Compact Antenna with Novel High Impedance Amplifier-diversity Module for Common Integration into Narrow Dielectric Parts of a Car’s Skin

In vehicles such as e.g. cabriolets, some parts of the skin are made of plastics e.g. the trunk lid. This makes the integration of antennas into these relatively narrow integration volumes possible. Since the radiation characteristics of a single antenna are restricted by a variety of boundary conditions in such a narrow environment, the overall directional characteristics of the antenna part can be optimised by using several of such very compact antenna elements and applying an antenna diversity system. It can be shown that the reception of such an integrated antenna diversity system leads to an excellent quality of reception, which is much higher than the one of a single mast antenna on the vehicle. Such compact diversity antennas in this narrow environment are possible due to an advanced concept of high impedance amplifiers which leads to a satisfying effective antenna height even for relatively narrow antenna structures. In this concept a good reception quality is achieved with selectable frequency dependence, which is nearly independent of the frequency dependence of the effective length and impedance of the antenna structure while a high noisesensitivity and a high linearity are ensured at the same time. A powerful automatic gain control of the active antenna is implemented as well, in order to prevent nonlinear effects. As antenna elements for mobile FMand TV-reception we use a novel ring structure made of copper wire, which is laid along the edges of the trunk lid in close proximity to the metal frame around the plastic trunk lid. The antenna is excited by an electric field which is concentrated at the edges of the metal frame as well as a magnetic field which occurs due to the edge currents along the metal frame around the plastic trunk lid. Since the antenna structure is only placed along the boundary of the dielectric trunk lid, there is space left inside the given area for the additional implementation of further antenna structures as for example for AM, SDARS, GSM and remote control services. In order to generate four independent FM-signals from antenna structures in a commonly very narrow volume of integration for the antenna diversity, two switching elements are inserted into the ring structure, acting as electronically controllable impedance networks. These circuit elements are used to separate the ring structure in the FM-band for the generation of the four diversity antenna signals and additionally to separate the FMand TV-frequency bands. In the amplifier module of the antenna system, which also contains the integrated FM-diversity processor, the ends of the ring structure are connected to high impedance FM-amplifiers. This antenna system yields a simultaneous diversity function for FM and TV at the same time without mutual interference from the FM band to the TV band and vice versa, which normally can be caused by switching activities. In the paper the novel integrated antenna system is presented and its reception quality is evaluated in comparison to the reception quality of state-of-the-art antenna concepts.