This letter presents a low spurious frequency setting algorithm for a triple tuned type PLL synthesizer driven by a DDS. The triple tuned PLL synthesizer is based on a single PLL configuration with two variable frequency dividers. The DDS is employed for a reference source of the PLL. The proposed algorithm determines appropriate frequency tuning values of the DDS frequency and the division ratios of two frequency dividers. The division ratios are selected to achieve a desired output frequency while the low spurious condition of the DDS has been maintained. A 5 to 10 GHz synthesizer with frequency step of 500 kHz demonstrated spurious level below -46 dBc with improvement of 13 dB.

Adaptive antenna is a promising to increase the spectral efficiency of mobile radio systems. We developed a compact, cost effective planar Butler Matrix as a beam forming network of a multi beam antenna. This circuit consists of a thin substrate that the conductor attaches to both sides, and two thick substrates that the ground conductor attaches to one side. In this circuit, coupling by crossover causes amplitude and phase error of the Butler Matrix. By narrowing the strip width of the crossover, crossover coupling can be suppressed 10 dB. The measurement results of the experimental 88 Butler Matrix were 0.75 dB amplitude deviation, 9.5 degree phase deviation and VSWR of less than 1.15 within the relative bandwidth of 10% at 900 MHz band.

This letter describes a novel coupled-transmission-line directional coupler using an asymmetrical suspended stripline with unequal conducting strips on both sides of a dielectric substrate. The directional coupler has a rang of coupling values from 5 to 9 dB which is difficult to be realized by a conventional symmetrical suspended stripline coupler.

This paper presents an even harmonic quadrature mixer (EH-QMIX) with a simple filter configuration and an integrated LTCC module including LNAs, band rejection filters (BRFs), and the proposed EH-QMIX for W-CDMA direct conversion receiver (DCR). Since the DCR has no spurious responses, a BRF instead of a high-Q band pass filter can be applicable for eliminating undesired signals and it can be built in the LTCC substrates easily. As LO frequency is half of RF frequency in the EH-QMIX, diplexer can be composed of simple filters and it can be also integrated in the substrates. As a result, the whole RF circuits of the EH-DCR using a proposed EH-QMIX are integrated in the LTCC module and miniaturization of the receiver is achieved. Moreover, in order to suppress the degradation of the amplitude and the phase imbalances in the quadrature mixer caused by interferences of signals, RF characteristics of the circuits in the mixer such as reflection coefficients, isolations are discussed. A developed LTCC module shows good performances for W-CDMA direct conversion receiver.

This paper presents an even harmonic mixer using self-biased anti-parallel diode pair (APDP). A proposed self-biased APDP is composed of a pair of diodes and self-bias series resistors. At high LO injection level, rectified current is generated by the diodes and reverse voltage is applied to the diodes by the self-bias resistor. Therefore, rapid degradation of conversion loss at high LO input level can be avoided. The effect of self-bias resistor is explained by using simplified behavior model and harmonic balance method, and is evaluated by the measurements of an L-band even harmonic type direct conversion mixer.

This paper presents novel phase-continuous frequency hopping (FH) control for a direct frequency synthesizer (DFS) using a quadrature mixer driven by two direct digital synthesizers (DDSs). To achieve wideband FH in both of the lower and the upper sidebands of a local frequency in a quadrature mixer, the proposed DFS decreases or increases the phase of DDS output signals corresponding to frequency offset from a local frequency of the quadrature mixer. To realize phase decrement, the proposed method adds a complement number in a phase accumulator of a DDS, while a conventional DDS does not use phase decrement but uses a switchable combiner. In addition, as the phase accumulator output changes continuously by summing phase increment, the proposed method always assures phase continuity of a DFS output signal, which ends up suppressing sidelobe level of frequency hopped signals. The calculation and measurement results indicate that a sidelobe of a signal spectrum using the proposed phase continuous method is approximately 10 dB better than that using a conventional phase discontinuous method.

This paper describes the distortion characteristics of an even harmonic type direct converter (EH-DC) used in earth stations for CDMA satellite communications. Direct conversion technique is known as a method to simplify circuit topologies of microwave transceivers. In satellite communications, multi carriers which have high and nearly equal level are provided to a quadrature mixer of the EH-DC. Hence, the third-order intermodulation degrades receiving characteristics. In this paper, we show the relationship between the distortion characteristics and noise figure of the EH-DC for CDMA satellite communication systems. Furthermore, we show NPR of even harmonic quadrature mixers caused by the third-order intermodulation. Experimental results in X-band indicate that the proposed EH-DC has almost the same BER characteristics compared with a heterodyne type transceiver.

An even harmonic quadrature mixer (EH-QMIX) with a balanced configuration is proposed for a direct conversion receiver. The unit even harmonic mixer (EHMIX) used for I/Q paths consists of two anti parallel diode pairs (APDPs) and a pair of diplexers. When the second harmonic of LO (2LO) from the LO section is applied to the LO port as a spurious component, a conventional single-ended EHMIX using APDP converts the 2LO leakage from the LO section into the baseband and the d.c. offset and the self-detected LO noise arise at the baseband degrade the sensitivity. This proposed balanced EHMIX configuration can cancel out the 2LO leakage in itself. Therefore, the d.c. offset and the LO noise are significantly suppressed and the degradation of the sensitivity can be avoided. The suppression characteristic of the d.c. offset and the LO noise are verified by the simulation and the measurements. By using this balanced configuration, the fabricated EH-QMIX achieves wider frequency band characteristic than that of the single-ended EH-QMIX, and it shows 20% relative bandwidth at L-band.

A highly accurate measurement method of parameters of MZ-type LN optical intensity modulators is presented. In this method, a CW optical signal is input to an optical terminal and small CW RF signal is applied to an electrode of the modulator. Then sideband levels of an output optical signal at different bias points are measured by using optical spectrum analyzer. By using 1st order sideband levels which are measured at two different bias conditions, and using a compensation method to measured levels, we can obtain accurate chirp parameter even when very small power of RF signal is applied to the modulator. In this method, the chirp parameter can be obtained in good accuracy when the input RF voltage is only 3% of the halfwave voltage.

This paper proposes a design method of a Doherty amplifier, which can determine the most efficient backed-off point of the amplifier by adjusting a load modulation parameter. The parameter is defined through the design of output transmission line of a carrier and a peak amplifier using a virtual open stub technique. This paper describes the design results using the technique to optimize efficiency of a Doherty amplifier for an orthogonal frequency division multiplexing (OFDM) signal, and parameter adjustment for a linearized Doherty amplifier using an adaptive digital predistortion (ADPD). Applying this method, the developed 250 W ADPD Doherty amplifier has achieved drain efficiency of 43.4% and intermodulation (IM) distortion of -48.3 dBc with output power of 44.1 dBm (10.1 dB output backed-off) at 563 MHz using an OFDM signal for integrated services digital broadcasting-terrestrial (ISDB-T).