Abstract: A high power radio frequency(RF) precision step attenuator includes a trim attenuator, a multi-step attenuator and a calibration/control circuit. The control circuit includes a memory for storing attenuator specific calibration data. The calibration data incorporates attenuator characteristics which are used by the control circuit to adjust the attenuator and compensate for manufacturing variances, temperature variations, and the like.

Abstract: A system and method are presented for stabilizing the electrical impedance of an electrical interconnecting apparatus including a pair of parallel planar conductors separated by a dielectric layer. The electrical interconnecting apparatus may be, for example, a PCB, a component of a semiconductor device package, or formed upon a surface of an integrated circuit substrate. The present method includes determining a characteristic impedance of the structure. An electrical resistance is electrically coupled between regions of the planar conductors near peripheries, wherein the electrical resistance has a value dependent upon the characteristic impedance of the structure. The electrical resistance may be a set of discrete electrical resistances (e.g., resistors) dispersed about regions near peripheries of the planar conductors, or a continuous "stripe" of electrical resistance between the regions.

Abstract: A microwave circuit having a coupler with two microstrip conductors on a front surface of a substrate, parallel to each other, and electromagnetically coupled to each other with a coupling coefficient wherein the substrate has a rear surface on which a grounding conductor is formed. A floating conductor is interposed between the microstrip conductors. A first terminal of a switching device is connected to one end of the floating conductor while a second terminal of the switching device is grounded. By selectively turning on and off the switching device, the coupling coefficient is changed.

Abstract: An absorbent amplitude filter for HF signals employs a reflective filter and an absorption circuit comprising a load resistor. The absorption circuit inventively comprises another .lambda./4 line upstream of the filter, which comprises, at the input side, a series connection consisting of another diode and the load resistor. This series connection is connected with the reference potential, whereby an HF block is connected in parallel to the load resistor.

Abstract: A split power control circuit includes a solid state switch and a circuit or circuit element, such as a relatively large resistance or reactance connected between an RF signal line and ground. In order to provide relatively more precise control and thus relatively finer adjustment of the RF signal line, the RF signal line is split into a plurality of branches, with the switched control circuit or element connected to one or more of the branches. In another embodiment of the present invention, a solid state switch and serially connected circuit or circuit element, such as a resistance or reactance, are connected between an RF signal line and ground. The gate terminal of the solid state switch is capacitively coupled to the switch terminal (i.e. drain or source) connected to the RF signal line, forcing the gate bias element to become a fixed, rather than switched, load, thereby minimizing errors due to the gate biasing element and enabling tuning reactances to be used to compensate for such gate loads.

Abstract: A process and implementing construction includes an electrically independent EMI loading device comprised of an inner foam core surrounded by an electrically conductive envelope. The device is strategically positioned in resonant cavities located within a system enclosure housing electronic components and circuit boards and. In an example, the loading device is installed in a resonant cavity between a board-mounted component and an adjacent circuit board and is effective to decrease electromagnetic emission from resonating cavities.

Abstract: A variable attenuator includes a resistance region, a signal line to which the resistance region is connected, a very high frequency signal being propagated through the signal line, and a voltage applying part which applies a dc voltage across the ends of the resistance region, the dc voltage controlling a magnitude of attenuation to the very high frequency signal.

Abstract: A harmonic filter is added to a radio frequency filter comprising at least one transmission line resonator (R1; R2; R3) to filter harmonic multiples of the filter's operating frequency. Coupling to the harmonic filter occurs through matching couplings and transmission lines (7; L1 to L9; L20; L28) in the filter or via the electromagnetic field of said transmission line resonator (R1; R2; R3). The harmonic filter advantageously comprises striplines (L13 to L19; L21 to L27; L29 to L49) manufactured in conjunction with the other stripline structures in the filter.

Abstract: Digital control of analogue beamformers utilising PIN diodes in a shunt circuit bi-phase attenuator arrangement is difficult because of the diodes extremely non-linear control response. There is disclosed a PIN diode circuit arrangement comprising a digital to analogue converter (DAC) with a reference voltage controller arranged to vary the DACs response to digital input signals to compensate for the PIN diode's non-linear response making this look substantially linear in the digital domain. The circuit preferably incorporates a feedback arrangement from the output of the DAC to its reference voltage input.

Abstract: A temperature compensating voltage variable attenuator includes at least two temperature variable resistors. The temperature variable resistors have different temperature coefficients of resistance, preferably, with one temperature variable resistor having a positive temperature coefficient of resistance and the other temperature variable resistor having a negative temperature coefficient of resistance. The temperature coefficient of resistance of the temperature variable resistors being such that the attenuation of the attenuator varies with changes in temperature of the attenuator. A voltage variable heater resistor is adjacent both temperature variable resistors so that a change in the voltage applied to the heater resistor changes the temperature of the heater resistor. The heat from the heater resistor is applied to the temperature variable resistors so as to change the resistance of the temperature variable resistors. This provides a controlled change in the attenuation of the attenuator.

Abstract: An attenuator includes a flat, substantially rectangular substrate of an insulating material having a surface. A plurality of termination areas of a conductive material are on the substrate surface and are spaced from each other. Three resistors are on the substrate surface and are connected in a series parallel combination between the termination areas. The resistors may be formed by three separate resistance layers extending between and connected to the termination areas, or a single resistance layer extending between and connected to the termination areas. A shunt capacitor is on the substrate surface and is connected to one of the resistors. The shunt capacitor is formed by an area of a conductive material on the substrate surface and overlapping a portion of the resistors, and a dielectric layer between the conductive area and the resistor.

Abstract: An attenuated cable is formed with an in-line attenuator conducted between two cable lengths wherein the cable lengths are rigidly joined together by a rigid hollow housing which encloses the attenuator therein. The attenuator circuit is housed within the housing, and is electrically connected to the cable lengths without the use of mechanical connections therebetween. The free ends of the cable lengths farthest from the housing are provided with standard connectors for connecting the cable to additional electrical devices such as microphones, mixers or amplifiers. Since the housing and attenuator circuit are relatively small and light relative to the larger cable lengths, the attenuated cable has substantially the same weight and flexibility as a continuous length of cable.

Abstract: A split power control circuit includes a solid state switch and a circuit or circuit element, such as a relatively large resistance or reactance connected between an RF signal line and ground. In order to provide relatively more precise control and thus relatively finer adjustment of the RF signal line, the RF signal line is split into a plurality of branches, with the switched control circuit or element connected to one or more of the branches. In another embodiment of the present invention, a solid state switch and serially connected circuit or circuit element, such as a resistance or reactance, are connected between an RF signal line and ground. The gate terminal of the solid state switch is capacitively coupled to the switch terminal (i.e. drain or source) connected to the RF signal line, forcing the gate bias element to become a fixed, rather than switched, load, thereby minimizing errors due to the gate biasing element and enabling tuning reactances to be used to compensate for such gate loads.

Abstract: A passive positive-gain equalizer comprises a ferrite (100, 300) electromagnetically coupled to a single conductor (111, 311) of a digital signal defined in the frequency domain by a plurality of frequencies. Although it has no external power source other than the digital signal, the equalizer amplifies some of the signal's frequencies. In one embodiment, the equalizer (100) comprises a "C"-shaped body portion (101) whose legs (103, 104) extend through holes in a PC board (110) to be spanned by an "I"-shaped body portion (102). A tunnel (106) formed thereby surrounds a stripline (111) and the PC board portion (112) which carries the stripline. In another embodiment, the equalizer (300) comprises an "E"-shaped body portion (301) whose legs (303-305) extend through holes in a PC board (310) to be spanned by an "I"-shaped body portion (302). A pair of tunnels (306, 307) is formed thereby, and the stripline (311, 511) loops through each of the tunnels one or more times.

Abstract: The present invention provides for a low power receiver protector and stepped attenuator for conditioning a received input signal within a microwave receiver front end. The low power receiver protector includes a detector for generating a surge signal in response to the received input signal exceeding a predetermined threshold, a delay line for delaying the received input signal for fixed duration, and a limiter for reducing the voltage of the received input signal in response to the generation of the surge signal. The stepped attenuator includes a plurality of cells each having an attenuation transmission path which includes an attenuator for providing a predetermined amount of attenuation of the received input signal. Each attenuation transmission path, bypass transmission path and delay line comprise a high temperature superconductor to provide minimal loss and reduced size.

Abstract: An extremely broad band high power termination (10) for microwave and millimeter frequency amplifiers combines a standard resistive low frequency termination (15) with a broad band high frequency absorptive element (13) using an absorptive material such as Eccosorb. A mid-band matching network (14) is provided between the resistive termination (15) and the Eccosorb absorptive element (13). The Eccosorb absorbs the energy of the higher microwave frequencies while the resistor absorbs energy at low frequencies. Accordingly, a much higher power handling capability in a compact planer environment is achieved. This termination (10) is suitable use for use in K-band power amplifier combiners (30) that require high isolation and high power handling capability of the isolated ports (35).

Abstract: A first bypass capacitor and a second bypass capacitor are connected in series between an input terminal and an output terminal for high frequency signals. A quart-wave line and a diode are connected between the connecting point of the first and second bypass capacitors and the ground, and a choke coil is connected between the connecting point and a D.C. voltage input terminal. When input signals are not to be attenuated, a D.C. voltage is fed from the D.C. voltage input terminal, and no D.C. voltage is fed when the signals are to be attenuated.

Abstract: An arrangement in which resistors are interposed on a bus line to attenuate reflected spurious pulses. The resistors are positioned on the bus so as not to be between a processor and its cache memory, but so as to be between the combination of the processor and cache memory and components such as a peripheral controller and a memory controller. The resistors reflect a portion of the pulse energy and attenuate the pulse energy passing through them. In another aspect of the invention, the traces making up the bus are arranged so that the intertrace distance is greater than a distance between the traces and an internal reference plane. This causes magnetic energy radiated by an aggressor trace to encounter the reference plane before it encounters a victim trace. This also reduces the amount of magnetic cross-coupling.

Abstract: A lossy capacitive circuit element, or DC scrubber, is printed on a circuit substrate and absorptively filters high frequency signals in circuit modules. A top conductor of the DC scrubber is separated from a ground conductor by a layer of high dielectric material. A resistive layer, positioned either above or below the top conductor absorbs high frequency signals applied to the top conductor while the dielectric layer shunts the signals to the ground conductor. Alternatively, a pair of DC scrubbers are stacked vertically to configure the lossy capacitive structures in parallel. Signal isolation provided by the DC scrubber and the stacked DC scrubber enables inexpensive DC interfaces to be used in the circuit modules.

Abstract: The switch attenuator of the invention includes: a first terminal connected to an antenna; a second terminal connected to a transmitter; and a third terminal connected to a receiver, thereby switching a first state and a second state.

Abstract: A signal distribution structure, or polyline, provides isolation between signal paths in high frequency systems, such as RF or microwave communication systems. The polyline has an inner conductor surrounded by a lossy insulator and a conductive shield. The conductive shield isolates the inner conductor from high frequency signals in the system while the lossy insulator attenuates high frequency signals present on the inner conductor. Low frequency signals on the inner conductor are relatively unattenuated by the polyline. Alternatively, an open polyline is formed in which the conductive shield is absent. The polyline and the open polyline are printed on a ceramic substrate or other type of carrier using known thick-film processing techniques.

Abstract: A billet of low-density carbon-bonded carbon fiber (CBCF) composite is machined into a desired attenuator or load element shape (usually tapering). The CBCF composite is used as a free-standing load element or, preferably, brazed to the copper, brass or aluminum components of coaxial transmission lines or microwave waveguides. A novel braze method was developed for the brazing step. The resulting attenuator and/or load devices are robust, relatively inexpensive, more easily fabricated, and have improved performance over conventional graded-coating loads.

Abstract: This invention is an inexpensive probe apparatus operating at high precision that can be used for both low-frequency and high-frequency measurements. A line with a first and second conductor is extended from a probe connected to a circuit component. A low-frequency or high-frequency device is alternately connected to the line. A third common conductor runs parallel to the aforementioned line and a resistor and capacitor is connected between the probe end of the aforementioned second conductor and the aforementioned common conductor.

Abstract: An electric power receiving and supplying circuit comprises: a microstrip patch antenna, having a feeding point, for receiving a microwave signal and supplying an electric power; a rectifier, for rectifying the electric power, having: a first diode having an anode, connected to the feeding point, and a cathode; a second diode having a cathode, connected to the cathode of the first diode through a junction point, and an anode; and a high-frequency grounding circuit for high-frequency-grounding the anode of the second diode, and a lowpass filter for low-pass filtering the rectified electric power to supply a dc supply power.

Abstract: A bridge T attenuator which includes PIN diodes in both the bridge arm and in the shunt arm, and in which the current through the shunt arm is controlled with respect to the current through the bridge arm, so that the product of these two currents equals a constant. This is accomplished by a feedback loop. Thus a relatively simple, inexpensive, and entirely analog solution is provided for a bridge T attenuator to be used with a radio frequency signal, so that a prescribed level of attenuation set by a user may be maintained while the impedance is maintained at a fixed value over the entire attenuation range.

Abstract: A wide-bandwidth variable attenuator/modulator incorporating a region of material comprising a combination of a ferromagnetic/nonmagnetic material which exhibits a Giant Magnetoresistance (GMR) effect.

Abstract: A ground conductor and a signal conductor are provided in an insulating magnetic body respectively. The insulating magnetic body is a compound member that combines ferromagnetic metal particles and an insulating resin. A signal transmission element, a connector or a circuit board with high frequency stopping and low pass characteristics which will ensure reliable absorption of high frequency components in the high frequency range, can be provided.

Abstract: A fully integrator RF attenuator performs gain control upon a received RF signal without the use of an off-silicon PIN diode. The attenuator includes a T-configuration pad in conjunction with a current source. A direct current signal biases a shunt element in the T-pad. Preferably, a voltage control signal which controls the direct current is generated as a negative feedback signal in proportion to the magnitude of the RF detected at the attenuator output.

Abstract: In a multi-plate high frequency parallel strip-line cable including a strip-shaped dielectric body made of either an electrical insulating material having a flexibility or another electrical insulating material having a plasticity, the dielectric body is composed of a pair of dielectric layers. A pair of thin-film-shaped earth conductors is formed on both surfaces of the dielectric body so as to oppose to each other, and a thin-film-shaped center conductor is formed between the pair of dielectric layers in the dielectric body so as to be located between a pair of earth conductors. Further, a circuit device part such as an impedance adjusting circuit, a filter, an attenuator or the like is formed between a pair of dielectric layers in the dielectric body so as to be electrically connected with the center conductor, thereby the parallel strip-line cable having either a flexibility or a plasticity.

Abstract: A minimum phase shift microwave attenuator circuit, providing very low insertion phase change with changing attenuation levels. Three PIN diodes are biased in parallel from a common node. The PIN diodes are held at zero or reverse bias for the "no attenuation" state, and are made slightly lossy to produce the attenuation state. In the attenuation state, the PIN diodes are utilized as current controlled lossy capacitors which change resistance with applied bias, but maintain constant capacitance, thereby providing low insertion phase deviation across wide attenuation levels.

Abstract: An attenuator for use with a current transformer. The attenuator includes an input voltage terminal, an input ground terminal, an output voltage terminal, an output ground terminal, an input resistive arm, a shunt resistive arm, an output resistive arm, and a compensation circuit. The input and output ground terminals are coupled together. The input resistive arm has a first end coupled to the input voltage terminal and a second end. The output resistive arm has a first end coupled to the output voltage terminal and a second end coupled to the second end of the input resistive arm. The shunt resistive arm has a first end coupled to the input and output ground terminals and a second end coupled to the second ends of the input and output resistive arms. The shunt resistive arm has a shunt resistance and an intrinsic inductance effectively in series with the resistance.

Abstract: A multifunction microwave modulator circuit has an input signal splitter to provide two equal amplitude signal components. A phase quadrature relationship between the two signal components is obtained by constructing the splitter as a Lange coupler. There is pair of circuit cells, each of which operates separately on one of the two signal components to electronically adjust a vector representation of the signal to provide a vector having a desired amplitude, ranging over both positive and negative values of amplitude, including zero amplitude. The signal vectors of the two cells are combined by means of a Wilkinson combiner to provide an output signal represented by a resultant vector which may have any direction within 360 degrees, and an amplitude scale factor which varies from unity to zero.

Abstract: The present invention discloses a reconfigurable microstrip transmission line network having a microstrip circuit consisting of an RF ground plan separated from a transmission layer by a dielectric layer. The transmission layer comprises a silicon material responsive to a plurality of excitation sources. The excitation sources generate excitation beams which upon interacting with the surface of the transmission layer actuate a conductive pathway. By alternately actuating and deactuating the excitation sources and varying the excitation beams, the configuration of the microstrip transmission line network upon the transmission layer may be reconfigured as desired.

Abstract: A current bias-type variable attenuator. Two PIN diodes are disposed in series to each other and in the forward direction on a bias current path. When a bias voltage is applied to a bias terminal, d.c. current flows in the order of a combination output port, an in-phase output port, a first PIN diode, an input port, a 900.degree.--delayed phase output port, and a second PIN diode, or in the order of the combination output port, the in-phase output port, the first PIN diode, the second PIN diode, the 900.degree.--delayed phase output port, and the input port. Since d.c. current flowing through the first PIN diode and d.c. current flowing through the second PIN diode have an equal value, an RF resistance of the first PIN diode and that of the second PIN diode are balanced.

Abstract: An electrical circuit (200) having an input terminal (201), an output terminal (202), and a signal common (203) is preferably used to attenuate an electrical signal. The electrical circuit (200) comprises four impedance elements (205-208) and an impedance transformer (210). A first impedance element (205) is coupled between the input terminal (201) and a first node (212), while a second impedance element (206) is coupled between the first node (212) and the output terminal (202). A third impedance element (207) is coupled between the input terminal (201) and the output terminal (202), while a fourth impedance element (208) is coupled between a second node (213) and the signal common (203). The impedance transformer (210) is coupled between the first node (212) and the second node (213) to complete the electrical circuit (200).

Abstract: An attenuator circuit which has a small insertion loss and also has a broad tolerance toward the fluctuation of the element parameter. An attenuator stage having the largest attenuation quantity of a plurality of attenuator stages is formed with a .pi.-type attenuator stage, and an attenuator stage having the smallest attenuation quantity of the plurality of attenuator stages is formed with a T-type attenuator stage. In this way, an attenuator stage having a large attenuation quantity whose precision of the attenuation quantity is apt to be detracted is formed with a .pi.-type attenuator stage so that the precision becomes high, further, an attenuator stage having a small attenuation quantity is formed with a T-type attenuator stage so that the insertion loss can be lowered.

Abstract: A digital-to analogue converter for producing an RF output signal proportional to a digital input word of N bits from an RF reference input, N being an integer greater or equal to 2. The converter comprises a plurality of power splitters, power combiners and a plurality of mixers or RF switches connected in a predetermined configuration.

Abstract: A low current vector modulator for continuously varying the amplitude and polarity of an RF signal includes first and second hybrid couplers electrically connected at their input ports to an RF source. The characteristic impedance of the hybrid couplers is twice the impedance of the RF source. First and second PIN diodes are electrically coupled to 0.degree. and 90.degree. phase ports of the first hybrid coupler, respectively, and third and fourth PIN diodes are electrically coupled to 0.degree. and 90.degree. phase ports of the second hybrid coupler, respectively. The first and second PIN diodes and the third and fourth PIN diodes also are electrically connected respectively to first and second biasing sources. Varying the biasing provided by the first and second biasing sources varies the amplitude and phase of first and second output signals generated by the first and second hybrid couplers.

Abstract: A step attenuator using a PIN diode for use with microwave circuits. The step attenuator circuit provides for stepwise controlling the current applied to the microwave monolithic integrated circuit. The step attenuator circuit comprises a driver circuit and a attenuator circuit coupled thereto. The driver circuit that comprises a temperature sensor, a comparator circuit coupled to the temperature sensor for comparing the temperature value sensed by the temperature sensor to predetermined reference voltages and for providing a plurality of output signals that are indicative of a respective plurality of temperature values sensed by the temperature sensor, and a resistor network coupled to the comparator circuit that is adapted to set the respective values or current provided by the driver circuit.

Abstract: A voltage variable attenuator is described including a quadrature hybrid coupler having an input port, an output port, a first reflective port and a second reflective port. The voltage variable attenuator further includes a first and a second impedance network, the first impedance network connected to the first reflective port of the quadrature hybrid coupler, the second impedance network connected to the second reflective port of the quadrature hybrid coupler, each impedance network including a first RF propagation network having a first end connected to the respective reflective port of the quadrature hybrid coupler. Each impedance network further includes a second end of the first RF propagation network connected to a field effect transistor having a drain electrode, a source electrode and a gate electrode, the drain electrode connected to the second end of the first RF propagation network.

Abstract: An RF step attenuator topology is optimized for use with GaAsFET switching devices, exploiting their high isolation while minimizing the effects of their relatively high insertion loss. The attenuator includes an attenuation network that has two inputs and two outputs, permitting four different attenuation levels to be selected by use of just one input switch and one output switch. The detailed embodiments feature high levels of attenuation (up to 140 dB in 10 dB steps), a minimum number of switches in the through-path (four), very wide band operation (250 KHz-2 GHz), and economical design.

Abstract: A passive RF limiting circuit device providing protection for receiver front ends and the like by utilizing PIN diodes acting as switching devices which transform a low-loss T-network attenuator circuit into a high-loss .pi.-network attenuator circuit under high power conditions.

Abstract: Integrated circuit structure and processing is provided for a high power limiter including at least a first anti-parallel array of monolithically integrated Schottky diodes. In a further embodiment, integrated circuit structure and processing is provided for an MMIC, microwave and millimeter wave monolithic integrated circuit, including an amplifier and a high power limiter monolithically integrated on the same substrate.

Abstract: A miniature potentiometer suitable for mechanical adjustment of microwave circuits is provided. Furthermore, there is provided a dual, ganged potentiometer also suitable for mechanical adjustment of microwave circuits. The dual, ganged potentiometer provides reliable tracking of tapers between the two variable resistance elements. Yet further, there is provided a complete, microwave, T-pad attenuator circuit which is mechanically adjustable. The T-pad attenuator uses two ganged potentiometers, whose tapers track in a known non-linear fashion. The tapers may be logarithmic.

Abstract: An absorptive temperature variable microwave attenuator is produced utilizing at least two different thick film resistors. The temperature coefficients of the resistors are different and are selected so that the attenuator changes at a controlled rate with changes in temperature while the impedance of the attenuator remains substantially constant. Substantially any temperature coefficient of resistance can be created for each resistor by properly selecting and mixing different inks when forming the thick film resistors. Furthermore, attenuators can be created having either a negative temperature coefficient of attenuation or a positive temperature coefficient of attenuation.

Abstract: A digital attenuator circuit for attenuating RF frequencies implemented as an MMIC having series microstrip transmission lines between an RF input terminal and an RF output terminal and having at least one shunt path comprised of a series combination of a MESFET able to be switched between a conducting state and a nonconducting state and a thin-film resistor, wherein the circuit employs a distributed topology whereby when the MESFET is in the conducting state the impedance of the microstrip transmission lines matches the impedance of the shunt elements thereby enabling the circuit to operate over a wide bandwidth.

Abstract: Apparatus for measuring electromagnetic radiation from an electronic component in which a transverse electromagnetic cell has a coaxial connector for receiving radiation, a septum extending from the connector to a facing wall of the apparatus, the facing wall having a flat surface and formed from ferrite particles dispersed through rigid material. The rigid material is ceramic and conveniently the facing wall is made from ceramic tiles incorporating the ferrite particles. With this wall structure, the apparatus may be of small size suitable for measuring radiation or electronic chips or connector assemblies.

Abstract: A high frequency PIN diode attenuator uses an inductive element in parallel with the PIN diode. The inductor resonates with the parasitic capacitance of the PIN diode to increase the attenuation level.

Abstract: A step attenuator comprises two branchline couplers with two coupling transmission lines therebetween. Attenuation is accomplished through switchable resistors, in series with switching diodes, shunted across the transmission lines. These resistors reflect and absorb incident power. Switching signals are provided to the diodes through the branchline couplers and the coupling transmission lines. The reflected power is absorbed by a matched termination at the port of the input branchline coupler that is isolated from the port at which the signal to be attenuated is coupled. Phase shift and insertion loss are minimized by tuning the series inductance inherent in the diode resistor combination with tuning capacitors in series therewith. These capacitors are by passed by low-susceptance inductors which provide a dc path to ground for the diodes.

Abstract: The present invention decribes a high-frequency attenuator using PIN diodes, which is especially intended as power control means in a radio-telephone transmitter, and in which the input and output impedances remain constant as the attenuation is varied. The attenuator comprises a longitudinal branch between the input and the output port, having PIN diodes (D1, D2) attenuating the RF signal, transverse branches connected with the input and the output port, each comprising a quarter-wavelength transformer (C1, Z1, C2; C4, Z2, C5) viewed from the signal path and a PIN diode (D3, D4). The same control direct current passes via all the diodes. In spite of the variations of the resistance of the PIN diodes, the input and output impedances of the attenuator do not change owing to the quarter-wavelength transformer.