Showing papers on "Balun published in 1976"

A New Impedance-Matched Wide-Band Balun and Magic Tee

Abstract: A new wide-band microwave balun particularly attractive for microstrip circuitry is described in which the normally balanced line is in the form of a pair of equal-amplitude and antiphase unbalanced lines. This novel method of input-output coupling allows a coplanar arrangement of input and output microstrip lines. Often the balanced and unbalanced line impedances in a balun are unequal, necessitating an impedance-matching network. A first-order reflection coefficient theory that mutually considers the impedance effects of the balun cavity, a compensating stub, and a quarter-wave transformer is used to design wide-band impedance-matched baluns. Curves of VSWR versus bandwidth are presented for several balanced-to-unbalanced line-impedance ratios. Experimental results are given for an octave-band impedance-matched balun with a balanced-to-unbalanced impedance ratio of 2:1. The new wide-band balun is adaptable to a microstrip magic tee. A proposed magic tee that relies on circuit symmetry for operation has multioctave bandwidth potential.

Broadband high frequency mixer

Abstract: A broadband mixer has two separate tapered ground plane microstrip baluns associated with a first signal port and two separate tapered ground plane microstrip baluns associated with a second signal port together with a frequency converter or mixer portion coupled between the baluns associated with the first and second signal ports and a third signal port. The frequency converter or mixer portion is comprised of eight diodes in a double balanced bridge arrangement having two sets of terminals associated with the first and second signal ports, each of the terminals of said two sets being separated from each of the terminals of the third signal port by a diode to electrically isolate their respective signals. The baluns associated with the first and second signal ports provide for the transformation of unbalanced input signals to balanced signals at the frequency converting diodes. Another balun coupled between the diode bridge arrangement and the third signal port provides an unbalanced signal at the third signal port in response to balanced signals at the diodes from signal inputs at the first and second signal ports. The baluns associated with the first and second signal ports are cross-connected so that their respective signals do not pass through to the opposite signal port. The circuit is reversible in that a signal may be input to or output from any signal port.

Doubly balanced mixer with optimized dynamic range

Abstract: A circuit for mixing first and second rf signals to produce an output signal containing a beat frequency comprises a pair of switches each of which has a four diode bridge controlled by the first rf signal. The first rf signal is coupled to a balanced current divider with common mode signal rejection. Load resistors coupled to the bridges provide matched termination of the first rf signal irrespective of the conductive state of the bridges. The value of the resistors and the characteristic impedance of the drive circuit is related to the characteristics of the diodes utilized to maximize the dynamic range of the mixer. Circuitry is provided for coupling all diodes of each bridge in series with respect to the average dc component of the first rf signal and to properly terminate the average dc component. The two diode bridges are conductive and nonconductive in opposing half cycles of the first rf signal. A hybrid has its summing port coupled to the switch port of one bridge and its difference port coupled to the switch port of the other bridge. The second rf signal is coupled to input port of the hybrid which includes a balun for balancing and rejecting common mode signals from the second rf signal. The beat frequency is provided at the output port of the hybrid which also includes a balun for rejecting common mode signals. The desired and filtered frequency components of the second rf signal are properly terminated.

Coaxial balun with doubly balanced heterodyne converter

Abstract: A coaxial line has a conductive surrounding shield connected from a first to a second point thereon. The outer conductor of the coaxial line shield is discontinuous at an intermediate point inside the shield so that it has two intermediate ends or terminals therein. A radio frequency signal applied to one end of the electrically unbalanced coaxial line will be supplied on the balanced intermediate terminals through a broadband transformation by the coaxial line with its shield, which constitutes a balun (balancing transformer). The length of each part of the coaxial line, from each intermediate terminal to the first and second points, is preferably one-quarter wavelength at the center frequency of an applied frequency band. The coaxial line may be used with another coaxial line mounted orthogonally to the first line, with both lines mounted within a common enclosure or shield, thereby to provide a dual balun. The intermediate terminals of the dual balun can be connected to opposite terminals of a four-diode bridge mounted between the baluns, thereby to form a doubly balanced heterodyne converter. A heterodyne output signal is derived at the intermediate terminals of one of the coaxial baluns by means of two quarter wave lines which are connected at their ends remote from the balun to form a heterodyne output terminal. The coaxial balun is capacitively coupled to the joint shield at its first and second points to avoid shorting the heterodyne output circuit.

Effects of Shield Impedance, Connector Resistance, and Coaxial Baluns on Ground Noise Interference in Nuclear Reactor Instrumentation Systems

Abstract: Electrical noise interference in low-level (approximately 50 ..mu..V), wide band (approximately 15 MHz) flux monitoring systems applied to nuclear reactor control causes safety and reliability problems. Others have shown that one predominant source of noise interference is conduction of currents in instrument cable shields and building conduits. Since these currents produce noise that is similar to signals produced by nuclear detectors, such noise interference reduces the ability of a reactor instrumentation system to determine the condition of a reactor. Model equations of ground noise interference were derived for a system model consisting of a sensor, coaxial cable, and an amplifier. These equations describe the effect of ground impedance, sensor impedance, transfer impedance, and connector resistance on both low-frequency (less than 100 kHz) and high-frequency (greater than 100 kHz) ground noise interference. Other model equations were derived for a system with a coaxial balun (a flexible coaxial cable wound around a ferrite core) added between the sensor and the sensor amplifier input. Analysis of the model equations reveals the effects of ground noise currents on instrumentation systems and the conditions for minimizing ground interference.