Hybrid Combiners Add Channels With Low PIM

Signal combining in cellular base stations and other systems requires components with high isolation between signal paths, low loss in those paths, and minimal passive intermodulation distortion (PIM) added to the signals. As the number of signals increases and bandwidth broadens, the requirements of radio base stations, distributed antenna systems (DASs), and in-building cable distribution networks have spurred designers of hybrid combiners to new levels of performance and integration. Suppliers of hybrid combiners include Microlab/FXR, MECA Electronics, Werlatone, Kathrein, Link Microtech, Tiger Microwave, dBSpectra, and Pasternack Enterprises.

Microlab/FXR a wholly owned subsidiary of Wireless Telecom Groupdeveloped the model CM-78N 4 x 4 hybrid combining matrix with 30 dB isolation and PIM of -160 dBc or less by minimizing impedance discontinuities in the signal paths. Designed for Personal Communications Service/Digital Communications Service (PCS/DCS), Advanced Wireless Service (AWS), and Universal Mobile Telecommunications Service (UMTS) bands from 1710 to 2170 MHz, it consists of four 3-dB couplers in a matrix configuration. Signals applied to any one of the four inputs are split equally among the four outputs. "This allows simple combining of multiple signals in the same wireless band to a common feeder cable, as might be required in a neutral host in-building DAS or the decoupled combining of four transmitter or receiver signals equally to four antennas," states Tony Ramsden, Microlab/ FXR's President.

Model CM-78N handles 100 W average power and 3 kW peak power per input. It targets both indoor and outdoor applications and is moisture sealed to meet IP67 standards. For different frequency bands, the firm offers the model CM-58N, which spans 1710 to 2700 MHz, and the CM-68N covering 698 to 960 MHz. As with the other hybrid combiners included here, standard units are supplied with Type N connectors but also available with 7-to- 16-mm DIN connectors.

To combine four signals without any interference, Microlab's model CM-14D/N 4 x 4 hybrid combiner spans 380 to 2500 MHz. It offers over 20 dB isolation and handles 100 W average power per input with 1.30:1 VSWR. It achieves PIM of -150 dBc or less. The firm also offers the model CM-81 3 x 3 hybrid combiner for use from 700 to 2700 MHz. The CM-81 boasts more than 25 dB isolation across the entire band and PIM of -150 dBc or less. Each input is rated for 60 W average power with a 3-kW peak power.

Ramsden also confides that Microlab has an 8 x 8 version in the works, which will be available around late summer. Designed to offer 30 dB isolation with PIM of -160 dBc or less, it provides 100 W average input power capability from 1710 to 2710 MHz. The 8 x 8 CM-X9 matrix consists of four 3-dB hybrid couplers and two 4 x 4 hybrids (Fig. 1). The assembly is configured so that the signals applied to any of the eight inputs will be split equally between the eight outputs.

To lower costs, MECA Electronics is adopting microstrip techniques and using higher-quality materials to lower insertion loss in its new hybrid-combiner line, which covers 0.4 to 6.0 GHz in a 10-percent bandwidth. The 2 x 2 700 series is a 180-deg. hybrid divider/combiner that exhibits insertion loss below 0.6 dB with 25 dB typical isolation and VSWR of 1.20:1. Capable of handling 150 W average power and 1 kW peak power, the 707 series meets IP65 specifications for stringent outdoor use. It is housed in a rugged package that measures only 2.5 x 2.0 x 0.82 in.

For applications covering 2.0 to 3.0 GHz, MECA has developed a 2 x 4 hybrid divider/combiner using stripline techniques (Fig. 2). Internally terminated in 50 , the 3705S-2.500 exhibits insertion loss to 0.6 dB with at least 20 dB isolation and maximum VSWR of 1.30:1. It is rated for 1 W average input power per port, although versions are available to 10 W.

Power And Bandwidth

Werlatone has long been known for its high-power components including broadband in-phase (0-deg.), 90-deg., or 180-deg. hybrid combiners/ dividers. With 90-deg. combiners, for example, the maker has extended the bandwidth to 10:1. A recent addition is the QH7349, a two-way, 90-deg. hybrid combiner that spans 100 to 1000 MHz at 50 W CW power. This non-connectorized 90-deg combiner exhibits 0.6 dB insertion loss with a VSWR of 1.30:1 and at least 20 dB isolation. The combiner offers phase balance of 5 deg. while amplitude balance reaches 1 dB. At a 10:1 bandwidth, the supplier claims to have developed 90-deg. hybrid combiners that can handle 250 W CW power. The 90-deg. hybrid-combiner portfolio comes in both connectorized and nonconnectorized versions.

In the 180-deg. hybrid-combiner line, Werlatone flaunts a 5:1 bandwidth with 200 W power capability. The twoway, 180-deg. H7492 combiner/divider, for example, covers 500 to 2500 MHz while exhibiting insertion loss of only 0.4 dB at 200 W input power. The combiner also boasts at least 20 dB isolation and 1.30:1 VSWR. It provides phase balance to 8 deg. with amplitude balance ranging to 0.4 dB. According to Sales and Marketing Manager Peter Kuring, Werlatone's hybrid combiners are mismatch resistant.

Germany's Kathrein also is in the race to supply highpower narrowband and broadband hybrid combiners. The company has developed the model 78210805 duplex (4 x 2) combiner for antenna-sharing applications. It covers 880 to 960 MHz with power-handling capability to 250 W. Other key features of the duplex hybrid include more than 25 dB isolation, 1.20:1 VSWR, and PIM of -160 dBc or less. Designed to meet IP66 specifications, the combiner comes with 7-to-16-mm DIN (F) connectors for indoor or outdoor use.

For broadband use at high power, the supplier's 2 x 1 hybrid (793555) spans 800 to 2200 MHz while handling 150 W at the input ports. This combiner boasts more than 22 dB isolation, 1.20:1 VSWR, and PIM of -160 dBc or less.

UK-based Link Microtek has added a range of 90-deg. hybrid combiners from makers like Lynx and Tiger Microwave. By adopting a stripline structure, the Lynx 113.A2032 series 90-deg. hybrid covers 2 to 4 GHz while exhibiting 0.30 dB insertion loss. It provides 22 dB isolation with VSWR of 1.20:1 while handling 50 W. The unit comes with SMA(F) connectors. Similarly, the supplier has expanded the 90-deg. hybrid-combiner portfolio with high-power parts from China's Tiger Microwave. Tiger's stripline-based TGPC-203, for example, covers 1710 to 1880 MHz while handling 450 W of CW power. It exhibits 0.3 dB insertion loss with input/output VSWR of 1.15:1 and 20 dB isolation.

To ease antenna sharing in mobileradio applications, dBSpectra has readied a number of multi-channel hybrid combiners spanning 118 to 960 MHz, including the new 700-MHz-band wireless-communication applications. By specializing in low-frequency design using ferrites, the maker has developed a number of narrowband and broadband multi-channel combiners aimed at the very-high-frequency (VHF) and ultra-high-frequency (UHF) bands. Offering rugged construction, these low-profile control-station and transmit combiners handle over 100 W. The units are air cooled with temperature sensors that trigger the fans only when high temperatures are reached.

Lastly, Pasternack Enterprises is using its latest launch to target applications requiring a sum total of multiple power amplifiers or splitting signals into lower-power multiple signals. The firm's portfolio of 90-deg. hybrid combiners ranges from 0.5 to 18 GHz.

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