Patent Application
20150092877
The present invention relates to the field of radio communication systems and, more particularly, the present invention relates to high throughput radio transceivers and antennas.
With the advent of FM radio and television stations, wireless networks began as one-way broadcast systems. Cellular networks changed that to two-way communications but still the throughput requirements were low by today's standards. The coming of the Internet age, however, made high throughput (i.e. broadband) communications a necessity. Wireless communications have a big future in this area which also represents a convergence of cellular and broadband systems.
The demand for high throughput communications systems is ever-increasing in order to accommodate myriad uses including cloud computing, remote data storage and backup, business and banking data transfers, enterprise and educational campus networking, high-definition video streaming, and an increasing prevalence of mobile devices and applications.
Communication latency is also a significant consideration for communications systems. Minimizing communication latency is important in connections among financial institutions, including the major stock exchanges in the U.S. and abroad. For example, many transactions in the equity markets depend upon the speed in which a transaction or trade order is communicated and executed. In these contexts, reductions in communication latency can result in increases in profitability. Minimizing communication latency is also important for cellular and other voice communications, particularly long-distance voice communications, and is increasingly important for industries that rely upon cloud computing, including financial, medical, educational, government, video delivery, and so forth.
Communication interference is an additional consideration for communications systems. As an increasing number of communications systems become more densely packed into urban areas in response to demand for such systems, the likelihood of inference among them increases. Costs incurred due to network outages caused by interference can be significant, resulting from losses in productivity, missed deadlines, and so forth.
Wireless medium is inherently shared and presents unique interference challenges. This is particularly true for backhaul (PTP) applications, such as used by cellular operators, though interference occurs in many contexts. Because frequency spectrum is a finite and scarce resource, spectral efficiency also plays an important role. This is especially true for those using unlicensed bands. Because there is no protection afforded to such operations, they are subject to any amount of interference from nearby systems. In these situations, interference mitigation or cancellation techniques are increasingly important.
Interference issues have been conventionally handled through the use of other channels in the unlicensed bands. Also, transmission protocols such as those using spread spectrum techniques are designed to operate in somewhat interfered environments. However, the number of 40 MHz channels in 2.4 GHz unlicensed band for example are two and, in busy or crowded locations such as apartment complexes, one quickly runs out of channels to choose from. As for techniques such as spread spectrum, they can only handle a small amount of interference.
Accordingly there is a need for communication systems that provide high throughput and low latency and that are resistant to interference.
A system for wireless transmission of signals is provided. A first radio unit is configured to communicate desired communication signals with a second radio unit. The first radio unit has a plurality of antennas configured to simultaneously receive a plurality of desired communication signals within a frequency channel. The first radio unit is configured to correlate signals received among its antennas to obtain one or more correlation coefficients, and using the correlation coefficients, the first radio unit is configured to multiply a received signal experiencing interference within the channel by an obtained correlation coefficient in order to remove interfering signals from the desired signals.
These and other advantages of the present invention will be apparent to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the drawings and figures.
The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:
The present invention generally is in the area of wireless broadband communications. In accordance with embodiments of the present invention, methods and systems are provided for cancelling interference in wireless broadband communication networks using multiple input and multiple output (MIMO) antennas that are optimally arranged. A network of such antennas along with the associated electronics can result in dramatic increases in capacity over conventional techniques. This allows a network to operate normally despite other networks existing in the same frequency spectrum region at the same time. It also allows these communication links to be secure such that only the intended receiver can decode the wireless signal while all other receivers at nearby locations cannot decode due to excessive interference and lack of information to pull the desired signal out of interference.
The present invention provides a method for simultaneously cancelling one to many interferers in a given frequency channel. There is no a priori knowledge of the undesirable interference signal characteristics. All needed properties of the signal are estimated in real time using the signals themselves.
In accordance with embodiments of the present invention, methods and systems for secure and high capacity broadband wireless transmission in interference prone environments are provided. Significant improvements in capacity are provided while also providing security of communications. An embodiment of the present invention also results in interference cancellation in the presence of strong co-channel interferers such as due to neighboring wireless backhaul links on the same channel. Embodiments of the present invention provide increases in network capacity as measured at radio equipment. In a mesh network configuration, embodiments of the present invention provide increases in data rate seen by any single mesh node or device. Embodiments of the present invention can also inhibit devices from decoding a signal at locations other than the location of a desired receiving station. Using polarization and direction sensing of interfering networks, embodiments of the present invention also allow networks and backhaul links to operate in fully co-channel interfered locations.
Embodiments of the present invention provide systems and methods for broadband wireless communication using multiple antennas at the radio equipment. In accordance with an embodiment, a base station, point-to-point (PTP) node or access point uses multiple sectorized antennas to transmit or receive multiple data streams, fully synchronized in time and frequency, on the same channel.
In accordance with embodiments of the present invention, signal processing and interference handling techniques can be used to cancel interference present in the same channel from other nearby networks or backhaul link devices. Each such device can have at least two antennas and can identify the interfering signal from the desired signal. In addition to facing different directions, the antennas can also be of orthogonal polarizations so that polarization of an interfering signal can be identified and the desired signal can be adaptively made orthogonal to it. In this case, radio units communicating the desired signal can agree through a control channel to use a polarization that is orthogonal to that of the interfering signal.
In point-to-multipoint (PTMP) embodiments, channel estimation algorithms can play a useful role. By nature of the scattering environment, the broadband channel characteristics are frequency dependent and also time dependent. However, both single carrier and orthogonal frequency division multiplexing (OFDM) techniques can be used in these embodiments to make such channel identification easier. Embodiments of the present invention are described in connection with a proprietary system. However, embodiments of the present invention can be utilized on top of, or in connection with, existing standards such as WiFi or WiMax. For PTP backhaul interference cancellation applications, single carrier systems can also be employed in which the antennas are housed in a single unit and have a constant or stationary channel between them.
A number of antennas positioned at a backhaul unit can transmit or receive wireless signals on the same channel at the same time and frequency as a nearby unknown interferer. In this embodiment, a wireless network can be operated in the presence of very strong interfering networks. Even if the interference is much stronger than the desired signal, a wireless network employing this embodiment of the present invention can keep functioning.
A PTP backhaul interference cancelling link, and for a PTMP multi sector system, is described herein and exemplified in the accompanying illustrations. It should be understood however that description herein is by no means intended to limit the scope of the invention which a person of ordinary skill can use in other embodiments. On the contrary, alternatives, modifications and equivalent embodiments, are within the spirit and scope of the invention as defined by the attached claims. In the following description of the embodiments of the present invention, specific details are given so as to provide a thorough understanding of the invention. It will be apparent that the present invention can be reduced to practice without some or all of these specific details or descriptions.
In accordance with an embodiment of the present invention, a system for wireless transmission of signals is provided. A first radio unit is configured to communicate desired communication signals with a second radio unit, the first radio unit having a plurality of antennas configured to simultaneously receive a plurality of desired communication signals within a frequency channel. The first radio unit is configured to correlate signals received among its antennas to obtain one or more correlation coefficients, and using the correlation coefficients, the first radio unit is configured to multiply a received signal experiencing interference within the channel by an obtained correlation coefficient in order to remove interfering signals from the desired signals.
The plurality of antennas of the first radio unit can comprise sum and difference antenna ports, each providing a corresponding in-phase sum and out-of-phase difference signal, the sum and difference signals being among the signals received by the antennas and used to obtain the one or more correlation coefficients. The plurality of antennas of the first radio unit can further comprise horizontal and vertical polarized antennas, each providing a corresponding horizontal and vertical polarized signal, the horizontal and vertical polarized signals being among the signals received by the antennas and used to obtain the one or more correlation coefficients. The plurality of antennas of the first radio unit can further comprise left and right side antennas, each providing a corresponding left and right signal, the left and right signals being among the signals received by the antennas and used to obtain the one or more correlation coefficients.
The first radio unit can be configured to correlate signals received among its antennas to obtain a matrix of correlation coefficients and to multiply received signals experiencing interference by an inverse of the matrix of correlation coefficient in order to remove the interfering signals from the desired signals.
The first radio unit and a third radio unit having multiple antennas can be located in close proximity to each other and connected to the same baseband digital processor such that the first and third radio units operate in the same frequency channel in a full duplex manner and wherein the interfering signals from are cancelled by the common digital processor.
The antennas of the first radio unit can be included in an antenna patch array that provides as output the in-phase sum signal and the out-of-phase difference signal, and wherein when the antenna patch array is pointed toward the second radio unit, the antenna patch array receives almost no desired communication signal on the difference antenna port thereby ensuring that an antenna matrix is invertible.
The antennas of the first radio unit can have at least a pair of orthogonal polarizations and wherein polarization of at least one interfering signal is identified and the desired signal is adaptively made orthogonal to it. The radio units of the pair can agree through a control channel to use the polarization that is orthogonal to the interfering signal. The pair of orthogonal polarizations and sum and difference signals at the first radio unit can be used simultaneously to enhance communication security by providing that a desired signal is decodable only by the first radio unit of the pair due to a nulling resulting from use of the orthogonal polarizations and the sum and difference signals.
A null of at least one antenna of the first radio unit can be steered in the direction of at least one interfering node and a null of another antenna of the first radio unit is steered in the direction of the desired signal so that the two antenna signals have a maximum separation.
The desired communication signals can be in accordance with a wireless communication standard, such as IEEE 802.11. The correlation coefficients can be obtained by analyzing received data packets that are scheduled to arrive sequentially and quasi periodically.
The first radio unit can be configured to communicate in accordance with OFDMA techniques and wherein a channel estimation and control channel is used to identify an optimal modulation technique usable for each of a plurality of sub carriers, the modulation technique being selected depending on fading and interference detected on each said sub carrier.
The first radio unit can be configured to communicate in accordance with OFDMA techniques and wherein a channel estimation and control channel is used to optimally allocate each of a plurality of sub carriers to a particular node in each sector.
Multiple antenna beamforming techniques can be used in each of a plurality of sectors for interference cancellation. Multiple antenna beamforming techniques can be used in each of a plurality of sectors for increasing communication range. Increasing of the communication range can be obtained through power level increase due to beamforming and traded off with interference cancellation efficiency.
One or more interfering nodes in proximity of one or both of the first and second radio units can simultaneously transmit one or more interfering signals in the same frequency channel used by the radio units.
In accordance with an embodiment of the present invention, a system for wireless transmission of signals is provided. A first radio unit is configured to communicate desired communication signals with a second radio unit. The first radio unit has a plurality of antennas configured to simultaneously receive a plurality of desired communication signals within a frequency channel. The antennas of the first radio unit are included in an antenna patch array that provides as output an in-phase sum signal and the out-of-phase difference signal, and wherein the plurality of antennas of the first radio unit further comprise horizontal and vertical polarized antennas, each providing a corresponding horizontal and vertical polarized signal, and wherein the plurality of antennas of the first radio unit further comprise left and right side antennas, each providing a corresponding left and right signal.
The first radio unit can be configured to correlate signals received among its antennas to obtain one or more correlation coefficients, and using the correlation coefficients, the first radio unit is configured to multiply a received signal experiencing interference within the channel by an obtained correlation coefficient in order to remove interfering signals from the desired signals.
The antenna patch array can comprise a plurality of planar antenna patches arranged on a substrate that measures approximately 5.5 inches by 5.5 inches. The plurality of planar antenna patches can each be approximately 3.5 centimeters by 3.5 centimeters. The plurality of planar antenna patches can be spaced apart by approximately one centimeter or less. The plurality of planar antenna patches can consist of 32 patches. The antenna patch array can include a plurality of planar antenna patches, wherein each patch has dual polarizations and wherein the patches are arranged is left and right groups and wherein a feed network coupled to the left and right groups provides as output the in-phase sum signal and the out-of-phase difference signal. The dual polarizations, left and right groups, and the in sum difference signals can effectively provide eight different antenna signals.
Exemplary Transmitting, Receiving Unit and Applications
In a transmit path, data to be communicated in the two channels via the radio transceiver 250 can be received from a network via the network interface 264 and processed by the digital signal processing section 262. Digital baseband signals from the digital signal processing section 262 for the vertical and horizontal polarizations for each of the two channels are then converted to analog signals by digital-to-analog converters of the analog-to-digital baseband processing section 260. The vertical and horizontal polarized analog signals for the first channel can be routed to RF integrated circuit processor 278 while the vertical and horizontal polarized analog signals for the second channel can be routed to RF integrated circuit processor 280. The signals to be transmitted can then be amplified by amplifiers 256 and routed to the appropriate transmit antennas 252 via switches TR1, TR2, TR3 and TR4.
Also shown in
In an embodiment, the interfering signals are received during periods when the desired signals are not being transmitted such as during switching periods. The interfering signals are then correlated to the desired signals and subtracted from the received desired signals in order to obtain an estimate of the transmitted desired signals in absence of the inference.
After encoding, encoded data blocks are sent to a module or modules 326, 328, 330, 332 that load each of a plurality of wireless channels with the proportional amount of data that it can carry. This level of adaptability can be helpful when multiple channels are aggregated. As shown in
As shown in
Interference Cancelation
Estimation of the signal properties of interference is done after the receiver turns on (switches from transmit to receive) but before the desired signal arrives from the remote unit. The typical duration of estimation cycle is 10 to 200 microseconds which corresponds to 1 to 20 miles round trip delay for electromagnetic signals in air medium. This approach ensures that a weak interference signal can be estimated and cancelled without noise due to the large desired signal. In cases where the interference is dominant, one can continue the interference estimation in the same manner during the entire receive cycle, or even have the transmitter pause in the middle periodically, allowing a quiet period for interference sensing or estimation
During estimation, a three multiplier based complex multiply and accumulate module 414 in the digital processor 262 correlates the signals of the sum and difference (eg. HLS and HLD) antenna ports. The complex conjugate of the difference signal is used for this. Also estimated is the variance of the interference signal.
By dividing the correlation result by the variance term, a normalized interference coefficient is derived. This is used during receive cycle after the desired signal starts to arrive, to scale the signal measured on the interference channel and subtracting the resulting interference estimate. Since the difference port extends a null toward the desired link direction, the signal on these ports is predominantly interference and so there is very little distortion in the desired signal as a result of these operations.
All these interference cancelation procedures work at line speed in the digital processor 262 and take up parallel resources. In the example case of a signal with 33 MHz bandwidth sampled at 100 MHz, the complex multiply and accumulate takes 3 multipliers, 5 adders and 1 accumulator. The variance estimator can share a single multiplier and one accumulator if it is assumed that the interference signal has a fixed variance or if the variance estimate can be carried during actual signal reception cycle.
The AGC (gain control) 412 is preferably performed before interference cancellation 414 so that the A/D and radio remain in a linear region of operation even though the interference signal can actually be stronger than the desired signal.
The approach outlined above can cancel interference that is up to 20 dB higher than the desired signal and bring the interference level to 30 dB below the signal, so that 256 QAM (highest modulation used in our system) with coding can be reliably used. Very close to 1 Gbps throughput can be expected under very high interference levels using these interference cancelation methods. Furthermore an interferer of the same power as the distant (10 km) desired transmitter, but only a meter away from the receiving unit can be cancelled to allow 256 QAM (1 Gbps in our exemplary system) signal from the distant unit. This corresponds to a total of 110 dB or 11 orders of magnitude reduction in the interference signal relative to the desired signal.
Channel Estimation
One of the components in accordance with certain embodiments of the present invention is a channel estimation algorithm and its performance. An embodiment of a channel estimation technique used is described below.
Assuming that OFDM is used as the underlying modulation technique, let the system parameters be: occupied bandwidth=20 MHz, delay spread expected <3 microseconds, adaptive modulation technique used—4, 16 and 64 QAM, Doppler spread=5 Hz, required S/(N+I) of 20 dB for 64 QAM. Then one can design an OFDM system with guard interval of 4 microseconds, OFDM symbol duration of 17 microseconds with 256 sub carriers. The channel estimation technique relies on the clients sending a special OFDM symbol—the equalization symbol every 4 milliseconds. The clients in each sector take turns sequentially sending their equalization symbols. The base station (e.g. connected to tower 502 in
The increase in channel power in each sub carrier by using OFDMA on the equalization or channel estimation symbols is notable. Higher signal power results in more accurate channel estimation that ultimately affects the entire system performance.
This particular embodiment described herein involves the use of OFDM and OFDMA techniques. It should also be noted that embodiments of the present invention can be used irrespective of the underlying standard or protocol of communication. While it certainly is easier to implement a scalable system with the full benefit of improvements described herein, in a proprietary embodiment, it is possible to implement such improvements on top of current standards such as 802.11. The OFDM and OFDMA methods presented in this description apply on top of the rest of the physical layer, its use can be limited to getting the base station information about the channel estimates of all the sector clients. In case of standards based systems such as those using 802.11b, the base station front end baseband—where embodiments of the present invention can be implemented—processes the acknowledgements or RTS packets or in general any uplink packet from the client to the base station, using an OFDM processing engine, gathers channel response or estimates on each of the defined sub carriers, and uses them to predistort the sector signal appropriately. Similar embodiments can be derived by one of ordinary skill in this art for other standards based systems such as those employing HSDPA (3G) or 802.16 (WiMax).
One can also use single carrier techniques for implementing embodiments of the present invention into other systems. In one such embodiment, Ethernet packets can be framed into constant bit rate frames, which are split into multiple streams each of which modulates a single carrier. A suitable pair of DAC and ADCs convert the signals from digital to analog and vice versa. The baseband analog signals are then converted to and from a desired RF carrier frequency. By using an RF combiner, several such single carriers are added together before the antenna. On the receiver side, a matched square root raised cosine filter, decision feedback equalizer, demodulator, timing and frequency and gain control loops convert the analog signal into digital data which then can be decoded (for example with a Reed Solomon decoder if such an encoder was used), the byte stream can be combined from all the carriers and then sent to a Ethernet packet framer.
Physical Layer
Baseband Block Processing Components
The transmitter section 601 of a base station or client includes an Ethernet interface, packets from which can be anywhere from 56 bytes to 65536 bytes (Jumbo packets). This is followed by a reformatting block 603 that breaks up the Ethernet packets into sizes appropriate for transmission over a wireless medium. Then an encryption algorithm such as advanced encryption standard (AES) can be employed in a block 605 to better secure communications. Following this, a CRC checksum can be added along with MAC level headers in block 606. Then the entire packet can be optionally subject to channel forward error correction encoding (FEC) in block 608 where in the packet is made insensitive to a limited number of bit errors, such as by use of turbo product codes (TPC). Tail bits can be inserted at block 607. Adaptive modulation can be performed in a block 609. The modulation scheme used in block 609 can be a trellis coded modulation (TCM) scheme that divides the constellation by 3 levels and employs a strong convolutional (2,1,7) or turbo codec to obtain a coding gain of up to 9 dB over all. The TCM symbols can be sent through an adaptive modulator in block 609, and then filtered by a pulse shaping filter such as a square root raised cosine filter (SRC) 616. A sign magnitude converter 618 can also be employed. The samples are then sent to a pair of DACs 619 and to an analog processor which can be a radio-frequency integrated circuit (RFIC) 631 and which can also be a direct conversion chip. The RFIC 631 preferably performs baseband amplification, filtering and upconverting to RF in a single stage, gain control and then filtering followed by a power amplification stage. The signal then passes through a Transmit/Receive switch and a balun to the antenna 621 for transmission. An oscillator 620 and clock signal generator 617 can generate clock signals for use by delay lock loops 604 and 614 which can control timing in the transmit processing path. On the receive side, the signal goes through the same antenna 621 and switch, in through a bandpass filter, low noise amplifier, gain control stage and then into a mixer where it is brought down to baseband. These steps can be performed by the RFIC 631. This can be followed by further filtering and gain control and conversion from analog to digital is performed by analog to digital converters 630. The digital samples then are filtered in blocks 629 (2's complement), 628 (SRC filter), 627 (decimation), and the cyclic prefix removed in block 626. An automatic frequency and timing correction (ATFC) algorithm is applied in block 625. At the same time, an automatic gain control circuit 633, 634 sets the signal level appropriately for the other subsequent blocks. Following the AFTC, adaptive equalization is performed in block 624 to clean up the signal of all the channel impairments. The demodulation technique used depends on the adaptive modulation algorithm used. After demodulation the raw bits and soft decision samples are sent to the channel codec (in or after TCM). The codec processing essentially mirrors processing in the transmitter 601, and can include slicer and Viterbi processing block 635, error correction decoding block 636, CRC checksum processing block 637 and advanced encryption standard (AES) block 639. The corrected bits are then packaged into bytes and packets that are decrypted and reformatted to Ethernet packets in block 640. These are finally sent to the host assuming the Ethernet CRC passes. If not, the transmitter is informed through a negative acknowledgement and the packet is rescheduled for transmission due to errors.
Also shown in
RF and Analog Circuitry
The radio frequency portion of a typical embodiment of the present invention performs the functions of filtering, amplification and mixing. In the transmission path, a task performed is the conversion of the digital samples into analog voltage or current based signals. This is achieved by the use of a pair of digital to analog converters or DACs 619 (
In the receive path, the antenna excitation signals are detected and amplified by a low noise amplifier (LNA) after passing through the switch and a front end RF filter of the RFIC 631. This LNA determines the noise entering the system as well. It is then followed by a gain adjustment stage and the signal then is mixed down in a single stage to baseband using the mixer. The baseband signal is further amplified, filtered before being sent out of the RFIC 631 in I and Q forms. These are digitally sampled by a pair of analog to digital converters (ADCs) 630 and the digital samples are sent to a logic processor such as an ASIC or FPGA (e.g. digital processor 262 of
Automatic Gain Control
There are three parameters that need to be synchronized between the transmitter and receiver in a typical broadband wireless radio. The receiver usually implements all these though it can also be done entirely at the transmitter or by both the transmitter and receiver. The first of these is power level adjustment usually done through an automatic gain control circuit (e.g. AGC 633). It is responsible for adjusting the RF gain control stages in the receive path. A reference known signal such as an equalization control channel symbol is used to compute the gain control settings needed for the data bearing signal to be successfully decoded. These gain control settings are then applied to the RFIC 631. A simple way of closed loop adjustment can involve monitoring the number of times the most significant bit of the samples is set, which signifies the signal level. This can be mapped via a table lookup to the actual registers that are set in the RFIC 631 register space to adjust the gain.
There is also a need for gain control on the transmit side. For example, in order to reduce overall interference the base station can set the transmit power levels of all the sector signals to be the same. To do this, the ASIC or FPGA of the system (e.g. digital processor 262) can set the variable gain amplifier's registers of the RFIC 631 to appropriate values.
Automatic Frequency and Timing Control
In OFDM embodiments, it can contribute to good system performance to have an accurate frequency and timing synchronization. While timing is less critical, usually one can achieve both using the same algorithms.
One method of frequency synchronization is by detecting the difference in the crystal frequency of the transmitter and the receiver. Frequency offset is essentially caused by this difference, and so is timing since the ASIC or FPGA (e.g. digital processor 262) also typically derive their clocks from this crystal.
A method for estimating the difference can involve the transmitter sending known timing symbols at deterministic intervals in time—e.g. 64 milliseconds apart. The receiver opens a window around this interval and searches for the timing symbol. By noting the difference of its local counter and the deterministic interval, the receiver can estimate the clock and therefore crystal frequency difference. This can then be mapped to a frequency offset in a straightforward manner and the offset can be used to drive a tone generator.
Modulation
Such a modulation scheme benefits from extra channel coding gain at very little complexity cost. Constellations similar to those of
Equalization
Exemplary System Link Analysis
As seen in
Antenna Systems
An aspect of interference cancellation embodiments described herein is that the interference cancelation can be successful in cases where the interferer is directly in line with the narrow beam of the desired signal. Such a situation may arise if the interferer is on the same tower as the desired unit but is also talking to another interferer that is on the same other tower that has the second desired unit (i.e. the two links are completely parallel). In such cases, by synchronizing to the time divisional duplex (TDD) timing or frequency divisional duplex (FDD) frequency plan, the problem of interference can be reduced to the near end problem where the interferer is transmitting on the tower at the same time as the distantly located desired transmitter. By doing so, the interference signal is reduced before it hits the antennas because of the difference in direction of arrival and also the MIMO antennas pick up different signal and interference content on each antenna, as previously described. This method of converting the far end parallel link interference to a near end “in the tower plane” interference is particularly useful in congested areas where there may only be a few towers and signals need to go between the towers because of the location of a fiber point of presence or colocation site near or at one of the towers.
The square patch size is preferably directly proportional to the wavelength. For example, the patch size is preferably approximately one wavelength tall and one wavelength wide, so for transmission in the 5 GHz frequency band, the patches are approximately 3.5 cm square. The 4 corner patches are preferably omitted since the feed network loss from the stripline running from the center to the corner is higher than the gain improvement by having those. This also helps in layout of components and features on the other side of the board due to a more open space becoming available. Overall 32 patches are used in the example implementation. A gain of about 17 dBi is obtained, and as can be seen, with 32 uncorrelated and independent patches, perfectly phase, one would expect about 15 dB gain over a single patch—or about 21 dBi (6 dB single patch gain adjusted for feed loss). So a price of about 4 dB in gain is paid for the improvements in planar rejection (through tapering) and small size benefits obtained.
For higher gain and directionality, a parasitic antenna board is employed with patches floating in air approximately 0.1 inch from the main antenna. This can be accomplished by attaching the parasitic antenna board to the main antenna board using spacers to provide an air gap between them. This tightly couples the electromagnetic waves in the forward direction. By using variable spacing and size for the patches on the parasitic board, a flatter frequency response of the antenna is obtained which contributes to good performance in the 5 GHz band due to the large bandwidth of operation (about 1 GHz). The feed network, patches and component layout are done iteratively so that the drilled via holes stay at least 50 mils from any RF signal carrying trace. This design rule helps to avoid signal distortions and loss. The race track in the middle of the antenna PCB shown in
As shown in
The foregoing detailed description of the present invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the embodiments disclosed. Accordingly, the scope of the present invention is defined by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 61/885,586, filed Oct. 2, 2013, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61885586 | Oct 2013 | US |
