EDGE-GUIDE MODE DIRECTIONAL COUPLER

Publishing Venue

Motorola

Related People

Abstract

Microstrip directional couplers are inherently directivity limited due to the dissimilarity of the even-mode and odd- mode impedances. The impedance variation results in unequal forward and reverse propagation velocities which leads to incomplete cancellation of energy in the reverse direction. In many instances the limitation in directivity is uacceptable and complex structures (multiple dielectric laminations) are used to offset the impedance variations.

0 M

MOTVROLA Technical Developments Volume 10 March 1990

EDGE-GUIDE MODE DIRECTIONAL COUPLER

by Robert C. Kane and Peter Nanni

   Microstrip directional couplers are inherently directivity limited due to the dissimilarity of the even-mode and odd- mode impedances. The impedance variation results in unequal forward and reverse propagation velocities which leads to incomplete cancellation of energy in the reverse direction. In many instances the limitation in directivity is uacceptable and complex structures (multiple dielectric laminations) are used to offset the impedance variations.

   An alternative to prior methods of directivity enhancement is the Edge-Guide Mode Directional Coupler. The Edge- Guide Mode Directional Coupler is implemented in microstrip as with the prior art with one notable variation. The transmis- sion line pattern is deposited on ferrite substrate rather than commonly used substrate wherein A =p ,,,

   With the pattern constructed on ferrite substrate and with a suitable biasing magnetic field applied, the energy propagating along the transmission line will be shunted to one edge of the upper conductor as shown in the accompany- ing illustration. The shifting effect is attributed to the dipole rotation in the ferrite substrate and is predicted analytically as the zeroeth mode. In a like manner, any reflected energy is shifted to the opposite edge of the upper conductor. If the upper conductor is wide enough, the two oppositely travelling components...