signal is taken out and q 1 39 s emitter and q 2 39 s base are connected with the balun 39 s balanced output therefore the anti phase rf signal via the balun is added at both base and emitter of each transistor q 1 and q 2 in contrast in conventional frequency multipliers the differential rf signal is added at the base of two transistors but their emitters are connected to an ac virtual ground therefore its rf signal 39 s swing across base and emitter is less that of frequency multiplier 100 thus frequency multiplier 100 is superior to the prior multipliers in terms of conversion gain in addition the impedance of the second coil of balun 106 acts as emitter degeneration which provides a negative feedback for the transistors it enables the conversion gain to be insensitive to the input rf power in other words the conversion gain can be kept constant within a certain range of rf input power to improve conversion gain the base of each transistor is biased at turn on voltage for example as shown in fig1 the base of q 1 is connected to voltage source vb through a resistor and the base of q 2 is also connected to voltage source vb through a resistor accordingly transistor q 1 and q 2 are turned on only within half period alternatively this results in a high efficiency which is defined as the ratio of output rf power to dc power consumption passive balun 106 provides differential rf signals for the capacitive coupled transistor pair at the output point the odd order harmonics are added in anti phase while the even order harmonics are.