The present disclosure relates to broadband, low profile, high isolation, two-port antenna.
The ever-increasing demand for wireless communications arising from the emerging technologies such as the Internet of Things (IoT) has put stringent conditions on the efficient use of the available frequency spectrum. The traditional approaches for enhancing the spectral efficiency of wireless systems such as advanced modulation methods, advanced coding, and Multiple Input Multiple Output (MIMO) techniques have been fully expended. The predicted increase in spectral efficiency using MIMO concept is based on unrealistic expectations that the channel matrix has full rank. However, the capacity gain of MIMO channels is limited in real operating scenarios due to erroneous channel estimation particularly in time-varying and low SNR channels and high level of channel fading correlation as the size of the MIMO system gets large. As the aforesaid methodologies for enhancing the channel capacity reach their maximum potential, alternatives must be created to push the limits not by discarding the foregoing achievements but by building on them. One of the possible solutions to be integrated with MIMO to meet the challenges of the future ultra-dense networks is to replace the current prevalent time-division and frequency-division duplex transceivers with full-duplex transceivers. In contrast to the former in which transmitting and receiving are operated either at different times or over different frequencies, full-duplex transceivers are designed to transmit and receive data at the same time and over the same frequency band resulting in a twofold increase in the channel capacity of the system. Enabling full-duplex operation using orthogonal polarizations has two advantages: 1) facilitating channel estimation as the size of the channel matrix becomes smaller and 2) reducing system complexity through reducing the number of required transmitters and receivers.
Operating in full-duplex, however, requires perfect self-interference suppression which has been extensively studied recently. Self-interference refers to the strong signal coupling from the transmitter to the co-located receiver whose level is much larger than the desired received communication signal to be detected. The required level for interference cancellation depends on the level of the transmitted signal. Assuming 0 dBm for the transmitted power and ˜−100 dBm for the noise floor (˜20 MHz Bandwidth), a scheme that can suppress the level of the interference signal beyond 100 dB is required. Different cancellation approaches have been reported to achieve such high level of cancellation.
Three main techniques and combination of them may be employed for this purpose including analogue cancellation, digital cancellation, and antenna cancellation methods. Analogue cancellation is performed based on the measured transfer function from Tx to Rx using an RF circuitry. This RF circuit consists of a coupler which picks up a copy of the transmitted signal and passes it through a gain stage and a phase shift stage. The gain and the phase shift are adjusted such that the output of the RF circuit is equal in magnitude and out of phase with the leaked signal from Tx to Rx. This signal is then injected to the receiver to achieve partial suppression of the interference signal. Practical RF cancellation circuits are reported to provide about 25 dB cancellation level. Likewise, digital cancellation may be envisioned after Analogue to Digital Convertor (ADC) module using different techniques such as successive interference cancellation and Zig Zag decoding. However, the sum of analogue and digital cancellation level based on these two methods cannot exceed 50 dB. An additional cancellation mechanism which will be referred to as antenna cancellation is, therefore, suggested to enable full-duplex operation.
This section provides background information related to the present disclosure which is not necessarily prior art.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
A two-port cavity-backed slot antenna is presented. The antenna includes: an antenna structure having shape of a cuboid and defining a cavity therein; a feed slot formed in a first of two opposing planar surfaces of the antenna structure; and one or more radiating slots formed in a second of the two opposing planar surfaces of the antenna structure. In one example, the feed slot is in the shape of a cross and comprised of a transmit slot and a receive slot. The one or more radiating slots are arranged symmetrically in relation to the feed slot. In one example, the one or more radiating slots are further defined as four radiating slots, where each radiating slot of the four radiating slots are in shape of a cross and the arms of each cross have same dimensions.
The antenna further includes a microstrip configured to deliver a transmit signal to the transmit slot. The microstrip includes two prongs symmetrically crossing over the transmit slot with one of the two prongs on each side of the receive slot. Portions portions of the two prongs overlapping with the transmit slot are preferably suspended in air.
In some embodiments, a plurality of metal septa disposed in the cavity of the antenna structure and arranged along edges of the transmit slot and the receive slot. Additional metal septa may be disposed in corners of the cavity of the antenna structure and configured to generate a standing wave at higher frequencies of the operating bandwidth.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
This disclosure introduces a compact, broadband, and common aperture slot antenna with high level of isolation between the two ports over 44% fractional bandwidth. The proposed antenna does not require any quadrature or out-of-phase hybrid. The devised antenna provides higher gain for both channels compared to previously reported full-duplex antennas as both channels share the entire available aperture. Other than polarization, the transmitting and the receiving radiation patterns are of the same shape.
With reference to
One or more radiating slots 16 are formed in a second of the two opposing planar surfaces of the antenna structure 12 as best seen in
Referring to
A cavity-backed slot aperture acts like a narrowband radiator by its nature. It has been shown that it is feasible to make a slotted cavity radiate over a wide bandwidth by appropriately loading the cavity by multiple metallic septa 19. The inserted septa increases the bandwidth through two different mechanisms. First, the septa excite evanescent modes and thus bring down the cutoff frequency. Second, the septa can be designed to merge different resonant frequencies. As a result, the modified slotted cavity exhibits broadband behavior. This cavity acts as a transducer between the wideband feed ports and the radiating aperture by properly tailoring the field distribution. Devised to have four cross-slots on the broad wall as common radiating elements for both transmit and receive channels, the cavity is fed by two perpendicular slots on the back wall to generate orthogonal transmit and receive polarizations.
In the example embodiment, a first series of metal septa are disposed in the cavity of the antenna structure and arranged along edges of the transmit slot and the receive slot. Additional metal septa disposed in corners of the cavity of the antenna structure. These additional metal septa are designed to generate a standing wave at higher frequencies of the operating bandwidth. The provision of these septa will allow formation of proper standing wave over the radiating slots which in turn facilitates radiation.
With reference to
E=iωμ∇×Πm (1)
and the vertical component of the electric field is simply obtained as
The discontinuity of the magnetic Hertz vector potential at the edges of the septa results in non-vanishing electric field in y-direction. This suggests that the metallic septa should be placed close to the edges of the slots as shown in
As frequency increases, the electrical distance between radiating slots increases. This can introduce a deteriorating effect on the radiation pattern and gain through increasing the level of the grating lobes. Appropriately placed, the inserted septa can be exploited to rectify this problem to some extent. Referring to
Each radiating slot bears some level of cross-polarized radiation. However, the symmetric geometry of the structure allows for cancellation of the cross-polarized radiation within the main beam.
Using orthogonal polarizations for transmit and receive channels, does not provide the required level of isolation. This is mainly due to depolarization of the wave as it propagates from Tx through the antenna structure. The depolarized wave is then partly captured by the Rx. To achieve higher level of self-interference cancellation, a symmetric feed configuration is employed. The schematic of the decoupling method is shown in
E1xc(x,y)=−E2xc(−x,y) (3)
and
E1yc(x,y)=E2yc(−x,y) (4)
To ensure the coupled field at the Rx slot would be cancelled, reciprocity can be used. That is by exciting the Rx slot, the field over the Rx slot aperture must satisfy the following conditions:
ExRx(x,y)=ExRx(−x,y) (5)
and
EyRx(x,y)=EyRx(−x,y) (6)
It will be shown that it is feasible to generate such electric field distribution by a compact broadband coaxial to waveguide transition which is connected to the Rx slot. The cancellation level achieved by this method is frequency-independent, such that the bandwidth of the structure is limited by the bandwidth of each channel not the bandwidth provided by the cancellation mechanism. This structure allows for sharing the entire available aperture by both channels and thereby, provides at least 3 dB higher gain or half area used by the antenna system compared to other reported full-duplex antenna systems in which separate elements are used for transmitting and receiving. The realization of the microstrip and waveguide feeds are described later in this disclosure.
In one embodiment, the microstrip feed line 71 is laid out on the back side of the cavity as depicted in
A perspective view of the microstrip feed 71 is shown in
To achieve a high level of isolation, the electric field across the Rx slot should satisfy (5) and (6). To create this electric field, a compact end-launch coaxial-to-waveguide transition is devised. An example embodiment of a suitable structure of the transition is shown in
Because the transition shown in
Simulation and experimental results of the proposed antenna are presented as proof of concept. The proposed complex antenna structure shown in
The S-parameters of the antenna are illustrated in
The antenna structure shown in
A two-port common aperture CBSA array with two different feeding structures is presented that exhibits a very high isolation level between its ports. High isolation is achieved using orthogonal polarizations and utilizing a symmetric structure. A radiating aperture which results in higher gain for a given available area. A low-loss air-dielectric microstrip feed is designed which can be integrated with the other parts of the antenna and is amenable to 3D printing technology. The proposed decoupling method does not require any kind of hybrid and can potentially provide nearly 90 dB of channels isolation over 44% fractional bandwidth. For the fabricated antenna, a minimum of 55 dB self-interference cancellation is measured from 4.8 to 7.5 GHz.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
This application claims the benefit of U.S. Provisional Application No. 62/850,600, filed May 21, 2019. The entire disclosure of the above application is incorporated herein by reference.
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Number | Date | Country | |
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