Szhau Lai

Estimation of Average Rician K-Factor and Average Mode Bandwidth in Loaded Reverberation Chamber

A well-stirred reverberation chamber without noticeable direct coupling between the transmitting and receiving antennas emulates an isotropic Rayleigh fading environment and can therefore be used for qualitative over-the-air (OTA) measurements of wireless devices with small nondirective antennas. By loading such a chamber, it is possible to generate a Rician environment. This letter introduces an average Rician K-factor that describes the reverberation chamber better than the normal K-factor, in particular when the chamber is provided with platform and polarization stirring. This letter shows how to estimate this average K-factor. The average mode bandwidth also changes by loading the chamber. While the average K-factor determines uncertainty, the average mode bandwidth determines the channel coherence bandwidth. They are therefore the two most important parameters for the characterizations of a reverberation chamber.

Direct coupling as a residual error contribution during OTA measurements of wireless devices in reverberation chamber

We have presented an improved theory for the uncertainty of measurements in reverberation chamber. The theory is obtained by including the error due to the direct coupling between the antenna under test and the wall-mounted antennas. The theory includes the Rician K-factor that can be estimated from simple formulas, and an empirical mechanical stirring bandwidth Bmech that is adjusted to get good agreement with the measured STDs. However, Bmech is fixed for a given chamber and stirrer configuration. The new theory is able to describe variations of uncertainty with frequency and loading, and it can very well predict the degradation when platform and polarization stirring is not used. The validation of the theory is representative for efficiency measurements, but it will be equivalent for measuring total radiated power and receiver sensitivity.

Low Phase Noise GaN HEMT Oscillators With Excellent Figures of Merit

This letter presents guidelines for the design of low phase noise oscillators in GaN high electron mobility transistor (HEMT) technology. The design starts from bias-dependent low-frequency (LF) noise measurements. Oscillator topology and bias point are then chosen for operation in regions where LF noise is low. The best LF noise properties are obtained for low drain voltage and current. Thus, the low phase noise can be achieved at low dc power which also means that power normalized phase noise figure of merit (FOM) will be good. Two different oscillators have been designed and measured. A 9.9 GHz common-gate balanced Colpitts oscillator operating in class C presents a phase noise of -136 dBc/Hz@1 MHz. The result is achieved for Vd =6 V and Id = 30 mA, giving FOM = 193 dBc/Hz. A 1.95 GHz negative-resistance oscillator operating in switched mode presents a phase noise of of -149 dBc/Hz@ 1 MHz offset. With drain voltage and current of Vd = 4 V and Id = 100 mA, this oscillator presents FOM = 189 dBc/Hz. To the best of the authors knowledge, these two oscillators present the highest reported FOM for GaN HEMT oscillators.

RF-MEMS Tuned GaN HEMT based Cavity Oscillator for X-band

This letter presents a radio frequency micro-electromechanical systems (RF-MEMS) tuned cavity oscillator for X-band. The active part of the oscillator is implemented in GaN-HEMT MMIC technology. The RF-MEMS-switches are realized on a quartz substrate that is surface mounted on a low loss PCB. The PCB is intruded in an aluminum cavity acting as an electrically moveable wall. For a three-row RF-MEMS setup, a tuning range of 5 % around an oscillation frequency of 10 GHz is demonstrated in measurements. The phase noise is as low as -140 dBc/Hz to -129 dBc/Hz at 100 kHz from the carrier, depending on the configuration of the RF-MEMS.

A MMIC GaN HEMT Voltage-Controlled-Oscillator with High Tuning Linearity and Low Phase Noise

This paper presents a MMIC GaN HEMT Voltage- Controlled-Oscillator (VCO). The VCO is tunable between 6.45-7.55 GHz with good tuning linearity, average output power about 1 dBm, and a good phase noise with little variation over the tuning range. For a bias of Vd /Id = 6 V/33 mA, the measured phase noise is -98 dBc/Hz @ 100 kHz and -132 dBc/Hz @ 1 MHz offset frequencies, respectively. To the authors best knowledge, this is the lowest phase noise reported for a VCO in GaN HEMT technology with comparable oscillation frequency and tuning range. The 1 MHz offset phase noise is also comparable to state-of-the-art GaAs-InGaP HBT VCOs with similar tuning range.

A method to lower VCO phase noise by using HBT darlington pair

The paper presents a novel method to enhance tank voltage swing in LC VCOs design using bipolar transistor. The method is successfully demonstrated in an InGaP/GaAs HBT MMIC process. A gm-boosted VCO and a modified version, using Darlington-pair transistors, are compared. The latter exhibits lower phase noise, increased tuning range, and less variation in output power. The gm-boosted VCO has tuning range of 22.8% centered at 5.7GHz and phase noise ranging from −103 to −95 dBc/Hz at offset frequency of 100kHz. The modified version using Darlington pair has tuning range of 26% centered at 5.9 GHz and phase noise ranging from −103.5 to −98.5 dBc/Hz at offset frequency of 100kHz.

A 12 Gbps analog QPSK baseband receiver based on injection-locked VCO

Injection locking based QPSK demodulation have been reported in several publication, however the data rate is less than Gbps. In this paper, the theory of an oscillator injection locks to a wideband modulated signal is studied. Based on the principle study, a proof of concept QPSK coherent baseband receiver is designed and verified. The receiver is able to demodulator QPSK signal with data rate up to at least 12 Gbps, which is limited by the mixer bandwidth. The receiver has a power consumption of 210 mW. It consists of a novel injection-locked VCO (ILVCO) based carrier recovery block, which can be used for even higher data rates if the theoretical condition proposed in this paper is met.

A 20 GHz Low Phase Noise Signal Source Using VCO and Mixer in InGaP/GaAs HBT

This paper presents a low phase noise 20 GHz signal source based on a voltage control oscillator(VCO) and a mixer integrated on a single MMIC. The mixer generates a third harmonic output by mixing the fundamental and the second harmonic signals of the VCO. Using a relatively low frequency VCO has the advantage of better Q factor and thus better phase noise. The MMIC-signal source is designed in a GaAs-InGaP HBT process. The VCO uses balanced Colpitts topology and the mixer is a high conversion-gain single-balanced mixer. The MMIC delivers signals in the frequency range 19.4-21.2 GHz with an excellent phase noise of -100 to -93 dBc/Hz at 100 kHz offset frequency. The output power ranges between -8 and -1 dBm.