Mobile antenna and through-the-glass impedance matched feed system

A through-the-glass feed system for a mobile antenna comprising:

• first and second inside conducting plate means, spaced apart from one another and affixed to an inside surface of the glass, and first and second outside conducting plate means, spaced apart from one another and affixed to an outside surface of the glass opposite the corresponding first and second inside plate means, for coupling radio frequency energy through the glass;
• coaxial feed means coupled to the inside plate means for coupling radio frequency energy to the inside plate means;
• antenna coupling means for coupling the antenna to both of the outside plate means;
• and
• matching means interposed between the coaxial feed means and the antenna for applying to the coaxial feed means from the antenna a substantially purely resistive impedance that substantially matches an impedance of the coaxial feed means.

A windshield-mounted antenna system comprising:

• antenna means for transmitting or receiving radio frequency energy;
• first and second inside conducting plate means adjacent an inside surface area of the windshield and spaced apart from one another, and first and second outside conducting plate means, spaced apart from one another and adjacent an outside surface area of the windshield opposite the corresponding inside surface area, for capacitively coupling radio frequency energy through the windshield at a low impedance;
• coaxial feed means for coupling radio frequency energy to or from the inside conducting plate means, an end of the coaxial feed means terminating adjacent the inside conducting plate means, a center conductor of said feed means being coupled to the first inside plate means and a shield conductor of said feed means being coupled to the second inside plate means;
• matching means for causing the magnitude of the radio frequency voltage across the outside plate means to substantially match the magnitude of the radio frequency voltage across the center conductor and shield conductor of the coaxial feed means, the matching means having two inputs, each connected to a different one of said outside plate means and further having one output coupled to both of the inputs and isolated from at least one of said outside plate means by a reactance;
• and
• antenna mounting means for isolating the antenna means from at least one of the first and second outside plate means, connecting the antenna means to the output of the matching means and mounting the antenna means outside and spaced apart from the windshield.

A feed system for coupling radio frequency energy through an insulator to and from an antenna having a characteristic antenna impedance, comprising:

• first and second inside conducting plate means, spaced apart from one another and affixed to an inside surface area of the insulator, and first and second outside conducting plate means, spaced apart from one another and affixed to an outside surface area of the insulator opposite the inside surface area, for coupling radio frequency energy through the insulator;
• two conductor transmission line means for coupling radio frequency energy to and from the inside conducting plate means, a first conductor of said transmission line means being coupled to the first inside plate means and a second conductor of said transmission line means being coupled to the second inside plate means, the transmission line means having a predetermined characteristic impedance;
• and
• external matching means, having inputs connected to the first and second outside plate means and having an output for connection to the antenna, for presenting across the inside plate means at a frequency of interest a substantially purely resistive impedance approximately equal to said transmission line means characteristic impedance;
• and
• antenna coupled means for connecting the antenna to the output of the matching means.

A windshield-mounted antenna system comprising:

• first and second inside conducting plate means adjacent an inside surface area of the windshield and spaced apart from one another, and first and second outside conducting plate means adjacent an outside surface area of the windshield opposite the inside surface area, the first inside and outside plate means forming a first coupling capacitor and the second inside and outside plate means forming a second coupling capacitor, for capactively coupling radio frequency energy through the windshield;
• two conductor transmission line means for coupling radio frequency energy to and from the inside conducting plate means, a first conductor of said transmission line means being coupled to the first inside plate means and a second conductor of said transmission line means being coupled to the second inside plate means, the two conductor transmission line means having a characteristic impedance;
• and
• antenna means for transmitting and receiving radio frequency energy and for coupling the radio frequency energy to and from the first and second outside conducting plate means, the antenna means including an antenna element and further including inductive means having an inductive reactance for cancelling the capacitive reactance introduced by the coupling capacitors, thereby to provide a resistive impedance across said inside conducting plate means that substantially matches the characteristic impedance of the transmission line means.

A moisture-insensitive method of coupling radio frequency energy from a two conductor transmission line having a characteristic impedance to an antenna through an insulator, comprising the steps:

• mounting first and second conducting plates adjacent an inside surface area of the insulator;
• spacing the second conducting plate apart from the first conducting plate;
• coupling a first conductor of the transmission line to the first conducting plate;
• coupling a second conductor of the transmission line to the second conducting plate;
• mounting third and fourth conducting plates adjacent an outside surface area of the insulator opposite said inside surface area;
• capacitively coupling the radio frequency energy through the insulator from the first and second plates to the third and fourth plates, respectively;
• providing a matching circuit having inputs connected to the third and fourth plates and having an output connected to the antenna, so as to present, across the first and second plates, a substantially purely resistive impedance which matches the characteristic impedance of the transmission line.

A method of coupling an unbalanced coaxial feed line through a windshield and driving an unbalanced antenna therefrom comprising the steps:

• connecting a center conductor of the feed line to an inside "hot" conducting plate mounted on an inside surface of the windshield;
• connecting a shield conductor of the feed line to an inside "common" conducting plate mounted on the inside surface of the windshield and spaced apart from the inside "hot" plate;
• capacitively coupling the inside "hot" and "common" conducting plates to outside "hot" and "common" conducting plates mounted on an outside surface of the windshield opposite said inside "hot" and "common" plates respectively;
• connecting an "L" network of reactive components across the outside "hot" and "common" plates;
• and
• driving the unbalanced antenna from an output of the "L" network between the outside "hot" and "common" plates.