Compound dielectric multi-conductor transmission line

Claim 1

An electromagnetic wave transmission line comprising: (a) a dielectric substrate layer of permittivity ε s , and having first and second parallel surfaces; (b) a conducting coating on said substrate layer second surface; (c) a dielectric guiding slab layer of permittivity ε g , where ε g >ε s , having first and second parallel surfaces of a predetermined dimension, said guiding slab layer having its second surface attached to said substrate layer first surface; (d) an elongated dielectric strip of permittivity ε 1 where ε g >ε 1 , having first and second parallel surfaces which are substantially narrower than said predetermined dimension, said dielectric strip having its second surface contiguous to said first surface of said guiding slab layer, the elongated dimension of said dielectric strip defining the electromagnetic wave direction of transmission; and (e) a conducting coating on said dielectric strip first surface, whereby single mode propagation is permitted over a relatively wide band and propagation of undesired modes in said substrate layer is suppressed and the characteristic impedance varies relatively little over a wide frequency range.