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A compact ultra-wideband in-phase power divider using a three-line coupled structure is proposed. The power division of the device depends on the coupling factors between the centreline and the two sidelines. For an enhanced isolation between the output ports, a 100 Ω chip resistor is connected between the ends of the two sidelines, whereas the end of the centre line is grounded. To verify the design, a prototype with 2:1 power division was fabricated and tested. The measured results validate the ultra-wideband performance with more than 12 dB return loss, more than 13 dB isolation and <0.2 dB and 4° amplitude and phase imbalances, respectively, across the band 3.1–10.6 GHz.

The authors proposed an in-phase/quadrature (I/Q) imbalance compensation technique for wideband digital receiver applications. An I/Q channel-based receiver can double the receiver working bandwidth. However, the amplitude/phase imbalance of an imperfect hybrid coupler can generate image signals thus reducing the receiver's instantaneous dynamic range. They developed a finite impulse response filter-based technique to mitigate deleterious effects because of the amplitude/phase imbalance. Both simulations and experiments were conducted to verify validity of the developed algorithm. The simulation and experiment results show that the proposed imbalance mitigation technique can reduce image signal powers by more than 24 dB or down to noise level. A receiver system level simulation is also conducted to demonstrate the practicality of the proposed imbalance mitigation method.

In this paper, a novel class of balun bandpass filters is presented on slot-line resonator (SLR) toward intrinsic balanced performance in amplitude and phase. The proposed balun filter consists of three inductive-coupled SLRs in the middle, one single-ended unbalanced port, and one balanced port with two terminals. According to the distinct field conversion from the slotline to the microstrip feeding line, good balanced performance in amplitude, and phase performance can be intrinsically realized over a wide frequency range. To validate the proposed technique, a prototype third-order balun filter is designed, fabricated, and measured. Both the simulated and measured results have demonstrated that the proposed balun filter can not only achieve good frequency selectivity but also exhibit intrinsic balanced performance in amplitude and phase.

A compact in-phase power divider utilising a stepped-impedance three-line coupled structure and microstrip-to-slotline transitions is presented. The equivalent circuit of the structure is used to predict the required dimensions for ultra-wideband performance. The length of the structure, excluding the input/output ports needed for the measurements, is around a quarter guided wavelength. The simulated and measured results for the two developed devices indicate equal in-phase power division with less than 0.1 dB and 2° amplitude and phase imbalances, respectively. The return loss at the three ports is more than 15 dB in one prototype, whereas the isolation is more than 13 dB in the other across the band from 3.1 to 10.6 GHz.

A broadband and high-K monolithic passive balun for silicon-based radio frequency integrated circuits (RFICs) are presented. It utilises the top level thick Cu metal and adopts a 16-side geometry. The proposed balun is designed and fabricated with a 0.13-μm CMOS mixed-signal 1P6M process. The measured results show that the amplitude imbalance is < 0.2 dB and the phase imbalance is within 4° from the frequency range of 0.1–7 GHz. Compared with the typical octagonal balun, the proposed design achieves the same coupling coefficients K and attains an enhancement in the transmission efficiency S21 within the frequency range of 0.1–20 GHz, and the consumed chip area is reduced by 3%.

Presented is a fat dipole antenna having square radiating elements fed by a broadband balun based on coplanar-waveguide (CPW)-to-slotline field transformation followed by multi-section slotlines for impedance transformation. The measured results of the broadband balun show a passband of 500 MHz to 5 GH and insertion loss less than 1 dB. The amplitude imbalance is approximately 0.38 dB and the phase imbalance is less than 4.5o over the entire operation range. In this design, by co-designing the radiating element with the broadband balun, a fat dipole antenna covering from 3 to 5 GHz with an omnidirectional radiation pattern and a maximum gain of 2 dBi is designed, while retaining a size of 38.9 × 80.6 mm.

The class J design space is investigated with half wave current excitation for a solid-state RF amplifier capable of delivering hundreds of watts. Unlike conventional class J designs, the present analysis aims to explore a continuous design space in order to operate a commercially available device, within its practical limits of drain voltage. This design analysis together with package effects and the inclusion of non-linear capacitor is verified experimentally by fabricating a high-power (550 W CW) high-efficiency (62.8%) solid-state amplifier operating at 505.8 MHz. This power was obtained by in-phase combining two similar continuous class J stages, each one contributing half of the total power. For high-power lateral diffused metal-oxide semiconductor devices, the class J design space is found to be more realisable than popular modes of operation in view of the large non-linear output capacitance of the device. The measured output power, efficiency, spurious response and large signal output reflection coefficients are satisfactory and as anticipated from the design analysis. Since the final application of this amplifier is for a solid-state transmitter, a study of repeatability in terms of phase and amplitude imbalances was carried out by fabricating and evaluating multiple amplifiers, each one working with the proposed design principle.

Novel closed form expressions for the error vector magnitude (EVM) are presented. The expressions combine the in-phase quadrature (IQ) amplitude and phase imbalances and the DC offsets along with the phase noise. Both the Gaussian and the Tikhonov probability density functions are utilised for the oscillator phase noise distribution. The explicit conditions when the EVM computations based on the Tikhonov distribution converge to a Gaussian based are investigated. Furthermore, the application of the proposed EVM expressions is demonstrated by including phase noise masks, providing a direct means to the phase locked loop/voltage controlled oscillator design parameters. The measurements are used to validate the proposed expressions.

In this study, a frequency-agile Butler matrix is proposed and designed to operate from 1.92 to 2.7 GHz, which can therefore be used in several different wireless applications, including the universal mobile telecommunications system, the wireless fidelity (WiFi) and the world interoperability for microwave access. Measured results show that the amplitude imbalance of this Butler matrix is less than 2 dB, while the average insertion loss is less than 2.7 dB. Meantime, the return loss is better than 15 dB, together with the isolation between input ports better than 17 dB. In addition, an antenna array fed by this frequency-agile Butler matrix is investigated. It exhibits good out-of-band suppression especially at the lower band, showing the advantages over other multiband and wideband counterparts. For example, when the multiple beam antenna operates at 1.95 GHz, the received power levels of 2.14, 2.35, 2.44 and 2.6 GHz are only 0.02, 0.46, 0.19 and 0.87%, respectively, compared with the reference received power level of 1.95 GHz.

A compact ultra-wideband balun topology suitable for on-chip integration is introduced in this paper. The balun is designed using an inverting transformer for the generation of the inverted signal, and a third inductor is incorporated to support the generation of the non-inverted signal. Through examining the transfer function and bandwidth limitations of existing on-chip voltage transformer and current transformer baluns, the broadband feature of the balun is clearly demonstrated through theoretical analysis and simulation, and further validated by a practical example. Measurement results confirm that a −3 dB relative bandwidth of approximately 167% is achieved, along with excellent amplitude and phase balance. The integrated ultra-wideband balun topology is also applied in a mixer design, resulting in a product with industry-leading RF and IF operating bandwidths.