Professor J. David Rhodes received the OBE and CBE from the Queen and also several Technology and Export Awards, along with distinguished prizes from such learned societies as the Royal Academy of Engineering, the Royal Society, the IET and the IEEE. He is also a fellow of the IEEE, IET, RAE, The Royal Society and a Foreign Associate of the Academy of Engineering (USA). He founded Filtronic plc more than 30 years ago and grew it into an international microwave company with ten operations on four continents. He retired four years ago and has grown a new business within the private company Isotek Electronics Ltd. in the area of microwave sub-systems, which has recently been acquired by Filtronic plc.

MWJ: After receiving your PhD in 1966 you worked for a brief period in the US. What was your motivation for making this step and what did you gain from it?

Rhodes: I was invited in 1967 by Drs. Henry Riblet and Ralph Levy to join MDL (Microwave Development Labs) in Natick, MA, to work on new developments in microwave filters and was encouraged to accept the offer by Leeds University to gain appropriate industrial experience. It was a motivating experience.

MWJ: In 1969 you returned to the University of Leeds as a lecturer in Electrical Engineering. Having gained a reputation in microwave engineering what prompted you to return to academia?

Rhodes: I always wanted to do research work within the university and after 18 months in the US I was offered a position in Leeds at one fifth of the US salary. I hesitated and decided to speak to Dr. Riblet, for whom I had a great respect, for a salary rise to stay with MDL. When asked what salary I required, he thought for a short while and said, “For that we can afford to let you go”. Hence, I returned to the UK but retained a consultancy with MDL.

MWJ: What were your main areas of research at that time?

Rhodes: My main R & D activity was on linear phase filters with some abstract work on propagation in inhomogeneous waveguides.

MWJ: While maintaining a part time role at the University of Leeds you founded Filtronic. Was this a difficult decision to take and what motivated you to do so?

Rhodes: In addition to consulting for MDL, I was also a consultant to Ferranti in the UK. Numerous new filter products were required for the Tornado aircraft but no company investment was forthcoming without it being fully funded by the Ministry of Defence. Thus, I founded Filtronic to design and produce the initial products which Ferranti could then manufacture in volume without any risk. Funding for Filtronic came primarily from research contracts with the European Space Agency for satellite borne filters and selling software for the design of multiplexers.

MWJ: Up until 1989 the company concentrated on developing components for electronic warfare. What significant products were developed during that period?

Rhodes: Many filter based products were developed for both airborne and shipborne requirements. Many of the products were based in Suspended Substrate Stripline technology producing compact filters and multiplexers. Additionally, the technology was used in a new form of reflection mode digital frequency discriminator using three phase devices and also in a new type of switched multiplexers. These switched devices were designed into the B2 interferometer receivers, and could operate in 216 different states whilst maintaining phase tracking.

MWJ: Describe your decision to move into the base station and mobile phone business and the formation of Filtronic Comtek (UK)?

Rhodes: The amount of engineering time required to produce a new product is independent of the volume produced. In defence requirements a few hundred products are required whereas in mobile communications, tens of thousands are required for base stations and tens of millions for the handset market. The key to the entry into the base station filter market was that we knew how to design and manufacture products to meet the theoretical optimum characteristics whilst meeting the high power and low passive intermodulation requirements at an acceptable cost.

MWJ: In the early to mid ’90s Filtronic actively established and acquired new companies. What was the business strategy behind this activity?

Rhodes: In the ’80s three attempts were made to establish a presence in the US defence market and all failed due to the non-US control. Thus, after the commercial activity was commenced in the UK a new operation was set up in the US to develop along similar lines and grew quickly after Filtronic Comtek became a public company in 1994.

In 1998 four companies were acquired – Filtronic Components Ltd., L.K. Products, Sage Laboratories and the Santa Clara division of Litton Industries, in addition to raising $170 million in the US Bond Market. The first was to reconsolidate all of the activities of Filtronic; the second in the handset market in Finland but primarily to establish a base station facility to supply Nokia in Finland; the third to establish a defence business in the US and the fourth to acquire a compound semiconductor capability.

MWJ: What were the drivers for Filtronic’s evolution into the compound semiconductors market and specifically the acquisition of the Fujitsu semiconductor plant in Newton Aycliffe?

Rhodes: Filtronic did not own any of the underlying technology in its products but only a unique engineering capability which it had successfully exploited. It was believed that future integrated designs in microwave engineering would require this capability. After persuading Prof. Snowden to leave Leeds University in 1998 to join Filtronic to develop a world beating compound semiconductor facility, we looked for a surplus DRAM lab in the UK. We purchased the Newton Aycliffe facility in 1999 which had cost $500 million to build for $20 million and set about establishing it as a PHEMT facility using stepper technology on 6 inch GaAs wafers. This proved to be very successful and eventually was producing more than one million multiway switches on a daily basis for the handset market. Other products included multifunction modules for the point to point market, power amplifiers for the phased array radar market and broadband optical modulators.

MWJ: Explain the effect that the slump in the mobile communications market had on Filtronic?

Rhodes: Filtronic did not experience a significant decline in sales mainly due to the position it had established in various markets. However, during the last five years most of its businesses have been sold.

MWJ: When did you end your involvement with Filtronic and what have been your business/R&D interests since?

Rhodes: I left Filtronic nearly five years ago. Shortly afterwards I was approached by the central R & D group to see if I would be willing to form a new filter based wireless infrastructure business. I owned a separate successful business, Isotek, which designed and supplied hyperbaric welding equipment for oil and gas pipes on the seabed. I used the income from this business to support the new activity which has grown and expanded into the US over a four year period. The wireless infrastructure business was sold to Filtronic in November 2010 for around $17 million.

During this period my R & D interests have been in developing new types of combiners for introducing WCDMA and LTE into existing GSM and CDMA base stations. Also, I have managed to devote a significant amount of time on the large signal behaviour of non-linear microwave devices.

MWJ: You are both an Officer of the Order of the British Empire (OBE) and Commander of the Order of the British Empire (CBE), which you received from the Queen. What does it mean to be recognised by your country?

Rhodes: It is a privilege and honour to be recognised by the Queen for my contributions to research, engineering and industry.

MWJ: You have also received distinguished prizes from such learned societies as the Royal Academy of Engineering, the Royal Society, the IET and the IEEE. What does it mean to receive such recognition from the microwave industry?

Rhodes: Most of the prizes have been for research work in circuits and systems and microwave engineering. It is very satisfying to be recognised by others for the original contributions which I believe I have made over several decades.

MWJ: This year’s MTT-S IMS will be held in Baltimore, Maryland. The region has a history of filter development that you contributed to. Can you explain how?

Rhodes: When I was at Filtronic we had six operations in the US in addition to those in the UK, Finland, Australia and China. The first commercial activity was in Maryland providing base stations filters for the wireless infrastructure market and rapidly increased in size to a level of sales exceeding $100 million. Three years ago, Isotek Electronics established a new wireless infrastructure business in Maryland which has subsequently been acquired by Filtronic.

MWJ: You will be a plenary speaker at the 2011 MTT-S IMS? After all your achievements do you still get a buzz from participating at such microwave events?

Rhodes: I consider it an honour and a pleasure to present new technical information at any technical conference. Ten years ago, I vowed never to present another lecture on business development and have stuck to that vow.

MWJ: You will be considering the “Migration of WCDMA and 4G LTE into Existing Cellular Bands”. Without giving too much away what will be your key messages be?

Rhodes: The simple answer is come and see. However, I will present in the simplest way possible how to combine new WCDMA and LTE base stations onto existing antenna structures supporting GSM and CDMA systems in such a way that any operator may gradually migrate to full 4G coverage on existing cellular bands without disrupting existing customers.

MWJ: What current areas of microwave R&D do you see having significant impact in the future and why?

Rhodes: I find this particular question very difficult to answer. It is easy to identify areas of research which are fundamentally wrong and have no meaningful applications. However, I still believe in the role of integrated circuits on compound semiconductor substrates. On a personal note related to my own work, I do believe that power amplifiers with a very high efficiency for signals with a 10 dB peak to average ratio would be very desirable for many applications.

MWJ: Professor Snowden once described you as being an outstanding engineer with the achievements of a highly successful entrepreneur and businessman? What is your philosophy for successfully combining engineering and business?

Rhodes: I am a research engineer and mathematician. I found that developing businesses was a necessary activity to be able to do the creative research work. Business is no more than applying common sense to produce products which customers want at the right price, ensuring that you protect your intellectual property rights. You also need to know your market and be willing to take appropriate levels of calculated risks.