In this issue:
• This week's focus: Matching Beamforming Networks
   to Complex Antenna Impedances
• The Multi-Mix PICO^TM Product Family
• Featured Reader Resources

This week's focus:

Matching Beamforming Networks to Complex Antenna Impedances

by Brian Dornan
Vice President & Chief Engineer Microwave Products Group at Merrimac Industries, Inc.

The continuing growth in the mobile communications and Global Positioning market place is leading the system operators to increase the capacity of their networks. Several options are available, such as more frequency spectrum, frequency-hopping techniques and microcell solutions. One additional avenue open to the system operators is to increase the effective radiated power of the system.

In a typical application the output power amplifier or amplifiers are interfaced to the antenna through a beam forming network. This beam forming network can be simple or complex passive network performing either a linear or tapered amplitude and phase distribution to the radiating elements. The radiating elements are designed for the specific application and system bandwidths. The radiating elements or antenna generally have an impedance matching requirement across the operating bandwidth of the system. As the system operators attempt to increase the capacity of their systems through increased frequency spectrum or through frequency hopping techniques, the impedance matching requirement for the antenna are increasingly more difficult to meet. An impedance match of the antenna of 2:1 results in only 90% of the possible output power being transmitted. If the impedance match were to be 3:1, then only 75% of the available power would be transmitted.

The system providers generate detailed specifications for both the antenna systems and beam forming networks working into the ideal 50 ohm world. The isolation specification for the beam forming network will be written with the knowledge that there will be a large amount of reflected power as a result of the unit working into the antenna system. Merrimac Industries proposes a design for the beam forming network to improve the impedance match between the antenna and the beam former and thus increase the output power of the system.

Merrimac Industries, Inc. has been designing and manufacturing beam forming networks for over 25 years. Most of the earlier designs were the typical 50 ohm input and output impedance designs. Recently, Merrimac has designed and fabricated a high power multi-port beam forming network with integrated impedance transformers at the antenna interfaces. The bandwidth of the beam forming network is greater than 30%. The design incorporates a central section that encloses the beam former that performs the amplitude and phase taper function. This section of the beam former is realized using a low loss stripline design. The individual antenna feeds (12 total) are coupled to the central beam former. The antenna feeds, with the integrated antenna matching networks, are realized in a low loss suspended substrate configuration. The antennas are directly attached to the matching networks at the ends of the low loss antenna feeds. This design approach also eliminates the need to purchase and install the expensive phase matched cables between the beam former and the antenna.

For more information, please contact Brian Dornan at brd@merrimacind.com or telephone 973.575.1300

The Merrimac Multi-Mix PICO^TM
Product Family

QHD-Z Series 3-dB 90 and 180° Hybrids: A family of low-insertion loss, high-isolation hybrids in a tiny outline. Accurate phase and amplitude balance make them ideal for applications involving IQ networks, power amplifiers, and signal distribution and processing. They measure only 0.18 x 0.18 x 0.09 in.

CSD-Z Series Directional Couplers: Low insertion loss combined with low VSWR and precise coupling and frequency sensitivity make these couplers an excellent choice for power amplifiers, signal distribution, and processing. They measure only 0.18 x 0.18 x 0.07 in.

PDD-Z Series Power Dividers: In-phase, binary power dividers with low insertion loss in an outline 90 percent smaller than conventional designs. Accurate phase and amplitude balance ensure optimum performance of IQ networks, power amplifiers, and other areas of the transmission chain. They measure only 0.18 x 0.18 x 0.10 in.

ILC-SH Series In-Line Couplers: An integrated power divider and combiner that delivers high isolation, low insertion loss in an exceptionally small footprint. They measure only 0.20 x 0.56 x 0.13 in.

The HJD-Z Series provides a 3 dB hybrid junction with low insertion loss, high isolation, and high power handling in a small outline. Accurate phase and amplitude balance make them ideal for use iigh isolation, and high power handling in a small outline. Accurate phase and amplitude balance make them ideal for use in PCS power amplifiers, beamforming networks, matching baluns, signal distribution and processing functions. They measure only 0.18 x 0.18 x 0.11 in.

Featured Reader Resources

Introduction To Beamformers
Beamformers are complex networks used to precisely control the phase and amplitude of RF energy passing through them.

Sub-Systems and Hi-Rel
Merrimac offers an impressive capability for designing and integrating various building blocks into highly capable, sophisticated sub-systems. This capability is applicable to military, scientific and commercial applications in terrestrial, maritime or aerospace environments.

Multi-Mix® Whitepaper
Multi-Mix®, a new 3-D multi-layer integrated packaging technology.