Related Applications

This application claims priority to and incorporates by reference U.S. Provisional Patent Application No. 62/033,244, filed August 5, 2014 and titled "Multiple-input Smart Bias Tee"

Background

Smart Bias Tees (SBT) are often used inside antennas to allow power and control signals for an actuator to be transmitted to the antenna via an RF coaxial cable rather than a separate multi-conductor cable. At the base of the tower, a first SBT puts the power and control onto the RF cable. At the top of the tower, a second SBT pulls it back off. See, for example, US Pat. App. Pub. No. 2007/0161348 (the "'348 Application"), which is incorporated by reference.

Using SBTs to provide DC power and control signals to tower-mounted equipment becomes more complex with dual polarized antennas and/or multi-band antennas. In particular, a current issue is that many antennas have multiple input ports that feed elements on different arrays, with different polarizations, or operating over different frequency bands, each with its own RF cable. The SBT at the base of the tower must be connected to the specific RF cable whose other end is connected to the antenna port that connects to the SBT internal to the antenna. In many cases the antenna is tens or hundreds of meters away from the SBT at the base of the tower. This makes it difficult for personnel at the base to determine which RF cable is the correct one to attach to the SBT. Summary of the invention

An antenna system configured to accept modulated control signals and DC power from a SBT on any RF input is provided. The antenna includes at least two RF feed terminations. A first low pass filter is coupled to a first RF feed termination and a second low pass filter is coupled to a second RF feed termination. A bias tee is coupled to the first and second low pass filters. The bias tee is configured to receive DC power and RF modulated control signals from the low pass filters, and to separate the DC power from the RF modulated control signals. The bias tee includes a demodulator to demodulate the RF modulated control signals into a serial digital control signal, such as an AISG compatible signal.

Brief Description of the Drawings

Figure 1 is a block diagram of a base station radio and antenna employing smart bias tees.

Figure 2 is a block diagram of smart bias tees for a base station radio and a base station antenna.

Figure 3 is a first example of a base station antenna system including a multiple-input smart bias tee configuration according to a first aspect of the present invention.

Figure 4 is a PCB layout of a dual diplexer having a low pass filter for a smart bias tee input according one aspect of the present invention.

Figure 5 is a second example of a base station antenna system including a multiple-input smart bias tee configuration according to a second aspect of the present invention. Description of the Invention

A known application of SBTs is illustrated in Fig. 1. An electrical downtilt of an antenna beam may be controlled by a Remote Electrical Tilt (RET) device 15. A Base Station may comprise three or more such antennas mounted on a tower. A system 10 comprises a control subsystem 16 which interfaces with the RETs 15, a radio 17 which interfaces with the antennae 13, and a DC power supply 18 which provides DC power for all components of the systems 10 and 12.

The control subsystem 16 generates RET control data which is transmitted over a point- to-multipoint serial network to the RETs 15, each of which is assigned a unique bus address, and the RETs generate RET status data which is returned to the control subsystem 16. Similarly, the radio 17 transmits downlink RF signals to the antennae 13, and receives uplink RF signals from the antennae 13.

The RET control data on line 26, a DC bias signal on line 51, and the downlink RF signals on line 52, are multiplexed onto a single coaxial RF feeder cable 24 by a first Smart Bias Tee 25 in the system 10. A second Smart Bias Tee 23 in the system 12 demultiplexes the RET control data onto a line 22, the DC bias signal onto a line 53, and the downlink RF signals onto a line 54. Similarly, the RET status data and the uplink RF signals are multiplexed onto the cable 24 by the second Smart Bias Tee 23, and the first Smart Bias Tee 25 demultiplexes the RET status data and uplink RF signals from the cable 24.

The Smart Bias Tees 23, 25 incorporate microprocessors 30, 40 shown schematically in Fig. 2. These microprocessors can be addressed for routine monitoring purposes, without requiring an operator to climb the tower 11 to attach specialist equipment, and without disturbing the RF path to the antennae 13. The Smart Bias Tees consist of these microprocessors 30, 40, configuration memories 31, 41, serial interfaces 32, 42, connecting switches 35, 45, modems 33, 43, multiplexer/demultiplexer elements 34, 44, and DC voltage and/or current measurement devices 55, 56.

A cellular radio base station 100 according to one aspect of the present invention is illustrated in Figure 3. "Cellular radio," as used herein, includes cell and/or sector based mobile radio communications, including GSM, 3 GPP, LTE, PCS, and like technologies. The cellular radio base station 100 has an antenna 112, a low band radio 114 and a high band radio 116. Antenna 100 may comprise a dual band cellular sector antenna, and further include a smart bias tee 100, a low band feed network 118 and a high band feed network 120.

Antenna 100 preferably includes one or more linear arrays of dual polarized RF radiating elements coupled to the feed networks. For example, an array of dual polarized low band radiating elements may be coupled to the low band feed network 118 and one or more linear arrays of high band radiating elements may be coupled to the high band feed network 120.

As used herein, "low band" refers to RF signals in the range of about 700 MHZ - 960 MHZ. "High band" refers to RF signals in the range of about 1.7 GHZ to 2.5 GHZ.

In the illustrated example, antenna 100 has four RF Ports: 1) low band +45°, 2) low band -45°, 3) high band +45°, and 4) high band -45°. A low pass filter 124 and an RF pass filters 126, 128 is coupled to each of these RF Ports. In the illustrated example, the low pass filters 124 separate out DC- 10 MHz spectrum from the RF spectrum. "DC" refers to Direct Current, e.g., 0 MHz. This DC-10 MHz is then coupled to the Smart Bias Tee 110. The RF pass filters 126, 128 are configured to pass at least radio frequency signals in the operating bands of the radios to which they are coupled. For example, RF pass filters 126 are configured to pass low band RF signals. RF pass filters 126 are coupled between the RF low band +/- 45° ports and low band feed network 118. RF pass filters 128 are configured to pass high band RF signals. RF pass filters 128 are coupled between high band +/- 45° ports and the high band feed network 120. The low band radio 114 is coupled to the low band ports of the Antenna 100 by RF Feeds 130. The high band radio 116 is coupled to the high band ports of the antenna 100 by RF Feeds 132.

In alternative examples, the low pass filter 124 may be configured to have a wider or narrower pass band, such as DC-5MHz, or DC-50MHz or more. However, the low pass filter 124 should be configured to block low band RF and high band RF signals from being combined at the Smart Bias Tee. Low pass filters 124 are typically passive devices, and due to the reciprocity of passive devices, if low pass filters 124 passed signals in the low band or high band, undesirable interference between ports would occur. The termination of the RF feeds should allow the low band RF and high band RF signals to pass through to the feed networks for the low band and high band radiating elements, respectively.

In the example as illustrated, the base station smart bias tee 134 is located on the low band -45° RF Feed of low band radio 114. However, it could have been located on any of the other RF Feeds illustrated in Fig. 3. This represents advancement since it is not necessary for the installer to keep track of which port of which radio is attached to the Smart Bias Tee. In some embodiments a single PCB may contain transmission lines for each RF port as well as the low pass filters that lead to the Smart Bias Tee. In other cases the low pass filters may be connected to the Smart Bias Tee via conductors. Since the low pass filter can be implemented simply in a small amount of space, the additional cost is easily outweighed by the labor savings associated with the simplified installation.

Referring to Fig. 4, according to one aspect of the invention, a dual diplexer is implemented on a single dual diplexer PCB 200. Each diplexer circuit includes an RF input 202, first RF output 204 and second RF output 206. Each output 206 may be DC isolated from input 202 by providing a break in the RF signal path and including capacitive coupling areas 207a, 207b (illustrated in the lower diplexer) adjacent to the break. A coupling section 207c

(illustrated in cross hatch in the upper diplexer) may be included on an adjacent layer of metallization to provide an AC signal path from coupling area 207a to coupling area 207b, without passing DC power. Each diplexer circuit also contains a low pass circuit 208. The two low pass circuits 208 connect together at a cable junction 210. The cable junction 210 is coupled by cable to the Smart Bias Tee circuit.

In another embodiment illustrated in Fig. 5, the dual band antenna 212 may have two ports, one for +45° polarization and one for -45° polarization. The dual band antenna 212 may be coupled to a dual band radio 214 by RF feeds 216. For each polarization, the dual band antenna 212 may further include diplexers 218 that couple each input port to two arrays of radiating elements, each operating at different frequencies. The diplexers 218 may comprise dual diplexers as illustrated in Figure 4. The diplexers couple low band signals to a low band feed network 220 via a low pass filter 222 and couple high band signals to a high band feed network 224 via a high pass filter 226. A very low pass filter 278 is coupled to each diplexer 218 to demultiplex control signals and DC power and couple the control signals and DC power to a Smart Bias Tee 230. The antenna 212 may contain radiating arrays arranged to radiate in different polarizations at each band, resulting in 4 arrays connecting to two RF ports. This is another way to reduce the number of cables running to the antenna. In this case the Smart Bias Tee can be connected to the two input ports, reducing the total cable count from 5 cables to 2 cables. In the illustrated example, SBT 232 of dual band radio 214 multiplexes DC power and control signals onto RF Feed 216.

Referring to Figure 6, a SBT 300 which may be employed in antenna 112 and/or 212 is illustrated. The SBT 300 is similar to the SBT 23 of Figures 1 and 2 in certain respects.

However, SBT 300 does not receive low band RF or high band RF signals, and does not require filters or other structure to separate out low band or high band RF signals. SBT 300 includes a filter 344 to separate out DC Voltage from the RF modulated control signal. SBT 300 includes a modem 443 which modulates/demodulates control information to / from the RF feed, depending on the direction of information flow. SBT 300 incorporates microprocessor 340 and

configuration memory 341. Microprocessor 340 may be addressed for routine monitoring purposes. Switch 345 routes information to/from microprocessor 340 or to RET equipment external to the SBT 300 via an AISG serial port. DC voltage block 356 maintains proper voltage levels.