A detailed analysis of a multilayer symmetric coupler employing symmetrical broad-side coupled lines is presented. We confirm that the coupler can be designed using a well-known even-odd mode analysis of two strip lines while the coupler has four strip lines. We also confirm that the previously reported poor isolation originates from port mismatching. To verify the analysis, couplers that have different dimensions are fabricated. One example exhibits a coupling loss of 4.50.5 dB, a return loss better than 15 dB, and isolation characteristics higher than 12 dB in the 6.5 to 15.1 GHz frequency range. These results agree well with the obtained simulation results. The results show that the coupler has the potential to provide tight and ideal coupling.

This paper presents analysis results of the intermodulation distortion (IMD) components compensation conditions for dual-band feed-forward power amplifier (FFPA) when inputting dual-band signals simultaneously. The signal cancellation loop and distortion cancellation loop of the dual-band FFPA have frequency selective adjustment paths which consist of filter and vector regulator. The filter selects the desired frequency component and suppresses the undesired frequency component in the desired frequency selective adjustment path. The vector regulators repeatedly adjust the amplitude and phase values of the composite components for the desired and suppressed undesired frequency components. In this configuration, the cancellation levels of the signal cancellation loop and distortion cancellation loop are depending on the amplitude and phase errors of the vector regulator. The analysis results show that the amplitude and phase errors of the desired frequency component almost become independent that of the undesired frequency component in a weak non-linearity condition, when the isolation between the desired band and the undesired band given by the filter is more than 40 dB. The amplitude errors of the desired frequency component are dependent on that of the undesired frequency component in a strong non-linear conditions when the isolation level sets as above. A 1-W-class signal cancellation loop and 20-W-class FFPA are fabricated for 1.7-GHz and 2.1-GHz bands simultaneous operation. The experimental results show that the analysis results are suitable in the experimental conditions. From these investigations, the analysis results can provide a commercially available dual-band FFPA. To our best knowledge, this is first analysis results for the dual-band FFPA.

This paper presents an extremely low-profile front-end configuration for a base station at quasi-millimeter wave band. It consists of integrated modules of patch antennas and substrate integrated waveguide filters using two printed circuit boards, and transmitter modules using compact GaAs pHEMT three-dimensional monolithic millimeter-wave integrated circuits. The transmitter modules are located around the integrated modules. This is because the proposed front-end configuration can attain extremely low profile, and band-pass filtering performance at quasi-millimeter wave band. As a demonstration of the proposed configuration, 26-GHz-band 4-by-4 elements front-end module is fabricated and tested. The fabricated module has the thickness of about 1 cm, while that offers the attenuation of more than 30 dB with 2 GHz offset from 26 GHz. The proposed configuration can provide base station that can be effective in offering sub-millimeter wave and millimeter-wave bands broadband services for 5G mobile communications systems.

This paper presents a novel isolator that employs a varactor that tunes the operating frequency for use in future multi-band mobile handsets. The proposed isolator employs only one varactor for compactness and has a three-fold symmetric structure to reduce the parasitic reactance at each port. Analytical and experimental results clarify the tuning range of the proposed isolator. This paper presents the fundamental characteristics of the proposed isolator such as the insertion loss, isolation, and adjacent channel leakage ratio (ACLR) using a W-CDMA signal. The impact of the proposed isolator on the system performance is described based on experimental evaluation of the ACLR with a multi-band transmission system consisting of a power amplifier and the proposed isolator.

This paper presents a highly efficient multi-band power amplifier (PA) with a novel reconfigurable configuration. It consists of band-switchable matching networks (BS-MNs) and a biasing network (BS-BN) that are available for multi-band operation. BS-MNs with a susceptance block (SB) require a shorter transmission line (TL) than those without the SB at some target impedances. This paper theoretically derives the relationships of the required TL lengths for the BS-MN with or without the SB and the target impedances. The required TL lengths at the target impedances are evaluated numerically in order to discuss the advantages of the proposed configuration. The BS-BN employing switches for band switching can supply DC power to an amplification device without additional DC power dissipation because the DC bias current does not flow through the switches. Numerical analyses confirm that a BS-BN can be configured with low loss in multiple bands. Based on the proposed configuration, a 1/1.5/1.9/2.5-GHz quad-band reconfigurable PA is designed and fabricated employing RF microelectro mechanical systems switches and partitioned low temperature co-fired ceramics substrates. The fabricated 1 W-class PA achieves a high output power of greater than 30 dBm and a maximum power added efficiency of over 40% in all operating modes.

A V-band compact monolithic up-converter and down-converter were designed and tested. Each frequency converter was highly integrated with RF and LO amplifiers into a single compact chip. To avoid undesirable resonance, the chip width was limited to 0.9 mm. The up-converter has a balanced configuration to suppress undesired LO leakage. Using the uniplanar concept, the chip size of each frequency converter was greatly reduced to only 2.6 mm2. Measured performance of the up-converter includes conversion gain of-10.6 dB3.3 dB for a bandwidth of 10 GHz, and LO leakage is more than 10 dB below LO input. The down-converter shows a conversion gain of -0.4 dB2.0 dB.

Research on wireless power transmission technology is being actively conducted, and studies on spatial transmission methods such as SSPS are currently underway for applications such as power transfer to the upper part of steel towers and power transfer to flying objects such as drones. To enable such applications, it is necessary to examine the configuration of the power-transfer and power-receiving antennas and to improve the RF-DC conversion efficiency (hereinafter referred to as conversion efficiency) of the rectifier circuit on the power-receiving antenna. To improve the conversion efficiency, various methods that utilize full-wave rectification rather than half-wave rectification have been proposed. However, these come with problems such as a complicated circuit structure, the need for additional capacitors, the selection of components at high frequencies, and a reduction in mounting yield. In this paper, we propose a method to improve the conversion efficiency by loading a high-impedance microstrip line as a feedback line in part of the rectifier circuit. We analyzed a class-F rectifier circuit using circuit analysis software and found that the conversion efficiency of the conventional configuration was 54.2%, but the proposed configuration was 69.3%. We also analyzed a measuring circuit made with a discrete configuration in the 5.8-GHz band and found that the conversion efficiency was 74.7% at 24dBm input.

This paper presents a theoretical analysis and experimental confirmation of a tunable ring resonator that can independently change its resonant frequency and bandwidth. The tunable ring resonator comprises a ring resonator, three tunable capacitors, and switches. The resonant frequency changes according to the capacitance of tunable capacitors, and the bandwidth varies by changing the state of the switches. The unique feature of the resonator is that the resonant frequency remains steady when the bandwidth is changed. The fundamental characteristics are shown based on linear circuit simulation and electromagnetic simulation results. The resonator is fabricated using GaAs FET single-pole single-throw switches. The fabricated resonator changes the resonant frequency from 1.5 GHz to 2.0 GHz and the fractional bandwidth from 5% to 30%.

This paper presents a novel design scheme for a band-switchable multi-band power amplifier (BS-MPA). A key point of the design scheme is configuring multi-section reconfigurable matching networks (MR-MNs) optimally in terms of low loss matching in multiple frequency bands from 0.7 to 2.5 GHz. The MR-MN consists of several matching sections, each of which has a matching block connected to a transmission line via a switch. Power dissipation at an actual on-state switch results in the insertion loss of the MR-MN and depends on how the impedance is transformed by the MR-MN. The proposed design scheme appropriately transforms the impedance of a high power transistor to configure a low loss MR-MN. Numerical analyses show quantitative improvement in the loss using the proposed scheme. A 9-band 3-stage BS-MPA is newly designed following the proposed scheme and fabricated on a multi-layer low temperature co-fired ceramic substrate for compactness. The BS-MPA achieves a gain of over 30 dB, an output power of greater than 33 dBm and a power added efficiency of over 40% at the supply voltage of 4 V in each operating band.

This paper presents a simple-structured tunable resonator employing semiconductor switches that can change its resonant frequency discretely but precisely. The tunable resonator comprises a transmission line with a comb-shaped pattern and multiple single-pole single-throw (SPST) switches placed between the teeth of the comb-shaped pattern. The resonator changes its resonant frequency according to the switch states, by controlling the path length carrying a high frequency current. The characteristics of the proposed resonator are evaluated through both method of moment electromagnetic simulation and fabrication, using GaAs FET SPST switches. The fabricated resonator changes its resonant frequency from 1.63,GHz to 1.85,GHz. This paper also introduces two circuit designs based on the proposed resonator that expands the tuning range of the resonant frequency or the number of resonant frequencies to be obtained.

In this paper, we consider a parallel ring-line rat-race circuit realized by replacing some parts of the ring-lines with composite right-/left-handed transmission lines (CRLH-TLs). For a conventional rat-race circuit, the minimum coupling factor is limited by the highest impedance of the ring-lines that can be manufactured by general printed circuit board (PCB) technologies. However, the coupling factor of the parallel ring-line type rat-race circuit proposed in this paper is determined by the difference between the admittances of the parallel ring-lines. As a result of designing parallel ring-line rat-race circuits having coupling factors of $-20$ and $-30$,dB for an operation frequency of 4,GHz, the proposed rat-race circuit realizes broadband characteristics of about 35.5% according to the numerical results for the $-20$,dB circuit. Furthermore, broadband characteristics including reflection, isolation, and couplings can be maintained for the fabricated $-20$,dB rat-race circuit up to an input power of 40,dBm.

A novel scheme for a multi-band power amplifier (PA) that employs a low-loss reconfigurable matching network is presented and discussed. The matching network basically consists of a cascade of single-stub tuning circuits, in which each stub is connected to a transmission line via a Single-Pole-Single-Throw (SPST) switch. By controlling the on/off status of each switch, the matching network works as a band-switchable matching network. Based on a detailed analysis of the influence of non-ideal switches in the matching network, we conceived a new design perspective for the reconfigurable matching network that achieves low loss. A 900/1900-MHz dual-band, 1 W class PA is newly designed following the new design perspective, and fabricated with microelectro mechanical system (MEMS) SPST switches. Owing to the new design and sufficient characteristics of the MEMS switches, the dual-band PA achieves over 60% of the maximum power-added efficiency with an output power for each band exceeding 30 dBm. These results are comparable to the estimated results for a single-band PA. This shows that the proposed scheme provides a band-switchable highly efficient PA that has superior performance compared to the conventional multi-band PA that has a complex structure.

This paper presents a novel frequency-controlled beam steering scheme for a phased-array antenna system (PAS). The proposed scheme employs phase-controlled carrier signals to form the PAS beam. Two local oscillators (LOs) and delay lines are used to generate the carrier signals. The carrier of one LO is divided into branches, and then the divided carriers passing through the corresponding delay lines have the desired phase relationship, which depends on the oscillation frequency of the LO. To confirm the feasibility of the scheme, four-branch PAS transmitters are configured and tested in a 10-GHz frequency band. The results verify that the formed beam is successfully steered in a wide range, i.e., the 3-dB beamwidth of approximately 100 degrees, using LO frequency control.

This paper presents a theoretical analysis of a tunable resonator using a coupled line and switches for the first time. The tunable resonator has the capability to tune its resonant frequency and bandwidth. The resonator has two suitable features on its tunable capability. The first feature is that the resonator retains its resonant frequency during bandwidth tuning. The second feature is that the on-state switch for tuning the bandwidth does not affect the insertion loss at the resonant frequency. These features are theoretically confirmed by its mathematically derived input impedance. The results from electromagnetic simulation and measurement of the fabricated tunable resonator also confirm these features. The fabricated tunable resonator changes the resonant frequency from 2.6 GHz to 6.4 GHz and bandwidth between 9% and 55%.

An S-band linearizer was developed using GaAs MMIC technology. We call it the even-order-distortion-implemented intermodulation distortion controller (EODIC). EODIC uses even-order intermodulation distortion (IM) components in the second harmonic frequency band to control its IM components in the fundamental frequency band. EODIC is a suitable tool to compensate near-saturated high power amplifiers (HPAs). We developed an EODIC using MMIC technology. This paper describes the principle of EODIC and then introduces the EODIC MMIC in detail. This paper also presents the IM reduction performance of an EODIC in a near-saturated HPA.