Ehab A. Etellisi

Wideband Monostatic Simultaneous Transmit and Receive (STAR) Antenna

A monostatic ultra-wideband simultaneous transmit and receive (STAR) antenna subsystem is introduced. An inherent geometrical symmetry of a four-arm spiral antenna and feeding rearrangement are exploited to achieve the simultaneous transmit (TX) and receive (RX) functionalities without any time, polarization, or frequency multiplexing. The antenna is configured such that one arm-pair is used for TX and the other for RX. Thus, even though the two antennas are spatially separated by 90°, they still share the same aperture and the system is considered monostatic. Theoretical and computational studies are conducted to demonstrate the feasibility of the proposed approach under ideal conditions as well as in the presence of feed network non-idealities. The experimental data indicate that isolation levels greater than 39.6-50 dB over multiple octaves are achievable with realistic components. To improve the TX and RX far-field patterns, the planar four-arm spiral aperture is grounded via resistor-loaded quadrifilar helix with the two-arm TX/two-arm RX feed arrangement preserved. Furthermore, to simplify the feed network and reduce the impact of hybrid imbalances, an impedance-transforming microstrip feed is integrated with each arm pair. Isolation > 37 dB and similar with high-quality measured and simulated TX/RX radiation patterns are obtained over the operating bandwidth.

Wideband simultaneous transmit and receive (STAR) bi-layer circular array

The main challenge with the full-duplex simultaneous transmit and receive (STAR) systems is achieving high isolation over a wide bandwidth while preserving identical (or similar) radiation patterns in both, the transmitting and receiving modes. In this paper, a novel low profile wideband bi-layer STAR circular array configuration is presented. The two layers, one for transmit and the other for receive, are identical and composed of four antenna elements. The proposed approach is based on exciting TX/RX layers with the circular mode 1 phase progression while applying a phase difference between the two layers. Virtually identical radiation patterns and TX/RX isolation >50dB over the wide bandwidth is demonstrated.

On wideband simultaneous transmit and receive (STAR) with a single aperture

Multi-arm spiral antennas have not only ability to radiate multiple frequency independent modes [1,2], but also inherent ability to act as monostatic co-channel simultaneous transmit and receive (STAR) apertures. Four-arm spirals are herein used for demonstrating this capability.

Ultra-wideband circularly-polarized simultaneous transmit and receive (STAR) antenna system

This paper presents a novel circularly-polarized simultaneous transmit and receive (STAR) monostatic antenna system based on the four-arm spiral-helix antenna. The four-arm spiral is configured such that two arms are used for transmitting and the other two arms for receiving. Microstrip feeds with impedance transformers are used to feed the two two-arm spirals and thus eliminate the need for 180° hybrids. Helix termination is used to improve the low-end performance. The symmetric features of the spiral antenna along with the arms orientation and the applied excitation enable a high isolation between the transmitting (TX) and receiving (RX) ports. Isolation>36dB is measured over >8:1 bandwidth. Symmetric and consistent TX/RX radiation patterns are obtained over the operating bandwidth.

Single and dual-polarized wideband simultaneous transmit and receive antenna system

A shared antenna aperture for simultaneous transmit and receive (STAR) operating from 0.5 to 45GHz with isolation >50dB over the entire band is discussed. The proposed system utilizes four distinct band breaks: 0.5–2.5GHz, 2–7GHz, 619GHz, and 18–45GHz. The transmitting and receiving apertures of each band are designed, fabricated, and integrated on 46cm×46cm ground plane. A monostatic STAR system based on a lens-loaded cavity-backed four-arm spiral antenna is used to cover 0.5–2.5GHz band requirements. Other bands have dual-polarization capability and rely on physically displaced TX and RX antennas, engineered antenna patterns, and implementation of high impedance surfaces (i.e. bed of nails) to achieve desired isolation level. A dual-polarized Vivaldi array recessed in a cavity and quad-ridge horns are employed for the 2–7GHz and 6–45GHz bands; respectively.

Wideband dual-mode monostatic simultaneous transmit and receive antenna system

A novel wideband monostatic simultaneous transmit and receive (STAR) antenna system based on eight-arm equiangular spiral aperture is proposed. The eight-arm STAR spiral is configured such that four arms are used for transmitting and the other four arms for receiving. The multi-mode characteristics of the four-arm spiral aperture along with applied excitation enable high TX/RX isolation for diverse circular-polarization modes of radiation (i.e. broadside and split-beam modes). The operational principles of the proposed system are discussed and the feasibility thereof is demonstrated computationally and experimentally. System isolation >40dB is obtained over 8:1 bandwidth for different modes of operation while maintaining similar high-quality TX/RX radiation characteristics.

Wideband monostatic spiral array for full-duplex applications

A novel co-polarized wideband monostatic antenna array for full-duplex or simultaneous transmit and receive (FD/STAR) applications is proposed. The developed approach incorporates antenna elements orientation and beam-forming network (BFN) to theoretically eliminate the interference from the TX to RX. The array is composed of four dual function TX/RX balun-fed two-arm Archimedean spiral antennas. Measured isolation with the RF enhancement layer of 40dB-60dB, VSWR<2, and TX BFN power loss <10% are achieved over 2:1 bandwidth. Good correlation between the TX and RX co-polarized radiation patterns is also demonstrated.

Wideband Multimode Monostatic Spiral Antenna STAR Subsystem

A wideband, multimode, and monostatic simultaneous transmit and receive (STAR) antenna subsystem is proposed. The configuration is composed of a single four-arm spiral and two analog circuit layers designed to maximize isolation between the transmitting (TX) and receiving (RX) channels. The first layer consists of two Butler matrix beamformer networks (BFNs); one for each TX and RX. The second layer integrates four, ideally phase-matched, circulators between the spiral arms and the BFNs. Theoretically, this configuration achieves infinite isolation irrespective of circulator’s quality. However, the BFN imbalances and the dissimilarities between the four circulators degrade the overall isolation. The operational principles are discussed under the ideal conditions and in the presence of circuit imperfections. For a four-arm spiral, the utilized BFN provides orthogonal modes 1, −1, 2, and 3, allowing STAR capability with multimode and diverse radiation patterns. The subsystem isolation and far-field performances are characterized experimentally and computationally for different modes of operation. A simple approach to achieve a dual-polarized STAR operation over narrower bandwidth with the proposed subsystem is also discussed. The multimode subsystem is demonstrated over 4:1 bandwidth with high isolation, VSWR < 2, consistent patterns, axial ratio < 3 dB over a wide field of view for the broadside modes (1, −1) and < 4.2 dB for other conical modes (2, 3).