Feed network comprised of marchand baluns and coupled line quadrature hybrids

#The subject matter disclosed herein relates generally to transmission line circuitry, and more particularly to feed networks for antennas.

#Various types of feed networks are used to feed radio frequency (RF) energy between one or more antennas and associated processing systems, such as transmitters, receivers, and/or transceivers. For example, a feed network may convert RF waves received by an antenna into RF electrical signals and deliver the RF electrical signals to the processing system, and/or vice versa. Known feed networks may include one or more various components for controlling the amplitude and phase of RF power at the antenna(s), and may include RF devices such as baluns, hybrid couplers, delay lines, phase shifters, and/or the like.

#Known feed networks are not without disadvantages. For example, a plurality of antennas are often grouped together in an array. Each antenna typically includes a dedicated feed network that serves that particular antenna. Accordingly, the antenna array typically includes a plurality of antenna and feed network pairs. But, there may be a limited amount of space for containing the antenna and feed network pairs, which may limit the minimum spacing between antennas in an array. For example, the length, width, and/or a similar dimension (e.g., a diameter and/or the like) of at least some known feed networks may limit the minimum spacing between antennas in an array. Electronically-steerable antenna arrays exhibit grating lobes in at least some angular regions for antenna element spacings greater than one-half of a wavelength at the frequency of operation. Thus, the minimum spacing between antenna elements can determine the maximum operating frequency of an antenna array.

#FIG. 1 is a schematic block diagram of an exemplary embodiment of a feed network.

#FIG. 2 is a perspective view of an exemplary embodiment of a printed circuit that defines an exemplary embodiment of a suspended-substrate stripline configuration of the feed network shown in FIG. 1.

#FIG. 3 is a cross-sectional view of the printed circuit shown in FIG. 2.

#FIG. 1 is a schematic block diagram of an exemplary embodiment of a feed network 12. The feed network 12 may have a wide variety of applications, such as, but not limited to, driving one or more antennas, use with microwave circuits, and/or the like. The feed network 12 includes at least three radio frequency (RF) devices constructed in a suspended-substrate stripline configuration. As used herein, a “suspended-substrate stripline configuration” is intended to mean a multi-layered printed circuit stackup having an upper substrate core that provides two conductive layers, a lower substrate core that provides another two conductive layers, and one or more dielectric bonding layers that provide physical separation between the upper and lower substrate cores. An exemplary suspended-substrate stripline configuration is shown in FIG. 3. In the exemplary embodiment of the feed network 12, the feed network 12 includes an input port 30, four feed ports 32, a Marchand balun 34, and two coupled-line quadrature hybrids 36. Accordingly, in the exemplary embodiment of the feed network 12, the three RF devices include only a single Marchand balun 34 and two coupled-line quadrature hybrids 36. The four exemplary feed ports 32 are labeled as feed ports 32a, 32b, 32c, and 32d, while the two coupled-line quadrature hybrids 36 are labeled as coupled-line quadrature hybrids 36a and 36b. The input port 30 may be referred to herein as a “sum port”. The Marchand balun 34 may be referred to herein as a “first” balun. The coupled-line quadrature hybrids 36a and 36b may each be referred to herein as a “first” and/or a “second” quadrature hybrid. Each of the feed ports 32 may be referred to herein as a “first”, a “second”, a “third”, and/or a “fourth” feed port.

#The Marchand balun 34 and the coupled-line quadrature hybrids 36 are operatively connected between the input port 30 and the feed ports 32 for feeding RF energy between the input port 30 and the feed ports 32. The Marchand balun 34 of the feed network 12 is configured to divide an RF signal into two RF signals that have approximately equal power amplitudes and are separated by a phase difference of 180°. Each of the coupled-line quadrature hybrids 36 is configured to divide an RF signal into two RF signals that have approximately equal power amplitudes with a phase difference of 90°. For purposes of the present disclosure, the term “RF” is used broadly to include a wide range of electromagnetic transmission frequencies including, for instance, those falling within the radio frequency, microwave or millimeter wave frequency ranges.

#The Marchand balun 34 and the coupled-line quadrature hybrids 36 are electrically arranged relative to the input port 30 and the feed ports 32 such that the four feed ports 32 have approximately equal amplitude power and a progressive 90° phase shift. For example, in the exemplary embodiment of the feed network 12, the Marchand balun 34 is electrically connected between the input port 30 and the coupled-line quadrature hybrids 36, while the coupled-line quadrature hybrids 36 are electrically connected between the Marchand balun 34 and the feed ports 32. Specifically, and as shown in FIG. 1, the Marchand balun 34 is electrically connected between the input port 30 and each of the coupled-line quadrature hybrids 36a and 36b. The coupled-line quadrature hybrid 36a is electrically connected between the Marchand balun 34 and the feed ports 32a and 32b. The coupled-line quadrature hybrid 36b is electrically connected between the Marchand balun 34 and the feed ports 32c and 32d.