STATEMENT REGARDING FEDERAL FUNDING

None.

TECHNICAL FIELD

This disclosure relates to antennas and reducing interference from a transmitting antenna to a receiving antenna.

BACKGROUND

Simultaneous transmit and receive (STAR) systems often require high levels of isolation, for example 140+ dB in electronic warfare (EW) applications. In the prior art, the bulk of the isolation is achieved through a combination of notch filters, backend digital filtering, and active cancellation circuitry. The coupling pathways between the transmit (Tx) and receive (Rx) apertures, as shown inFIG. 1A, are often unmitigated and require the apertures to be placed far apart from each other in order to meet the required overall system isolation requirements. The filtering electronics and cancellation circuitry are fairly compact; therefore, the overall compactness of STAR systems is often limited by distance between Tx and Rx antennas which must be spaced sufficiently far apart to generate the needed, isolation beyond that provided by the electronics. Shrinking these systems would ease their deployment on compact platforms such as UAVs and decoys.

A transmitter/jammer can interfere with receivers on the same platform through two main pathways: coupling through free-space propagation including multi-path effects, and surface coupling or “skin effects. While there are operational techniques that can be used to distinguish jamming signals from received signals, such as by using frequency management, where the receiver performs its search function in bands that are not being jammed, physically increasing the isolation between these signals enables more flexibility in system design and reduces the burden on the signal processing/filtering electronics.

In the prior art, physical isolation is achieved by placing metallic chokes, radar absorbing material, or electromagnetic band-gap (EBG) structures, or simply space, between the antennas. These account for about 15-20 dB of isolation, necessitating expensive cutting-edge electronics to handle the rest of the needed isolation.

Traditional EBG structures are narrowband and only affect the surface component of interference. Besides only affecting the surface component, MAGRAM is heavy and its effectiveness degrades at low frequencies (below 2 GHz). Prior art metallic chokes are essentially metal walls that are placed between the Tx and Rx antennas to prevent them from “seeing” each other. The metallic chokes are simple to fabricate but do not create deep isolation. Furthermore, radiating currents on the metallic choke walls produce parasitic interference and can affect coupling and modify the pattern of the original antennas.

Electromagnetic band-gap (EBG) structures are described by D. Sievenpiper, Lijun Zhang, R. F. J. Broas, N. G. Alexopolous and E. Yablonovitch, in “High-impedance electromagnetic surfaces with a forbidden frequency band,” in IEEE Transactions on Microwave Theory and Techniques, vol. 47, no. 11, pp. 2059-2074, November 1999, which showed that a propagation stop-band can be created by using metal patches on a grounded substrate with vias.

Metamaterial structures for isolation are described by M. Agarwal and M. K. Meshram, “Isolation improvement of 5 GHz WLAN antenna array using metamaterial absorber,” 2016 URSI Asia-Pacific Radio Science Conference (URSI AP-RASC), Seoul, 2016, pp. 1050-1053. Metamaterial structures are placed between antennas to improve isolation; however, they do not stop free-space coupling.

What is needed is an improved apparatus and method for providing isolation between a transmitter and a receiver. The embodiments of the present disclosure answer these and other needs.

SUMMARY

In a first embodiment disclosed herein, a tunable antenna isolator comprises a first metallic wall, a second metallic wall, and an electromagnetic band-gap (EBG) structure located between the first metallic wall and the second metallic wall.

In another embodiment disclosed herein, a method for providing a tunable antenna isolator comprises providing a first metallic wall, providing a second metallic wall, and providing an electromagnetic band-gap (EBG) structure located between the first metallic wall and the second metallic wall.

In yet another embodiment disclosed herein, a tunable antenna isolator comprises a first electromagnetic band-gap (EBG) structure, a second electromagnetic band-gap (EBG) structure, and a third electromagnetic band-gap (EBG) structure located between the first electromagnetic band-gap (EBG) structure and the second electromagnetic band-gap (EBG) structure.

In still yet another embodiment disclosed herein, a method for providing a tunable antenna isolator comprises providing a first electromagnetic band-gap (EBG) structure, providing a second electromagnetic band-gap (EBG) structure, and providing a third electromagnetic band-gap (EBG) structure located between the first electromagnetic band-gap (EBG) structure and the second electromagnetic band-gap (EBG) structure.

These and other features and advantages will become further apparent from the detailed description and accompanying figures that follow. In the figures and description, numerals indicate the various features, like numerals referring to like features throughout both the drawings and the description.

