Magic Tee Research Articles

A Design of Magic Tee with Coplanar Arms

Magic tee is a widely used component in microwave systems; the four arms of conventional magic tee direct at four different directions, which give inconveniences to the assemblage of a system. In this paper, a broad-wall slot directional coupler and an E-plane dielectric loaded waveguide phase shifter is used to form a magic tee with four arms in the same E-plane. The magic tee is analyzed exactly with mode match method; and the simulated annealing method is used to optimize the performance of the magic tee. Simulation results are presented, which show good performance.

Covariant and contravariant bilinear transformation of quadripole scattering matrix and matching strategy for a quadripole type domestic microwave oven

The author obtains two formulations for calculating the image scattering matrix of a quadripole through a linear octopole circuit, which become equivalent when the octopole circuit is reciprocal. Thus bilinear transformation can be used for quantifying that a magic tee can match perfectly any quadripole type applicator or any domestic microwave oven to two generators.

Preliminary design of high-power wave-guide/transmission system for multimegawatt CW requirements of 100 MeV proton LINAC

Development of a 100 MeV CW proton LINAC has been planned at CAT. This LINAC will be needing CW rf power in the frequency ranges of 350 MHz and 700 MHz for its RFQ and DTL/CCDTL/SFDTL structures respectively. The power to the accelerating structures will be produced by either 1 MW CW or 250 kW CW klystrons/inductive output tubes (HOM IOTs). The power needed by respective feed points in the structure is max. 250 kW which will be powered by splitting the power from 1 MW klystron/klystrode into four channels by using a wave-guide system. In case of using 250 kW tubes the power to the structures will be provided directly from each tube. Two types of wave-guide transmission system have been considered, viz, WR 2300 for 350 MHz rf needs and WR 1500 for 700 MHz rf needs. The typical wave-guide system has been designed using the 1 MW CW klystron followed by wave-guide filter, dual directional coupler, high-power circulator, three 3 dB magic TEE power dividers to split the main channel into four equal channels of 250 kW each. Each individual channel has dual directional couplers, flexible wave-guide sections and high power ceramic vacuum window. The circulator and each power divider is terminated into the isolated ports by high power CW loads. Out of the four channels three channels have phase shifters. Present paper describes the technological aspects and design specifications-considerations for these stringent requirements.

A novel method for measuring complex reflection coefficient using a four-port reflectometer

A novel method for precise measurement of complex reflection coefficient using a four-port reflectometer is presented. First, three new complex system constants are introduced, which depend only on the scattering parameters of the four-port reflectometer. Therefore, the stability of the reflectometer is greatly improved. Then, these complex system constants are used to determine the complex reflection coefficient Γ of the device under test by calibrating the reflectometer. Finally, a four-port reflectometer comprising a magic tee and a power detector is constructed and excellent experimental results are obtained.

Improving Electric Field Distribution in a Microwave Heating Device

The authors describe a microwave reheater for food products in which two magnetrons and a magic tee are used for decoupling the waves emitted and for obtaining good impedance matching. Symmetric and asymmetric parts of the electric field pattern can be separately adjusted and optimized for best results.

A self-diplexing quasi-optical magic slot balanced mixer

Drawing on the principles of operation of the magic tee balanced mixer, a quasi-optical magic slot balanced mixer is proposed. The mixer exploits a diametrically fed annular slot radiator which radiates two orthogonal polarizations which are used as signal and local oscillator input ports. The idea has been tested at microwave frequencies. The measured radiation impedances, radiation patterns and conversion efficiency show that reasonable performance is readily obtained over a 30% bandwidth and that this quasi-optical balanced mixer is suitable for submillimeter wave applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Four-port finline circulator

The coupled-mode behaviour of a ferrite coupled section (FCS) with longitudinal magnetisation is briefly discussed. Experimental results are presented which demonstrate the nonreciprocal behaviour of an FCS fabricated in finline and connected to a waveguide magic tee junction.

Design of Broad-Band Dielectric Waveguide 3-dB Couplers

It is shown how 3-dB couplers with bandwidths on the order of 30 percent can be designed by appropriately taking advantage of the dispersion and the frequency dependence of coupling per unit length between two dielectic waveguides with asymmetrical cross sections. Theoretical methods for computing frequency responses of such couplers are discussed. It is shown how the phase response can be simply compensated to give approximately symmetrical-coupler-type or "magic tee" coupler-type phase-difference responses over comparable bandwidths. Experimental results confirming theoretical calculations are presented.

Improved X-Band FM Discriminator (Short Paper)

The technique of coherent carrier-addition, using injection synchronization of a narrow-band Gunn oscillator, for improving the performance of an X-band frequency discriminator has been examined in detail. The discriminator is implemented from a single magic tee, two adjustable AM detectors, two sliding shorts, a circulator, an isolator, and a difference amplifier of gain unity. Experimental results are presented in partial support of the conclusions of the analysis. Normal operation of the discriminator in absence of the coherent carrier is also described as a special case of the above analysis.

Electromagnetic Energy and Plasmas: Super Power Klystrons for Fusion Plasma Heating

AbstractFor fusion plasma heating, two types of 2 GHz 1 MW klystrons were developed. They were 6-cavity, frequency-tunable klystrons which could deliver 1 MW continuous output power for 10 s duration. Each klystron has a similar electron gun with a modulation anode, and an evaporation-cooled collector.A prototype klystron was tested for 1 MW performance successfully and a two-window version was also manufactured in order to reduce the thermal stress of the window material. A high-power magic tee was used in order to combine the two power outputs and to produce more than the 1 MW power output. The window temperature was observed to rise, with light emission. The measured temperature rise was about 16°C at the end of 10 s duration, when the klystron was operated at the power level of 500 kW per window.An external digital computer was used to control the high-speed tuning mechanism several times during every one pulse operation.

Breakdown and Resonance Behaviour of the SRS Waveguide

During the early running of the SRS storage ring the energy was limited to 1.8 GeV because of unexpected electrical breakdown in the waveguide-cavity system. This occurred at roughly 120 kW, half the rated power of the klystron. High power tests showed an unacceptably large amount of third harmonic generated by the klystron, which was found to be produced by a faulty component in the feeder system. Low power investigations indicated that the waveguide-cavity system had a rich resonance spectrum, which could be tuned by changes to any of the movable system components. With the system as initially set, one particular mode could be readily tuned to the third harmonic frequency. The faulty component was replaced and the waveguide system rearranged. With these changes and with the system adjusted to avoid any third harmonic modes, the rf system was immediately able to operate at full power. The SRS has since operated consistently at its design energy of 2 GeV with no rf trips from these effects. The low power tests also revealed that the magic tees only provide good isolation at the 500 MHz operating frequency; the waveguide system thus forms a feedback loop at higher order mode frequencies withmore » the circulating beam and the cavities. This may explain some of the beam instabilities observed in the SRS. This paper delineates the waveguide layout, the parameters of the high and low power tests, and the test results which led to the foregoing conclusions.« less

Balanced cavity scheme for saturation transfer dispersion electron paramagnetic resonance

Dispersion electron paramagnetic resonance (EPR) suffers from high AM noise levels due to discrimination of FM noise from the klystron by the high Q cavity. If the EPR cavity is placed in one arm of a magic tee, and a similar cavity in the other arm, then this noise can be removed by arranging the two (correlated) noise components to cancel. Signal-to-noise ratio improvements of a factor of 40 are easily attainable. Only minor modifications to commercial instruments are required.

Measurement of symmetrical waveguide discontinuities using the eigenvalue approach

The behaviour of symmetrical 2-port networks is usually described in terms of their scattering, impedance or admittance matrices. Since the entries of these matrices are linear combinations of their eigenvalues the latter quantities provide an alternative description of network parameters provided they can be readily measured. In the case of symmetrical 2-port networks the eigenvectors necessary to establish the eigenvalues at any port correspond to either in-phase or out-of-phase signals at each port. One simple eigenvalue test set is a magic tee with the network under test connected between the symmetrical H-plane ports and a single input at either the H-or E-plane ports. The paper includes some experimental results obtained on simple inductive posts, a capacitive iris and inclined resonant slots.

Actively controlled SAW power divider

The operation and construction of a new actively controlled SAW power divider is presented. The amount of power delivered to either of two outputs can be controlled with a voltage less than +30 V. The two essential components of this device are a SAW magic tee fabricated on yz LiNbO3 and an acoustoelectric phase shifter which uses silicon air-gap coupled to the LiNbO3.

The Analysis and Design of Broad-Band Fractional Efficiency Multistrip Couplers

Abstrocr-By extending a field theoretical model originally developed by Maerfeld and Tournois, a general theory has been developed which is applicable to surface acoustic wave (SAW) multistrip coupler (MSC) components of arbitrary geometrical and material characteristics. When applied to MSC components requiring fractional transfer efficiency, especially the -3dB coupler, it was found that the response characteristics of the MSC could be conveniently modified by varying the strip spacings in each track of the coupler. Specifically, fractional efficiency couplers with broad symmetrical passbands were designed and demonstrated. A nonideal phase characteristic was observed when the broadband MSC geometries were employed. However, the general theory was used to explain the phase characteristic, and it was found to be compensatable by incorporating an offset to cancel the observed delay. The approach was used successfully to demonstrate a SAW 90” hybrid junction, a nonreflecting tapped delay line, and a echo trap. It was also shown though not demonstrated that the SAW reflector and reflecting track changer will benefit using the approach. However, because of the requirement for a frequencydependent phase offset, no significant bandwidth advantage results when the technique is applied to the acoustic unidirectional transducer or magic tee.

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

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.

Tapered Asymmetric Microstrip Magic Tee (Short Papers)

The design, development, and construction of a very compact decade-(1-10-GHz) bandwidth microstrip --8.34-dB coupler are described. Calculations are given for the voltage coupling coefficient and the low-frequency cutoff, and the method of determing the physical dimensions of the circuit is described. Also, the feasibility of a decade-bandwidth microstrip magic tee by cascading two -- 8.34-dB couplers is demonstrated by comparing the actual and theoretical results of a coupler.

Microwave Measurement of Complex Dielectric Constant of Semiconductor using Partially Loaded Waveguide

A comparison method is presented for measurement of dielectric constant of semiconductor at microwave frequencies. The semiconductor sample partially loads one of the waveguide channels. The transmission through the above channel is compared with another similar but unloaded waveguide channel using magic tee. The propagation coefficient in semiconductor loaded waveguide is related to complex dielectric constant of semiconductor sample using a variational integral. Some curves are presented to obtain value of dielectric constant graphically at X-band frequencies. Finally, some experimental and theoretical results are compared.

A matched termination for use with a switched Q-band radiometer

A compact Q-band magic tee with matched loads built into the main arms has been used to check the noise performance of a two-input switched radiometer. The output temperature changes from the magic tee are well below the rms noise of the radiometer.

Comment on "Tapered transmission line computer program using Collin's derivation"

Impedance versus distance data are provided on a -8.34 dB tapered coupler suitable for use in a broad-band -3 dB magic tee, correcting data previously presented by Fuchs.