A quadrature transmitter is described that comprises: a first transmitter path and a second transmitter path that are matched. Each transmitter path comprises: at least one input arranged to receive respective first or second sets of quadrature baseband signals; at least one local oscillator, LO, port configured to receive respective first and second sets of quadrature LO signals; at least one mixer stage coupled to the at least one input and configured to respectively multiply the sets of quadrature baseband signals with the respective first or second sets of quadrature LO signals to produce a respective output radio frequency, RF, signal; and a combiner configured to combine the output radio frequency signals of the first transmitter path and the second transmitter path. The first set of quadrature signals is a substantially 45° phase shifted version of the second set of quadrature signals; and the first set of quadrature LO signals is a reverse substantially 45° phase shifted version of the second set of quadrature LO signals.