793 results about "Balun" patented technology

The invention discloses an ultra-wideband low-profile dual-polarization curved surface phased-array antenna, and belongs to the field of antenna engineering technology and wireless communication. The phased-array antenna comprises a plurality of pitching surface sub-arrays which are arranged along the axial direction; the pitching surface subarray is composed of a plurality of curved surface antenna units which are uniformly distributed along the circumference, and the whole pitching surface subarray is fan-shaped; the curved antenna unit comprises a curved dielectric block, a metasurface matching layer, a radiator layer, a vertical feed balun, a wave-absorbing resistance layer and a metal floor layer, wherein the metasurface matching layer and the radiator layer are conformally arranged on the upper surface and the lower surface of the curved dielectric block. According to the antenna, the flexible dielectric plate is used as a carrier of a radiation dipole and is matched with the PCB metal floor, so that the normal active standing-wave ratio of the antenna is smaller than 3.0 in ten octaves in two linear polarization directions of horizontal polarization and vertical polarization, and + / -60-degree scanning is realized in an azimuth plane.

Apparatus and methods for reconfigurable power amplifiers are disclosed. In certain embodiments, a mobile device includes a transceiver configured to generate a first radio frequency signal of a first frequency band and a second radio frequency signal of a second frequency band, and a front-end system including a push-pull power amplifier configured to selectively amplify one of the first radio frequency signal or the second radio frequency signal based on a band control signal. The push-pull power amplifier includes an input balun, an output balun, and a pair of amplifiers coupled between the input balun and the output balun. The band control signal is operable to control an output capacitance of the pair of amplifiers.

The application discloses an RF push-pull power amplifier chip, wherein the second end of the first capacitor is connected to the first pad of the chip, and the second end of the second capacitor is connected to the second pad of the chip, and the first pad is bonded to the second pad by a wire. The first capacitor, second capacitor and wire form an impedance matching circuit, which participates in impedance matching of the chip together with the first balun. In this way, the RF push-pull power amplifier chip can support a larger bandwidth, and the equivalent inductance can be changed by adjusting the length of the wire, so that the impedance matching circuit can be adjusted more flexibly in a limited chip area. Therefore, the bandwidth performance of the RF push-pull power amplifier chip would not be affected, and the occupied area of the chip can be reduced.

A tight coupling array antenna based on an integrated microstrip balun is composed of a plurality of polarization units, each polarization unit comprises an antenna floor, a magnetic wave-absorbing material is arranged above the antenna floor, a supporting material is arranged above the magnetic wave-absorbing material, a radio frequency connector is arranged in the antenna floor, the radio frequency connector is connected with one end of a coaxial feeder line, and the other end of the coaxial feeder line is connected with the antenna floor. The other end of the coaxial feeder line sequentially passes through the antenna floor, the magnetic wave-absorbing material and the supporting material; a lower substrate is arranged above the supporting material; a feed balun is printed on the upper surface of the upper-layer substrate, and a multiplexing oscillator arm is printed on the lower surface of the upper-layer substrate; the multi-layer board technology is adopted, the antenna radiator, the coupling body and the feed balun are printed on different copper layers of the multi-layer board respectively, space optimization is achieved, antenna impedance matching is further optimized, and the antenna has the advantages of being excellent in performance and easy to install; according to the invention, the feed balun in the form of the multi-order microstrip transmission line is adopted to optimize all-order microstrip transmission line models, so that the compactness of the antenna unit is effectively improved.

The present application relates to the field of antenna technology, and in particular to a radiation unit and a base station antenna. The radiation unit includes a radiation component, a feed balun and a feed core, wherein the radiation component is supported on the feed balun and electrically connected to the feed balun, and the feed balun has a first feed hole; the feed core is inserted into the first feed hole, and one end of the feed core is electrically connected to the feed balun, and the other end passes through the first feed hole and is bent to form a first connection portion, and the first connection portion is used to electrically connect to the strip line circuit in the phase shifter. By setting the bending direction and bending angle of the first connection portion, the spacing between the positive feed core and the negative feed core can be adjusted to adapt to the connection of cavities of different widths, and by adjusting the bending direction and bending angle of the first connection portion, the angle between the first connection portion and the strip line in the cavity can be reduced, thereby reducing the difficulty of electrical connection and improving the connection quality.

The disclosure relates to a planar balun structure for routing millimetre-wave radar signals. Example embodiments include a planar balun structure (200) for routing millimetre-wave radar signals, the balun structure (200) comprising: a single-ended side (201); a differential side (203); a half-wavelength path (204) connecting the differential side (203) to the single-ended side (201), wherein the half-wavelength path (204) surrounds the single-ended side (201).

Disclosed is a packaged semiconductor device comprising a semiconductor die comprising a MMIC having a differential output; a package substrate, comprising first second and third metal layers, and electrically connected to the semiconductor die by a plurality of pillars between the semiconductor die and the first metal layer, wherein the first and third metal layers comprise a ground plane, and the second metal layer, therebetween, comprises a single-ended stripline; wherein the differential output is galvanically connected to the first metal layer by a pair of pillars aligned along a first axis; wherein the packaged semiconductor device comprises a balun coupler between the differential output, and the single-ended stripline aligned along a second axis; wherein the balun coupler comprises an opening in the first metal layer, the opening comprising two arms extending in a first direction parallel to the second axis.

Apparatus and methods for reconfigurable power amplifiers are disclosed. In certain embodiments, a mobile device includes a transceiver configured to generate a first radio frequency signal of a first frequency band and a second radio frequency signal of a second frequency band, and a front-end system including a push-pull power amplifier configured to selectively amplify one of the first radio frequency signal or the second radio frequency signal based on a band control signal. The push-pull power amplifier includes an input balun, an output balun, and a pair of amplifiers coupled between the input balun and the output balun. The band control signal is operable to control an input capacitance of the pair of amplifiers.

The invention discloses a transmitter system which comprises a shielding shell, a trigger signal interface, a power interface, a time delay control interface and an output interface are arranged on the shielding shell, a pulse source circuit board is arranged in the shielding shell, and the power interface supplies power to a circuit on the pulse source circuit board. A trigger shaping circuit, an adjustable delay circuit, two Gaussian pulse generation circuits, a transformer balun circuit and a clipping shaping circuit are arranged on the pulse source circuit board. According to the transmitter system disclosed by the invention, the circuit adopts a module-level design, and subsequent upgrading is convenient. The transformer balun circuit is adopted to carry out positive and negative pulse superposition synthesis, the circuit is simple, and implementation is convenient.

The invention discloses an ultra-wideband compact circularly polarized antenna based on a miniaturized phase shifter, and belongs to the technical field of antenna engineering. According to the antenna, the feed network and the Vivaldi antenna are cascaded, so that the antenna has the characteristic of wide bandwidth; the broadband matching characteristic is realized by designing a metal coupling sheet, a zigzag structure, an inverted L-shaped balun and the like; a novel miniaturized ultra-wideband 90-degree phase shifter is designed by adopting an n network and a negative group delay circuit; and the Vivaldi antenna layer and the feed network layer both adopt a PCB (Printed Circuit Board) technology, so that the processing is easy, and the cost is low. Compared with a traditional phase shifter, the size of the phase shifter is reduced by 75%, and the size of the phase shifter is 67 mm * 44.5 mm (0.071 lambda 1 * 0.047 lambda 1). Meanwhile, a simulation result shows that the provided circularly polarized antenna has a 10dB impedance bandwidth of 0.32 to 1.2 GHz (3.75: 1) and a 3dB axial ratio bandwidth of 0.32 to 1.15 GHz (3.59: 1).

The invention discloses a biconical antenna balun equivalent circuit modeling optimization method based on a multi-conductor transmission line, and belongs to the technical field of electromagnetic simulation. The method comprises the following steps: firstly, establishing a three-dimensional electromagnetic model of a biconical antenna balun based on a finite element method, and setting ports and defining boundary conditions in combination with an actual current transmission path; then, distribution parameters among conductors are extracted through a multi-conductor transmission line theory, and a Balun circuit topological structure is constructed; and finally, taking the antenna coefficient as an optimization target, carrying out iterative optimization on equivalent circuit element parameters by adopting a multi-target genetic algorithm, considering a plurality of optimization targets in a broadband range, and finally obtaining a high-precision equivalent circuit model. Through combination of electromagnetic simulation and an intelligent optimization algorithm, high-efficiency extraction of complex Balun structure distribution parameters and adaptive optimization of circuit parameters are realized, and the simulation precision of the biconical antenna is remarkably improved.

The invention discloses an anti-interference ultra-wideband radiation unit and an anti-interference ultra-wideband antenna, and the radiation unit comprises a light guide sheet which is located above a radiation surface and is used for expanding the bandwidth; the radiating surface consists of four folded dipole radiating arms and is printed on a first substrate of which the dielectric constant is 4.4, the loss tangent is 0.005 and the thickness is 0.762 mm, and every two folded dipole radiating arms are connected together through a high-impedance lead; the balun comprises an inductance circuit and a capacitance circuit on the front surface and the back surface, the inductance circuit is arranged in a bending manner and is electrically conducted through a metalized via hole, the capacitance circuit performs energy coupling through a gap of the substrate thickness to form a gap capacitor, and the balun is connected with each folded dipole radiation arm and is used for providing broadband impedance matching; and the base is connected with the balun and is used for converting the feed type, so that the coaxial cable is welded in parallel to the base, the electromagnetic interference between different frequency bands can be effectively reduced, and the gain can be improved.

Systems and methods for differential antenna driving are provided. In one aspect, a front end system includes at least one power amplifier configured to receive a first transmit radio frequency signal from a baseband processor, amplify the first transmit radio frequency signal, and output the amplified first transmit radio frequency signal. The front end system further includes at least one balun configured to receive the amplified first transmit radio frequency signal. The at least one balun includes a positive output coupled to a first monopole of at least one antenna and a negative output coupled to a second monopole of the at least one antenna.

The embodiment of the utility model provides a dual-polarization dielectric dipole antenna, the antenna comprises a cross-shaped radiation unit and a guide sheet, the cross-shaped radiation unit comprises a first dielectric plate and a second dielectric plate which are in cross-shaped vertical cross connection; the feed balun circuit on the second dielectric plate crosses the side edge of the top of the first dielectric plate and is connected with the radiation arm on the same side surface of the second dielectric plate; a through hole is formed in the position, at the crossed connection position of the first dielectric plate and the second dielectric plate, of the second dielectric plate and is flatly attached to the first dielectric plate, so that the feed balun circuit on the first dielectric plate is connected to the radiation arm on the same face of the first dielectric plate through the through hole along the penetrating plane. According to the embodiment of the invention, the number of holes in the cross-shaped radiation unit is reduced, so that the antenna is simple to manufacture, and the production cost and the intermodulation distortion risk are reduced. In order to further reduce radiation unit holes, the two groups of feed balun circuits can be wound and crossed from the top, or one group of radiation arms are optimized into slot coupling feed, and coupling perforation is canceled.

Low noise amplifiers (LNAs) are disclosed herein. In certain embodiments, an LNA includes an input balun configured to convert a single-ended radio frequency (RF) receive signal to a differential RF receive signal, an amplifier chain configured to amplify the differential RF receive signal to generate a differential amplified RF receive signal, and an output balun configured to convert the differential amplified RF receive signal into a single-ended amplified RF receive signal. The LNA's amplifier chain is operable in multiple gain modes, and includes a first differential amplification stage, a second differential amplification stage, and a third differential amplification stage.

Disclosed is a packaged semiconductor device, comprising: a semiconductor die comprising an MMIC, the MMIC having a differential output; a package substrate including a first metal layer, a second metal layer, and a third metal layer, and electrically connected to the semiconductor die through a plurality of pillars between the semiconductor die and the first metal layer, where the first metal layer and the third metal layer include a ground plane, the second metal layer between the first metal layer and the second metal layer comprises a single-ended strip line; wherein the differential output is galvanically connected to the first metal layer through a pair of struts aligned along a first axis; wherein the packaged semiconductor device comprises a balun coupler between the differential output and the single-ended stripline aligned along a second axis; wherein the balun coupler comprises an opening in the first metal layer, the opening comprising two arms extending in a first direction parallel to the second axis.

The invention relates to the technical field of microelectronics, semiconductors and communication, and discloses a radio frequency switch chip, and the circuit structure of the radio frequency switch chip comprises a transformer type differential inductor T-L1, a transformer type differential inductor T-L2, a capacitor C1, an NMOS transistor M1, an NMOS transistor M2, a gate resistor RG1, and a gate resistor RG2. The radio frequency switch chip provided by the invention adopts a differential structure, so that the parasitic inductance effect of a grounding key and a wire during packaging and testing can be eliminated, and the insertion loss and the isolation performance are improved; compared with a single-end port, the lower impedance of the differential port is more beneficial to improving the power capacity of the switch; the differential structure allows the transformer type differential inductor to use differential signal characteristics, the equivalent quality factor of the inductor is improved, and the circuit performance is improved; the differential structure can improve the linearity of the circuit, especially the second-order intermodulation effect; the differential structure can be compatible with a modern silicon-based CMOS radio frequency system, and an additional balun is not needed for signal conversion.

Provided in the present application are a radiating unit, an antenna and a base station. The radiating unit comprises two pairs of radiating arms which are orthogonally arranged in a polarized manner, and a pair of baluns for respectively feeding the two pairs of radiating arms, wherein each balun comprises a dielectric plate and a balun line; the balun line comprises a balun feeder which is arranged on a front face of the dielectric plate and a balun grounding wire which is arranged on a back face of the dielectric plate; and the balun feeder and the balun grounding wire respectively feed two radiating arms of the same polarization. The radiating unit respectively feeds the two pairs of radiating arms by means of the pair of baluns, and the balun feeder and the balun grounding wire of each balun respectively feed two radiating arms of the same polarization, such that two radiating arms of the same polarization can be fed by using one balun, so that the number of baluns is reduced, thereby reducing the size of the radiating unit, reducing the mutual coupling interference between baluns of two adjacent radiating units, and thus facilitating antenna integration.

The invention is suitable for the technical field of antennas, and provides a low-frequency symmetrical oscillator and an antenna thereof, the low-frequency symmetrical oscillator comprises a radiation sheet, a PCB balun and a plastic part, the radiation sheet comprises a first radiation unit arm group and a second radiation unit arm group which are orthogonal to each other, the first radiation unit arm group comprises two first sub radiation unit arms, and the second radiation unit arm group comprises two second sub radiation unit arms. The first radiation unit arm group comprises two first sub-radiation unit arms, the second radiation unit arm group comprises two second sub-radiation unit arms, the two first sub-radiation unit arms are diagonally arranged, the two second sub-radiation unit arms are diagonally arranged, the radiation sheet is arranged at the top of the plastic part, and the PCB balun comprises a first feed sheet and a second feed sheet. The first feed piece is attached to the upper end of the radiation piece to feed the radiation piece in a coupling mode, one end of the second feed piece penetrates through the radiation piece and is connected with the first feed piece, and the other end of the second feed piece is inserted into the plastic part and is fixed to the lower end of the plastic part. Therefore, light weight and miniaturization of the antenna are realized.

The invention relates to the technical field of antennas, in particular to a high-isolation double-frequency common-caliber miniaturized phased-array antenna which comprises a high-frequency-band linear polarization end-fire metal patch array structure, a low-frequency-band linear polarization end-fire metal patch array structure, a public metal reflection floor and a single-layer dielectric substrate. Radiation structures of the high-frequency-band linear polarization end-fire metal patch array structure and the low-frequency-band linear polarization end-fire metal patch array structure are formed by improved dipoles of microstrip balun feed with out-of-band rejection, so that linear polarization is achieved, and then the dipoles are fed through the improved microstrip balun with out-of-band radiation rejection. The suppression on high frequency is further deepened and the decoupling bandwidth is expanded; in addition, a decoupling structure is added between the adjacent common-frequency antennas to improve the isolation and radiation capability between the adjacent common-frequency antenna units, high isolation and wide beam coverage of the dual-frequency common-aperture phased-array antenna can be realized, the performance of the antenna is improved, and the dual-frequency common-aperture phased-array antenna is simple in process and low in cost.

The utility model discloses a ripple anti-interference test system, which comprises an artificial power supply network, a single-phase power supply quality immunity simulator, an oscilloscope, a high-voltage differential probe, an industrial personal computer, an attenuator, a power probe, a power meter and a balun, and is characterized in that the industrial personal computer is connected with the attenuator, the single-phase power supply quality immunity simulator and the power meter; the single-phase power supply quality immunity simulator is connected with the attenuator, the attenuator is connected with the power probe, the power probe is connected with the power meter, the power meter is connected with the balance-unbalance converter, the balance-unbalance converter is connected with the artificial power supply network, and the artificial power supply network is connected with a product to be tested and the high-voltage differential probe. The high-voltage differential probe is connected with an oscilloscope. Through mutual cooperation of the industrial personal computer, the attenuator, the power probe and the power meter, an interference signal sent by the single-phase power supply quality immunity simulator can be controlled within a reasonable range, and the intensity of an interference limit number can be monitored and fed back to the industrial personal computer.

The invention provides an antenna assembly, an antenna and a base station, the antenna assembly comprises a reflection plate, a phase shifter and at least one radiation unit, the radiation unit and the phase shifter are respectively arranged on the front and back surfaces of the reflection plate, the phase shifter comprises a cavity and a phase shift circuit arranged in the cavity, and the phase shift circuit is arranged in the cavity. The radiation unit comprises a radiation part, a feed core and a first balun structure, the first balun structure penetrates through the reflecting plate to be connected with the radiation part and the cavity, and the feed core is arranged in the first balun structure to be electrically connected with the radiation part and the phase shift circuit. The first balun structure penetrates through the reflecting plate to be connected with a cavity of the phase shifter to realize grounding, the feed core is arranged in the balun, the feed core is directly and electrically connected with the phase shifter and the radiation unit, so that the phase shifter and the radiation unit do not need to be connected through a coaxial cable, and the reflecting plate, the phase shifter and the radiation unit are arranged in a split manner, so that the radiation unit is not required to be connected through a coaxial cable. And production and manufacturing are facilitated.

The invention provides an ultra-wideband bidirectional active phase shifter based on reconfigurable PPFs, and belongs to the technical field of microwave radio frequency, the bidirectional active phase shifter adopts a symmetrical structure, and comprises two groups of single-ended to differential ultra-wideband Marchand baluns, two two-order reconfigurable PPFs, four bidirectional variable gain amplifiers and a digital control module; wherein the PPF adopts a two-order adjustable resistor and adjustable capacitor structure, the bandwidth can be expanded to realize the ultra wide band, and when the phase shifter carries out steering operation, the impedance is changed due to switching of a switch, so that an error is introduced, and the impedance is adjusted and the error is reduced by adjusting the resistor and the capacitor. According to the phase shifter, the advantages of an active phase shifter and a passive phase shifter are combined, the area can be further reduced while bidirectional phase shifting operation is achieved and the phase shifting precision is guaranteed, and the problems that a traditional active vector synthesis phase shifter can only conduct unidirectional phase shifting operation, and the area of a passive phase shifter is large are solved.

The invention provides a dual-band oblique polarization common-caliber array antenna based on a tight coupling effect. The dual-band oblique polarization common-caliber array antenna comprises a dielectric substrate, a low-frequency antenna, a high-frequency antenna and a metal floor which are perpendicular to one another, the low-frequency antenna comprises a low-frequency modification dipole, a low-frequency feed balun and a low-frequency metal wide-angle impedance matching layer, and the high-frequency antenna comprises a high-frequency modification dipole, a high-frequency feed balun and a high-frequency metal wide-angle impedance matching layer. The design of the common-caliber array antenna is realized in a mode that the dual-band antenna is vertically inserted and the metal floor is shared. The antenna has the advantages of ultra wide band, beam scanning and oblique polarization, and can be used for broadband radar wireless communication.

The present invention provides a broadband filtering unit, which includes a grounding support base, a feeding balun, and a square radiation surface. Both the front and back surfaces of the square radiation surface are copper-clad. Among them, the shape of the copper cladding on the front is similar to four combined square structures. Two square structures located on the diagonal form two oscillator arms in one polarization direction. The middle positions of each oscillator arm are all hollowed out. The oscillator arm is composed of multiple cascaded LC circuits. Multiple open-circuit filtering stub segments are also arranged on the oscillator arm. The present invention is used in a multi-frequency and multi-array combined antenna, which can well avoid interference with adjacent arrays. Its special multiple filtering structure can adapt to various irregular arrays, effectively reduce the size of the antenna, improve the performance of the antenna interleaved array, and has a simple structure, convenient installation, and low cost. At the same time, by adjusting the positions of the LC circuits and the lengths of the filtering stub segments on the unit radiation surface, the expansion of different frequency bands and the filtering of different frequency bands can be achieved.

A broadband tight-coupling Vivaldi array antenna comprises N + 2 antenna sub-arrays arranged along an H plane, each antenna sub-array is formed by tightly arranging a plurality of tight-coupling Vivaldi antenna units along an E plane, each tight-coupling Vivaldi antenna unit comprises a dielectric substrate, a radiation patch and a metamaterial patch are printed on the upper surface of the dielectric substrate, a feed balun is printed on the lower surface of the dielectric substrate, and the feed balun is arranged on the upper surface of the dielectric substrate. A radio frequency coaxial connector is arranged at the bottom of the dielectric substrate, a needle-shaped inner conductor end of the radio frequency coaxial connector is connected with the feed balun, and a cylindrical outer conductor end of the radio frequency coaxial connector is in contact with the radiation patch; according to the invention, the miniaturization of the Vivaldi antenna array is realized by utilizing the coupling effect between the units, the edge current path is prolonged by introducing the edge piece and the dummy element at the edge of the array, the active standing-wave ratio of the Vivaldi antenna array during angle scanning is improved to a certain extent, and 60-degree beam scanning is realized on the E surface and the H surface; moreover, the antenna is simple in structure, simplifies the design process of the antenna, and is lower in machining difficulty and cost.

The invention relates to a radiation unit and a base station antenna. The radiation unit comprises a radiator, a feed assembly and a balun structure, the radiator comprises at least one polarization, and one polarization comprises at least two radiation arms; the feed assembly comprises a feed core, and the feed core is used for being connected with a feed network so as to feed the radiator; the balun structure is located at the bottom of the radiator, a first balun and a second balun are correspondingly arranged below two radiation arms of one polarization respectively, the first balun comprises at least one first balun cavity, and the feed core and the first balun cavity jointly form a strip line structure. According to the radiation unit provided by the embodiment of the invention, the space dimension can be fully utilized, and the anti-interference capability of the antenna is improved.

The present invention is directed towards an apparatus and method to detect electromagnetic radiation or signals emitted by plasma comprising a sensor unit, the sensing unit comprising a first sensor for detecting electromagnetic radiation or signals; an electromagnetic barrier wherein the electromagnetic barrier is configured to surround the first sensor to prevent ambient electromagnetic radiation reaching the first sensor; a first port through which electromagnetic radiation can pass, the port configured for coupling to a port of a plasma chamber such that electromagnetic radiation or signals emitted from the plasma can reach the first sensor; and a first output coupled with a balun and a dual coaxial system whereby a signal sensed is grounded and a phase reversed version of the signal is grounded. A signal acquisition system (SAS) for detecting electromagnetic radiation emitted by a plasma is also described.

The invention belongs to the technical field of antennas, and relates to a common-caliber dual-polarization tight coupling array antenna capable of wide-angle scanning, which comprises a low-frequency antenna array surface, a low-frequency vertical branch knot, a low-frequency feed balun, a high-frequency antenna array surface, a low-frequency feed network and a coaxial connector. According to the invention, a traditional ultra-wideband tight coupling array antenna is decomposed into two antennas with small bandwidths, and loading of resistive materials is avoided through common-caliber configuration. Wherein an upper-layer low-frequency antenna unit is divided into a plurality of sub-units, electromagnetic transparency of a lower-layer high-frequency antenna is realized by adopting a winding line design, mutual interference of high and low frequencies is further inhibited by loading a vertical branch knot, and the fractal low-frequency sub-units are synthesized into a large unit through a power divider. According to the dual-polarization ultra-wideband antenna, the average efficiency reaches 85% in the working frequency bands of 2-6GHz and 7-18GHz, the active standing-wave ratio is smaller than 4 in the scanning range of + / -60 degrees, and the problem that in a traditional design, ultra-wideband, high efficiency, wide-angle scanning and dual polarization cannot be achieved at the same time is solved.

According to an embodiment, a plasma processing system includes a plasma chamber, an RF source, a matching circuit, a balun, and a resonating antenna. The resonating antenna includes a first and a second spiral resonant antenna (SRA), each having an electrical length corresponding to a quarter of a wavelength of a frequency of a forward RF wave generated by the RF source. The first end of the first SRA is coupled to a first balanced terminal of the balun and the second end of the first SRA is open circuit. The first end of the second SRA is coupled to a second balanced terminal of the balun and the second end of the second SRA is open circuit. The first and the second SRA are arranged in a symmetrically nested configuration having a same center point.