High-data-rate communications require generous amounts of bandwidth, a valuable commodity with the growing number of spectral users for wireless applications. Several years ago, the United States Federal Communications Commission (FCC) designated previously unused bands of 71 to 76 GHz, 81 to 86 GHz, and 92 to 95 GHz as available for gigabit-speed wireless communications links. Of course, developing practical wireless links at these E-band frequencies requires affordable, high-performance components. In response, K & L Microwave (Salisbury, MD) has developed an E-band diplexer that separates the bands of 71 to 76 GHz and 81 to 86 GHz in order to prevent interference of receivers by transmitters. It supports line-of-sight communications at transmit and receive data rates in excess of 2.488 Gb/s even during adverse atmospheric conditions, such as heavy snowfall and rainfall. The E-band duplexer allows the use of frequency-division duplexing (FDD) with a single transceiver at each end of a wireless communications link.

The model 7WZ01-00064 E-band diplexer (see figure) is designed for use in high-density fixed-wireless services operating over distances of one mile or more. It is essentially a pair of waveguide bandpass filters with passbands of 71 to 76 GHz and 81 to 86 GHz, maintaining high isolation between the two bands and minimum insertion loss within each passband.

For example, the E-band diplexer is specified for maximum passband insertion loss of 0.7 dB from 71 to 76 GHz, with typical insertion loss of 0.5 dB over that 5-GHz bandwidth. The minimum return loss is 14 dB from 71 to 76 GHz, with better than 60 dB transmit-to-receive isolation. In the higher-frequency passband of 81 to 86 GHz, the maximum insertion loss is also specified as 0.7 dB with typical insertion-loss performance of 0.5 dB from 81 to 86 GHz. The minimum return loss from 81 to 86 GHz is 14 dB, with at least 60-dB transmitter- to-receiver isolation.

The waveguide diplexer relies on the propagation of a specific combination of modes to achieve its high performance, and can deliver these loss and isolation performance levels without need of time-consuming (and costly) manual tuning during production. Typically, millimeter-wave signals provide relatively secure (difficult-to-intercept) communications at E-band due to narrow signal beamwidths between transmitter and receiver. Because the antennas used at these frequencies tend to have diameters of about 2 feet, the transmitted signal beams are so narrow that interference among multiple links is rare. As a result, the FCC offers a simple and inexpensive site licensing procedure for E-band communications links.

The E-band diplexer is constructed with WR-12 waveguide flanges. Tight rejection skirts are achieved by placing a pair of transmission zeros, while preserving the low loss at the band edges. The E-band diplexer is ideal for gigabit-rate, point-to-point millimeterwave transceivers, where signal power is limited and insertion loss must be minimized, and in installations where running fiber-optic cables is impractical. K & L Microwave, Inc., 2250 Northwood Dr., Salisbury, MD 21801; (410) 749-2424, FAX: (443) 260- 2268, e-mail: sales@klmicrowave.com, Internet: www.klmicrowave.com.