 free space. Using an antenna with additional gain, the intended receiver will dramatically increase COMMUNICATION TRANSMITTER JAMMER S/J = 20 dB S/J = -20 dB AREA DENIED TO SS COMMUNICATION WITH 30 dB PROCESSING GAIN AREA OF CONVENTIONAL COMMUNICATION S/J = 10 dB S/J = - -10 dB ASSUMPTIONS: S/J = 3 dB * EQUAL POWER S/J = 0 dB S/J = -3 dB 10 dB SNR REQUIRED AT RECEIVER * FREE SPACE PROPAGATION Figure 3.1. Jamming power versus processing gain. Commercial Applications the region of operation in this interference environment. The operation region is defined by the SIJ measured at the antenna output of the receiver. This SIJ depends on the antenna gain in the direction of the transmitter (determines S) and the antenna side lobe attenuation of the receiver antenna in the direction of the jammer (determines J). Here. the region of operation will be a complex region determined by the antenna pattern of the receiver. If the transmitter and jammer also have directional antennas, then this region will be complicated by all three antenna patterns. For fixed locations for the radios, antenna polarization can be used to separate signals. Normally, for narrowband signals, antenna polarization may not provide adequate isolation when radios are located in the same area. Since spread-spectrum signals have additional protection against interference when different codewords are used, antenna polarization can be used very effectively to increase capacity. Spread-spectrum radios allow for a much more flexible application of antenna techniques for increasing capacity. It is clear that the determination of the number of radios that can work effectively in a given area is a very complex matter. Spread-spectrum radios are less sensitive to interference and can operate with smaller SIJ than con- ventional narrowband signals. These signals, however, require more band- width. Narrowband radios may be able to use this same band by creating many non-interfering frequency channels. Typically, up to 20 percent of this frequency band may be wast