Showing papers on "Quarter-wave impedance transformer published in 1986"

Impedance matching arrangement

Abstract: An impedance matching arrangement is suitable for use with a frequency hopping radio communications system which is operable over a wide frequency band, so as to match the operating impedance of the antenna at each of the frequencies used. As the frequency of the radio system hops from one frequency to another, a note of any impedance mismatch is noted and data derived therefrom is stored for future use when that frequency is next selected so as to reduce any impedance mismatch.

Glass mounted antenna

Abstract: A mobile transmitting and receiving communications antenna assembly for use on a vehicle, includes a primary radiating element a secondary radiating element having first and second radiating elements, normal to a longitudinal axis of the primary radiating element to form a ground plane therefor. Impedance matching means, comprising a tuned circuit tuned to the nominal resonant frequency of the capacitively loaded antenna and electrically connected to the second electrically conductive coupling member in the immediate proximity thereof to resonate in conjunction with said primary radiating element. The impedance matching means displaying an impedance which varies between a first impedance at the connection to the second electrically conductive coupling member which is substantially equal to the impedance at the base end of the primary radiating element and a second impedance at least several orders of magnitude less than the first impedance. Means for connecting transmission line means to the impedance matching means at a point where the impedance of the impedance matching means is substantially equal to the impedance of the transmission line. In a first embodiment the primary and secondary radiating elements are mounted on opposite sides of a dielectric panel such as a window which capacitively couples the primary radiating element to the transmitter and/or receiver. In an alternative embodiment, the primary and secondary radiating elements are commonly mounted to the interior surface of a dielectric panel.

Inductive impedance of a spirally wound Li/MoS2 cell

Abstract: The impedance of cylindrical lithium molybdenum disulfide cells has been measured in the frequency range of 1 kHz to 10 MHz. In this frequency range, it is shown that the inductance associated with the spiral geometry of the cell electrodes contributes significantly to the cell impedance. It is also shown that the resistive component of the impedance at high frequency is attributable in part to damping of induced currents in the can and central mandrel of the cell, and to radial ion flow between electrodes in the spiral winding.

Adaptive impedance mismatch detector system

Abstract: An adaptive impedance mismatch detector system (10) for determining whether or not a particular load impedance (30) is matched or mismatched to the characteristic impedance of a transmission line (at 20). The detector system is capable of determining if a particular load impedance has a value outside of an impedance threshold circle (24) having a center (22) at a location other than at the center of the Smith Chart (Fig. 2). The system changes the radius and/or center of the threshold circle in response to changes in circuit operating conditions or parameters. This flexibility enables the detector to be more selective in determining improper load conditions.

Impedance of a horizontal coil above a conducting half-space

Abstract: The induction of eddy currents by a circular, air-cooled coil of rectangular cross section, carrying a low-frequency alternating current and with its axis parallel to the surface of a homogeneous conducting half-space is considered. An exact, closed-form expression for the coil impedance is derived. The calculations are in excellent agreement with experiment and agree with an independent calculation of coil impedance which is valid in the limit of small skin depth.

Active matching transmit/receive module

Abstract: A transmit/receive module is disclosed that provides selectable impedance matching between: a power amplifier and the antenna of a phased array when the radar is transmitting, and selectable impedance matching between the antenna and a low noise amplifier when the radar is receiving. The transmit/receive module replaces the conventional fixed impedance matching system with a microprocessor, a plurality of switches and sets of pairs of electrical capacitors, resistors, and inductors. Since the antenna impedance characteristics change with changes of beam angles, the microprocessor directs the switches to configure the electrical components into any one of a number of impedance matching circuits. The microprocessor selects an optimum impedance matching circuit for the power amplifier to maintain maximum power transfer for radar transmission and another optimum impedance matching circuit for the low noise amplifier for minimum noise upon radar signal reception.

Impedance of a large circular loop antenna in a magnetoplasma

Abstract: The input impedance of a large circular loop antenna with arbitrary orientation in a cold magnetoplasma is calculated by using a transmission line theory. New impedance resonances for antennas of finite size in a magnetoplasma in the frequency region below and near the electron cyclotron frequency are indicated theoretically. The resonance peak of the impedance at the lower hybrid resonance frequency is also predicted to exist for arbitrarily oriented antennas of finite size. The experiments on the impedance of a large circular loop antenna are carried out for the cases of normal and parallel orientation of the magnetic field with respect to the plane of the loop immersed in a radio frequency-generated laboratory plasma. The newly predicted impedance resonances for the antenna of finite size are observed. It is also shown that the measured impedances agree fairly well with the calculated ones.

Reduced height waveguide circulator

Abstract: A conductive waveguide structure has a central cavity of full height and input/output ports of a second reduced height emanating therefrom. A smaller ferrite circulator element is centrally disposed within the cavity and has outer extremities spaced from the inner edges of the reduced height input/output ports by a predetermined gap dimension "G" which is chosen to achieve an appropriate impedance match between the impedance of the ferrite element and the higher impedance of the wavguide without the necessity for the usual quarter-wave dielectric impedance matching transformer sections.

Radiation hard memory cell circuit with high inverter impedance ratio

Abstract: A memory cell circuit has a pair of cross-coupled inverters. One inverter has an output impedance at least 10 times, preferably, at least 50 times, that of the other inverter so that during a radiation pulse the chance of a change in logic state is reduced. In a particular embodiment, the one inverter has an output impedance of 135 times that of the other inverter.

Energy storage transformer power conditioning systems for Megajoule class flux compression generators

Abstract: Circuit and energy storage transformer configurations are developed to match high impedance loads to low impedance sources. With the secondary open, a large di/dt is produced in the primary circuit by inserting a resistance, characteristic of an opening switch, and the load circuit is connected using a preset spark gap. Transformer design concepts using a foil-MYLAR ''sandwich'' for the secondary winding are described, permitting close primary-secondary coupling. Transformer experiments driven by a 0.25 MJ capacitor bank support the overall system concepts. A compact flux compression generator-transformer system is described.

A system for transmission of high-frequency electromagnetic signals

Abstract: A system for transmitting high- frequency electromagnetic signals comprises a frame aerial of one or more turns in which one or more capacitors C' are disposed. The capacitors are symmetrically disposed with respect to the feed for the aerial which may include a quarter wave transformer or a balun.

An Octave - Wide Matched Impedance Step and - Quarterwave Transformer

Abstract: An impedance step can now be matched - Gamma <= 0.02 - over a frequency band corresponding to at least an octave in wavelength by using a shunt inductor before and -capacitor behind, but almost a quarterwavelength apart. A shortened quarterwave impedance transformer could be matched with the shunt capacitor only. For high transformer ratios, part of a taper was used. Ultra-short X-band transformers and-transducers could be realized from rectangular w.g. to flat-square-, circular-, ridge w.g., finline and partly or fully dielectric-filled w.g. Although realized in X-band w.g., its principle is very general and can be applied to any dominant-mode transmission line.

Multi-section transmission line transformer of arbitrary length

Abstract: A simple approach for matching a purely resistive load impedance to a given transmission line is presented. The parameters of the transformer can be accurately computed from presented equations. In this approach, the length of each section, as well as the characteristic impedance, can be properly chosen in order to minimize the total length of two sections while obtaining relatively wider bandwidth compared with the case of two sections of equal length. This approach provides much shorter total length and reduces the insertion loss of the matching section, while providing almost the same bandwidth property as compared with a single quarter-wavelength transformer section.

Microwave therapy unit

Abstract: A microwave therapy unit for human and veterinary medicine is described, in which the microwave power is generated in a magnetron, as used, in particular, for microwave ovens, and guided via a coaxial line to the microwave applicator and applied by the latter to the biological tissue to be treated. Connected directly to the magnetron, which is designed primarily for waveguide connection, without the interposition of a waveguide transition is a microwave output coupling which employs coaxial technology and, firstly, effects a coaxial impedance step-down transformation of the internal impedance of the magnetron to the characteristic impedance of commercially available coaxial lines with 50 or 60 ohms, and secondly contains a microwave bypass which represents a low impedance for microwave currents of nominal frequency and a high impedance for low-frequency control currents, and thirdly contains a coaxial low-pass filter whose output impedance is matched to the characteristic impedance of conventional coaxial lines with 50 or 60 ohms.

Input Impedance Characteristics of a T-Shaped Ridged Waveguide

Abstract: This paper presents input impedance characteristics of a T-shaped ridged waveguide calculated by a magnetic wall model. They are also confirmed experimentally.

The impedance matching element of dielectric image line

Abstract: In this paper, the wave impedance of the dielectric image line as a function of geometry dimensions and frequency is analysed. Both necessity and possibility of matching impedance is studied. An optimal matching element is put forward. The bandwidth with VSWR≤1.10 can reach 10.5GHz.