Yongchae Jeong

Design of low-pass filters using defected ground structure

A method to design low-pass filters (LPF) having a defected ground structure (DGS) and broadened transmission-line elements is proposed. The previously presented technique for obtaining a three-stage LPF using DGS by Lim et al. is generalized to propose a method that can be applied in design N-pole LPFs for N/spl les/5. As an example, a five-pole LPF having a DGS is designed and measured. Accurate curve-fitting results and the successive design process to determine the required size of the DGS corresponding to the LPF prototype elements are described. The proposed LPF having a DGS, called a DGS-LPF, includes transmission-line elements with very low impedance instead of open stubs in realizing the required shunt capacitance. Therefore, open stubs, teeor cross-junction elements, and high-impedance line sections are not required for the proposed LPF, while they all have been essential in conventional LPFs. Due to the widely broadened transmission-line elements, the size of the DGS-LPF is compact.

Bandwidth Enhancement of an Analog Feedback Amplifier by Employing a Negative Group Delay Circuit

We will demonstrate an alternative topology to greatly increase the operating bandwidth of an analog RF feedback power amplifler. A limited operating bandwidth due to the group delay mismatch of a feedback loop discouraged the use of an RF feedback technique in spite of its powerful linearization performance and great tolerance capability. By introducing a negative group delay circuit (NGDC) in the feedback loop, group delay match condition could be satisfled. With the fabricated 2-stage distributed element negative group delay circuit with a 30MHz of bandwidth and a i9ns of group delay for a wideband code division multiple access (WCDMA) downlink band, the proposed feedback amplifler with the proposed topology experimentally achieved an adjacent channel leakage ratio of i53:2dBc with a cancellation bandwidth of over 50MHz.

Design of Dual-Band Bandpass Filters with Controllable Bandwidths Using New Mapping Function

In this paper, a novel design method for a dual-band bandpass fllter (BPF) with arbitrary controllable bandwidths based on a simple frequency mapping function is proposed and its analytical design equations are also derived. The circuit conversion techniques are employed for implementation with distributed transmission line. To validate the proposed dual-band BPF with controllable bandwidths, a low temperature co-flred ceramic (LTCC) transmission line as well as microstrip lines are used, respectively. The two types of design for the dual-band BPF have the same and signiflcantly difierent fractional bandwidths (FBWs), respectively. The flrst type of dual- band BPF with same FBWs are implemented at 2.11{2.17 and 3.45{ 3.55GHz. The second type of dual-band BPF with difierent FBWs are implemented at 3.40{3.60 and 5.15{5.25GHz. The measured and theoretical results show good agreement, signiflcantly validating the proposed frequency mapping function methodology.

A NEW CALCULATION METHOD FOR THE CHARACTERISTIC IMPEDANCE OF TRANSMISSION LINES WITH MODIFIED GROUND STRUCTURES OR PERTURBATION

In this paper, a new calculating method for the characteristic impedance (Zc) of transmission lines with perturbation and periodic modifled ground structure (MGS), such as defected ground structure (DGS), photonic bandgap (PBG), and substrate integrated artiflcial dielectric (SIAD), is discussed. The proposed method is based on simple transmission line theories and proper related equations. The previous method to flnd Zc of transmission lines with MGS or perturbation produces the ∞uctuating Zc value depending on frequency, while the proposed method results in a constant value without frequency-dependence. As examples, several microstrip lines with DGS, PBG, and SIAD structure are simulated and measured, and their Zc values are calculated from S-parameters by the previous and proposed methods. It is shown that the Zc obtained by the proposed method is much more reliable than that calculated by the previous method for all examples.

A New Design of Doherty Amplifiers Using Defected Ground Structure

In this letter, a new Doherty power amplifier having the ideal harmonic termination condition that has been usually ignored is proposed. A defected ground structure (DGS) is adopted on the ground pattern of the output lambda/4 impedance inverter of the carrier amplifier and output offset transmission line of the peaking amplifier that are essential for proper load modulation operation of a conventional Doherty amplifier. As a result of the second and third harmonic termination, excellent improvement in power added efficiency (PAE), gain, maximum output power as well as linearity is obtained. The acquired improvements in gain, maximum output power (P1 dB), PAE, and adjacent channel leakage ratio to wideband code division multiple access 2FA signal are 0.33 dB, 0.42 dB, 12.7%, and 5.1 dB, respectively. Moreover, physical length of microstrip line is shortened fairly by DGS, therefore the whole amplifier circuit size is considerably reduced

A DUAL-BAND RF ENERGY HARVESTING USING FREQUENCY LIMITED DUAL-BAND IMPEDANCE MATCHING

In this paper, a novel dual-band RF-harvesting RF-DC converter with a frequency limited impedance matching network (M/N) is proposed. The proposed RF-DC converter consists of a dual-band impedance matching network, a rectifler circuit with villard structure, a wideband harmonic suppression low-pass fllter (LPF), and a termination load. The proposed dual-band M/N can match two receiving band signals and suppress the out-of-band signals efiectively, so the back-scattered nonlinear frequency components from the nonlinear rectifying diodes to the antenna can be blocked. The fabricated circuit provides the maximum RF-DC conversion e-ciency of 73.76% and output voltage 7.09V at 881MHz and 69.05% with 6.86V at 2.4GHz with an individual input signal power of 22dBm. Moreover, the conversion e-ciency of 77.13% and output voltage of 7.25V are obtained when two RF waves with input dual-band signal power of 22dBm are fed simultaneously.

Cross Cancellation TechniqueEmploying an Error Amplifier

In this letter, we propose a new distortion cancellation mechanism for a balanced power amplifier (PA) structure using the cross cancellation technique employing an error amplifier. The proposed cross cancellation balanced linear PA is implemented in the IMT-2000 ( 2.14GHz) band. With commercial PAs with a peak power of 240 W for base-station application, the proposed system shows 18.6 dB improvement at an average output power of 40 dBm for adjacent channel leakage ratio measurement with wideband code division multiple access 4FA signal. The efficiency of the proposed structure is about 2% higher than the conventional feedforward amplifier for modulated carrier.

A Research on the Magnitude/Phase Asymmetry Measurement Technique of the RF Power Amplifier Based on the Predistortive Tone Cancellation Technique

This paper proposes a novel memory effect measurement technique in RF power amplifiers(PAs) using a two-tone intermodulation distortion(IMD) signal with a very simple and intuitive algorithm. Based on the proposed predistortive tone cancellation technique, the proposed measurement method is capable of measuring the relative phase and magnitude of the third-order and fifth-order IMDs, as well as the fundamental signal. The measured relative phase between the higher and lower IMD signal for specific tone spacing can be interpreted as the group delay(GD) information of the IMD signal concerned. From the group delay analysis, we can conclude that an adaptive control of GD as well as the magnitude and phase is a key function in increasing the linearization bandwidth and the dynamic range in a predistortion(PD) technique.

Dual-band predistortion power amplifier for digital cellular and IMT-2000 base-station application

This paper proposes a dual-band predistortion power amplifier using diplexer for digital cellular (f/sub 0/=880MHz) and IMT-2000(f/sub 0/=2140MHz) base station. Each high power amplifier is linearized by using predistortion method. The implemented predistorter uses reflection type IM generator with 3dB hybrid coupler for good reflection characteristic. The diplexer is composed of low pass filter using defected ground structure(DGS) microstrip line and high pass filter using high-Q lumped capacitors and distributed elements. For a forward link one-carrier CDMA IS-95 and WCDMA signal, the proposed dual-band predistortion power amplifier shows ACPR improvement of about 10dBc and 9.36dBc for cellular and IMT-2000 band of operation, respectively.

A Design of Predistortive High Power Amplifier using Carrier Complex Power Series Analysis

In this paper, a new carrier complex power series for linearizing the distortion effects of a HPA (High Power Amplifier) is proposed. Amplitude (AM-to-AM) and phase(AM-to-PM) nonlinear characteristics of HPA are combined to generate carrier complex power series. Inverse carrier complex power series of predistortor is also proposed. The fabricated HPA of IMT- 2000 band with a measured gain and P1dB are 34.06dB and 35.4dBm. With proposed series, C/I (Carrier to Intermodulation) ratio of HPA is improved by 17.01dB(@Pout = 25.43dBm/tone) with 2-tone at 2.1375GHz and 2.1425GHz.