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A LOW COST MILLIMETER WAVE PHASE SHIFTER USING DIELECTRIC INSERTS

IP.com Disclosure Number: IPCOM000009492D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-28
Document File: 5 page(s) / 206K

Publishing Venue

Motorola

Related People

Kenneth V. Buer: AUTHOR [+3]

Abstract

In the design of high power solid state microwave amplifiers one common way of achiev- ing higher power is to power combine multiple power amplifier devices. If the RF power from sep- arate solid state power amplifiers is summed in phase, the resulting output power is additive. However, if there is a phase difference in the RF waveform at the amplifier output (which can result from manufacturing tolerances, changes in device parasitics etc.) the resulting output power will be less than the combined total of the individual ampli- fier output powers.

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Developments Technical 0 M MO'IYIROLA

A LOW COST MILLIMETER WAVE PHASE SHIFTER USING DIELECTRIC INSERTS

by Kenneth V. Buer, Dean L. Cook and Charles E. Woods

  In the design of high power solid state microwave amplifiers one common way of achiev- ing higher power is to power combine multiple power amplifier devices. If the RF power from sep- arate solid state power amplifiers is summed in phase, the resulting output power is additive. However, if there is a phase difference in the RF waveform at the amplifier output (which can result from manufacturing tolerances, changes in device parasitics etc.) the resulting output power will be less than the combined total of the individual ampli- fier output powers.

  The reduction in total output power is referred to as combining phase loss. At millimeter wave fre- quencies, the tolerances become much tighter, and any variation in assembly of amplifiers results in substantial combining phase loss.

  To help to reduce the amount of combining phase loss at millimeter wave frequencies to an acceptable level (typically less than 0.1 dB), the individual amplifiers are preferably phase aligned to within about 17 degrees of each other. This could be accomplished through RF tuning, which is a time consuming and expensive assembly operation. The phase alignment could also be accomplished with MMIC or diode based phase shifters, but that adds an expensive component to the design.

  This paper outlines a novel method and appara- tus for achieving acceptable phase alignment in high power amplifier modules without added cost, time and complexity.

  Figure 1 shows a conceptual drawing of a dielectric insert placed over a microstrip line.

Fig. 1 Dielectric Insert Phase Shifter

0 Motomla, 1°C. ,999 162 September 1999

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MOTOROLA Technical Developments

  A predetermined size block of low loss dielec- around the microstrip line where the dielectric is tric is used. The block of dielectric material removed. This causes less of the electric field to changes the effective dielectric constant of the reside in the dielectric which results in less dielec- microstrip line causing an increase in the phase tric mismatch. This alternative embodiment reduces length of the segment of microstrip under the dielec- the phase change per unit distance, resulting in a tric To prevent substantial VSWR degradation, the VSWR versus size trade-off. Since the dielectric dielectric material has a dielectric constant, which is bricks can be molded, stamped or otherwise cheaply preferably equal to or less than the dielectric con- fabricated plastic components, it is also easy to taper stant of the microstrip substrate. To further improve the shape and size of the dielectric block resulti...