L-shaped indoor antenna

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L-SHAPED INDOOR ANTENNA ANDREW CORPORATION C: 39767

L-SHAPED INDOOR ANTENNA

BACKGROUND OF THE INVENTION

In conventional cellular and PCS (personal communications system) wireless systems, signals transmitted from a base station (cell site) to a user (remoter terminal) are usually received via an omni-directional antenna; often in the form of a stub antenna. 5 These systems often sacrifice bandwidth to obtain better area coverage, stemming from the result of less than desirable signal propagation characteristics. For instance, the bit (binary digit) to Hz ratio of the typical digital Cellular or PCS system is often less than 0.5. Lower binary signal modulation types, such as BPSK (Binary Phase Shift Keying) are used, since the effective SNR (Signal to Noise Ratio) or C/I (Carrier to Interference 10 Ratio) are often as low as 20 dB. In fact, for voice based signaling, the threshold C/I (or S/N) ratio for adequate quality reception of the signal is about 17 dB.

For wireless systems directed towards data applications, it is desirable to significantly increase the SNR or C/I in order to employ higher order (binary) modulation techniques, such as QAM-64 (Quadrature Amplitude Modulation, with 64 points in the is complex constellation). These higher order modulation schemes require substantially greater C/I (or SNR) thresholds; typically higher than 26 dB. For the case of MMDS (multi-user multipath distribution system) signals, where the carrier frequencies are higher (around 2500 MHz), the propagation characteristics are even worse. There is a need therefore for transmission systems that can both satisfy the coverage (propagation) 20 demands, as well as generate high C/I or SNR levels.

One option is to increase the size of the terminal equipment (TE), or remote, antenna gain. This requires increasing the size. Additionally, it helps to increase the elevation (i.e., vertical height above ground level) of the antenna. The higher you place an antenna, the better the system gain. For a simple planar earth model, the total system 25 path loss (attenuation) is a function of each (transmit and receive) antenna’s directive gain (towards one another). However, this path loss is also a function of the height (from ground level) of each antenna. Thus, as you increase the height, from ground, the total system path loss decreases, which is an increase in the overall system link performance, or system gain. The link performance (system) gain increases 6 dB every time you double 30 one of the antenna’s height from the ground level. If you double both (i.e., transmitting 1 CHICAGO 128032vl 47176-00508 and receiving) antennas’ heights, the total gain (link performance) goes up by 12 dB (6 dB + 6 dB). Therefore, doubling the height from the ground is equivalent to quadrupling the size (area) of the antenna, which produces 4X (or 6 dB) of directive gain.

In conventional analog MMDS systems, this (i. e., increase of SNR or C/I) has 5 been traditionally accomplished by installing a large reflector type antenna (with up to 30 dBi of directional gain) on a rooftop, or a pole. The disadvantages are a complex, difficult, and costly installation; as well as poor aesthetics.

The migration of the MMDS frequency spectrum, from an analog video system, to a wireless data and Internet system, demands a more user friendly (easier) installation io method, with much lower cost. The difficulty here is designing a system with sufficient directional gain, as to overcome loss with transmission through walls, as well as being easy to install, and orient; by the consumer, or other persons without specialized skills.

SUMMARY OF THE INVENTION is In accordance with one aspect of the invention, there is provided an easy to install, high gain, omni-directional “indoor” antenna which provides omni-directional coverage. No installation, “pointing” or orientation is required, and the antenna may be installed indoors in a corner of a room.

In accordance with another aspect of the invention, four antenna elements are 20 formed as a “book,” that is, two each, back to back; with the pairs oriented at 90° to each other, such that each separate antenna covers a 90° sector, so that the coverage of the antennas when summed creates a full 360° coverage.

BRIEF DESCRIPTION OF THE DRAWINGS 25 FIG. 1 is a perspective view showing an antenna in accordance with the one form of the invention; FIG. 2 is a top plan view of the antenna of FIG. 1; FIG. 3 is a perspective view, showing an antenna in accordance with the invention placed in a typical room; 30 FIGS. 4 and 5 are views similar to FIG. 1, showing antennas in accordance with two further embodiments of the invention; FIG. 6 is a schematic showing of a summation/splitting device; CHICAGO l28032vl 47176-00508 FIG. 7 is a view similar to FIG. 1 showing an antenna in accordance with yet another embodiment of the invention; FIG. 8 is a schematic view, similar to FIG. 6, further illustrating a summer/splitter; FIG. 9 is a schematic view illustrating use of a 4:1 RF switch with control from a modem; FIG. 10 is a diagrammatic showing of an antenna in accordance with one form of the invention, having an internal RF summer/splitter; FIG. 11 is a view similar to FIG. 10 showing an RF transceiver or transverter incorporated into the antenna assembly; and FIG. 12 is a view similar to FIGS. 10 and 11 showing both a transceiver and modem incorporated into the antenna assembly.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring initially to FIG. 1 and FIG. 2, there is shown the general structure for a “book” antenna system 20 in accordance with the invention, having two rectangular (shown square in FIG. 1) sections 22, 24 joined along a common edge. The two sections, 22, 24 are joined at a 90 degree angle, thus allowing the antenna 20 to fit squarely into a corner, between two walls, in a room (see FIG. 3), so as to resemble an open “book” in appearance. ,

Using micro strip (patch) antenna technology allows the thickness of the sections 22, 24 to be well under one inch. Each section 22, 24 is comprised of a front (26, 28) and a back (29, 30), with each face (front and back) containing an antenna element 32, 34, 36, 38 (or multiplicity of elements, in an array, see, e g., FIGS. 4, 5 and 7). Thus there are four (4) distinct antenna faces, each pointing in opposing or orthogonal directions from one another. FIG. 2 shows a top view of the antenna system, denoting the four distinct faces 26, 28, 29 and 30. Each face contains a microstrip/patch antenna 32, 34, 36 and 38. For this particular example, each patch antenna 32, 34, 36, 38 generates a 90° azimuth beam width. The combination of the four 90 degree beams generates an effective 360 degree coverage; thereby emulating an omni-directional antenna. FIG. 3 shows the placement of the antenna 20 at the corner of two walls 42, 44.

For optimal performance the antenna system should be placed as high as possible (i.e. CHICAGO 128032vl 47176-00508 00 0 A tr. 1------» ’ near the ceiling 46) to maximize signal reception and transmission to a base station (not shown). FIGS. 4 and 5 show two different variants of antenna element types, which can be used as or in place of the antenna elements 32, 34, 36, 38 of the preceding embodiments. s FIG. 4 shows a vertical array (multiplicity of elements) of patch/microstrip antenna elements 52, 54, on each face 26a, 28a of a “book” antenna 20a. It will be understood that similar arrays are on the rear faces which are not visible in FIG. 4. For the case of a multiplicity of antenna elements (on each face) a parallel or series corporate feed structure (not shown) would be used, designed for correct amplitude and phase matching, to io generate the desired elevation beam. FIG. 5 shows the same sort of arrays, however, using dipole antenna elements 62, 64, on faces 26b, 28b of “book” antenna 20b. Similar arrays of dipoles are used on the other two faces which are not visible in FIG. 5. FIG. 6 shows a summation/splitting mechanism 72, in which the input/output path(s) from the antenna element(s) on each face of the “book” antenna of any of the is preceding figures is RF summed to generate a single RF input/output path to/from the antenna system. For each of the four faces, the array corporate feed (or RF transmission line, for the case of a single element) is summed, in phase, with the other faces, to generate a single RF input/output.

Up to this point, it has been assumed that the transmit and receive bands of the 20 system are all within the VSWR bandwidth of a single patch/microstrip (or dipole) element. However, for the case where the transmit and receive bands of the system are further apart (say, more than 10% of the carrier frequency), then two different arrays can be used for each face. Shown in FIG. 7, is the case where there is a transmit (Tx) patch/microstrip (or dipole) array (vertical) 82, 86 and a receive (Rx) array (vertical) 84, 25 88, on each face 26c, 28c of antenna 20c. The same arrangement of Tx and Rx elements would be used on the faces which are not visible in FIG. 7. Two distinct sum/split circuits of the type shown in FIG. 6 would be used (see e.g., FIG. 8) - one for Tx and one for Rx, generating two distinct, separate RF ports (one for the transmit band, and one for the receive band). The antenna system can therefore output two different RF transmission 30 lines, or cable, or (frequency) diplex them (via a frequency diplexer module 95, see FIG. 8) into a single RF transmission line, or cable 90. CHICAGO !28032vl 47176-00508

The concept as described thus far generates an omni-directional system, which splits the power (four ways) from the input/output transmission line, to each independent 90 degree sector “face,” as indicated in FIG. 8. However, this splitting/summing device 72 (72a) has the effect of reducing the overall system directional gain by 6 dB. One 5 method to overcome this is to substitute a 4:1 RF switch 92 as shown in FIG. 9. This can be a combination of PIN diodes (not shown), which are biased/controlled via a control line 94 (or set of control lines) from a modem 96. The modem 96, or an associated contoller or “PC” 98 can be programmed to sequentially switch the RF path to each antenna face, measure the RF power, and then select the face with the maximum power. io A suitable RF transceiver/transverter (Tc) 100 is interposed between the 4:1 RF switch 92 and the modem 96. In this case, the system would still have omni-directional capability, yet would increase the overall system (directive) gain by 6 dB. This additionally reduces the amount of signal scattered throughout the network, and increases the overall network C/I. This also increases the user friendliness of the system, allowing easier installation by is the user, with the antenna “pointing” done by the system itself. FIG. 10 shows one embodiment of the “book” antenna 20 of the invention at a corner of two walls 42, 44, with an internal (i.e., built into the antenna structure) RF Summer/Splitter or a 4:1 RF switch 110, with control from the modem 96 shown by the dotted line in the case of a 4:1 RF switch. The RF output (coaxial line) 90 from the 20 antenna system can run down the comer of the wall into the RF transceiver 100 (or “transverter”, as it is denoted in the MMDS industry). The RF transceiver 100 is interfaced to the modem 96 via an IF cable 102 (coaxial or twisted pair). The RF switch 110 may be physically mounted to the surface of the substrate or backplane (such as a printed circuit board or card) which forms one of the sections 22, 24. 25 FIG. 11 shows an embodiment where the RF transceiver (“transverter”) 100 is also incorporated into the antenna assembly. This can be accomplished via a separate (transceiver) box attached to the unit, or by incorporating the transceiver electronics onto the same PCB material as the microstrip antennas. FIG. 12 shows incorporation of both the transceiver 100 and modem 96 into the 3o antenna assembly. Here, an Ethernet or USB (Universal Serial Bus) cable 120 is run down the wall corner directly to the PC 98, or LAN network server. CHICAGO 128032vl 47176-00508

The antenna of the invention may be used in many applications including without limitation: MMDS (Wireless Internet) MMDS (analog video) 5 Cellular (indoor) PCS (indoor) 3G systems

While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the 10 precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims. CHICAGO 128032v 1 47176-00508