lengths and uniform heights to approximate the lumped circuit parameters of the filter, and the dimensions are then optimized to provide the closest approach to the desired performance characteristics.

Abstract: A waveguide circulator includes a resonator body which is separated from a waveguide side by a dielectric spacer disc. The spacer disc has an interface turned toward the waveguide side in which defined electromagnetic boundary conditions are to prevail. The thickness of the spacer disc and the dielectric constant of the disc material are matched so that the disc thickness equals a quarter wavelength, referred to a wave propagating in the disc perpendicular to the waveguide side.

Abstract: A divider is made from a layer (1) of conducting material carried on an insulating support (2). A first slotline (3) is formed in the conducting layer extending from a first input port (A). A second slotline (5, 6, 7) is formed at right-angles to and spaced from the end of the first slotline (3), extending between first and second output ports (C and D). Third and fourth slotlines (8, 9) extend from the end of the first slotline (3) to points on the second slotline spaced by a distance which is electrically short compared with one-quarter of a wavelength. The third and fourth slotlines (8, 9) are an odd multiple of quarter-wavelengths long. A resistor (10) is connected across the second slotline substantially midway between the ends of the third and fourth slotlines, and has a resistance such that the output ports are correctly terminated.

Abstract: A multiple waveguide junction such as a magic T is described capable of coupling large average and peak powers with a low standing wave ratio over a wide bandwith. The magic T structure employs waveguide arms which meet at a common junction region and has a plane of symmetry that bisects both the E and H input waveguide arms. The latter arms each have necked down segments so as to improve the bandwidth of the structure. Impedance matching elements are employed in the junction region. One element has a ridge-like shape selected to provide an impedance match to the H input waveguide arm. Other matching elements are employed to provide a low SWR over a bandwidth that approaches a 3:1 ratio.

Abstract: A matched lossless reciprocal five-port junction can be constructed as a tapered five-fold symmetric star. The dimensions of the leads are tapered in toward the center, such that the cutoff frequency is the upper band frequency divided by 1.66.

Abstract: In a microwave circulator having a ferrite core axially aligned along the axis of a junction of waveguides and surrounded by an insulating sleeve seated in counterbores in opposed metal transformers seated in opposed waveguide broad walls, one end of the ferrite core is highly polished and bonded with a silver epoxy to one of the metal transformers and spaced from the other by an insulating disk. Opposed rare-earth cylindrical magnets embedded in the broad wall axially aligned along the junction axis bias the ferrite core and establish a magnetic field along the junction axis inside the ferrite core.

Abstract: A generally fan shaped electrically conducting base member defining a waveguide cavity with a waveguide input/output in communication with the cavity at the apex thereof and a plurality of output/input waveguides in communication with the cavity equal angularly spaced along the arc of the base member. The inputs and outputs are formed in the plane of the cavity so that losses are substantially reduced and all of the output/input waveguides are equally spaced along radii of the base member and are of equal length so that signals at the outlets thereof are of equal amplitude and phase without requiring phase shifters and the like.

Abstract: A microwave power distributing and synthesizing device includes: a first base and a second base facing the first base at a predetermined distance and having a hole. A coaxial line element including an inner conductive member coaxially penetrates through the hole of the second base and is spaced from an inner wall of the hole by the second base of a predetermined distance. The coaxial line element is supported on the first base at a bottom end and forms an antenna protruding from the hole of the second base into an input waveguide at a top end. At least one electric field distributing and synthesizing member is arranged perpendicularly to the coaxial line element and a plurality of waveguides are connected to the electric field distributing and synthesizing member.

Abstract: A circular waveguide dual antenna feed for TVRO reception, which transfers horizontally and vertically polarized received signals in the circular waveguide simultaneously into two coaxial lines parallel with and offset from the circular waveguide axis. For coupling to existing LNA's, the separate coaxial lines from the circular waveguide are extended into a rectangular waveguide which couples to the input-mixer of the conventional LNA. Alternatively, the separate coaxial lines can be coupled separately to two LNA's or they can be combined into a single output terminal. Switching means are provided in each channel so that each channel can be rendered operative or inoperative, as desired. Diode switches are shown. The device requires no moving parts.

Abstract: A waveguide structure operable as a power combiner or a power divider at millimeter-wave frequencies and having desirably low losses, large bandwidth and high power transmitting characteristics. The structure includes a single rectangular input/output waveguide, coupled to a circularly symmetrical waveguide section, which is in turn coupled to a radial waveguide. The radial waveguide has disposed about its periphery multiple transitions to rectangular output/input waveguides.

Abstract: The signal to be amplified is applied to a quadrature coupler which splits the signal equally to provide two output signals in phase quadrature. The quadrature signals are amplified equally, which generates a second harmonic in each of the signals 180 degrees out of phase. The amplified signals are combined in an in-phase power divider to provide a single amplified output signal wherein the out-of-phase second harmonic signals cancel.

Abstract: A compact apparatus for the accurate measurement of complex reflection coefficients and VSWR of a device over a bandwidth of an octave or greater by preferably measuring three power levels at detectors associated with the device. The device is formed by the junction of 5 transmission lines two of which are used for receiving a test signal and for transmitting the signal to the device being measured. The other three transmission lines are connected to detector arms each having a detector associated therewith. The techniques of the invention are embodied herein in a waveguide embodiment, a stripline embodiment and a microstrip embodiment of the invention.

Abstract: An improved magic tee constructed to maximize the power that can be transferred from the H-plane arm to the collinear side arms and vice versa. The matching post is designed to maximize the breakdown voltage between the post tip and the walls of the E-plane arm. This is accomplished by selecting the post diameter to produce a ratio of the E-plane arm height to post diameter which develops a characteristic impedance corresponding to that of a coaxial transmission line constructed to withstand the maximum breakdown voltage between the transmission line center conductor and conductive shielding for a given shield separation.

Abstract: A microwave apparatus comprises a waveguide section including a stepped septum. The septum is positioned so as to divide the waveguide into two channels. The steps comprise a plurality of first steps which advance progressively in one direction and at least one second step, or the equivalent, which follows the first steps and which returns in an opposite direction. The invention is intended to enable the production of a circularly polarized microwave signal without requiring the use of phase adjustment techniques.

Abstract: In orthogonal mode transducers, typically a first rectangular waveguide capable of carrying a signal having a first polarization and a second rectangular waveguide capable of carrying a signal having a second polarization orthogonal to the first polarization are coupled to a common central waveguide which is capable of carrying signals having both the first and second polarizations. However, in the past, difficulties have been encountered in manufacturing such orthogonal mode transducers because of the necessity of matching these respective waveguides which do not have the same cross-sectional shape and which must be oriented in a particular manner relative to one another to achieve the desired result.

Abstract: A single terminal for a radio transmitter and receiver is connected to a first antenna for transmitting, and simultaneously to the first antenna or a second antenna for receiving. The connection is provided by a three port circulator having a first port connected to the first antenna, a second port connected through a quarter wavelength transmission line to a PIN diode and the second antenna, and a third port connected to the radio terminal. The radio transmitter is normally connected to the first antenna through the circulator, and the first or the second antenna is selectively and simultaneously connected to the radio receiver depending upon the conductive condition of the PIN diode.

Abstract: A novel arrangement to achieve high power amplification of a microwave signal by summing the contributions of many small power amplifiers. This arrangement comprises the equivalent of a divider network to distribute an incoming signal to an arbitrary number of small power amplifiers, and a combiner to sum the outputs of all amplifiers into a single output. This arrangement combines the series-fed circuit concept with a dual mode transmission media (a transmission line capable of transmitting two independent orthogonal modes, for example, the circular waveguide TE.sub.11 mode) for the divider and combiner.

Abstract: A 3dB waveguide directional coupler for coupling two rectangular waveguides of the same dimensions and having parallel longitudinal axes is disclosed. The waveguides to be coupled are joined so that one of the wider side walls of the first waveguide adjoins one of the wider side walls of the second waveguide. The interiors of the two waveguides communicate via an aperture in the adjoining side walls. When energy is input from one end of the first waveguide toward the aperture, virtually all of it is transmitted to the second wave guide, part of the transmitted energy traveling away from the aperture in each direction along the longitudinal axis of the second waveguide. This is preferably achieved by providing a waveguide system in the aperture oriented perpendicular to the longitudinal axes of the first and second waveguides.

Abstract: A polarization separator or diplexer for ultra-high frequencies utilizing waveguide sections of rectangular and/or round cross-section in which the signals passing through are phase synchronized over a particular frequency range and which can be manufactured very inexpensively and is operable over a broad frequency band and wherein the arms of the series branching waveguides and the E and H offset portions have a ratio of the narrow to wide sides of at least 1:4 and the first portion of the double branching for providing a connection and transition to the coaxial waveguide comprises an impedance level transformer which has variations in the cross-section of the inner conductor and the outer conductor.

Abstract: A multiple channel amplifier providing both gain and/or phase shift to a microwave signal is formed of a set of transmission lines connected in parallel by means of a power splitter at the input end and a power combiner at the output end of the set of transmission lines. The transmission lines are disposed in a cylindrical array of electrically conducting bars which support amplifying and/or phase shifting elements between the bars and withdraw heat from the amplifying and/or phase shifting elements. The transmission lines may be slotted or severed for directing power flow towards an output terminal of the amplifier. The amplifying and/or phase shifting elements are conveniently mounted on a set of heat sinks to form modules, each of which is readily inserted and detached from the cylindrical array.

Abstract: Transmission line apparatus for transmitting TE dominant electromagnetic waves is provided in accordance with the teachings of the present invention. The transmission line apparatus according to the present invention relies upon a transmission waveguide having a uniform cross-section which is substantially larger in dimension than that required for propagation of only the TE dominant electromagnetic wave desired to be transmitted. The transmission waveguide is in fact so large with respect to the transmission frequency for the TE dominant electromagnetic wave selected that a plurality of waves can form and be propagated, however, losses along the waveguide are markedly reduced. The transmission waveguide is provided with guides in the form of structure present in the waveguide which prevents a rotation of the plane of polarization of the TE dominant electromagnetic waves being transmitted.

Abstract: An electronic waveguide switch of a latching type particularly suitable for the microwave and millimeter range. The switch comprises a standard three port housing connected to three waveguides. A switchable junction ferrite is disposed in the center of the housing, the ferrite being of the latching type. A driver ferrite is disposed outside of the housing. All ferrite elements have a substantially cylindrical shape.

Abstract: A crossover for microwave electromagnetic radiation is constructed in a planar configuration for the transference of all of the power of a wave in a first transmission line to a wave in a second transmission line. The crossover is formed of two pairs of cross arms wherein, in each pair, the arms are spaced apart by an electrical length of ninety degrees along the first and the second transmission lines, and couple power of the waves between the first and second transmission lines with an introduction of a quarature phase relationship. The impedance presented to a wave of a cross arm is less than the corresponding impedance of the first and the second transmission lines by a factor of the square root of two to inhibit the generation of relections at junctions between a cross arm and the first or the second transmission line. Each junction provides for a diversion of one-half the power of the wave from the first or the second transmission line to a cross arm.