Shin-ichi Betsudan

A compact broad-band helical antenna with two-wire helix

A new method of increasing the bandwidth of normal-mode helical antennas (NMHA) is proposed. The antenna has length of around 0.1 of the target wavelength, and consists of a helix constructed with two flat wire strips. The method exploits the two current modes of the two-wire design to obtain wideband response. Based on an analysis of the equivalent circuits of the two modes and subsequent optimization of design parameters, a final two-strip NMHA design is proposed that is demonstrated to have a bandwidth of 12% in the 760-MHz band at a voltage standing wave ratio of less than 2.

High efficient bridge rectifiers in 100MHz and 2.4GHz bands

This paper describes the high efficient bridge rectifier topology and its implementations in 100MHz and 2.4GHz bands. The rectifier topology realizes full-wave-rectification without large sized filters used in single-shunt type rectifiers. By employing the topology, further downsizing and integration can be achieved easily. High impedance operation with impedance transformer or the high-impedance antenna is employed to improve the rectification efficiency. Also formulas of the rectification efficiency on the proposed topology are described in the paper for clarification of effectiveness. Experimental investigations demonstrate confirmation of the derived formulas. Also 94% efficiency of the 100MHz band rectifier and 80% efficiency of the 2.4GHz rectenna are achieved. These values are the top-level performance with the commercial-based Si-SBD. Also the size of the 2.4GHz band rectifier is 4.5mm × 4.8mm that is the smallest implementation than the past works.

A broadband plate antenna with slits

As a small antenna of handsets for personal communication systems, a two-strip meander-line antenna and a normal mode helical antenna have been suggested. The values of quality factors of both antennas are from 20 to 30 when the size of the antennas are smaller than 0.1 wavelength. The quality factor Q is really important to evaluate the bandwidth of an antenna. The bandwidth is in inverse proportion to Q. Therefore, if the quality factor can be small, the bandwidth becomes broadband. A plate antenna whose quality factor is smaller than those of the meander line antenna and the normal mode helical antenna can be obtained with broadband characteristics. In order to realise the impedance matching, the antenna consists of two plates, and the currents of the two plates are produced in imbalance and balance modes. In this paper, the small plate antenna with slits is treated. The impedance characteristics of the antenna is made clear and increasing the bandwidth by using two plates is also discussed.

Fundamentals of the bridge RF rectifier with an impedance transformer

This report describes the fundamentals of the bridge RF rectifier with an impedance transformer. The rectifier allows full-wave-rectification with no additional circuit, enabling further downsizing and integration of the circuit. To improve the rectification efficiency, an impedance transformer is added between the input port and the bridge diode. From this configuration, we have derived rectification efficiency formulas showing that the design conditions of an impedance transformer are equivalent to the impedance matching conditions. We have assembled a trial circuit to verify the validity of the formulas and confirm improvements in the rectification efficiency with the impedance transformer.

Increasing the bandwidth of a two-strip meander-line antenna mounted on a conducting box

A meander-line antenna consisting of two strips (two-strip MLA) is applied to a conducting box as a handset model in order to increase the bandwidth of a built-in antenna. The analysis of an MLA mounted on a conducting box leads to its resonant frequency f/sub r/, and radiation resistance R/sub r/ at f/sub r./ Using the two-strip MLA with balance mode impedance, broadbanding of the antenna in the impedance characteristics is considered.

PMC characteristics of capacitance grid with metal plate

This paper provides PMC characteristics of a capacitance grid with a metal plate and the design method using an equivalent circuit model is also provided. Measured results of very thin PMC model with the thickness of 1/150 wavelength are also provided.

Increasing the bandwidth of a normal mode helical antenna consisting of two strips

A normal mode helical antenna (NMHA) is usually used for handsets in personal communication systems. As the small NMHA has low radiation resistance, it requires a matching circuit. The matching circuit has loss and the radiation efficiency decreases. An NMHA consisting of two wires (the 2-wire NMHA) has been suggested (Noguchi et al., 1997). The radiation impedance of the 2-wire NMHA can be matched by itself to the characteristic impedance of the feed line. The impedance matching is carried out by use of current modes that include balance and unbalance modes. However, it is difficult to increase the bandwidth of the 2-wire NMHA because reactance components of the antenna can not be eliminated by reactance in the balance mode of two wires. A small meander-line antenna of two strips has been suggested to increase the bandwidth of the antenna without a matching circuit (Noguchi et al., 1997). The reactance component of the antenna can be eliminated by reactance in the balance mode over a wide frequency range. In this paper, a small NMHA consisting of two strips (the 2-strip NMHA) is presented. The method of increasing the bandwidth is applied to this antenna.

Theoretical bandwidth of folded small antennas

Theoretical maximum bandwidth is derived for an equivalent circuit of small antennas consisting of a folded structure. Based on the equivalent circuit, input admittance as a function of frequency deviation is derived. Under the conditions of double resonance characteristics, the maximum bandwidth and characteristic impedance in balance mode are expressed with relation of the allowable VSWR and Q. As an example of design, a folded inverted-L antenna is presented.

High linear even harmonic mixer driven by the pulsed LO

This paper presents the high linear even harmonic mixer driven by the pulsed LO for achieving high power and low distortion performance. For the objectives, positive and negative pulses pump an anti-parallel diode pair as the LO voltage. Duty ratio of each pulse is 25% for the LO period. This means that the pumped conductance Gj of the anti-parallel diode pair includes the highest level of the second order harmonic. This can reduce LO dependence on the conversion efficiency of the even harmonic mixer. Theoretical and experimental investigations confirm effectiveness on the high power and the low distortion performance of the even harmonic mixer with the proposed LO waveform.

Broadband matching of a RFID antenna by using a T-type circuit

RFID usage is steadily increasing in the world, and its frequency bands are assigned in each country. RFID in UHF band is mainly used in 900MHz band. Allocated frequency bands of Europe, the USA and Japan are included from 860 to 960MHz. Broadbanding of the IC and antenna is needed to manage the worldwide RFID frequency band. This paper proposes broadband matching of a RFID antenna by using a T-type circuit. The antenna consists of a meander-line and a T-type circuit that realizes conjugate impedance matching to the IC impedance. Equivalent circuits of the antenna are shown and evaluated by parametric study. Prototype of the antenna is realized and its numerical analyses are examined.