Man Seok Uhm

A dual-passband filter of canonical structure for satellite applications

Due to the complex arrangement of frequency plans and spatial coverages in modern satellite communication systems, channels that are noncontiguous in frequency may be amplified by a single power amplifier and transmitted to the ground through one beam. In this letter, a dual-mode canonical filter with dual-passband is presented. The filter adopts dual-mode technique for mass and volume reduction. Canonical structure is adopted for maximum zero realization. To validate the design technique, a six-pole dual-mode dual-passband filter of canonical structure for Ka-band (30/20GHz) satellite transponder is realized. The measured frequency response of the filter shows good agreement with the computed one.

Synthesis of a self-equalized dual-passband filter

This letter describes synthesis method for a self-equalized dual-passband filter. Compared to a conventional dual-passband filter, the self-equalized dual-passband filter can reduce bit-error rate (BER) in digital data communications and does not need an external equalizer for group delay equalization. To validate the synthesis method described in this letter, a 10-pole dual-passband filter which has two self-equalized five-pole elliptic-response passbands is synthesized.

K-Band Substrate-Integrated Waveguide Resonator Filter With Suppressed Higher-Order Mode

In this letter, we present a design method for K-band substrate-integrated waveguide (SIW) resonator filters utilizing TM02 mode. More importantly, a methodology for suppressing an unwanted higher-order mode ( TM11) close to the passband is demonstrated. It is shown that suppressing the unwanted mode give rise to the improved stopband performance. In addition, the resonator used in this filter design has capability of adjusting the resonant frequency, and this allows for compensating the fabrication error. Verification of the presented design method has been carried out by fabricating and measuring the filter.

Simultaneous reduction of amplitude and group-delay variation of input demultiplexer for Ku band satellite transponder

In this paper, design and realization of input demultiplexer(IMUX) for Ku band satellite transponder is described. Circulator chain structure has been used for demultiplexing each channel. Each channel consists of channel filter and external equalizer. External equalizers are designed to reduce the group delay variation and amplitude variation of channel filters simultaneously. Dual-mode technique is adopted for reducing the mass and volume of both the channel filters and external equalizers. Channel filters are designed to have 8-pole elliptic response and equalizers to be of 2-pole reflection-type. For good temperature stability characteristics, INVAR material is used for cavities, irises, and tuning srews of channel filters and external equalizers. The frequency drift has been taken into consideration in design procedure and measured by thermal test. Input demultiplexer is shown to be suitable for Ku band satellite transponder.

An efficient optimization design of a manifold multiplexer using an accurate equivalent circuit model of coupling irises of channel filters

In this paper, an efficient optimization design method for a manifold multiplexer is proposed. For an efficient optimization, equivalent circuit models for coupling irises of channel filters are presented. Equivalent circuit models are obtained from the results of electromagnetic field (EM) analysis. To validate the presented optimization design method, a manifold multiplexer for Ka-band satellite applications is designed and realized. The good agreement between theoretical result and measured one is shown.

Design of the Multipaction Free High Power Ka-band Diplexer with an E-plane T-junction

In this paper, the design and performance of a low-PIM and multipaction free Ka-band (20/30 GHz) waveguide diplexer with an E-plane T-junction is described. The waveguide diplexer consists of a transmit filter and a receive filter combined to the antenna port via an E-plane T-junction. The reason why E-plane T-junction structure was selected is to reduce PIM (passive intermodulation) level. In order to handle high power the multipaction analysis was performed in design stage as the peak voltage in the resonator with minimum gap is much smaller than the threshold voltage recommended by ESA/ESTEC. The multipaction analysis margin is greater than 12 dB. The manufactured diplexer has good pass band return loss (>24 dB) and high isolation (>52 dB) for both transmit and receive frequency bands. The diplexer does not need any post fabrication tuning. Those mean the analysis results of the waveguide diplexer are verified through the electrical performance test

A tuning method using a dummy cavity for dual-mode cavity filters

A tuning method using short-ended dummy cavity is presented for dual-mode cavity filters. Tuning is based on the match of the computed and measured phase response of reflection coefficient. Equivalent circuit model is adopted for computing required phase response of reflection coefficient. This proposed method is applied to 4-pole in-line type dual-mode elliptic response filter for demonstration of this new method. It is shown that this method shows good agreement between the experimental and computed result, and no additional tuning procedure is required.

Practical Method for Obtaining Maximum Channel Temperature of GaAs MMIC

[Abstract] Regressive equations that calculate the maximum channel temperature of a GaAs monolithic microwave integrated circuit (MMIC) have been made through a lot of finite element (FE) analyses. And this paper suggests how to estimate the maximum channel temperature with those regressive equations for frequent cases. As an example, a medium power amplifier’s maximum channel temperature was calculated and its result was larger than that of a complete FE model by about 4%. The medium power amplifier’s temperature distribution was obtained through an infrared scan and, even though the maximum channel temperature could not be obtained due to the test’s inherent shortcoming, temperature other than gate fingers showed good agreement with FE analysis results. Therefore it can be said that the practical method for obtaining the maximum channel temperature using regressive equations can give thermal resistance of a GaAs MMIC very easily and quickly without time-consuming FE analyses.

A Ka-Band Coaxial-to-Waveguide Transition Including Coaxial Airline

A Ka-band coaxial-to-waveguide transition, which is composed of a WR34 waveguide and a commercial SMA 3.5 connector exhibiting a cutoff frequency of 26.5 GHz, has been successfully developed using a protruding part of the inner conductor of the SMA 3.5 connector as a coupling probe. Coaxial airline between waveguide and coaxial line enables a stable operation over the 30 GHz frequency range. The measured maximum insertion loss is 0.28 dB and the minimum return loss is 15 dB over 28.6 GHz ~ 31.3 GHz.

Synthesis of a dual-passband elliptic filter with equalized group delay

This paper describes synthesis method for a self-equalized dual-passband elliptic filter. Compared to a conventional dual-passband elliptic filter, the self-equalized dual-passband elliptic filter can reduce BER (bit error rate) in digital data communications and does not need an external equalizer for group delay equalization. To validate the synthesis method described in this paper, a 10-pole dual-passband filter which has two self-equalized 5-pole elliptic-response passbands is synthesized.