To optimize the introduction of either WCDMA (wideband code division multiple access) or LTE (long term evolution) into existing cellular bands it is desirable to produce combiners for the new and existing base stations to utilize the same antenna structure. If it is assumed that the output of the base stations consist of diplexers separating their own transmit and receive bands then the critical additional requirements for the combiner are: 1) To minimize the transmission loss over the transmit bands; for a given Q of resonators it is necessary to only have 15dB of attenuation for each transmit band over the other transmit bands to minimize loss and to provide the full isolation requires higher degree filters with higher Q's to achieve the same loss. 2) To have sufficient isolation between the transmitters to minimize the IM products generated in the receive bands by the transmitters; an isolation level of 30dB between the base stations can be readily achieved with a balanced filter and is sufficient to prevent unacceptable levels of IM products. 3) To minimize the loss in the receive bands or capture the noise figure and intercept points with sufficient gain for the given base station; over the receive bands either a balanced filter solution can be used in the same way as the transmit bands or a receive LNA can be incorporated to feed both base stations. 4) In the case of WCDMA, to have an acceptable level of group delay distortion of the transmit signal; if the guard band between the base station frequencies is small then group delay equalization will be required in the transmit filter for WCDMA signals.

All of these issues will be addressed and design techniques will be presented which optimize the solution for both the WCDMA and LTE problems. The performance of several different combiners will be given which successfully achieve all of the objectives.