A DUAL-BAND ANTENNA COUPLER FOR CELLULAR AND PCS APPLICATIONS
In today's fast-growing cellular phone systems throughout the world the amount of congestion, especially in urban areas, is becoming a significant issue. Major system providers are scrambling to find adequate solutions to the problem. The original cellular frequency band (890 to 915 MHz GSM in Europe) was later expanded by 10 MHz to 880 to 915 MHz to help ease the traffic load. This expanded band is known as extended GSM. Now even that band is full and the choice is to go to the higher assigned 1850 to 1910 MHz PCS band in the US and the 1710 to 1880 MHz DCS-1800 band in Europe.
At the present time single-band phones for PCS and GSM are being sold in the US and Europe. Soon, multiband phones will be made available to allow use of the same phone throughout the world. However, the tremendous increase in cellular phone use and tight local environmental control on sight expansion, particularly in urban areas, has put much pressure on system providers to enhance and expand their services. One solution is to use the existing base station facilities and add PCS capability to the cellular facility by using dual antennas that operate over the PCS and cellular frequency bands within the same housing. Using the model SL-7871 dual-band antenna coupler, these dual antennas now may be combined into a single cable to the base station and then separated again with an identical coupler to be fed to their respective processing equipment.
The new dual-band coupler accomplishes the combination or separation by means of combline cavity filters that introduce a mere 0.3 dB of loss in each band while isolating the two frequency bands by as much as 70 dB from each other. In addition, the SL-7871 unit has been designed to exhibit very low intermodulation while maintaining a return loss of 20 dB minimum, making antenna impedance matching easy.
Fig. 1 The dual-band antenna coupler's passband response at the (a) cellular and (b) PCS bands.
Fig. 2 The coupler's frequency band selectivity.
The new coupler is designed to handle a minimum RF power of 500 W at cellular frequencies and 250 W at PCS frequencies. In addition, it can be easily modified to accommodate GSM-900 and GSM-1800. Figure 1 shows the actual coupler passband response for both cellular and PCS frequencies. Figure 2 shows the coupler's measured band selectivity.
The dual-band unit is supplied with DIN 7/16 connectors for the common port and type-N female connectors for PCS and cellular ports. The coupler's housing measures 1.25" ¥ 3.00" ¥ 9.00". Additional information is available via e-mail at firstname.lastname@example.org.
Reactel Inc., Gaithersburg, MD (301) 519-3660.
Circle No. 320