Power shared linear amplifier network

The present invention relates to an antenna system utilizing a power sharing network to facilitate linear operation of power amplifiers by equally distributing an electromagnetic communication signal to the plurality of power amplifiers provided in the antenna system of the present invention. The power sharing network configuration enables linear power amplifier sharing with an input signal. In particular, the present invention antenna system provides a circuit arrangement providing a greater number of linear power amplifiers relative to antenna elements provided.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to a power shared linear amplifier network 
which includes a plurality of amplifiers which are arranged to equally 
amplify an input communication signal, and more particularly relates to an 
antenna system incorporating a greater number of amplifiers than antenna 
elements provided. 
2. Description of Related Art 
It is desirable to configure a system to receive and transmit all of the 
electromagnetic signals within a transceiver's capability as limited by 
sensitivity and bandwidth. Signals of interest are usually incident from 
widely diverse directions. Therefore, prior art methods have utilized 
antennas having a wide azimuth beam width, such as omni directional 
broadbeam antennas, as the systems receptor and transmitter element. 
A severe limitation of this approach is that it does not permit directional 
narrowbeam resolution of multiple signals. Such resolution is usually 
desirable to prevent garbling of signals that cannot otherwise be resolved 
in frequency or time-of-occurrence. Directional resolution is also 
desirable in cases where the direction of incidence of the signals is to 
be estimated. 
An attempt to overcome the above mentioned disadvantages is the utilization 
of narrow-beam antennas. In such a system, multiple antennas, each 
producing a narrow beam, are arranged in a circular pattern wherein their 
RF beams are contiguous and point radially outward. In yet another system, 
a single cylindrical array antenna is configured to form multiple RF beams 
which are contiguous and point radially outward. Therefore, in both 
aforementioned systems, each RF beam port of the antenna(s) is connected 
to a separate dedicated transceiver, power amplifier and associated 
antenna components, enabling its respective system to exhibit the 
advantages of both good directional resolution and complete simultaneous 
directional coverage. Further advantages provided are reduction in 
co-channel interference, reduction in the RF signal delay spread, 
reduction in amplifier power and reduction in the required number of cell 
sites. 
However, there are shortcomings associated with the above-mentioned 
systems. Such shortcomings include the high cost of multiple dedicated 
receivers and transmitters which are compartmentalized by each RF beam. 
Further, when many narrow RF beams are present at a cell site, the traffic 
in each RF beam may fluctuate. Moreover, a narrowbeam antenna typically 
requires a large antenna aperture, and when there are N narrow RF beams, 
the required antenna aperture is N times larger. 
Yet another severe limitation of the aforementioned narrowbeam antenna 
systems are the provision of multiple dedicated power amplifiers being 
individually coupled to each RF beam port of the aforementioned 
antenna(s). Such dedicated amplifiers are both costly and inefficient in 
view of that a single power amplifier may operate with a considerable 
higher output power level at any given time in comparison to the remaining 
power amplifiers of the antenna system since a particular RF beam of the 
antenna system may have to handle considerably more RF signal traffic in 
comparison to the remaining RP beams of the prior-art antenna system. 
Thus, there exists a need to provide an antenna system which enables the 
sharing of the base station antenna associated components (i.e., 
transmitters, receivers and signal amplifiers) by all narrow 
electromagnetic beams at a cell site base station. Such sharing will 
facilitate increased trunking efficiency as well as enable the handling of 
unexpected concentrations of calls from a particular electromagnetic beam, 
such as during rush hour jams. 
SUMMARY OF THE INVENTION 
The present invention relates to an antenna system which incorporates a 
power sharing network for enabling equal component distribution in 
conjunction with an electromagnetic signal being processed therein. The 
antenna system includes a plurality of antenna elements for providing 
directional narrowbeam resolution of multiple electromagnetic transmission 
beams. The antenna system further includes a first power sharing network 
coupled to a plurality of linear power amplifiers, which in turn are 
coupled to a second power sharing network. Preferably, the first and 
second power sharing networks each include a Butler Matrix. The plurality 
of antenna elements are respectively coupled to the output ports of the 
second power sharing network. In particular, there is provided a greater 
number of linear power amplifiers than antenna elements provided. 
The first power sharing network is operative to equally distribute a 
received input signal from one of its input ports to the plurality of 
linear power amplifiers coupled thereto in substantially equal power 
levels and being staggered in phase relative to one another. The plurality 
of linear power amplifiers then independently amplify each aforementioned 
respective output signal of the first power sharing network. The second 
power sharing network is operative to receive the aforementioned phase 
staggered amplified signals (which are a function of the input signal) and 
provide an output signal which has an average power level relative to the 
combined power level of each aforementioned phase staggered amplified 
input signal to the second power sharing network. The averaged output 
signal is then applied to one of the narrowbeam antennas whereby it is 
radiated therefrom in a directional electromagnetic narrowbeam 
transmission signal

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, in which like reference numerals identify 
similar or identical elements, FIG. 1 illustrates a prior art example of a 
compartmentalized narrow beam antenna base station, designated generally 
by reference numeral 10. The base station 10 includes N narrow beam 
antennas 12, with each narrow beam antenna 12 having an associated 
electromagnetic beam 14. Further, each narrow beam antenna 12 is coupled 
to a dedicated power amplifier 16 which in turn is coupled to a summing 
circuit 18. Each summing circuit 18 is further coupled to M modulators 20, 
wherein there are M modulators 20 per electromagnetic beam 14. Thus, the 
N-beam base station 10 is ideally configured to serve M.times.N RF 
channels. However, in commercial applications the aforementioned N-beam 
base station 10 is unable to serve M.times.N RF channels, since calls are 
blocked at a much higher rate because channels are not shared between 
beams. 
Further, in the event of a heavy concentration of users utilizing a 
particular beam, an individual narrowbeam antenna 12 may be required to 
transmit to the aforementioned heavy concentration of users. To 
accommodate the increased usage, the power amplifier 16 of the narrow beam 
antenna 12 associated with the aforementioned heavy concentration of users 
will have to increase its output power to such a level which may 
potentially overload the aforementioned power amplifier 16. 
FIG. 2 illustrates an antenna system constructed in accordance with the 
present invention and designated generally by reference numeral 100. 
Antenna system 100 has N broadbeam antenna elements 110 coupled to a power 
sharing network 112. Briefly, as will be described in more detail below, 
the power sharing network 112 preferably includes N input ports 113 and N 
output ports 115, and is operative such that when an input signal is 
applied to one of its input ports 113, a plurality of output signals 
(which are a function of the input signal) are provided at the N output 
ports 115 in equal power levels and staggered in a predefined angular 
phase relationship to one another. The power sharing network may encompass 
any known circuitry such as quadrature hybrids, lange couplers, branchline 
couplers or any equivalent structure adapted to receive an input signal 
and provide at least two output signals in substantially equal power 
levels and staggered in a predefined angular phase relationship to one 
another. Typically, the output signals have a angular phase stagger 
relative to one another of: 
##EQU1## 
wherein .+-.K is the beam number. 
With reference now to FIGS. 3 and 3a, and in accordance with a preferred 
embodiment of the present invention, the power sharing network 112 is to 
be described in terms of a Butler Matrix device, designated generally by 
reference numeral 117. Butler Matrix 117 is a passive and reciprocal 
microwave device which performs the standard mathematical transform (i.e., 
a spatial fourier transform) of a linear array. Butler matrices and their 
operation are known in the art. Butler Matrix 117 of FIG. 3 is a four port 
butler matrix, which has a set of four inputs A, B, C and D and a set of 
four outputs A', B', C' and D'. Butler Matrix 117 includes four 90.degree. 
phase lead hybrids 118 (FIG. 3a) and two 45.degree. phase shifters 120 
interconnected to one another and to the two sets of four inputs A, B, C 
and D as shown. The four port matrix 117 is considered here for 
simplicity, but one skilled in the art will appreciate that Butler 
Matrixes can be designated with any number of desired ports (i.e., Butler 
Matrix 117 of FIG. 2 is a log.sub.2 N stage Butler Matrix having N input 
and output ports) as is described in a paper entitled "Butler Network 
Extension to any Number of Antenna Ports" by H. E. Foster and R. E. Hiatt, 
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, (November 1970). 
In the traditional use of the aforementioned Butler Matrix 117, ports A, B, 
C and D would be the input ports, and ports A', B', C', and D' would be 
the output ports and would be attached to radiator elements of an antenna 
system. In particular, and in accordance with the base station 100 of the 
present invention, each input port of the Butler Matrix 117 is decoupled 
from the remaining N-1 other input ports. Therefore, there is no inherent 
loss if RF signals are combined into the same frequency band. Further, the 
Butler Matrix 117 is configured such that the signal applied at one input 
port (A, B, C or D) is divided equally among all the output ports which 
results in signals of equal amplitude and linear phase gradient at output 
ports A', B', C' and D' whereby the phase gradient is determined by which 
input port is excited. Further, exciting a single input port results in a 
specific far field radiation or mode pattern. Thus, the signal phases from 
the output ports of Butler Matrix 117 are configured to form distinctive 
narrow electromagnetic beams from the output ports which are unique to 
each input port. A Butler Matrix 117 which is suitable to be implemented 
in the antenna systems of the present invention described herein is Part 
No. P.O.- CJEO43992, commercially available from Anaren. 
However, as mentioned above, the power sharing network 112 is not to be 
understood to be limited to the aforementioned Butler Matrix 117, but 
rather may encompass any equivalent circuitry, such as a quadrature hybrid 
coupler as illustrated in FIG. 4, designated generally by reference 
numeral 119. Quadrature hybrid couplers 119 are known in the art and 
therefore do not need to be described herein. 
Referring back to FIG. 2, the power sharing network 112 enables antenna 
aperture sharing whereby N narrow electromagnetic beams 124 are formed by 
N broadbeam antenna elements 110 (coupled to power sharing network 112) 
since the power sharing network 112 properly phases the signal from an 
input port 113 to a corresponding radiated beam 124. Thus, instead of N 
narrow beam antenna apertures for N electromagnetic beams (as in the prior 
art narrow beam antenna system of FIG. 1) a single broadbeam antenna 
aperture having an array of broadbeam antenna elements 110 is used to form 
N narrow electromagnetic beams 124. Further, since the aforementioned 
narrow electromagnetic beam 124 formation facilitated by power sharing 
network 112 is provided by the N broadbeam antenna elements 110 which each 
have less than a 120.degree. beamwidth, an omni directional base station 
coverage thus requires at least three power sharing networks 112, which 
results in an antenna aperture of a single narrowbeam antenna 
(360.degree.). 
Antenna system 100 further includes N linear power amplifiers 126 
respectively coupled intermediate the N broadbeam antennas elements 110 
and the N output ports of power sharing network 112. Each N linear power 
amplifier 126 is operative to increase the power level of a RP signal 
radiated from a respective broadbeam antenna element 110 coupled thereto, 
wherein the output signal of the linear power amplifier 126 is essentially 
proportional to its input signal. An example of aforementioned linear 
power amplifier 126 and broadbeam antenna 110 adapted for implementation 
in the antenna system of the present invention described herein is 
respectively Part No. ZHL-2-50P3, commercially available from 
Mini-Circuits and Part No. AG-1384, commercially from Radiation systems, 
Inc. 
Therefore, power sharing network 112 is operative to enable each N 
electromagnetic narrowbeam 124 to equally distribute usage of the N linear 
power amplifiers 126. The aforementioned equal distribution of the N 
linear power amplifiers 126 preferably corresponds to the situation when 
all the N electromagnetic narrowbeams 124 of the N broadbeam antenna 
elements 110 share a common planar antenna aperture (i.e., forming N 
electromagnetic narrowbeams over a 120.degree. sector). 
As mentioned above, each linear power amplifier 126 is coupled to a power 
sharing network 112 which is configured to distribute each N input signal 
158 to all N linear power amplifiers 126 with equal power distribution. 
Therefore, regardless of how RF transmitting signals are distributed among 
the N input ports of the power sharing network 112, the N linear power 
amplifiers 126 equally handle the same average power relative to the 
transmitting electromagnetic signals. 
The aforementioned equal power distribution of the N linear power 
amplifiers 126 provides advantages over the prior art base station 10 
(FIG. 1) in that the power level in each linear power amplifier 16 (FIG. 
1) varies in accordance with the RF traffic distribution therein with a 
particular narrow beam antenna 12. The maximum average power per linear 
power amplifier 126 in accordance with the present invention is 
proportional to the maximum number of RF channels (K) served by the 
antenna system 100 and the number (N) of linear power amplifiers 126 
provided therein. For example, in the prior art, if M is to be designated 
the number of RF channels served by any given electromagnetic beam, then 
the average power per linear power amplifier is only proportional to M. 
However, with the aforementioned antenna system 100 of the present 
invention, the average power per linear power amplifier 126 is 
proportional to K/N when functioning with K number of RF channels which is 
advantageous in that it prevents over-saturation of the linear power 
amplifiers 126 while increasing trunking efficiency. 
FIG. 5 illustrates an antenna system 200 adapted to have transmitting 
capabilities and which incorporates an intermediate frequency (IF) 
crossbar switch 210 which is functional to reduce the number of modulators 
needed to serve K electromagnetic channels. Crossbar switch 210 is a 
switch having a plurality of vertical paths, a plurality of horizontal 
paths, and electromagnetically-operated mechanical means for 
interconnecting any one of the vertical paths with any one of the 
horizontal paths. The antenna system 200 further includes a power sharing 
network 212 which has its N outputs respectively connected to N linear 
amplifiers 214, which in turn are respectively coupled to N broadbeam 
antenna elements 216. As mentioned above, each broadbeam antenna element 
216, in conjunction with the power sharing network 112, is adapted to 
respectively provide an electromagnetic narrowbeam 218, and to equally 
share in the power distribution of the N linear power amplifiers 214 
coupled thereto. The N input ports of the power sharing network 212 are 
respectively coupled to the IF crossbar switch 210, which in turn, is 
coupled to K modulators 220. The arrangement of the IF crossbar switch 210 
being coupled to the power sharing network 212 provides advantages over 
the prior art system of FIG. 1, in that it reduces the number of 
modulators needed to serve K RF channels from M.times.N . An example of 
the modulators 220 and IF crossbar switch 210 which may be implemented in 
the antenna system of the present invention described herein are 
commercially available as a single unit from AT&T as an Auptoplex.RTM. 
cell site base station. 
Referring now to FIG. 6, an antenna system 250 is shown having signal 
reception capabilities. Antenna system 250 incorporates a power sharing 
network 112 and is substantially similar to the antenna system 200 of FIG. 
5 except for the exclusion of the K modulators 220 and the provision of K 
demodulators 254 thereof being coupled to the IF crossbar switch 210, and 
the exclusion of the N linear power amplifiers 126 and the provision of N 
pre-amplifiers 258 thereof. Pre-amplifier 258 is an amplifier connected to 
a low-level signal source (broadbeam antenna elements 216) and is adapted 
to present suitable input and output impedances and provide an appropriate 
amount of gain whereby the electromagnetic signal may be further processed 
without appreciable degradation in the signal-to-noise ratio. The K 
demodulators 254 enable antenna system 250 to have receiving capabilities, 
wherein the K demodulators 254 are operative to de-modulate a received 
signal 256, via antenna elements 216, to its original modulating wave. 
Antenna system 250 is adapted to provide an electromagnetic narrowbeam 
signal to each aforementioned K demodulator 254, via the N broadbeam 
antenna elements 216. The aforementioned electromagnetic narrowbeam 
signals are provided by the power sharing network 112 through antenna 
aperture sharing of the broadbeam antenna elements 216 associated 
therewith. 
With reference now to FIG. 7, the above-described transmitting and 
reception antenna systems 200 and 250 may preferably be coupled to one 
another so as to form an antenna system having both a transmitting portion 
200 and a reception portion 250. Preferably, the aforementioned N 
broadbeam antenna elements 216 are coupled to both the transmitting 200 
and reception portion 250 of such an antenna system. For example, to 
enable the aforementioned diplexing operation between the transmitting 
portion 200 and the receiving portion 250 of the above mentioned antenna 
systems, N conventional diplexers and/or circulators 260 may preferably be 
provided to facilitate simultaneous transmission or reception of two 
signals utilizing a common broadbeam antenna element 216. 
Another alternative embodiment of the present invention is illustrated in 
FIG. 8, wherein antenna system 300 is adapted to equally distribute the 
power of N linear power amplifiers 352 to N narrowbeam antennas 354. Each 
narrowbeam antenna 354 has its own antenna aperture, thus the antenna 
system 300 is adapted to equally distribute linear amplifier 352 power to 
an input signal at an RF channel 364. To effect such power distribution, 
antenna system 300 includes a first power sharing network 356 and a second 
inverse power sharing network.sup.-1 358. Briefly, the inverse power 
sharing network.sup.-1 358 includes an inverse Butler Matrix in comparison 
to the Butler Matrix employed in the first power sharing network 356. The 
second power sharing network 358 essentially identical to the first power 
sharing network 356 with the exception that the output ports are now used 
as input ports. An RF signal fed into one port of the first power sharing 
network 356 will only appear at the corresponding output port of the 
inverse power sharing network.sup.-1 358. The correspondence between input 
ports of 356 and output ports of 358 are found by reversing the 
left-to-right sequence to right-to-left. Briefly, the output signal of the 
inverse power sharing network.sup.-1 358 is an inverse fourier transform 
relative to the output signal of the first power sharing network 356. 
The first power sharing network 356 has N input ports 362 which are 
respectively coupled to N RF channels 364. Power sharing network 356 is 
further provided with N output ports 366 which are respectively coupled to 
the N linear power amplifiers 352. These amplifiers are respectively 
coupled to the N input ports 360 of the second power sharing 
network.sup.-1 358, wherein the N output ports 362 of the second power 
sharing network 358 are respectively coupled to the N narrowbeam antennas 
354. In operation, the first power sharing network 356 distributes the N 
input signals 364 (each signal consisting of a group of RF channels 
destined for a given antenna beam) from one of its respective input ports 
362 to the N linear power amplifiers 352, via output ports 366, with equal 
power distribution. The second power sharing network.sup.-1 358 is 
operative to concentrate the aforementioned amplified input signals back 
to the originally destined narrowbeam antenna 354 by exciting only the 
output port 362 of the second power sharing network.sup.-1 358 which 
corresponds to a particular input port 362 of power sharing network 356 to 
which the input signal was applied. 
Yet another alternative embodiment of the present invention antenna system 
is illustrated in FIG. 9, designated generally by reference numeral 400. 
Briefly, antenna system 400 is adapted to equally distribute the power of 
N linear power amplifiers 352 to a plurality of broadbeam antenna elements 
402. Antenna system 400 is similar to antenna system 300 described above 
in that antenna system 400 utilizes the above described arrangement of the 
first power sharing network 356 and second power sharing network 358 to 
effect equal power distribution of the N linear power amplifiers 352 
coupled therebetween. However, as will be described below, antenna system 
400 utilizes a plurality of broadbeam antenna elements 402 for providing 
directional resolution of multiple RF signal transmission beams therefrom, 
in contrast to the narrowbeam antenna elements 352 of antenna system 300. 
Antenna system 400 includes an RF switching network 404 having M input 
ports 408 and N output ports 410, wherein its M input ports 408 are 
respectively coupled to M RF transmitters 406, while its N output ports 
410 are respectively coupled to the N input ports 355 of the first power 
sharing network 356. A plurality of third power sharing networks 412 are 
coupled to the N output ports 361 of the second inverse power sharing 
network 358. Coupled to the respective output ports 413 of each third 
power sharing network 412 is a broadbeam antenna element 402. 
Therefore, antenna system 400 is configured such that an RF signal from one 
of the M RF transmitters 406 is received at one of the M input ports 408 
of the RF switching network 404. The RF switching circuit 404 then 
selectively switches the aforementioned RF signal to one of its N output 
ports 410. The RF signal is then coupled to a corresponding N input port 
355 of the first power sharing network 356, wherein the RF signal is 
distributed and equally amplified by the N linear power amplifiers 352. 
The second inverse power sharing network 358 receives the N amplified RF 
signals at its respective N input ports 357 and is operative to 
concentrate the aforementioned amplified RF signals to an N output port 
361 which corresponds with the N input port 355 of the first power sharing 
network 356 which originally received the RF signal, via the RF switching 
network 404. The aforementioned concentrated RF signal is then received at 
a corresponding input port 411 of a third power sharing network 412 
associated with the aforementioned output port 361 of the second inverse 
power sharing network 358 which provides the concentrated RF signal. The 
third power sharing network 412 is then operative to radiate the 
concentrated RF signal from the broadbeam antenna elements 402 associated 
therewith in directional narrowbeam transmission signals, as described 
above. 
Still another preferred embodiment of the present invention antenna system 
is illustrated in FIG. 10, designated generally by reference numeral 500. 
Antenna system 500 is similar to antenna system 300 described above in 
that antenna system 500 utilizes the above described arrangement of the 
first power sharing network 510 and second power sharing network 512 to 
effect equal power distribution of the M linear power amplifiers 502 
coupled therebetween. However, as will be described below, antenna system 
500 utilizes a greater number of amplifiers 502 relative to antenna 
elements 506. 
Briefly, antenna system 500 is provided with M linear power amplifiers 502 
and N transmitters 504 and antenna elements 506, wherein M&gt;N. This 
arrangement is advantageous in that the increased number of linear power 
amplifiers 502 provides a more efficient antenna system. In particular, 
the increased number of linear power amplifiers 502 preferably enables the 
utilization of lower level power amplifiers relative to the power level of 
a linear power amplifier when there are N linear power amplifiers and 
antenna elements. The aforementioned utilization of the foregoing 
comparatively low level power amplifiers 502 is advantageous in cost 
efficiency as the monetary cost of power amplifiers considerably increases 
as its power rating increases, as is well known. 
Further, the redundancy effect of having M linear power amplifiers 502 
serving N antenna elements 506 (wherein M&gt;N) is advantageous in that if 
one or more linear amplifiers 502 fail, antenna system 500 still remains 
operable in that each antenna element 506 receives an amplified signal 
equally from the remaining operable linear power amplifiers 502. For 
example, in the prior art system (See FIG. 1), each antenna element 14 was 
coupled to a dedicated power amplifier 16, and when such a dedicated power 
amplifier 16 failed, the antenna element 14 coupled thereto was inoperable 
to radiate an electromagnetic beam therefrom. 
Yet a further advantage of employing M low level power amplifiers 502 is a 
lessening in the cooling requirements for the antenna system 500, since 
the cooling requirements for a linear power amplifier increases as its 
power rating increases, as is well know. 
Antenna system 500 includes first and second power sharing networks 510 and 
512 each respectively having M input ports and output ports. As mentioned 
above, each first and second power sharing network 510 and 512 is 
preferably a Butler matrix having M input ports and M output ports wherein 
a spatial fourier transform is interpolated on an input signal thereinto. 
Coupled to the N of the M input ports of power sharing network 510 is 
respectively N RF transmitters 504 each being adapted to provide an input 
RF signal. Thus, only N of the M input ports of power sharing network 510 
are utilized. Coupled to the M output ports of power sharing network 510 
are the M linear power amplifiers 502, which are further respectively 
coupled to the M input ports of the second power sharing network 512. 
Coupled to N of the M output ports of the second power sharing network 512 
is the N antenna elements 506, wherein the N utilized output ports of the 
second power sharing network 512 respectively corresponds to the 
aforementioned N utilized input ports of the first power sharing network 
510. Each antenna element 506 is preferably a narrowbeam antenna element 
being configured to radiate a directional resolution electromagnetic 
signal therefrom. 
In operation, an RF input signal is provided by one of the N transmitters 
504 and is received by one of the M input ports of the first power sharing 
network 510 and is provided at the M output ports thereof, as described 
above. The input RF signal is then distributed to the M linear power 
amplifiers 502 coupled thereto for amplification, as also described above. 
The M amplified RF signals are then respectively received at the M input 
ports of the second power sharing network 512, whereby the second power 
sharing network 512 is operative to concentrate the aforementioned 
amplified input signals back to the originally destined narrowbeam antenna 
506 by exciting only the utilized N output port of the second power 
sharing network 512 which corresponds to the particular input port of the 
first power sharing 510 to which the input signal was applied, via a 
corresponding N transmitter 504. 
An additional advantage of using M amplifiers for N beams with M&gt;N is that 
the intermodulation between different beam signals introduced by 
nonlinearities in the various amplifiers can often only appear at unused 
output ports of network 512 and thus terminate instead of being radiated 
therefrom. 
Still another preferred embodiment of the present invention antenna system 
utilizing the foregoing arrangement of providing a greater number of power 
amplifiers relative to antenna elements is illustrated in FIG. 11, 
designated generally by reference numeral 600. Briefly, antenna system 600 
is similar to antenna system 500 described above, however antenna system 
600 is adapted to equally distribute the power of M linear power 
amplifiers 602 to N broadbeam antenna elements 606 for providing 
directional resolution of multiple RF signal transmission beams therefrom, 
in contrast to the narrowbeam antenna elements 506 of antenna system 500. 
As with antenna system 500, antenna system 600 provides the aforementioned 
advantages of having a greater number (M) of amplifiers 602 relative to 
the number (N) of antenna elements 606. 
Antenna system 600 includes an intermediate frequency (IF) crossbar switch 
614 having K input and N output ports. Respectively coupled to the N input 
ports of switch 614 are K modulators 616 which in turn are each coupled to 
an RF signal source 617. The N output ports of switch 614 are coupled to N 
of the M input ports of the first power sharing network 610. The M output 
ports of the first power sharing network 610 are coupled to M linear power 
amplifiers 602 which are respectively coupled to the M input ports of the 
second power sharing network 612. N of the M output ports of the second 
power sharing network 612 are coupled to the N input ports of the third 
power sharing network 618, wherein N output ports of the third power 
sharing network 618 are each respectively coupled to a broadbeam antenna 
element 606. As described above, each respective first and second power 
sharing network 610, 612 is preferably a Butler Matrix having M input and 
output ports, while the third Butler Matrix includes N input and output 
ports. As also mentioned above, only N of the M input ports of the first 
Butler Matrix 610 and the corresponding N output ports of the second 
Butler Matrix 612 are utilized by antenna system 600. 
Antenna system 600 is operational such that the first power sharing network 
610 receives an input signal at one of the N utilized input ports and 
outputs the received signal at all of its M output ports so as to be each 
respectively amplified by the M linear power amplifiers 602 coupled 
thereto. The M amplified signals are then respectively received at the M 
input ports of the second power sharing network 612 which is operational 
to concentrate the aforementioned amplified signals to a particular 
utilized N output port which corresponds with the utilized N input port of 
the first power sharing network 610 which originally received the RF 
signal, via switch 614. The aforementioned concentrated signal is then 
received at a corresponding N input port of the third power sharing 
network 618 which is operative to provide an output signal at each of its 
N output ports which are a function of the concentrated RF signal, wherein 
each output signal is in substantially equal power levels and is staggered 
in angular phase relationship to one another, as described above. As also 
described above, each output signal is radiated from a respective 
broadbeam antenna element 606 providing directional resolution of an RF 
signal transmission beam from the combination of antenna elements 606. 
In operation of the above described antenna systems of the present 
invention, electromagnetic narrowbeam transmission and reception at 
preferably a centrally located Advanced Mobile Phone Service (AMPS) base 
station incorporating one of the above described antenna systems is 
provided with either increased coverage range or a reduction in the 
required transmitter power and interference. Further, no frequency reuse 
is involved, (i.e., handing off from electromagnetic beam to 
electromagnetic beam does not involve a new channel assignment and is 
handled by switching in the same base station to different narrow 
electromagnetic beams). For example, if omni directional coverage is 
divided into 10 electromagnetic narrow beams, a 10 dB signal power gain 
advantage is achieved and the total average interference power is reduced 
significantly. 
The above described base stations of the present invention constituted as 
improvement over prior art antenna systems by utilizing a Butler Matrix to 
effect equal component (antenna, linear power amplifier, modulators, 
demodulators, etc.) distribution. This "improvement factor" is defined as: 
MN.backslash.K, wherein N is the number of RF antenna beams, K is the 
maximum channel demand that can be served per base station, and M is the 
channel demand that each electromagnetic beam would be equipped to meet 
under non-distributing conditions. This factor is derived by solving for M 
as a function of both N and K, under the assumption of uniform RF traffic. 
For example, if all the equipment at a base station is shared through the 
use of Butler Matrixes, as described above, the blocking probability (B) 
of the base station is given in terms of the overall Erlang traffic demand 
(a) and the number of transponders (K), by the Erlang B formula, which is 
defined as: 
##EQU2## 
In another example, a scenario of no antenna sharing is considered where it 
is assumed that the signal traffic demand has uniform independent 
probability distribution among the N electromagnetic beams. In order to 
handle the same overall RF traffic, the traffic per beam would be a.sub.b 
=a/N. Therefore, in order for each user in any given electromagnetic beam 
to see the same service as would experience in the totally shared base 
station, it is required that the blocking probability per beam (B.sub.b) 
be the same as the overall blocking probability (B) of the totally shared 
base station. Therefore, by inserting a.sub.b and B.sub.b back into the 
Erlang B formula, it is determined that by substituting M for K, wherein M 
is the minimum number of transponders per beam that provides a per beam 
blocking probability (B.sub.b) is less than or equal to B. Further, if K 
and N are known values, and B is specified, then the required value for M 
is determined as described above to determine the improvement factor; 
MN/K. 
Referring now to FIG. 12, the solid curves which represent MN.backslash.K 
versus N, with K as a parameter, wherein B is prescribed to equal 0.01 
(which is when the peak demand occurs for which a given base station is 
designed, the probability that all of the N beams will meet their demands 
is 99%). The dashed curves in FIG. 10 are representative of the 
corresponding results for when B is to equal 0.10. It is particularly 
noted that the improvement factor grows with N and diminishes with K, 
which results in that traffic fluctuates more from electromagnetic beam to 
electromagnetic beam when the average per electromagnetic beam demand 
(K.backslash.N) is small. 
While the invention has been particularly shown and described with 
reference to certain preferred embodiments, it will be understood by those 
skilled in the art that various modifications in form and detail may be 
made therein without department from the scope and spirit of the 
invention. Accordingly, modification to the preferred embodiments will be 
readily apparent to those skilled in the art, and the generic principles 
defined herein may be applied to other embodiments applications without 
departing from the spirit and scope of the invention. Thus, the present 
invention is not intended to be limited to the embodiments shown, but it 
is to be accorded the widest scope consistent with the principles and 
features disclosed herein.