Patent Application
20130207870
A common application for phased array antenna systems is steerable radar systems. Typically, the antenna elements of the steerable radar system are driven from a common source or connected to a common detection channel to produce a controlled emission or detection pattern. This enables the radar system to rapidly change the detection pattern to simultaneously track multiple targets, for example.
More recently, arrays of small radio frequency (RF) antennas have been used for capturing over the air content, such as broadcast television, and then streaming the captured content to users via a public network, such as the Internet.
An example of a system for capturing and streaming over the air content to users via the Internet is described in, “System and Method for Providing Network Access to Antenna Feeds” by Kanojia et al., filed Nov. 17, 2011, U.S. patent application Ser. No. 13/299,186, (U.S. Pat. Pub. No.: US 2012/0127374 A1), which is incorporated herein by reference in its entirety.
When capturing over the air content with arrays of antennas, it is important to maximize the number of antennas at the installation location. One way to maximize the number of antennas is to create a three dimensional array of antennas. The three dimensional array is created by implementing two dimensional arrays on antenna array cards, and then installing multiple antenna array cards in close proximity to create the three dimensional array.
One issue is that the three dimensional arrays of antennas often are installed in or on buildings or towers where there are size and/or weight limitations. Additionally, many of the arrays will be installed in large metropolitan cities where the cost of renting/leasing space for the arrays is expensive. Furthermore, there are often power consumption limitations at the installation locations. Reducing the size of each individual antenna and also the power consumption of the supporting circuitry for the arrays make the system less costly to deploy, maintain, and operate.
Another benefit of having an array with numerous small antennas is redundancy. If an antenna fails (or multiple antennas fail), then one of the other antennas is able to replace the non-functioning antenna without disrupting service.
The present invention is directed to antennas for the reception of radio waves preferably of at least two different frequency bands. More specifically, the purpose of the invention is to enable reception with electrically small antennas. This invention is applicable to individual antennas, two dimensional antenna arrays, three dimensional antenna arrays, and/or other antenna array systems constructed for high volumetric efficiency and/or density.
By implementing multi-band antennas, a wider frequency reception is achieved and a greater density of antennas is possible within the antenna array. Generally, the multi-band antennas are constructed from at least two electrically small loop antenna elements. Operation is based on the out of band impedance of the antenna elements. A tuning feed network is implemented with resistors, capacitors, varactors, inductors, or ferrite beads to control the tuning frequency of each antenna element. Additionally, each antenna is multiply resonant. This enables each antenna to have optimal performance and provide filtering of adjacent signals and/or avoid interference from signals that may be in the same band as the desired signal.
In general, according to one aspect, the invention features an antenna system comprising a circuit board having an antenna section and a tuner/demodulator section, an array of antennas installed on the antenna section that is controlled by and provides antenna feeds to tuners and demodulators in the tuner/demodulator section, and tuning feed networks for the antennas that connect the antennas to corresponding tuners and demodulators.
In general, according to another aspect, the invention features an antenna system for receiving television signals. The system includes an antenna element having a partial perimeter length of less than 4.3 centimeters and a tuning feed network for the antenna element.
In general, according to another aspect, the invention features an antenna system for receiving television signals. The antenna system comprising an antenna that includes at least a pair of antenna elements connected to a common pair of feed lines and a frequency tuning section for each antenna element of the antenna that receives tuning voltage via at least one of the feed lines.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:
In the illustrated circuit diagram, the multi-band antenna 102-1 is shown as a dual band antenna, which is also referred to as an antenna element pair. In the illustrated example, the antenna 102-1 further includes a low frequency antenna element 102A-1 and a high frequency antenna element 102B-1. In alternative embodiments, however, additional antenna elements could be implemented to form a tri-band antenna or a multi-band antenna with three or more antenna elements. In still other embodiments, the antenna is constructed from only a signal antenna element that covers both bands of interest or only a signal band.
In a typical implementation, the low and high frequency antenna elements 102A-1, 102B-1 are electrically small loop antennas. Loop antennas have an inductance that is proportional to the area carved out by the loops. Here, the antenna elements 102A-1, 102B-1 are rectangular. Other shapes such as circular shaped loop antennas known in the art could also be implemented. Electrically small antennas are defined for a particular wavelength lambda (λ) and radius “a” of the sphere enclosing an antenna. Then, if 4πa<λ(4*pi* is less than lambda), the antenna is considered electrically small. See Wheeler, “Fundamental limitations of Small Antennas, Proceedings of the IRE, Vol. 35, Dec. 1947, pp 1479-1484.
Generally, the antenna 102-1 is multiply resonant. This enables the antenna 102-1 to have optimal performance at a wide range of frequencies and reject interference from other signals that may be in the same band as the desired signal.
In a current implementation, the antenna elements 102A-1, 102B-1 are each approximately 0.5 inches in height, 0.5 inches wide, or about 1.3 centimeters (cm) by 1.3 cm, and have a thickness of approximately 0.030 inches, or about a 1 millimeter (mm). In general, the three sided length (or partial perimeter) of the antenna elements 102A-1, 102B-1 is less than 1.7 inches (4.3 cm), with a total length of all 4 sides being less than 2.3 inches (5.8 cm).
In general, smaller antennas are preferable to achieve higher density, yet smaller antennas typically have a lower gain. As a result in other embodiments larger antennas/antenna elements are used, such as antennas/antenna elements with a total length of up to 20 cm, or even up to 50 cm or 100 cm, and possibly even larger understanding that there is a concomitant decrease in packing density.
A resonance of the antenna 102-1, and each antenna 102-1 to 102-n, is controlled via the tuning feed network 200. The tuning feed network 200 includes a radio frequency (RF) coupling and direct current (DC) injection section 203, a high frequency tuning section 205, and a low frequency tuning section 207.
In the illustrated example, the low frequency tuning section 207 and low frequency antenna element 102A-1 are designed to receive carrier signals in the VHF (Very High Frequency) range or 174 MHz to 216 MHz. The high frequency tuning section 205 and high frequency antenna element 102B-1 are designed to receive carrier signals in the UHF (Ultra High Frequency) range or 470 MHz to 700 MHz.
In a typical implementation, antennas (e.g., reference numerals 102-1 to 102-n in
Generally, the antennas (reference numerals 102-1 to 102-n in
Returning to
In alternative embodiments, the RF connection is made with band pass filters, high pass filters, diplexers and/or multiplexers.
Capacitors C1 and C3 connect to low frequency tap points 220a, 220b of the low frequency antenna element 102A-1. The low frequency tap points 220a, 220b are designed to present the desired impedance from the low frequency antenna element 102A-1 to the feed lines FEED_P, FEED_N. The location of the intersection of the low frequency tap points 220a, 220b with the low frequency antenna element 102A-1 and the area cut out between the tap structure contribute to the impedance transformation.
Capacitors C2 and C212 are in parallel with the varactor diode pairs D1 and D2. In the illustrated example, capacitor C2 has a capacitance of 15 picoFarads and capacitor C212 has a capacitance of 18 picoFarads. The varactor diodes pairs D1, D2 resonate with the inductance of the low frequency antenna element 102A-1 to set the tuning frequency. The bandwidth is determined by the value of resistor R4 along the parasitic resistances in the wire of the low frequency antenna element 102A-1 and the varactor diode pairs D1 and D2. Resistors R1, R2, and R3 provide high impedance connections for DC tuning voltages that are supplied on the feed line FEED_P to the varactor diode pairs D1 and D2. The high impedance serves two purposes. First, the high impedance provides isolation to the feed lines FEED_P, FEED_N so that RF signal is not lost. Second, the high impedance provides isolation from the varactor diode pairs D1 and D2 so they are not disrupted by other impedance/capacitive effects.
Referring to the high frequency tuning section 205, while there are some differences in the components used and their values, the basic functionality of the circuit is the same as the low frequency tuning section 207. For example, the high frequency antenna element 102B-1 is generally identical to the low frequency antenna element 102A-1 in a current embodiment. Additionally, capacitors C4 and C7 provide an RF connection from the high frequency antenna element 102B-1 to the high frequency tuning section 205. Likewise, capacitors C4 and C7 form a DC block (high frequency tuning section DC block 216). Capacitors C4 and C7 each have a capacitance value of 24 picoFarads (compared to 2.2 nanoFarads for C1 and C3). Resistor R7 and R5 provide a high impedance connection for the tuning voltages provided on feed line FEED_P to varactor diode pair D3. The parasitic resistances in the wire of the high frequency antenna element 102B-1 and the varactor diode pair D3 set the bandwidth. Lastly, high frequency tap points 222a, 222b are designed to present the desired impedance from the high frequency antenna element 102B-1 to the feed lines FEED_P, FEED_N.
The feed lines (FEED_N and FEED_P) connect the high frequency tuning section 205 and the low frequency tuning section 207 to the RF coupling and DC injection section 203. The feed lines (FEED_N, FEED_P) carry the received RF signal from the antenna elements 102A-1, 102B-1, to the RF coupling and DC injection section 203. In a typical implementation, the physical distance from the RF coupling and DC injection section 203 and the antenna elements 102A-1, 102B-1 can be relatively large. For example, in one embodiment the physical distance is twenty or more inches (approximately 0.5 meters). In alternative embodiments, however, the physical distance is only a few inches (e.g., approximately 5 to 8 centimeters).
The RF coupling and DC injection section 203 includes an analog control line (ACNTL) connection 206 and two logical interfaces: DIFF_N 202 coupled with DIFF_P 204. The two logical interfaces DIFF_N 202, DIFF_P 204 are differential radio frequency connections that carry received carrier signals to a receiver (or tuner) and demodulator (reference numerals 104-1 and 106-1 in
In an alternative embodiment, the control signal could be a differential control signal. In this embodiment, another input control signal is injected at GND-2 and connected at the end of resistor R6 (GND-2 would be removed/replaced).
Capacitors C5 and C8 are blocking capacitors and form a DC block (RF coupling and DC injection DC block 208). The RF coupling and DC injection DC block 208 provides the ability to superimpose the control signal from ACNTL connection 206 on the same feed line (FEED_P) as the received carrier signals from the low and high frequency antenna elements 102A-1, 102B-1.
Typically, when creating a multi-band antenna, two or more antenna elements are put in parallel. There are several important factors to account for when combining multiple antenna elements. For example, in band (where the antenna is tuned), the impedance as measured at the low frequency tap points 220A, 220B will look like a single pole bandpass (complex pole-pair) filter having a desired impedance at the resonant frequency. Below the tuned frequency, the impedance will look like a short circuit. Above the tuned frequency, the impedance will approach an open circuit. When implementing the low frequency tuning section DC block 214, the low frequency tuning section 207 approaches an open circuit at higher frequencies.
Because the low frequency antenna element 102A-1 looks like an open circuit when the tuning feed network 200 is operating at higher frequencies, the low frequency tuning section 207 is typically able to connect to the high frequency tuning section 205 without issue. However, the high frequency antenna element 102B-1 looks like a short circuit when the tuning feed network 200 is operating at lower frequencies. To protect the low frequency antenna element 102A-1 when operating at lower frequencies, high frequency tuning section DC block 216 is used to electrically open the high frequency antenna element 102B-1.
In alternative embodiments, different capacitors values are able to be implemented for the high frequency tuning section DC block 216. In the illustrated example, the 24 picoFarad capacitor is selected. Similar design considerations are applied when combining additional antennas elements to create tri-band or multi-band antenna elements with, for example, three or more loop antennas.
The antenna array 102 is mounted on the antenna array card 152 to form a two dimensional array of antennas (reference numerals 102-1 to 102-n in
The array 102 is mounted on an antenna section 111 of the antenna array card 152. The antenna array card is typically a circuit board for mounting electronic components such as antenna elements, tuners, demodulators, and feed lines, to list a few examples.
Each antenna (reference numerals 102-1 to 102-n in
In the illustrated implementation, the tuners 104-1 to 104-n are ATSC (Advanced Television Systems Committee) tuners. The tuners 104-1 to 104-n convert received radio frequency signals to a much lower, fixed intermediate frequency signal that the demodulators 106-1 to 106-n are able to demodulate. The demodulators 106-1 to 106-n recover synchronization and decode the signal to MPEG-2 format because it is currently a standard format for the coding of moving pictures and associated audio information. In alternative embodiments, the signal could be decoded to other audio/video formats known in the art.
Typically, the antenna array card 152 is fabricated from a dielectric insulator material. The components are mounted to the antenna array card 152 and are connected via conductive pathways (or tracks). In one embodiment, the antenna array card is approximately 25 inches wide by 21 inches long, or about 0.6 meters (m) by 0.5 m.
An air dam 210 divides the antenna section 111 and the tuner/demodulator section 109. Additionally, the air dam 210 acts as part of a Faraday shield to prevent unwanted interference from the components on the tuner/demodulator section 109 leaking and interfering with the antenna section 111 (and vice versa). Additionally, the air dam 210 acts to constrain airflow to enable adequate cooling of the integrated circuits such and components (e.g., 104-1 to 104-n and 106-1 to 106-n).
A data link connector 160 is installed in a card base plate 161, which is typically formed on the antenna array card 152. The data link connector 160 takes the demodulated signals from the demodulators 106-1 to 106-n and pushes them to the remainder of the encoder system (reference numeral 103 in
Referring back to
The antennas 102-1 to 102-n in the illustrated example are pairs of rectangular shaped loop antenna elements 102A, 102B. The antennas 102-1 to 102-n are arranged create a two dimensional matrix (or array) on the antenna array card (152 in
The side, top, bottom and front walls 150 of the card cage structure 151 are fabricated from a conductive material to maximize Faraday shielding of the antenna elements from the active electronics. The front wall of the card cage provides an open port as the boresight of the antenna array and faces the transmitting antennas. The rear wall 156 includes data transport interfaces that connect to an encoder system 103.
The encoder system 103 is typically located in a basement or ground level building and is comprised of encoding components such as transcoders, computer servers, and storage devices. In a typical implementation, demodulated signals from demodulators 106-1 to 106-nare transmitted to transcoders (not shown) of the encoding system 103. The transcoders transcode the demodulated signals to transcoded content in real time. Typically, the transcoders transcode into MPEG-4 format (also known as H.264), but the transcoders could transcode the demodulated signals into other formats in alternative embodiments. The transcoded content is then indexed and stored in the storage devices and/or streamed to client devices via the Internet.
Within the card cage structure 151, the antenna array boards 152-1 to 152-n are generally spaced about an inch (2.5 centimeters) apart within the enclosure. This distance enables a relatively high density for the antenna array cards 152-1 to 152-n, while reducing unwanted interference between antenna elements to acceptable levels. This configuration helps to further maximize Faraday shielding of the antennas from the active electronics on the antenna array cards.
In a typical implementation, the air dams 210-1 to 210-n act to block the airflow for the antenna array cards 152-1 to 152-n and fill in the gap between the cards such that the air dam of each card engages the backside of its adjacent card. Additionally, the air dams 210-1 to 210-n also act as part of the Faraday shields to reduce interference between the components (e.g., 104-1 to 104-n and 106-1 to 106-n) and the antennas. Typically, the antenna array cards 152-1 to 152-n are orientated vertically, with the antenna elements horizontal to create a horizontally polarized (Electric Field) half omni-directional antenna array. Additionally, the antennas protrude out of the front of card cage 151 to further help reduce interference between the components and the antennas.
Alternatively, if over the air content from the broadcasters has a vertical polarization, which occurs in some locales, then orientation of the antenna array cards 152-1 to 152-n and antennas should be changed accordingly. The illustrated example shows the orientation of the antennas for broadcasters with horizontal polarization.
In the illustrated example, multiple antenna array cards 152-1 to 152-n are installed in the card cage structure 151 and orientated in a vertical position. While only four antenna arrays cards are shown in the illustrated example, the card cage structure 151 is capable of housing between 8 and 32 antenna array cards (or more). If the card cage structure 151 is not filled to capacity, then blank slot cards 180-1 to 180-n are installed to fill the empty slots of the card cage structure.
When antenna array cards 152-1 to 152-n (and antennas) protrude from the card cage structure 151, a three dimensional array of antennas 402 is created.
In some embodiments, multiple card cage structures are housed together in rack mounted chassis (not shown) to further increase the density of antenna array cards where the card cage structures are installed.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/533,813, filed on Sep. 13, 2011, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61533813 | Sep 2011 | US |
