K&L Microwave part number SPCL-00636 is a four channel tunable combiner.  It can be factory adjusted covering the UHF band with each channel featuring a 2 MHz bandwidth.  Channel to channel isolation, at 15 MHz channel spacing, is 40 dB with passband insertion loss of 2.0 dB max and power handling of 25 Watts CW / 100 Watts peak.  The small size of 5.5" x 4.4" x 2.0" makes this part usable for either ground based or airborne applications.