Junhyung Jeong

Design of tunable negative group delay circuit for communication systems

In this paper, a design of tunable microstrip transmission line negative group delay circuit (NGDC) using p-i-n diodes is proposed. The design was based on reflective parallel R-L-C circuit and group delay (GD) can be varied with help of variable resistance. To get the variable resistance, the transmission line (TL) terminated with p-i-n diode is used. The GD is varied with help of bias voltages of p-i-n diodes. Both design equations and design procedures are presented. The measured GD time variation range is 0 ~ -20 ns and well agreed with simulation results.

Negative group delay circuit with independently tunable center frequency and group delay

In this paper, a design of negative group delay circuit (NGDC) with independently tunable center frequency and group delay (GD) is presented. Since the proposed structure consists of a parallel RLC resonance circuit, it is possible to obtain a variable negative GD by using a variable resistor and an adjustment of center frequency of GD is possible due to a variable inductor. To get the pure variable resistor, the transmission line (TL) terminated with the PIN diode is used. Similarly, the variable inductor is realized by TL terminated with the varactor diode. To show the effectiveness of the proposed NGDC, it is designed at 2.14 GHz of WCDMA downlink band. The measured negative GD time is -2 ~ -20ns, and are able to change the center frequencies of negative GD in the range of 2.04 ~ 2.24 GHz.

Compact negative group delay circuit using defected ground structure

A novel design of compact negative group delay circuit (NGDC) using U-shaped defected ground structure (DGS) is presented in this paper. The required group delay (GD) time can be controlled by an external resistor connected across the DGS slot. For experimental verification, a single stage NGDC is designed, fabricated, and compared with a circuit simulation. To enhance NGD bandwidth, two stages NGDC with the different center frequencies in cascade are demonstrated and GD of -3.8 ns with maximum signal attenuation of 37.10 dB was obtained on 3.45-3.55 GHz.

A design of negative group delay power divider: Coupling matrix approach with finite unloaded-Qu resonators

In this paper, a novel approach to design a power divider with the predefined negative group delay (NGD) is presented. The proposed topology is based on a coupling matrix with a finite unloaded quality factor (Qu) of resonators, which does not require any lumped elements such as resistor for generating NGD. The NGD bandwidth and magnitude flatness can be controlled by inter-resonating couplings. As an experimental illustration, a microstrip line NGD power divider is designed and fabricated at center frequency of 2.14 GHz. The measurement results are in good agreement with simulations.

High Selectivity Coupled Line Impedance Transformer with Second Harmonic Suppression

This paper presents a design of an impedance transformer (IT) with high frequency selectivity characteristics. The frequency selectivity can be controlled by even- and odd-mode impedance of a shunt coupled transmission line (TL). For experimental validation, a 50- to 20- Ω IT was implemented at a center frequency (f0) of 2.6 GHz for the long-term evolution signal. The measured results were in good agreement with the simulations, showing a return loss higher than 19 dB over a passband bandwidth of 0.63 GHz (2.28–2.91 GHz) and good sharp frequency selectivity characteristic near to the passband. The series coupled TL provides a transmission zero at 5.75 GHz, whereas the shunt coupled TL provides three transmission zeros located at 2 GHz, 3.1 GHz, and 7.14 GHz.

Negative Group Delay Circuit with Improved Signal Attenuation and Multiple Pole Characteristics

This paper presents a design of a transmission line negative group delay (NGD) circuit with multiple pole characteristics. By inserting an additional transmission line into a conventional NGD circuit, the proposed circuit provides further design parameters to obtain wideband group delay (GD) and to help reduce signal attenuation. As a result, the number of gain compensating amplifiers can be reduced, which can contribute to stable operation when integrated into RF systems. The multiple pole characteristics can provide wider NGD bandwidth and can be obtained by connecting resonators with slightly different center frequencies separated by quarter-wavelength transmission lines. For experimental validation, an NGD circuit with two poles GD characteristic is designed, simulated, and measured.

Time Mismatch Effect in Linearity of Hybrid Envelope Tracking Power Amplifier

In this letter, a linearity degradation according to the time mismatching between RF and envelope paths in the hybrid envelope tracking (ET) power amplifier (PA) has been mathematically analyzed. From analysis, an asymmetric IM3 level of ET PA can be found due to the time mismatching between RF and envelope paths and AM-to-PM distortion of PA. For the experimental demonstration, the hybrid ET PA was designed for a wideband code division multiple access downlink band operating at a center frequency of 2.14 GHz. For the accurate time matching, the group delay time adjustor (GDTA) with 5 ns variation was employed in front of the RF PA. In the experiment, 4.78 dB improvement of ACPR for 4-FAs (frequency allocations) WCMDA signal of 20 MHz channel bandwidth was obtained by the optimum group delay tuning of the GDTA.

Microwave Negative Group Delay Circuit: Filter Synthesis Approach

This paper presents the design of a negative group delay circuit (NGDC) using the filter synthesis approach. The proposed design method is based on a frequency transformation from a low-pass filter (LPF) to a bandstop filter (BSF). The predefined negative group delay (NGD) can be obtained by inserting resistors into resonators. To implement a circuit with a distributed transmission line, a circuit conversion technique is employed. Both theoretical and experimental results are provided for validating of the proposed approach. For NGD bandwidth and magnitude flatness enhancements, two second-order NGDCs with slightly different center frequencies are cascaded. In the experiment, group delay of 5.9±0.5 ns and insertion loss of 39.95±0.5 dB are obtained in the frequency range of 1.935–2.001 GHz.

A power divider with positive and negative group delay characteristics

In this paper, a power divider is suggested for predefined positive and negative group delay characteristics. The positive group delay (PGD) is obtained in between transmission paths 2 and 1, whereas the negative group delay (NGD) is in between transmission paths 3 and 1. The PGD and NGD are controlled by characteristic impedance of horizontal transmission line Z1 and shunt resistor R. Perfect input and output matching characteristics as well as perfect isolation are obtained at a center frequency (f0). For an experimental demonstration, microstrip line power divider with the PGD and NGD of 0.6 and -0.5 ns, respectively, was designed and fabricated at f0 of 2.14 GHz. The measurement results are agreed well with simulation results and theoretical predicated values.

Power divider with tunable positive and negative group delays using parasitic compensated PIN diode

This paper presents a design of power divider with tunable positive and negative group delays. The positive group delay can be obtained between paths 2 and 1 whereas negative group delay (NGD) between paths 3 and 1. The NGD is controlled by varying bias voltage of parasitic compensated PIN diodes. For experimental verification, power divider was designed and fabricated at center frequency of 2.14 GHz. Measurement results had a good agreement with simulation results.