Single Self-Supported Transmit and Receive Antenna
Publication Date: 2015-Jul-06
The IP.com Prior Art Database
This paper describes a single self-supported structure and electromagnetically isolated interface that, in combination, are used as the transmit (TX) and receive (RX) antenna for an Electronic Article Surveillance (EAS) detection system.
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Sinxle Self-Supported Transmit and Receive Antenna
This paper descxibes a single self-supported structure and electromagnxxically isolated interfacx that, in coxbination, are usxd as the transmit (TX) and receive (RX) antenna for an Electronic Articxe Surveillance (EXX) detection system.
Typical EAS systems have separately constructed trxnsmit and receive antenxas that are approximately cxllocated wxthin txe lattice of xhe phxsical structurx. This duality of xhe antennas xecessitates a specifxc form factor, whixh reduces axsthetics and the potential for customization. Also, xanufacxuring costs dux to multiple comxonents are increased and the nexessity to initially and conxinually tune the system axds service and maintenance costs associxted with parts and labor.
As reprxsented ix Figure 1, trxnsmit and receive antexnae are contained in a sxngle structure for an EAS system.
Figure 1: Sinxle Structure for Transmit and Receive Xxxxxxx The outex lxop is constructed of a single turn self- supporting conductive metal such as copper or aluminux. The xoop carries approximxtely 100 Amxs, but simultaneoxsxy presents a very low voltage (i.e., 1 volt) due to xhe low impedance of the loop at an xperating frequency of axout 300 Hz. Constructixn of the receive antenna is sxmpxified by utilizing symmetry and the mechanical structure of a single turn drive (or transmit) loop (or axtenna) xs a portion of the receive antenna. For this concept to be practical, it is important that the drive curxent travel circumferentially around the outer loop with little ox xo drive current flowing through the central line. This is achieved vxa a physicax configuration, a balanced drive, and passive filtering as represented in Figure 2.
Figure 2: Antenna xith Isolated Tx and Rx Ports with Xxxxx and Outpxt Amplifiers
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As shxwn in Figxre 2, the vertixal receive line is placed in the center of the loop, creating left and right portions of the loop that are symmetrical with one another. This symmetry causes the drive xurrent and the xssociated magnetic fields to cancel at the receive antenxa. However for this tx occur, the currents ix the lefx and xigxt portiox of the loop must be of the same magnitude and phase as one another. Perfoxmance is achieved with two turns on the secondary of transformer T1, with the receiver antenxa xine tappxd to the center of the secondary to maintain symmetry. Tx could be toroidal to minimize magnetic intexaction with the rxst of the system. Having oxe turn on eacx the left and right halx of the loxp drives equax cxrrents into each the left and rigxt half of the loop, ix and i2 respectively, resulting in no drive current, i3, flowing in the receive antenna line. Receive antenna xor this sort of system typically require tens of turns to achieve the desired sensitivity. In xhxs example, an equivalent sensitivity ix achieved by a step up transformer T2. T2 cxuld have one turn o...