A new structure of a low-loss high temperature superconducting (HTS) filter is proposed by using quarter-wavelength coplanar waveguide (CPW) resonators. A 4-pole Chebyshev band-pass filter with the center frequency 5.0 GHz and the 0.01 dB-ripple fractional bandwidth 3.2% is designed based on the theory of direct-coupled resonator filters using K- and J-inverters. This filter is fabricated by using a high-Tc superconductive YBCO film deposited on a MgO dielectric substrate. The frequency response of the filter measured at 60 K agrees very well with the theoretical one. The insertion loss is 0.22 dB. The insertion loss of this filter is the lowest in HTS-CPW filters presented so far.

Scan-based side-channel attacks retrieve a secret key in a cryptography circuit by analyzing scanned data. Since they must be considerable threats to a cryptosystem LSI, we have to protect cryptography circuits from them. RSA is one of the most important cryptography algorithms because it effectively realizes a public-key cryptography system. RSA is extensively used but conventional scan-based side-channel attacks cannot be applied to it because it has a complicated algorithm. This paper proposes a scan-based side-channel attack which enables us to retrieve a secret key in an RSA circuit. The proposed method is based on detecting intermediate values calculated in an RSA circuit. We focus on a 1-bit time-sequence which is specific to some intermediate values. By monitoring the 1-bit time-sequence in the scan path, we can find out the register position specific to the intermediate value and we can know whether this intermediate value is calculated or not in the target RSA circuit. We can retrieve a secret key one-bit by one-bit from MSB to LSB. The experimental results demonstrate that a 1,024-bit secret key used in the target RSA circuit can be retrieved using 30.2 input messages within 98.3 seconds and its 2,048-bit secret key can be retrieved using 34.4 input within 634.0 seconds.

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.

A novel high temperature superconducting interdigital bandpass filter is proposed by using coplanar waveguide quarter-wavelength resonators. The CPW resonators are arranged in parallel, and consequently the filter becomes very compact. The filter is a 5-pole Chebyshev BPF with a midband frequency of 5.0 GHz and an equal-ripple fractional bandwidth of 3.2%. It is fabricated using a YBCO film deposited on an MgO substrate. The measured filtering characteristics agree well with EM simulations and show a low insertion loss in spite of the small size of the filter.

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.

This paper proposes a novel high-temperature superconducting dual-band bandpass filter (HTS-DBPF), that employs a broadside coupling structure, in which quarter-wavelength resonators are formed on opposite sides of each substrate. This structure provides a dual-band operation of the BPF and flexibility, in the sense of having a wide range in selecting two center passband frequencies of the HTS-DBPF. This paper employs the ratio of the lower and higher center passband frequencies, α, as a criterion for evaluating the flexibility. The obtained α ranges are from 1 to 4.7, which are the widest for DBPFs for mobile communications applications, to the best knowledge of the authors. This paper presents a 2.4-/2.9-GHz band HTS-DBPF, as an experimental example, using a YBCO film deposited on an MgO substrate. The measured frequency responses of the HTS-DBPF agree with the electromagnetic simulated results. Measurement and simulation results confirm that the proposed filter architecture is effective in configuring a DBPF that can set each center passband frequency widely.

An ultra low-noise and highly selective, experimental 2-GHz band cryogenic receiver front end (CRFE) has been newly developed for cellular base stations. It utilizes a high-Q superconducting filter, a very low noise cryogenic amplifier, and a highly reliable cooler that is very compact. Fundamental design of the CRFE is investigated. First, the equivalent noise temperature of the CRFE and the effect of improving CRFE sensitivity on base station reception are discussed. Next, essential technologies and fundamental characteristics of each component are described. Finally, influence of antenna noise, such as ground noise and man-made noise, is estimated through field tests both in urban and suburban areas.