Western Multiplex Corp., a provider of broadband wireless systems, agreed to buy Adaptive Broadband Corp. for $645 million to expand its services and gain customers. Adaptive shareholders will get 1.345 Western Multiplex shares for each Adaptive share, Western Multiplex said. That values Adaptive shares at $17.15 each, 34% above Friday's close. Shares of Western Multiplex plunged $3.75 to close at $9 in Nasdaq trading, while Adaptive fell $1 to $11.81, also on Nasdaq. James McIlree, an analyst with Tucker Anthony Capital Markets, said the shares were falling because of a "weak market." Both companies are based in Sunnyvale, Calif.