Abstract: A superconducting variable phase shifter providing improved performance in the microwave and millimeter wave frequency ranges. The superconducting variable phase shifter includes a transmission line and an array of superconducting quantum interference devices (SQUID's) connected in parallel with and distributed along the length of the transmission line. A DC control current I.sub.DC varies the inductance of the individual SQUID's and thereby the distributed inductance of the transmission line, thus controlling the propagation speed, or phase shift, of signals carried by the transmission line. The superconducting variable phase shifter provides a continuously variable time delay or phase shift over a wide signal bandwidth and over a wide range of frequencies, with an insertion loss of less than 1 dB. The phase shifter requires less than a milliwatt of power and, if one or more of the Josephson junctions fails, the whole device remains operational, since the SQUID's are connected in parallel.

Abstract: A phase shifter network which alternates between structurally dual networks is provided. In particular, the phase shifter has a topography which permits the network to be configured as alternatively T or .pi. networks of low pass and high pass delay circuits in accordance with states of a single control signal fed to the phase shifter.

Abstract: A delay circuit of ultrasonic diagnostic apparatus comprising a delay line consisting of a plurality of unit portions connected in cascade, in each of which an anode of a first variable capacitance diode and a cathode of a second variable capacitance diode are connected with a connecting point of two inductors connected in series, or a delay line obtained by replacing capacitances in a second order all pass type delay line by variable capacitance diodes, or a delay line, in which variable capacitance diodes and inductors form a balanced circuit; and control circuit for applying a reverse bias voltage to each of the variable capacitance diodes; and an amplifier or a variable resistance circuit using FETs serving as a matching circuit for the delay line, capable of varying continuously an input impedance by using a control voltage from the exterior.

Abstract: An RF phase shifter combines a non-reciprocal ferrite 180.degree. stage with one or more reciprocal diode phase shifting stages to produce an essentially planar phase shifter that is ultra small, efficient and lightweight. Such phase shifter elements may be used in phased arrays to produce an array offering major improvements over existing planar substrate all diode phase shifters while maintaining the phase gradient between array elements and without switching the ferrite shifter between the transmit and receive modes.

Abstract: In this invention, a distributed constant line on a microwave IC is formed of a Schottky metal, and a semiconductor conductive layer contacting the distributed constant line at least at one position and an ohmic contact electrode contacting the semiconductor conductive layer are arranged. According to this invention, characteristics of ICs can be optimized against a variation in elements combined with a circuit comprising the distributed constant line after the manufacture of ICs.

Abstract: A parallel branched N-state design method is used for discrete increment signal processing systems, such as incremental phase shifters and attenuators. These systems are implemented using parallel branched signal processing networks, each with N parallel discrete increment branch circuits (i.e., without being restricted to binary-state networks). In comparison with conventional cascaded binary-state networks, the parallel branched N-state design achieves reduced complexity and insertion loss. An exemplary embodiment of a phase shift system providing 32 phase increments (or states) uses three cascaded phase shift networks--two quaternary-state networks (Quits 10, 20) and a single binary-state network (Bit 30). The most significant Quit (10) illustrates the N-state design, providing the four most significant phase states (reference, +90.degree., -180.degree., -90.degree.

Abstract: A hybrid element for phase shifting an input signal and providing a phase shifted output signal includes conductive plates which are capacitive coupled together. The hybrid element includes four terminals: an input terminal for receiving an input signal, an isolation terminal capacitive coupled with the input terminal and for providing an output signal, a through terminal connected directly with the input terminal, and a coupling terminal capacitive coupled with the input terminal. A distributed constant line and an FET are connected in pair with the through and coupling terminals, respectively, the other end of the distributed constant line being connected with earth. When the FET is turned on or off, the amount of phase shift in the phase shifter is controlled. Since the FET and distributed constant line are connected together in parallel, the amount of phase shift can be adjusted easily by turning the FET on or off.

Abstract: A low loss reflection-type analog phase shifter circuit producing a large range (nearly 360.degree.) of phase shift at X-band while achieving low attenuation (insertion loss) and little amplitude variation over all phase states. The results are achieved, in part, by using a terminating impedance which includes parallel-connected hyperabrupt varactor diodes. The circuit is implemented readily in a monolithic microwave integrated circuit using GaAs.

Abstract: A variable delay line has a first optical fiber to transmit an optical signal and a plurality of second optical fibers adapted to receive simultaneously the optical signal from the first fiber. Each second fiber has a predetermined length, the length of each second fiber being different from each other second fiber. The predetermined length determines the propagation delay of the optical signal along each second fiber. An opto-electronic switch is made responsive to the optical energy on a selected one of the second fibers. The switch detects the delayed optical energy and couples the delayed optical energy on an electrical analog thereof to a device. The selected second fiber is chosen for the propagation delay associated therewith.

Abstract: Disclosed is a 90-degree phase splitter utilized in QPSK modulator and demodulator. The 90-degree phase splitter uses a transistor thereby converting a voltage source into a current source, and accordingly obtains two outputs having same in magnitude but different in phase by 90 degrees through output circuits comprising reactors and resistors.

Abstract: An electronically variable delay line having adjustable delay and bandwidth characteristics is provided. A varactor diode functioning as a variable controlled capacitance is coupled between a signal conductor and a ground reference conductor, thereby segmenting the signal conductor into two, individual smaller segments of conductor which function as fixed inductances. The delay characteristic of the line is adjusted by varying the varactor's biasing voltage which, in turn, varies the varactor's capacitance. A staggered termination technique is implemented to stabilize the insertion loss characteristics of the delay line.

Abstract: A variable bi-phase modulator circuit for microwave signals includes a quadrature power divider (1) having signal input and output ports (2 and 3) and two control ports (4 and 5), and two variable resistors each having an input port (11). Each of the two variable resistors includes first and second microwave field-effect transistors (F1 and F2), the drains of which are coupled together via an intermediate resistor (R). These resistors can be formed using microwave monolithic integrated circuit technology and can have very good impedance characteristics. The input port (11) of the variable resistor has a connection to the intermediate resistor (R) and to the drain of the first transistor (F2). Each transistor is connected with zero dc bias between its source and drain and has a channel resistance which changes with change in gate voltage (VG1, VG2).

Abstract: In one embodiment a diode phase shifter has a four port coupler formed of a pair of RF coupled transmission lines. The coupler has an input port on one transmission line and an output port on the other, and each transmission line has a tunable port. Serially interconnected RF isolated gateable diodes are provided, one diode is coupled to the tunable port on one transmission line and the other diode is connected to the other tunable port. The diodes approximate a microwave open circuit when reverse biased and approximate a microwave short circuit when forward biased to a conducting state. In another embodiment a diode phase shifter employing a single stripline is described.

Abstract: A 180 degree ultraminiature phase shifter. Only two switching devices and very few passive circuit elements are required, thus allowing an extremely small and low loss device to be fabricated. When power is applied to switching devices, a low pass pi section low pass filter is realized which provides +90 degrees of phase shift. When power is absent from the switching devices, a T section high pass filter is realized which provides -90 degrees of phase shift.

Abstract: A microwave element includes an impedance control circuit for controlling the capacitance between the source and the drain of an FET in the off state including a series-connected diode and capacitor connected in parallel between the source and drain of the FET and a circuit for applying a variable bias voltage to the diode. A microwave switch including two FETs includes two impedance control circuits for controlling the capacitances of the FETs. A microwave switched line phase shifter includes two transmission lines of different electrical lengths and four FETs, two of the FETs being connected in series at each of the ends of the two transmission lines. Impedance control circuits for controlling the capacitances of each of the FETs are included.

Abstract: A programmable microwave network test device is capable of establishing a multitude of reflection and transmission coefficients determined by a set of digital inputs. The programmable network enables the collection of groups of measurements which are used to characterize a non-linear or linear device. The microwave structure of the network is comprised of a series of PIN diodes interconnected through microstrip transmission lines. The lengths of the transmission lines between the PIN divide are proportioned so as to allow use of the network over a broad frequency range, with a minimization of repeated reflection coefficients in a use of the network, the device to be characterized would be placed at the input port of the network with the output port of the network terminated in its characteristic impedance.

Abstract: A loaded line phase shifter using striplines diposed on a semiconductor substrate includes a main stripline having an electrical length of one-half wavelength, loaded striplines connected to respective ends of the main stripline, a field effect transistor having its source electrode and its drain electrode connected to the respective load lines, a bias circuit connected to the gate electrode of the field effect transistor for controlling the bias voltage applied to the gate electrode, and a resonant stripline connected between the source electrode and the drain electrode.

Abstract: An analog voltage-controlled phase shifter is disclosed which is smaller in size and provides a larger phase shift for a smaller change of capacitance of presently available voltage controlled phase shifters. These unexpected advantages are obtained by using lumped elements to simulate the normally used .lambda./4 transmission lines of the hybrid portion of the phase shifter and by eliminating or reducing the value of the capacitors normally present at the varactor nodes of the hybrid. The capacitance fully or partially removed from the varactor nodes of the hybrid can be selectively fully or partially added to the varactors.

Abstract: A varactor controlled phase shifter device is disclosed wherein the phase velocities through the device are substantially equal at all frequencies, thus resulting in the phase constant of the phase shifter device being proportional to frequency. The magnitude of phase shift is selectable over a predetermined range by a continuously variable external control voltage, and this phase shift is linearly proportional to frequency. The device may also be used as a variable length transmission line, useful for such applications as frequency selective impedance matching.

Abstract: A switched loop/180.degree. phase shift device is disclosed, having the additional capability of an aperture shutter that can be selected to produce either a noncorrelated reflection in one mode of operation, or to absorb RF energy that enters the radiating aperture port in the other mode.

Abstract: Disclosed is a microwave phase shifter which is capable, in response to a control signal, of generating either a phase shift that is substantially zero or a phase shift that is substantially equal to .pi.. It comprises a FET that is preferably symmetrical and works in an amplifier assembly. Low-frequency switching-over means make it possible, by reversing the biases at the source and the drain, to invert the FET. This inverting causes a phase shift by .pi. in the microwave signal taken at the output of the circuit.

Abstract: A digitally controlled active phase shifter with vernier control consists of a 180 degree phase bit in series with a 90 degree bit and a digitally controlled active vector generator with vernier control. The digitally controlled active vector generator consists of an active power divider with digitally adjustable amplitude, a pair of phase delay networks with an active power combiner employing vernier control. The power divider consists of two sets of parallel pairs of FET's in cascode configuration with all input nodes connected together and all output nodes from the same set tied together. The FET at the output node of each pair is a common gate configuration with its gate RF grounded through a bypass capacitor. The gate bias voltage is applied to the common gate FET to switch it ON or OFF to thereby provide a set of desired signal amplitudes which can be obtained by selecting the gain of each of the cascode stages in each of the parallel pairs.

Abstract: A monolithic microwave integrated circuit (MMIC) phase shifter is implemented in push-pull configuration with the quadrant selection and vector modulation functions combined. These functions are provided by four sets of adjustable gate-width dual-gate FETs and a pair of lumped element filter networks with a relative differential phase shift of 90.degree..

Abstract: Disclosed are microwave phase shifter circuits which achieve phase shifts of elementary values and of whole number multiples of the values. The phase shifter circuit is made by utilizing of strip lines arranged in candlestick form on one face of a substrate and a slot line arranged on the other face. The length of the branches of the candlestick differ by b/4, b being the wavelength, and the ends of the branches are short-circuited or not short-circuited by utilizing of diodes which can be forward biased or reverse biased.

Abstract: A very low loss microwave modulator having two phase states: O, .pi.; the modulator comprising the following between an input (E) which receives a pure carrier at a frequency f.sub.O, and an output which delivers a carrier modulated with two phases states: a first switching element (17); in parallel therewith, a second switching element (18) connected in series with a main transmission line (19); and a control system (20) for causing a selected one of the first and second switching elements (17, 18) to be conductive and for causing the other one to be non-conductive. The invention is particularly suitable for microwave transmission.

Abstract: An analog phase shifter is provided by cascading T high pass filter and .pi. low pass filter sections. The low pass filter network is selected to have a cut-off frequency above the highest frequency in a predetermined frequency range of the phase shifter and includes a fixed inductor element as a series element of the network and a pair of variable capacitor elements disposed in shunt between said inductor element and ground. The high pass filter network has a cut-off frequency below the lowest frequency of the predetermined frequency band. The network includes a fixed inductor element disposed as a shunt element of said network and a pair of variable capacitor elements disposed in series. The inductor element is coupled between a common connection of said pair of variable capacitor elements and the reference potential. The .pi. network and the T network are cascaded connected between the pair of terminals of the network.

Abstract: Disclosed is a hyperfrequency device which includes a triple plate line in which at least two diodes exert their action at the same point on the suspended line. Instead of connecting the two diodes on both sides of the suspended line, they are mounted on the same side, this is possible by providing two subsidiary line sections orthogonal to the main line and in the same hyperfrequency plane. A diode is connected to the end of each subsidiary line at a point distant by .lambda.g/2 from the central point of the main line. The action of the two diodes is thus brought back to this point.

Abstract: A time delay shifter imparts a constant time delay to an electromagnetic signal, preferably a signal at a microwave frequency, over a band of frequencies. The phase shift imparted to the signal is a linear function of frequency. The shifter comprises a finite number of delay units (1) each having four single-pole single-throw switches (11-14). Closure of the first and third switches (11, 13) causes the signal to traverse a first path (2) containing a preselected length of transmission line that imparts a fixed time delay to the signal. Closure of the second and fourth switches (12,14) causes the signal to traverse a minimum-delay path (3) which is shorter than the delay path (2). The paths (2,3) are fabricated of coplanar waveguide. Each switch (11-14) is resonated by an inductor (21-24) for purposes of increasing isolation. An attenuator (70) is inserted in each minimum-delay path (3).

Abstract: A continuous microstrip phase shifter suitable for use in a phased array microwave hyperthermia system operating at 915 MHz is provided. The phase shifter utilizes a three dB quadrature hybrid coupler in conjunction with microstrip lines to change the phase of a transmitted wave. The phase change is introduced through the reflection ports of the coupler which are loaded with identical parallel resonant circuits. An abrupt junction varactor capacitance in parallel with a distributed inductance forms a voltage-tunable resonant circuit. The resonant element values are chosen to give a specified continuous phase variation with minimum transmission loss. This is accomplished without additional microwave circuit elements.

Abstract: The invention comprises a Schottky barrier type infrared photodetector which is monolithically integrated on a silicon waveguide. A Schottky barrier contact is positioned directly on a silicon waveguide to absorb grazing incidence optical signals passing through the waveguide. The Schottky contact is operated in the avalanche or reverse bias mode to generate a useable electrical signal.

Abstract: The invention provides a phase-shifting device for inclusion into a microwave transmission line to effect a predetermined, constant, broadband shift in phase of transmitted signals. The device comprises, in its preferred form, two Gallium Arsenide field effect transistors, connected in parallel, serially included in the line, and means for switching the transistors between alternate states to effect the phase shift.

Abstract: The invention relates to a voltage controlled analog phase shifter for operation at millimeter and microwave wavelengths using MMIC (Monolithic Microwave Integrated circuit) fabrication techniques. The phase shifter is formed of an artificial transmission line consisting of multiple unit elements in which each unit element contains a serial transmission line-inductance and a shunt diode capacitance which is variable as a function of an applied potential. In the design, the interconnecting transmission lines may be a small fraction of a wavelength, substantially less than one-quarter wavelength, and of high impedance relative to the characteristic impedance of the phase shifter. In consequence of the lumped design, each unit element, and a phase shifter using a plurality of such unit elements may be very small. The design also exhibits a low to negligible power consumption.

Abstract: A non-reciprocal phase shifter including a transmission medium connected between first and second terminals and having a predetermined phase shift which is the same in each direction and an amplifier circuit connected between the first and second terminals for introducing its inherent phase shift in one direction and a phase shift in excess of its inherent phase shift in the other direction for establishing a non-reciprocal phase shift; and a circulator made from such a phase shifter.

Abstract: The present invention relates to a reflection diode phase shifter that achieves amplitude equality between phase shifts of incident energy. Amplitude equality is achieved by placing a resistor R to ground in parallel with the transmission lines connecting a four-port coupler to symmetric reflection terminators having an impedance that is varied by a diode. The resistor is placed at a point on the transmission line having the lowest voltage when the greatest power loss is realized by the phase shifter.

Abstract: A variable dual phase shifter for simultaneously varying the phase shifts in two signal paths by equal and opposite amounts comprises two 90.degree. hybrids in the respective signal paths, and a pair of substantially identical transmission lines connecting output ports of one hybrid to output ports of the other. A number of variable-impedance radio-frequency devices, which are preferably p-i-n diodes, are connected to the transmission lines at positions spaced apart along the length of the lines, the positions on one line corresponding to those on the other line. The impedances of the devices are controlled to create a reflective termination at a selected position on one line and a reflective termination at the corresponding position on the other line, so that the phase shift applied to each signal is determined by the distance of the reflective termination from the respective hybrid. The devices may be arranged in pairs, each device of a pair being coupled to a respective one of the transmission lines.

Abstract: A network is provided which is selectively configurable as a high pass and low pass filter. A pair of sets of field effect transistors FETS is provided, each set comprising three FETS connected in a T-configuration. A pair of the FETS in each set have a drain electrode of one FET coupled to the source electrode of the other FET to provide a series element of the T-configured set. The third FET has drain and source electrodes coupled between the common connection of the pair of FETS and ground to form a shunt element of the T-configured set. The gate electrodes of the series elements of a first one of the sets of FETS and the shunt element of the other set of the FETS are each fed a common control voltage signal. A first one of the sets of FETS is capacitively coupled between the input and output terminals of the network, and the second one of the set of FETS is inductively coupled between the input and output terminals of the network.

Abstract: Transversal characteristic filter using a magnetostatic-wave device having amplitude weighted transducer assemblies. The input transducer includes a multi-fingered conductive layer with each finger being equally dimensioned and spaced. Each finger is separately connected to a contact of a field effect transistor integrated onto a semiconductor chip. A separate transistor is available for connection to each finger. The contact widths of the transistors vary depending upon the location of the connected finger from the center-most finger. A distribution approaching sin(x)/x is desirable in most applications. At the output or combining end of the device, the transducer fingers are separately connected to the gates of individual transistors whose junction widths vary symmetrically about the width of the junctions of the transistor connected to the center-most finger.

Abstract: A monolithic chip phase shifter consists of a PIN diode which is laterally elongated and shaped into a microstrip-like transmission line. The transmission line has characteristics determined in part by the capacitances associated with the intrinsic layer of the diode. Alternating-current (AC) signals are coupled through the transmission line. Direct-voltage reverse bias, no bias or direct-current forward bias are applied to select the appropriate value of equivalent shunt capacitance of the transmission line to provide the desired phase shift of the AC signals passing therethrough. A high-impedance coupling device couples the bias to the transmission line to prevent leakage of signal to the bias source.

Abstract: A TEM-mode transmission line such as a microstrip or coplanar line includes a pair of conductors, at least one of which is elongated. A semiconductor junction or junctions are coupled across the conductors. If a single junction is used, the junction may be laterally elongated or distributed. If discrete semiconductor junction devices are used, plural devices may be coupled across the transmission line. The capacitance of the junction(s) controls the phase shift imparted by the transmission lines to AC signals traversing the line. The capacitance of the semiconductor junctions in controlled by light coupled into the junction region. The light is coupled to the junction region by fiber-optic cables or by means of light illuminating the junction.

Abstract: A radar phase shifter is described, of the type which includes several phase shift devices whose phase shift angles can be added together, which produces a minimal VSWR and an accurately controllable total phase shift. A five bit phase shifter includes devices that phase shift by angles that are nominally 11.25.degree., 22.5.degree., 45.degree., 90.degree., and 180.degree.. The 45.degree. device is located between the 90.degree. and 180.degree. devices to minimize the VSWR. In addition to the preset phase shift devices, an analog phase shifter device is provided which compensates for the inaccuracy of the other devices.

Abstract: Steerable phased array antennas of the tapered type in which the antenna ment power is maximum at the center of the array and tapers off on either side thereof. The phase shifters of each antenna element are of the binary digital type with the number of stages and hence the phase accuracy being maximum for the high power center antenna elements and tapering off on either side thereof. Redundant stages for the binary phase shifters can be provided to increase reliability.

Abstract: A two-state microwave signal phase shifter comprising a first signal conductor disposed in a first plane, a second signal conductor electromagnetically coupled to the first signal conductor and disposed in overlapping relationship therewith in a second plane parallel to and spaced from the first plane, a ground plane element disposed in a third plane parallel to and spaced from the first plane, third and fourth signal conductors connected to the second signal conductor and disposed perpendicular to the second signal conductor; fifth and sixth conductors disposed in the second plane; switching diodes connecting the opposite ends of the third and fourth conductors to the fifth and sixth conductors; and a seventh conductor connected to the fifth and sixth conductors.

Abstract: A reflective hybrid analog phase shifter is detailed which is operable in the X-band, and which exhibits minimal phase shift variation with higher power loadings. A pair of back-to-back connected Schottky varactor diodes are serially connected to each of the phase shifting ports of a 3 dB coupler. The Scottky varactor diodes are reverse biased to permit continuous variation of the phase shift as a function of analog bias potential. A monolithically fabricated implementation of this circuit design is detailed.

Abstract: A transceiver element for controlling the phase of a microwave signal passing therethrough. The transceiver element includes a plurality of switching means arranged to steer a microwave frequency signal provided by a radar system through a nonreciprocal phase shifter to a phased array antenna during a transmit mode, and to steer a microwave frequency signal received by the phased array antenna through the nonreciprocal phase shifter to the radar system during a receive mode. The microwave frequency signal passes through the phase shifter in the same direction during both the transmit and receive modes. A set of control signals is fed to such switching means and the phase shifter of the transceiver element to provide collimated and directed beams of microwave energy during the transmit mode and the receive mode.

Abstract: A low pass T-section digital phase shifter apparatus having a pair of serially connected inductor-diode combinations connected in series which includes a parallel circuit connected between the common junction and ground. The parallel circuit has an inductor in parallel with a series capacitor and diode to provide a balanced insertion loss at each diode switching state. When the diodes are in the forward-biased state they act as closed short circuit switches. When the diodes are reversed-biased, the inductance in the series circuit resonates with the diode capacitance to provide a short path to the RF signal to pass the center frequency of the RF signal at the desired phase.

Abstract: A variable phase shifter based on the slow-wave effect for operation in the millimeter wave region, comprising a GaAs substrate for mechanical support; an n.sup.+ doped semiconductor layer disposed on the GaAs substrate for operation as a first ground plane; an n doped semiconductor layer disposed on the n.sup.+ semiconductor layer with a thickness to permit only one mode at millimeter wave frequencies to propagate, while suppressing higher order millimeter wave modes; and a Schottky metal microstrip with first and second ends disposed on top of the n doped semiconductor layer. Means are provided in the form of ohmic contacts for electrically connecting the n.sup.+ semiconductor layer to ground electrical potential. These ohmic contacts are disposed on top of the n doped layer, but are provided with a very large surface area contact to the n doped layer in order to significantly reduce the resistance between the ohmic contact and to the n.sup.+ semiconductor layer.

Abstract: A phase shifting device including a coupling device having an input port, an output port and a further port. The further port is connected to a transmission line, along the length of which are connected a number of switches. Each switch is operable to connect a low impedance across the transmission line such that an input signal applied to the input port is reflected at a connected one of the switches to produce an output signal at the output port whose phase is shifted relative to that of the input signal by an amount dependent on the length of transmission line traversed by the input signal. Alternatively the capacitance of each of the switches may be operated so as to vary the propagation constant of the transmission line to thereby produce the required phase shift.

Abstract: A digitally controlled reflective type phase shifter wherein radio frequency energy is fed to an input/output port of the phase shifter and then coupled from the phase shifter at the input/output port, the phase shifter providing one of a plurality of predetermined phase shifts between the fed energy and the coupled energy selectively in accordance with a control signal.

Abstract: A low pass .pi. section digital phase shifter apparatus having an inductor and a diode connected in series between two identical parallel circuits. The parallel circuits connect to the series inductor/diode circuit at both the input and output and each circuit has inductor connected in parallel with a capacitor and a diode to provide balanced insertion loss at each diode switching state. When the diodes of the circuit are in the forward biased state they act as closed short circuit switches. When the diodes are reversed biased, the inductance in the series circuit resonates with the diode capacitance to provide a short circuit path to the RF signal to pass the center frequency of the RF signal at the desired phase.

Abstract: Digital phase shifter bits of predetermined phase shift capability and lumped element network component fabrication arrangement are described. A variety of phase shifter bits including the capability of eleven and one-quarter, twenty-two and one-half, forty-five, ninety, and one hundred eighty degrees of phase shift are included. Also included are a number of high-pass/low-pass and switching transistor inclusive phase shifter bit arrangements. Both electrical schematic diagram and integrated circuit embodiments of the phase shifting networks are also disclosed.