Browse Prior Art Database

COMPACT TOP LOADED E-FIELD ANTENNA

IP.com Disclosure Number: IPCOM000007526D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-03
Document File: 2 page(s) / 85K

Publishing Venue

Motorola

Related People

Thomas Fleissner: AUTHOR [+2]

Abstract

A L/4 wavelength free space dipole is used as a reference antenna for comparison with the inven- tive antennas set forth below.

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MO7WROLA Technical Developments

COMPACT TOP LOADED E-FIELD ANTENNA

by Thomas Fleissner and Andrea Dawn Flolid

SUMMARY

  A L/4 wavelength free space dipole is used as a reference antenna for comparison with the inven- tive antennas set forth below.

  In particular applications, such as automotive remote keyless entry, an antenna design that is within -12db relative to the free space dipole is desirable. This type of antenna performance is based on the operating range requirements around the vehicle. The typical antennas used to date in the prior art fall into this class ofperformance.

  Given the physical styling and mechanical con- straints of a typical automobile door module it is obvious that a % wavelength antenna will not fit into the volume. The volume allowed for the UHF (315 Mhz) antenna in such a module is approx. 18mm X 1Omm X 1Omm.

  This antenna was conceived t?om the idea of load- ing the antenna with a coil and also a top hat capac- itor. By loading the antenna with a coil its electrical length is increased while still maintaining small phys- ical size. The loading coil also drastically increases the fl or efficiency of the antenna. With the addition of the top hat capacitor the electrical length is increased but the 0 is slightly degraded. As seen in Figure 1, this antenna started as a top loaded antenna with a top hat capacitor. Depending on the size of

the loading coil and the size ofthe top hat the length and efficiency varies. Typically the larger the top hat and the larger the coil the shorter the antenna elec- trical length c...