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This article proposes a new class of box-like substrate integrated waveguide (SIW) filters with wide stopband. First, a two-pole doublet bandpass filter with one finite-transmission zero (FTZ) is proposed using a new planar dual-mode rectangular SIW cavity, which is realized by TE201 and TE103 modes. TE102, TE202, and TE104 modes are suppressed intrinsically by arranging feeding lines at the horizontal centerline of the dual-mode SIW cavity. Then, a four-pole box-section filter with one FTZ is proposed using one dual-mode and two single-mode rectangular SIW cavities, and the two single-mode cavities have different width-length ratios to further improve the stopband performance. To further improve the cutoff skirt, a new design method for five-pole quasi-elliptic SIW filter is proposed, which is achieved by the four-pole filter loaded by one single-mode SIW cavity. Some design examples with the center frequency of 10 GHz are presented to verify the performance of the proposed dual-mode SIW filters and the design method.

This brief presents a novel shape tunable reflective analog predistortion (RAPD) linearizer with a simple structure. The power-dependent impedance matching network (PIMN) based on parallel Schottky diode is applied to the RAPD linearizer to achieve the shape tuning function. Influence of the PIMN on the impedance of the nonlinear load is analyzed in detail. Two different types of shape tunable linearizers for the solid state power amplifier (SSPA) and the travelling wave tube amplifier (TWTA) are proposed and simulated. The shape tuning capability has been verified by a fabricated C-band RAPD linearizer. Good linearity improvement has been achieved for a C-band 20 W SSPA with the proposed linearizer.

Analog predistortion (APD) is an effective technique to improve the linearity of the traveling-wave tube amplifier (TWTA). This paper presents a novel APD linearizer with independently tunable gain and phase conversions. Based on symmetrical dual-branch vector synthetic topology, which avoids introducing the additional delay line, this linearizer achieves a simple circuit structure. Independent tuning of gain and phase conversions of this linearizer is realized by changing the bias voltages of the two branches. Theoretical analysis and tuning process of this linearizer are discussed in detail. Simulated and measured results are in a good agreement, and both of them verify that this linearizer has the independent tuning ability. Furthermore, a 250-W Ka-band TWTA is linearized by this linearizer, and the measurement results demonstrate the effectiveness of this linearizer in TWTA linearization.