Active integrated antenna with simultaneous transmit and receive

An active antenna with simultaneous transmit and receive function, integrate an active devices onto a printed antenna to improve its performance or combine functions within the antenna itself. Such antenna are of increasing interest, as system designers require more complex functions to be implemented in reduced space. This paper discusses the integration of active antennas by combining both transmit and receive functions into one single antenna. Four main components in the design are circular polarized microstrip patch antenna, rat race coupler, power divider and amplifiers. All the simulations are done using the Agilent ADS. The circular polarized antenna resonates at 2. 4 GHz. Two MESFET amplifiers have been used to transmit and receive the channel separately. The rat race coupler isolates the two channels and a Tee junction power divider is connected the two channels to the input and output port. The channels are of the same frequency. The simulation and measurement results of the microstrip patch antenna for S11 are lower than -10 dB at frequency of 2.4 GHz. The antenna polarization is confirmed as a circular polarized, as can be seen in the radiation pattern from the measured and simulated results. The amplifier biasing circuit is supplied by two power sources; one is the drain voltage (Vds) which is positive and the other is the gate voltage (Vgs), which is negative. After integrating all of the components, the radiation pattern is measured for both transmit and receive. The beamwidth of the antenna is in the range of 60o – 70o for H plane. The radiation pattern for E plane is smaller compared with the H plane. The comparison between the passive and the active integrated antenna shows that the active integrated antenna has 3 dB extra gain compared to the passive antenna for both transmit and receive. The isolation between transmit and receive is between 20 – 25 dB

Novel High Isolation Antennas for Simultaneous Transmit and Receive (STAR) Applications

Radio frequency (RF) spectrum congestion is a major challenge for the growing need of wireless bandwidth. Notably, in 2015, the Federal Communications Commission (FCC) auctioned just 65 MHz (a bandwidth smaller than that used for WiFi) for more than $40 billion, indicating the high value of the microwave spectrum. Current radios use one-half of their bandwidth resource for transmission, and the other half for reception. Therefore, by enabling radios to transmit and receive across their entire bandwidth allocation, spectral efficiency is doubled. Concurrently, data rates for wireless links also double. This technology leads to a new class of radios and RF frontends. Current full-duplex techniques resort to either time- or frequency-division duplexing (TDD and FDD respectively) to partition the transmit and receive functions across time and frequency, respectively, to avoid self-interference. But these approaches do not translate to spectral efficiency. Simultaneous transmit and receive (STAR) radios must isolate the transmitter from the receiver to avoid self-interference (SI). This SI prevents reception and must therefore be cancelled. Self-interference may be cancelled with one or more stages involving the antenna, RF or analog circuits, or digital filters. With this in mind, the antenna stage is the most critical to reduce the SI level and avoid circuit saturation and total system failure. This dissertation presents techniques for achieving STAR radios. The initial sections of the dissertation provide the general approach of stage to stage cancellation to achieve as much as 100 dB isolation between the receiver and transmitter. The subsequent chapters focus on different antennas to achieve strong transmit/receive isolation. As much as 35 dB isolation is shown using a new spiral antenna array with operation across a 2:1 bandwidth. Also, a new antenna feed is presented showing 42 dB isolation across a 250 MHz bandwidth. Reflections in the presence of a dynamic environment are also considered

Aperture-Level Simultaneous Transmit and Receive (STAR) with Digital Phased Arrays

In the signal processing community, it has long been assumed that transmitting and receiving useful signals at the same time in the same frequency band at the same physical location was impossible. A number of insights in antenna design, analog hardware, and digital signal processing have allowed researchers to achieve simultaneous transmit and receive (STAR) capability, sometimes also referred to as in-band full-duplex (IBFD). All STAR systems must mitigate the interference in the receive channel caused by the signals emitted by the system. This poses a significant challenge because of the immense disparity in the power of the transmitted and received signals. As an analogy, imagine a person that wanted to be able to hear a whisper from across the room while screaming at the top of their lungs. The sound of their own voice would completely drown out the whisper. Approaches to increasing the isolation between the transmit and receive channels of a system attempt to successively reduce the magnitude of the transmitted interference at various points in the received signal processing chain. Many researchers believe that STAR cannot be achieved practically without some combination of modified antennas, analog self-interference cancellation hardware, digital adaptive beamforming, and digital self-interference cancellation. The aperture-level simultaneous transmit and receive (ALSTAR) paradigm confronts that assumption by creating isolation between transmit and receive subarrays in a phased array using only digital adaptive transmit and receive beamforming and digital self-interference cancellation. This dissertation explores the boundaries of performance for the ALSTAR architecture both in terms of isolation and in terms of spatial imaging resolution. It also makes significant strides towards practical ALSTAR implementation by determining the performance capabilities and computational costs of an adaptive beamforming and self-interference cancellation implementation inspired by the mathematical structure of the isolation performance limits and designed for real-time operation

PERFORMANCE SIMULATION AND OPTIMIZATION OF A SIMULTANEOUS TRANSMIT AND RECEIVE PHASED ANTENNA ARRAY USING ADAPTIVE BEAMFORMING AND GENETIC ALGORITHM TECHNIQUES

The development of simultaneous transmit and receive capabilities is on the cutting-edge of research in phased array technology [1, 2, 3]. The large disparity in power between the transmitted and received signals in antenna systems has traditionally prevented operation in a simultaneous mode. However, simultaneous transmit and receive offers great opportunities for increased capabilities and performance in communications, radar, and electronic warfare applications [3]. This technology will be made feasible by realizing a high level of isolation between the transmitted and received signals through a variety of techniques. This work explores the feasibility of choosing non-standard array partitions that--when paired with the appropriate beamforming techniques--significantly reduce the self-interference between transmit and receive channels

Techniques for Achieving High Isolation in RF Domain for Simultaneous Transmit and Receive

With the growth of wireless data traffic, additional spectrum is required to meet consumer demands. Consequently, innovative approaches are needed for efficient management of the available limited spectrum. To double the achievable spectral efficiency, a transceiver can be designed to receive and transmit signals simultaneously (STAR) across the same frequency band. However, due to the coupling of the high power transmitted signal into the collocated receiver, the receiver\u27s performance is degraded. For successful STAR realization, the coupled high-power transmit (Tx) signal should be suppressed by 100-120 dB over the entire operational bandwidth. So far, most STAR implementations are narrowband, and not useful for ultra wideband (UWB) communications. In this paper, we present a review of novel approaches employed to achieve improved cancellation across wide bandwidths in RF and propagation domains. Both single and multi-antenna systems are considered. Measurements show an average cancellation of 50 dB using two stages of RF signal cancellation

Lens Based High Directivity Simultaneous Transmit and Receive Systems

Simultaneous transmit and receive (STAR) has the potential to theoretically double the capacity of wireless networks making it a highly desirable technology for modern wireless systems. Self interference (SI) is the chief challenge and high Tx/Rx isolation (greater than 100 dB) is required to mitigate this issue and realize STAR operation. The required isolation level is typically achieved by using a multi-layer cancellation approach across the antenna, analog, and digital domains. A well-designed antenna or propagation layer can provide a significant portion of the SI cancellation (SIC) enabling simplified and more practical transceiver realization. For typical wireless networks and electronic warfare systems, monostatic or shared-aperture STAR antennas are often required to maintain the aperture compactness. At millimeter waves, high directivity and beam steering characteristics are highly desired; particularly for access point and backhaul antennas, to overcome the path loss, achieve the required communication range, and improve the signal-to-noise ratio in dynamic multi-user environments. A co-polarized, co-channel STAR antenna system utilizing a two-layer, spherically stratified lens with nominal directivity of 24.3 dBic is demonstrated in the 27 to 29 GHz frequency band. The STAR operation is achieved with a WR28 waveguide-implemented balanced circulator beam forming network (BC-BFN), which relies on two 90deg hybrids and two circulators along with antenna symmetry to cancel the circulator leakages and achieve theoretically infinite isolation between the transmit and receive ports. The sensitivity of the BC-BFN to alignment and other imperfections is studied. To comply with the BC-BFN's symmetry requirements, a highly symmetric WR28 waveguide ortho-mode transducer (OMT) is developed. Tx/Rx isolation of 30 and 34 dB is measured with and without the lens, respectively, indicating acceptable impact of the lens on system isolation. To demonstrate STAR with the beam steering in an equatorial field of view, the proposed configuration is modified into a mechanically rotated half spherical lens over a ground plane. The experiments show that the isolation of the rotating half-lens system degrades compared to the full-lens counterpart due to the break of the geometrical symmetry. However, respectable isolation greater than 27 dB and high quality circularly polarized radiation patterns are still maintained over the operational bandwidth. Another co-polarized, co-channel, lens-based STAR system based of the same BC-BFN and OMT subsystem but using a compact planar graded index (GRIN) lens is also introduced. The compact lens achieves broadside directivity greater than 24 dBic in the band centered about 28 GHz. The beams are steered by mechanically rotating the proposed compact lens, maintaining the focal point on the antenna's phase center. A maximum scan loss of 4.5 dB is seen in an 80deg conic field of view while preserving system isolation. The measured system maintains 30 dB of isolation with at most 2 dB degradation in isolation at the more severe inclination angles. Finally, closed-form expressions are derived for the component of the radar cross section (RCS) due to the BFN in the context of retrodirective systems. The ability to accurately predict the effect of feedback and infinite reflections is shown with numerical simulations. The derived equations allow calculating the bounds for the maximum loop gain for the system before feedback leads its response into the non-linear domain. The potential of using STAR to improve the performance of retrodirective systems is evaluated with the spherical lens antenna and BC-BFN subsystem. Improvements of 20 dB are obtained when data from the fabricated STAR system is used in the equation and compared to passive lens reflectors.</p

Techniques for Simultaneous Transmit and Receive with All-Digital Arrays

The increased flexibility provided by all-digital array architectures allows for the development of improved techniques toward achieving multi-function capability. In an all-digital array, element-level control can be utilized to create a variety of subarray configurations that can be operated independently to form multiple simultaneous transmit and receive (STAR) beams. This thesis describes how STAR can be implemented on an all-digital array by partitioning the array into subarrays, and details various techniques to improve the STAR performance by increasing the isolation between subarrays. A metric to quantify subarray isolation is provided, which incorporates both transmit/receive gain and the leakage power produced by mutual coupling between subarrays. The strategies used to increase subarray isolation leverage knowledge of the scattering parameters of the array, which describe the mutual coupling between subarrays. By formulating the leakage power between subarrays in terms of the scattering parameters of the array, adaptive beamformers can be designed on both transmit and receive to minimize the incident leakage and increase subarray isolation. Digital cancellation of the leakage signals can be used to further increase subarray isolation, with an estimate of the leakage signal provided by the scattering parameters. The proposed techniques for STAR provide insight into the multi-function capability afforded by all-digital arrays, and may become more sophisticated as the use of all-digital arrays becomes ubiquitous

Simultaneous Transmit and Receive (Star) Antennas for Geo-Satellites and Shared-Antenna Platforms

This thesis presents the analysis, design, and experimental characterization of antenna systems considered for shipborne, airborne, and space platforms. These antennas are innovated to enable Simultaneous Transmit and Receive (STAR) at same time and polarization, either at the same, or duplex frequencies. In airborne and shipborne platforms, developed antenna architectures may enhance the capabilities of modern electronic warfare systems by enabling concurrent electronic attack and electronic support operations. In space, and more precisely at geostationary orbit, designed antennas aim to decrease the complexity of conventional phased array systems, thereby increasing their capabilities and attractiveness. All antennas researched are first designed as a standalone radiator, then as entity of a platform having multiple different antennas.An ultrawideband, lossless cavity-backed Vivaldi antenna array for flush-mounting applications is first investigated. Eigen-mode analysis is used to analyze antenna-cavity interaction and to show that the entire structure may resonate within the band of interest resulting in a significant degradation of antenna performance. A simple approach based on connecting the array’s edge elements in E-plane to the cavity walls is proposed to eliminate the deleterious impact of these cavity resonances. The designed antenna is a 3 × 4 array with 3 elements in E-plane and 4 elements in H-plane, fabricated using stacked all-metal printed circuit board technique. Scan performance of the proposed cavity-backed antenna is investigated in two principal planes and is shown to have similar performance compared to its free-standing counterpart. A simplified version of this single-polarized antenna, when used for broadside only applications is developed. This antenna, excited with a single coaxial feed is shown to have a smaller aperture than the 3 × 4 array. Isolations between two of these antennas when mounted on a compact shared-antenna platform are investigated through computation and experiments.To extend the capability of systems relying on these designed antennas, frequency reuse is enabled through dual-polarized functionality. A dual-polarized, flush mounted, Vivaldi antenna, directly integrated with an all-metal cavity is introduced as an alternative to coax-fed quad-ridge horns. An approach based on shaping the side walls of the cavity is used to eliminate the occurrence of resonances. The proposed dual-polarized resonant-free antenna has two orthogonal 2 × 1 arrays with two elements in the E-plane, one element in the H-plane. It is fed using two 2-way power dividers that can be easily designed to maintain low amplitude and phase imbalances. The antenna is fabricated as a single piece and experimentally shows a monotonic gain increase with low cross-polarization over 4:1 bandwidth.Phased array antennas operating at geostationary orbit are required to scan within Earth’s field of view, without any grating lobe appearance. For dual-polarized applications, this requirement has limited the widespread and attractiveness of these systems at frequencies such as X-band. The narrow 150 MHz guard range between transmit and receive bands, leads to impractical diplexers in conventional dual-polarized systems. This research introduces a dual-polarized subarray architecture for X-band phased array systems which enables high isolation between closely separated TX and RX bands. The proposed approach either eliminates the need for diplexers, or significantly decreases their required complexity

Wideband Monostatic Co-Channel Simultaneous Transmit and Receive (C-STAR) Antenna and Array Systems

Most modern wireless communication systems operate either at different times or frequencies to avoid self-interferences. With these duplexing techniques, more resources are required due to the increased demand for higher data rate. Therefore, alternative solutions not involving more use of the time or frequency spectrum are needed. One of the possible solutions that has been recently gaining increased interest is often referred to as co-channel simultaneous transmit and receive (C-STAR). C-STAR is considered by many as a key enabling technology for the next-generation wireless networks operating in spectrum congested environments. C-STAR allows transmitting (TX) and receiving (RX) at the same time and over the same frequency channel which may result in significant improvements in throughput and spectral efficiency. The chief challenge associated with these C-STAR systems is the required very high TX/RX isolation (110-140 dB) to suppress the self-interference. To obtain the necessary isolation over any bandwidth, a C-STAR transceiver is typically divided into several self-interference cancellation stages. Specifically these include antenna, analog, and digital layers. Clearly, the antenna array layer plays an important role in maximizing the overall system isolation since ~30-50% of the required isolation is achieved with a well-designed C-STAR antenna subsystem, then the overall system becomes feasible. In this Ph.D. thesis, several novel wideband co-polarized circulator and circulator-less monostatic antenna and array designs are presented. Developed theoretical concepts are validated with full-wave simulations and measurements. The monostatic C-STAR apertures utilizing multi-arm spiral antennas are first demonstrated where a set of arms is used for transmitting and the other set for receiving. Then, different novel omnidirectional and broadside C-STAR arrays utilizing closely-spaced spiral, monocone, or discone antennas are introduced. Phase mode orthogonality principle, antenna orientation, and beam-former cancellation are all combined to achieve the desired performance. All proposed C-STAR configurations have theoretically infinite isolation between TX and RX ports. Practically, the achieved isolation is limited by the electrical asymmetries of the used components. Overall, consistent wideband operation, high measured isolation, and good far-field performance are achieved for all proposed C-STAR antenna array sub-systems without taking advantages of any time-, frequency-, polarization-, pattern-, antenna-, and spatial-multiplexing