Fundamental wave phase-locked dual-band push-push DRO using out-of-phase Wilkinson power combiner

Abstract

A new push-push phase-locked dielectric resonator oscillator (PLDRO) with dual-band (C/Ku) output capability is presented. An out-of-phase Wilkinson power combiner is used to provide the fundamental ( f 0 ) output. The phase-locking is implemented at f 0 as an alternative to direct locking the push-push output frequency (2f 0 ) using prescalers. The push-push PLDRO has shown a fundamental suppression of 35.12 dBc and a second-harmonic suppression of 34.77 dBc at the 2f 0 output and the f 0 output, respectively. Experimental results also indicate a maximum spur level of 277.4 dBc, and phase noise values of 2109.6 and 2143 dBc/Hz at 10 kHz and 1 MHz offsets, respectively, from a 12.6 GHz carrier.Introduction: For low phase noise applications, such as satellite communication and radar, it is desirable to phase lock the free running push-push dielectric resonator oscillator (DRO) [1-3] to a high stable crystal oscillator for further improving the phase noise. The phaselocking can be implemented at f 0 , or at 2f 0 . In [3], a push-push PLDRO is designed by locking the 2f 0 . However, the use of a high frequency prescaler increases the cost and power consumption of the system. Lee et al.[4] designed a 60 GHz planar-type push-push VCO with an integrated frequency divider working near 30 GHz. As a result, a 60 GHz frequency synthesiser can be realised by locking relative lower frequencies. Besides the phase noise considerations, next generation wireless systems, such as multimode transreceivers and cognitive radios, require the push-push DRO to have dual-band output capability.Thus, the f 0 signal should also be coupled out at the condition that the fundamental suppression and phase noise of the 2f 0 output are not deteriorated. Moreover, the output power of the f 0 signal should be sufficient for local oscillator applications.This Letter introduces a new push-push PLDRO. Compared with conventional designs, it provides not only the 2f 0 signal but also the f 0 signal by using an out-of-phase Wilkinson power combiner. Furthermore, as the phase-locking is implemented at the fundamental frequency, the increased phase detector gain helps reduce the risk of locking failures and phase noise. The concept proposed here can also be applied to millimetre-wave PLDRO designs where phase-locking becomes more difficult.

Implementation of a Pldro With a Fractional Multiple Frequency of Reference

“…The conventional PLDRO uses a reference crystal oscillator and a SPD, which compares the harmonic frequency of the reference and the feedback signal from VCDRO to generate an error signal for the loop filter [6]. As a variation, the fundamental VCDRO is replaced with a push-push VCDRO [7,8], and the SPD is replaced with a mixer [8]. However, the aforementioned PLDROs have the same limit: the output frequency must be an integer multiple of the reference frequency, typically 100 MHz.…”