A power amplifying system configured to operate for a plurality of frequency bands, comprising: an input matching network configured to perform input impedance matching for input signals in the plurality of frequency bands; one or more transistors configured to receive the input signals in the plurality of frequency bands and amplify the input signals to generate output signals in the plurality of frequency bands; a bias circuit to bias the one or more transistors; and an output matching network configured to perform output impedance matching for the output signals in the plurality of frequency bands; characterised in that the system further comprises: a first frequency selecting module that is connected to the input matching network and includes at least one frequency selector comprising a composite right and left handed, CRLH, structure configured to transmit a signal in a frequency band associated with the frequency selector to an input signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector; and a second frequency selecting module that is connected to the output matching network and includes at least one frequency selector configured to transmit a signal in a frequency band associated with the frequency selector to an output signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector. an input matching network configured to perform input impedance matching for input signals in the plurality of frequency bands; one or more transistors configured to receive the input signals in the plurality of frequency bands and amplify the input signals to generate output signals in the plurality of frequency bands; a bias circuit to bias the one or more transistors; and an output matching network configured to perform output impedance matching for the output signals in the plurality of frequency bands; characterised in that the system further comprises: a first frequency selecting module that is connected to the input matching network and includes at least one frequency selector comprising a composite right and left handed, CRLH, structure configured to transmit a signal in a frequency band associated with the frequency selector to an input signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector; and a second frequency selecting module that is connected to the output matching network and includes at least one frequency selector configured to transmit a signal in a frequency band associated with the frequency selector to an output signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector. a first frequency selecting module that is connected to the input matching network and includes at least one frequency selector comprising a composite right and left handed, CRLH, structure configured to transmit a signal in a frequency band associated with the frequency selector to an input signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector; and a second frequency selecting module that is connected to the output matching network and includes at least one frequency selector configured to transmit a signal in a frequency band associated with the frequency selector to an output signal path for that frequency band, and remove signals in one or more frequency bands that are different from the frequency band associated with the frequency selector.