Interlayer Stripline Transition

NASA's Jet Propulsion Laboratory, Pasadena, California

A proposed multilayer metal-film/dielectric-plate laminate would serve as a passive radio-frequency (RF) interlayer stripline transition. This device is designed to provide RF coupling from (a) an input transmission line of the stripline type spanning the first through third metal layers, with characteristic impedance Z_0s to (b) an intermediate transmission line of the parallel-line type spanning the first through fifth metal layers, with characteristic impedance Z_0p ≈ Z_0sto (c) an output transmission line of the stripline type spanning the third through fifth metal layers, with characteristic impedance Z_0s.

Figure 1. The Absence of Through-the-Thickness Interconnections eases fabrication. Interlayer coupling is achieved solely via the interlayer electromagnetic field.

The main advantage of this device lies in its purely planar geometry. Generally, interlayer stripline coupling is achieved by use of vertical probes; that is, through-the-thickness electrical interconnections, which contribute to difficulty of fabrication. The present design provides for RF coupling via the interlayer electromagnetic field, eliminating the need for vertical probes and thereby easing fabrication.

Figure 2. Return and Insertion Losses vs. frequency were calculated by a finite-difference time-domain method for the design described in the text.

The basic configuration of the device is illustrated in Figure 1. All of the dielectric layers (not shown) between the metal layers are assumed to be of equal thickness h and equal relative permittivity ε_r. The quarter-wavelength slots in the input and output regions of layer 3 suppress undesired components of interlayer propagation in those regions. Specific dimensions can be altered somewhat (for example, slot lengths can be made to differ slightly from a quarter wavelength) to suit specific applications, without deviating from the overall design concept.

A trial design for an operating frequency of about 1 GHz specifies the following parameters:

h = 0.125 in. = 3.175 mm
ω_s= 7 mm
ω_p= 15 mm
L = 60 mm
t = 15 mm
ε_r= 1.1
Z_0s= 61 Ω
Z_0p= 60 Ω

Figure 2 shows return and insertion losses calculated for this design.

This work was done by Ann N. Tulintseff of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Systems category. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to