In this article, a microstrip-fed stepped open slot antenna is presented which is suitable for GSM 1800, WiFi, WiMAX, PCS, and ITM-2000 applications. The proposed geometry is composed of a circle-shaped tuning stub, a feed structure, and deformed ground plane. The proper tuning of resonating modes (f r1 , f r2 , f r3 and f r4) and wideband frequency response are acquired by adjusting the dimension of stairs, tuning the stub and an elliptical slot. The experimental result demonstrates that this antenna covers the frequency range from 1.375 to 5.6 GHz with measured fractional bandwidth (BW (%) = 200 * (f h − f l)/(f h + f l)) of 121.14% for S 11 < −10 dB. This antenna also exhibits resonance at frequencies (measured) 1.625, 2.52, 2.82, 3.75, 4.67, and 5.42 GHz. After investigating the surface current distribution, the mathematical equations are deduced for simulated resonating frequencies of 1.35, 2, 3.8, and 5.22 GHz. Due to asymmetry in structure, asymmetric far-field patterns are found in E-plane with omnidirectional patterns in H-plane.

In this paper we consider the design of a four-cavity, high-gain K-band gyroklystron experiment for high gradient structure testing. The frequency doubling gyroklystron utilizes a beam voltage of 500 kV and a beam current of 200 A from a magnetron injection gun (MIG) originally designed for a lower-frequency device. The microwave circuit features input and gain cavities in the circular TE011 mode and penultimate and output cavities that operate at the second harmonic in the TE021 mode. We investigate the MIG performance and study the behavior of the circuit for different values of perpendicular to parallel velocity ratio (α = V⊥ / Vz). This microwave tube is expected to be able to produce at least 20 MW of power in 1μs pulses at a repetition rate of at least 120 Hz. A maximum efficiency of 26% and a large signal gain of 58 dB under zero-drive stable conditions were simulated for a velocity ratio equal to 1.35

In this communication, a novel design of a hybrid open slot antenna is investigated and experimentally verified. The proposed structure comprises a slotted tuning stub, a proximity fed parasitic element, and slotted ground plane. Tuning and overlapping of best matching frequencies f r1 , f r2 , f r3 , f r4 , f r5 , f r6 , and f r7 are accomplished by varying the dimension of the parasitic element and elliptical slot. The experimental results reveal that this antenna covers the fractional bandwidth (BW(%) = 200 * (f h − f l)/(f h + f l)) of 139.5% from 0.98 GHz to 5.5 GHz for |S 11 | < −10 dB which is suitable for GSM 1800, WiMAX, PCS, and ITM-2000. After the analysis of current distribution, mathematical equations are developed for frequencies 1.04, 1.52, 3.06, 3.67, and 4.58 GHz. The structural analysis is also carried out for optimization and to know the electromagnetic behaviour of the antenna. Asymmetric radiation patterns are found at resonating frequencies due to open slot geometry.

The University of Maryland Gyroklystron Program has as a goal the production of 80 MW of peak power at 17 GHz, using a 500 kV, 500 A electron beam'. Frequency-doubling gyroklystron circuits that had 3-4 cavities and that were driven by a 150 kW, X-Band have to date only produced maximum powers of about 27 MW. The root cause of this inability to achieve the designed operating parameters has been non-uniform emission from the temperature-limited Magnetron Injection Gun (MIG). The azimuthal current density varies by more than + 50% due in large part to a 60°C temperature variation on the emitter surface. A new MIG with superior azimuthal current uniformity has been constructed by Calabazas Creek Research, Inc. and has been installed in the UM test bed2.In this paper we describe the design and hot test results for a four-cavity coaxial circuit being driven by this new MIG. The input cavity operates at 8.568 GHz in the TEOB, mode while the remaining cavities operate at twice the drive frequency in the TE021 mode. The tube is predicted to have an efficiency of 34% for an average perpendicular-to-parallel velocity ratio of 1.4. The large signal gain is about 46 dB at the desired operating point. Tube cold-test results, as well as the hot test characterization of tube dependence on voltage, current, velocity ratio, and magnetic field, will be given. Tube stability and output mode purity will also be assessed.Recently the regime of simultaneous excitation of several axial eigenmodes of the gyrotron cavity was studied in relativistic gyrotron with output power of hundreds of kW' 2. It was shown that such regimes exist predominantly with a proper reflector position, when the Q-factors of neighboring eigenmodes are close to each other. The paper is devoted to theoretical and experimental studies of this phenomena in 10-20 kV sub-relativistic gyrotrons.Experimental studies were carried out at the Kaband technological gyrotrons at the Forschungszentrum Karlsruhe (in the regime of 20 ms electron pulse duration) and the Institute of Applied Physics (CW operation), which were operated at the TE12 mode when the millimeter-wave output window was strongly mismatched and was used as external reflector.Two different situations were realized experimentally. In the first, when the Q-factors of axial modes were quite different, only the steady-state oscillations at two different frequencies were observed. In the second, when the Q-factors were close, the regime of two frequency oscillations was realized.These results are in a good agreement with "cold" electrodynamic studies and non-stationary PIC-code simulations. The possibilities of increasing the efficiency in the non-stationary regimes are discussed.

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