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DESIGN IMPROVEMENTS FOR AN ECCOSORB BASED MICROSTRIP ATTENUATOR

IP.com Disclosure Number: IPCOM000009422D
Original Publication Date: 1999-Sep-01
Included in the Prior Art Database: 2002-Aug-22
Document File: 2 page(s) / 102K

Publishing Venue

Motorola

Related People

Kenneth V. Buer: AUTHOR [+4]

Abstract

A millimeter wave attenuator consisting of a CRS-124 insert positioned directly over a microstrip line has been shown to provide broadband pre- dictable and consistent attenuation values. This configuration is shown in Figure 1. This paper describes design improvements which make the attenuator more practical for use in millimeter wave circuits.

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Developnwus Technical 0 M MOTOROLA

DESIGN IMPROVEMENTS FOR AN ECCOSORB BASED MICROSTRIP ATTENUATOR

by Kenneth V. Buer, Dean L. Cook, Phil Denisuk and John "Marty" Pietz

  A millimeter wave attenuator consisting of a CRS-124 insert positioned directly over a microstrip line has been shown to provide broadband pre- dictable and consistent attenuation values. This configuration is shown in Figure 1. This paper describes design improvements which make the attenuator more practical for use in millimeter wave circuits.

Fig. 1 Previous Attenuator Configuration

  The first problem with the configuration shown in Figure 1 is that of dielectric mismatch causing poor VSWR. Since the dielectric constant of CRS- 124 is high, &r=22, when inserts are used in this fashion, the dielectric loading of the insert causes an impedance change on the microstrip line which leads to poor VSWR. In experiments with 50 ohm micmstrip on Rogers Duroid 6002 substrate material (&r=2.94), the dielectric mismatch of the insert caused the return loss to degrade to less than 1OdB at Ka-band frequencies. The dialectric mismatch is much less severe when alumina substrate (Et~9.9) are used, but return loss was still found to degrade to less than 17dB. These poor return loss results are unacceptable for many broadband applications because of the substantial passband ripple introduced when poor VSWR interfaces are interconnected.

  Another problem solved by these design improvements is the need to more accurately control the attenuation value for a given insert. Since the insert is very lossy in the attenuator configuration, small changes in size due to manufacturing toler- ances can cause large changes in attenuation.

  Yet a third problem addressed is the ability to fabricate small value attenuator inserts without reducing the overall insert size to something that is unmanageably small. In the previous methods, a small insert (100 mils) caused over 5 dB attenuation at Ka-Band. In many applications it is necessary to control the attenuation in 1 dB or smaller incre- ments, but reducing the size of the insert to ~20 mils is impractical in assembly.

  To impro...